FREEZING OF GASHOLDER SEAL.—The danger attendant upon the congelation of the seal in an acetylene holder is very real, not so much because of the fear that the apparatus may be burst, which is hardly to be expected, as because the bell will be firmly fixed in a certain position by the ice, and the whole establishment lighted by the gas will be left in darkness. In these circumstances, hurried and perhaps injudicious attempts may be made to thaw the seal by putting red-hot bars into it or by lighting fires under it, or the generator-house may be thoughtlessly entered with a naked light at a time when the apparatus is possibly in disorder through the loss of storage-room for the gas it is evolving. Should a seal ever freeze, it must be thawed only by the application of boiling water; and the plant-house must be entered, if daylight has passed, in perfect darkness or with the assistance of an outside lamp whining through a closed window. [Footnote: By "closed window" is to be understood one incapable of being opened, fitted with one or two thicknesses of stout glass well puttied in, and placed in a wall of the house as far as possible from the door.] There are two ways of preventing the seal from freezing. In all large installations the generator-house will be fitted with a warm-water heating apparatus to protect the portion of the plant where the carbide is decomposed, and if the holder is also inside the same building it will naturally be safe. If it is outside, one of the flow-pipes from the warming apparatus should be led into and round the lowest part of the seal, care being taken to watch for, or to provide automatic arrangements for making good, loss of water by evaporation. If the holder is at a distance from the generator-house, or if for any other reason it cannot easily be brought into the warming circuit, the seal can be protected in another way; for unlike the water in the generator, the water in the holder-seal will perform its functions equally well however much it be reduced in temperature, always providing it is maintained in the liquid condition. There are numerous substances which dissolve in, or mix with, water, and yield solutions or liquids that do not solidify until their temperature falls far below that of the natural freezing- point. Assuming that those substances in solution do not attack the acetylene, nor the metal of which the holder is built, and are not too expensive, choice may be made between them at will. Strictly speaking the cost of using them is small, because unless the tank is leaky they last indefinitely, not evaporating with the water as it is vaporised into the gas or into the air. The water-seal of a holder standing within the generator-house may eventually become so offensive to the nostrils that the liquid has to be renewed; but when this happens it is due to the accumulation in the water of the water-soluble impurities of the crude acetylene. If, as should be done, the gas is passed through a washer or condenser containing much water before it enters the holder the sulphuretted hydrogen and ammonia will be extracted, and the seal will not acquire an obnoxious odour for a very long time.
Four principal substances have been proposed for lowering the freezing- point of the water in an acetylene-holder seal; common salt (sodium chloride), calcium chloride (not chloride of lime), alcohol (methylated spirit), and glycerin. A 10 per cent. solution of common salt has a specific gravity of 1.0734, and does not solidify above -6 deg. C. or 21.2 deg. F.; a 15 per cent. solution has a density of 1.111, and freezes at -10 deg. C. or 14 deg. F. Common salt, however, is not to be recommended, as its solutions always corrode iron and steel vessels more or less quickly. Alcohol, in its English denatured form of methylated spirit, is still somewhat expensive to use, but it has the advantage of not increasing the viscosity of the water; so that a frost-proof mixture of alcohol and water will flow as readily through minute tubes choked with needle- valves, or through felt and the like, or along wicks, as will plain water. For this reason, and for the practically identical one that it is quite free from dirt or insoluble matter, diluted spirit is specially suitable for the protection of the water in cyclists' acetylene lamps, [Footnote: As will appear in Chapter XIII., there is usually no holder in a vehicular acetylene lamp, all the water being employed eventually for the purpose of decomposing the carbide. This does not affect the present question. Dilute alcohol does not attack calcium carbide so energetically as pure water, because it stands midway between pure water and pure alcohol, which is inert. The attack, however, of the carbide is as complete as that of pure water, and the slower speed thereof is a manifest advantage in any holderless apparatus.] where strict economy is less important than smooth working. For domestic and larger installations it is not indicated. As between calcium chloride and glycerin there is little to choose; the former will be somewhat cheaper, but the latter will not be prohibitively expensive if the high-grade pure glycerins of the pharmacist are avoided. The following tables show the amount of each substance which must be dissolved in water to obtain a liquid of definite solidifying point. The data relating to alcohol were obtained by Pictet, and those for calcium chloride by Pickering. The latter are materially different from figures given by other investigators, and perhaps it would be safer to make due allowance for this difference. In Germany the Acetylene Association advocates a 17 per cent. solution of calcium chloride, to which Frank ascribes a specific gravity of 1.134, and a freezing-point of -8 deg. C. or 17.6 deg. F.
Freezing-Points of Dilute Alcohol. Percentage of Specific Gravity. Freezing-point. Alcohol. Degs. C. Degs. F. 4.8 0.9916 -2.0 +28.4 11.3 0.9824 5.0 23.0 16.4 0.9761 7.5 18.5 18.8 0.9732 9.4 15.1 20.3 0.9712 10.6 12.9 22.1 0.9689 12.2 10.0 24.2 0.9662 14.0 6.8 26.7 0.9627 16.0 3.2 29.9 0.9578 18.9 -2.0
Freezing-Points of Dilute Glycerin. Percentage of Specific Gravity. Freezing-point. Glycerin. Degs. C. Degs. F. 10 1.024 -1.0 +30.2 20 1.051 2.5 27.5 30 1.075 6.0 21.2 40 1.105 17.5 0.5 50 1.127 31.3 -24.3
_Freezing-Points of Calcium Chloride Solutions._ __________ Percentage of Specific Gravity. Freezing-point. CaCl_2. ___ ____ ____ Degs. C. Degs. F. 6 1.05 -3.0 +26.6 8 1.067 4.3 24.3 10 1.985 5.9 21.4 12 1.103 7.7 18.1 14 1.121 9.8 14.4 16 1.140 12.2 10.0 18 1.159 15.2 4.6 20 1.170 18.6 -1.5 ___ ____ __ __
Calcium chloride will probably be procured in the solid state, but it can be purchased as a concentrated solution, being sold under the name of "calcidum" [Footnote: This proprietary German article is a liquid which begins to solidify at -42 deg. C. (-43.6 deg. F.), and is completely solid at -56 deg. C. (-69) deg. F.). Diluted with one-third its volume of water, it freezes between -20 deg. and -28 deg. C. (-4 deg. and-l8.4 deg. F.). The makers recommend that it should be mixed with an equal volume of water. Another material known as "Gefrierschutzfluessigkeit" and made by the Floersheim chemical works, freezes at -35 deg. C. (-3 deg. F.). Diluted with one-quarter its volume of water, it solidifies at -18 deg. C. (-0.4 deg. F.); with equal parts of water it freezes at -12 deg. C. (10.4 deg. F.). A third product, called "calcidum oxychlorid," has been found by Caro and Saulmann to be an impure 35 per cent. solution of calcium chloride. Not one of these is suitable for addition to the water used in the generating chamber of an acetylene apparatus, the reasons for this having already been mentioned.] for the protection of gasholder seals. Glycerin itself resembles a strong solution of calcium chloride in being a viscid, oily-looking liquid; and both are so much heavier than water that they will not mix with further quantities unless they are thoroughly agitated therewith. Either may be poured through water, or have water floated upon it, without any appreciable admixture taking place; and therefore in first adding them to the seal great care must be taken that they are uniformly distributed throughout the liquid. If the whole contents of the seal cannot conveniently be run into an open vessel in which the mixing can be performed, the sealing water must be drawn off a little at a time and a corresponding quantity of the protective reagent added to it. Care must be taken also that motives of economy do not lead to excessive dilution of the reagent; the seal must be competent to remain liquid under the prolonged influence of the most severe frost ever known to occur in the neighbourhood where the plant is situated. If the holder is placed out of doors in an exposed spot where heavy rains may fall on the top of the bell, or where snow may collect there and melt, the water is apt to run down into the seal, diluting the upper layers until they lose the frost- resisting power they originally had. This danger may be prevented by erecting a sloping roof over the bell crown, or by stirring up the seal and adding more preservative whenever it has been diluted with rain water. Quite small holders would probably always be placed inside the generator-house, where their seals may be protected by the same means as are applied to the generator itself. It need hardly be said that all remarks about the dangers incidental to the freezing of holder seals and the methods for obviating them refer equally to every item in the acetylene plant which contains water or is fitted with a water-sealed cover; only the water which is actually used for decomposing the calcium carbide cannot be protected from frost by the addition of calcium chloride or glycerin—that water must be kept from falling to its natural freezing-point. From Mauricheau-Beaupre's experiments, referred to on page 106, it would appear that a further reason for avoiding an addition of calcium chloride to the water used for decomposing carbide should lie in the danger of causing a troublesome production of froth within the generator.
It will be convenient to digress here for the purpose of considering how the generators of an acetylene apparatus themselves should be protected from frost; but it may be said at the outset that it is impossible to lay down any fixed rules applicable to all cases, since local conditions, such as climate, available resources, dimensions, and exposed or protected position of the plant-house vary so largely in different situations. In all important installations every item of the plant, except the holder, will be collected in one or two rooms of a single building constructed of brick or other incombustible material. Assuming that long-continued frost reigns at times in the neighbourhood, the whole of such a building, with the exception of one apartment used as a carbide store only, is judiciously fitted with a heating arrangement like those employed in conservatories or hothouses; a system of pipes in which warm water is kept circulating being run round the walls of each chamber near the floor. The boiler, heated with coke, paraffin, or even acetylene, must naturally be placed in a separate room of the apparatus-house having no direct (indoor) communication with the rooms containing the generators, purifiers, &c. Instead of coils of pipe, "radiators" of the usual commercial patterns may be adopted; but the immediate source of heat should be steam, or preferably hot water, and not hot air or combustion products from the stove. In exposed situations, where the holder is out of doors, one branch of the flow-pipe should enter and travel round the seal as previously suggested. Most large country residences are already provided with suitable heating apparatus for warming the greenhouses, and part of the heat may be capable of diversion into the acetylene generator-shed if the latter is erected in a convenient spot. In fact, if any existing hot-water warming appliances are already at hand, and if they are powerful enough to do a little more work, it may be well to put the generator-building in such a position that it can be efficiently supplied with artificial warmth from those boilers; for any extra length of main necessary to lead the gas into the residence from a distant generator will cost less on the revenue account than the fuel required to feed a special heating arrangement. In smaller installations, especially such as are to be found in mild climates, it may be possible to render the apparatus-house sufficiently frost-proof without artificial heat by building it partly underground, fitting it with a double skylight in place of a window for the entrance of daylight, and banking up its walls all round with thick layers of earth. The house must have a door, however, which must open outwards and easily, so that no obstacle may prevent a hurried exit in emergencies. Such a door can hardly be made very thick or double without rendering it heavy and difficult to open; and the single door will be scarcely capable of protecting the interior if the frost is severe and prolonged. Ventilators, too, must be provided to allow of the escape of any gas that may accidentally issue from the plant during recharging, &c.; and some aperture in the roof will be required for the passage of the vent pipe or pipes, which, in certain types of apparatus, move upwards and downwards with the bell of the holder. These openings manifestly afford facilities for the entry of cold air, so that although this method of protecting generator-houses has proved efficient in many places, it can only be considered inferior to the plan of installing a proper heating arrangement. Occasionally, where local regulations do not forbid, the entire generator-house may be built as a "lean-to" against some brick wall which happens to be kept constantly warm, say by having a furnace or a large kitchen stove on its other side.
In less complicated installations, where there are only two distinct items in the plant to be protected from frost—generator and holder—or where generator and holder are combined into one piece of apparatus, other methods of warming become possible. As the reaction between calcium carbide and water evolves much heat, the most obvious way of preventing the plant from freezing is to economise that heat, i.e., to retain as much of it as is necessary within the apparatus. Such a process, clearly, is only available if the plant is suitable in external form, is practically self-contained, and comprises no isolated vessels containing an aqueous liquid. It is indicated, therefore, rather for carbide-to- water generators, or for water-to-carbide apparatus in which the carbide chambers are situated inside the main water reservoir—any apparatus, in fact, where much water is present and where it is all together in one receptacle. Moreover, the method of heat economy is suited for application to automatic generators rather than to those belonging to the opposite system, because automatic apparatus will be generating gas, and consequently evolving heat, every evening till late at night—just at the time when frost begins to be severe. A non-automatic generator will usually be at work only in the mornings, and its store of heat will accordingly be much more difficult to retain till nightfall. With the object of storing up the heat evolved in the generator, it must be covered with some material possessed of the lowest heat-conducting power possible; and the proper positions for that material in order of decreasing importance are the top, sides, and bottom of the plant. The generator may either be covered with a thick layer of straw, carpet, flannel, or the like, as is done in the protection of exposed water- pipes; or it may be provided with a jacket filled with some liquid. In view of the advisability of not having any organic or combustible material near the generator, the solid substances just mentioned may preferably be replaced by one of those partially inorganic compositions sold for "lagging" steam-pipes and engine-cylinders, such as "Fossil meal." Indeed, the exact nature of the lagging matters comparatively little, because the active substance in retaining the heat in the acetylene generator or the steam-pipe is the air entangled in the pores of the lagging; and therefore the value of any particular material depends mainly on its exhibiting a high degree of porosity. The idea of fitting a water jacket round an acetylene generator is not altogether good, but it may be greatly improved upon by putting into the jacket a strong solution of some cheap saline body which has the property of separating from its aqueous solution in the form of crystals containing water of crystallisation, and of evolving much heat in so separating. This method of storing much heat in a small space where a fire cannot be lighted is in common use on some railways, where passengers' foot-warmers are filled with a strong solution of sodium acetate. When sodium acetate is dissolved in water it manifestly exists in the liquid state, and it is presumably present in its anhydrous condition (i.e., not combined with water of crystallisation). The common crystals are solid, and contain 3 molecules of water of crystallisation—also clearly in the solid state. Now, the reaction
NaC2H3O2 + 3H2O = NaC2H3O2.3H2O
(anhydrous acetate) (crystals)
evolves 4.37 calories (Berthelot), or 1.46 calorie for each molecule of water; and whereas 1 kilo. of water only evolves 1 large calorie of heat as its temperature falls 1 deg. C., 18 grammes of water (1 gramme-molecule) evolve l.46 large calorie when they enter into combination with anhydrous sodium acetate to assist in forming crystals—and this 1.46 calorie may either be permitted to warm the mass of crystals, or made to do useful work by raising the temperature of some adjacent substance. Sodium acetate crystals dissolve in 3.9 parts by weight of water at 6 deg. C. (43 deg. F.) or in 2.4 parts at 37 deg. C. (99 deg. F.). If, then, a jacket round an acetylene apparatus is filled with a warm solution of sodium acetate crystals in (say) 3 parts by weight of water, the liquid will crystallise when it reaches some temperature between 99 deg. and 43 deg. F.; but when the generator comes into action, the heat liberated will change the mass of crystals into a liquid without raising its sensible temperature to anything like the extent that would happen were the jacket full of simple water. Not being particularly warm to the touch, the liquefied product in the jacket will not lose much heat by radiation, &c., into the surrounding air; but when the water in the generator falls again (after evolution of acetylene ceases) the contents of the jacket will also cool, and finally will begin to crystallise once more, passing a large amount of low-temperature heat into the water of the generator, and safely maintaining it for long periods of time at a temperature suitable for the further evolution of gas. Like the liquid in the seal of an isolated gasholder, the liquid in such a jacket will last indefinitely; and therefore the cost of the sodium acetate in negligible.
Another method of keeping warm the water in any part of an acetylene installation consists in piling round the apparatus a heap of fresh stable manure, which, as is well known, emits much heat as it rots. Where horses are kept, such a process may be said to cost nothing. It has the advantage over methods of lagging or jacketing that the manure can be thrown over any pipe, water-seal, washing apparatus, &c., even if the plant is constructed in several separate items. Unfortunately the ammonia and the volatile organic compounds which are produced during the natural decomposition of stable manure tend seriously to corrode iron and steel, and therefore this method of protecting an apparatus from frost should only be employed temporarily in times of emergency.
CORROSION IN APPARATUS.—All natural water is a solution of oxygen and may be regarded also as a weak solution of the hypothetical carbonic acid. It therefore causes iron to rust more or less quickly; and since no paint is absolutely waterproof, especially if it has been applied to a surface already coated locally with spots of rust, iron and steel cannot be perfectly protected by its aid. More particularly at a few inches above and below the normal level of the water in a holder, therefore, the metal soon begins to exhibit symptoms of corrosion which may eventually proceed until the iron is eaten away or becomes porous. One method of prolonging the life of such apparatus is to give it fresh coats of paint periodically; but unless the old layers are removed where they have cracked or blistered, and the rust underneath is entirely scraped off (which is practically impossible), the new paint films will not last very long. Another more elegant process for preserving any metal like iron which is constantly exposed to the attack of a corrosive liquid, and which is readily applicable to acetylene holders and their tanks, depends on the principle of galvanic action. When two metals in good electrical contact are immersed in some liquid that is capable of attacking both, only that metal will be attacked which is the more electro-positive, or which (the same thing in other words) is the more readily attacked by the liquid, evolving the more heat during its dissolution. As long as this action is proceeding, as long, that is, as some of the more electro- positive material is present, the less electro-positive material will not suffer. All that has to be done, therefore, to protect the walls of an acetylene-holder tank and the sides of its bell is to hang in the seal, supported by a copper wire fastened to the tank walls by a trustworthy electrical joint (soldering or riveting it), a plate or rod of some more electro-positive metal, renewing that plate or rod before it is entirely eaten away. [Footnote: Contact between the bell and the rod may be established by means of a flexible metallic wire; or a separate rod might be used for the bell itself.] If the iron is bare or coated with lead (paint may be overlooked), the plate may be zinc; if the iron is galvanised, i.e., coated with zinc, the plate may be aluminium or an alloy of aluminium and zinc. The joint between the copper wire and the zinc or aluminium plate should naturally be above the water-level. The foregoing remarks should be read in conjunction with what was said in Chapter II., about the undesirability of employing a soft solder containing lead in the construction of an acetylene generator. Here it is proposed intentionally to set up a galvanic couple to prevent corrosion; there, with the same object in view, the avoidances of galvanic action is counselled. The reason for this difference is self-evident; here a foreign metal is brought into electrical contact with the apparatus in order that the latter may be made electro-negative; but when a joint is soldered with lead, the metal of the generator is unintentionally made electro-positive. Here the plant is protected by the preferential corrosion of a cheap and renewable rod; in the former case the plant is encouraged to rust by the unnecessary presence of an improperly selected metal.
OTHER ITEMS IN GENERATING PLANT.—It has been explained in Chapter II. that the reaction between calcium carbide and water is very tumultuous in character, and that it occurs with great rapidity. Clearly, therefore, the gas comes away from the generator in rushes, passing into the next item of the plant at great speed for a time, and then ceasing altogether. The methods necessarily adopted for purifying the crude gas are treated of in Chapter V.; but it is manifest now that no purifying material can prove efficient unless the acetylene passes through it at a uniform rate, and at one which is as slow as other conditions permit. For this reason the proper position of the holder in an acetylene installation is before the purifier, and immediately after the condenser or washer which adjoins the generator. By this method of design the holder is filled up irregularly, the gas passing into it sometimes at full speed, sometimes at an imperceptible rate; but if the holder is well balanced and guided this is a matter of no consequence. Out of the holder, on the other hand, the gas issues at a rate which is dependent upon the number and capacity of the burners in operation at any moment; and in ordinary conditions this rate is so much more uniform during the whole of an evening than the rate at which the gas is evolved from the carbide, that a purifier placed after the holder is given a far better opportunity of extracting the impurities from the acetylene than it would have were it situated before the holder, as is invariably the case on coal-gas works.
For many reasons, such as capacity for isolation when being recharged or repaired, it is highly desirable that each item in an acetylene plant shall be separated, or capable of separation, from its neighbours; and this observation applies with great force to the holder and the decomposing vessel of the generator. In all large plants each vessel should be fitted with a stopcock at its inlet and, if necessary, one at its outlet, being provided also with a by-pass so that it can be thrown out of action without interfering with the rest of the installation. In the best practice the more important vessels, such as the purifiers, will be in duplicate, so that unpurified gas need not be passed into the service while a solitary purifier is being charged afresh. In smaller plants, where less skilled labour will probably be bestowed on the apparatus, and where hand-worked cocks are likely to be neglected or misused, some more, automatic arrangement for isolating each item is desirable. There are two automatic devices which may be employed for the purposes in view, the non-return valve and the water-seal. The non-return valve is simply a mushroom or ball valve without handle, lifted off its seat by gas passing from underneath whenever the pressure of the gas exceeds the weight of the valve, but falling back on to its seat and closing the pipe when the pressure decreases or when pressure above is greater than that below. The apparatus works perfectly with a clean gas or liquid which is not corrosive; but having regard to the possible presence of tarry products, lime dust, or sludge, condensed water loaded with soluble impurities, &c., in the acetylene, a non-return valve is not the best device to adopt, for both it and the hand-worked cock or screw- down valve are liable to stick and give trouble. The best arrangement in all respects, especially between the generator and the holder, is a water-seal. A water-seal in made by leading the mouth of a pipe delivering gas under the level of water in a suitable receptacle, so that the issuing gas has to bubble through the liquid. Gas cannot pass backwards through the pipe until it has first driven so much liquid before it that the level in the seal has fallen below the pipe's mouth; and if the end of the pipe is vertical more pressure than can possibly be produced in the apparatus is necessary to effect this. Omitting the side tube b, one variety of water-seal is shown at D in Fig. 7 on page 103. The water being at the level l, gas enters at a and bubbles through it, escaping from the apparatus at c. It cannot return from c to a without driving the water out of the vessel till its level falls from f to g; and since the area of the vessel is much greater than that of the pipe, so great a fall in the vessel would involve a far greater rise in a. It is clear that such a device, besides acting as a non-return valve, also fulfils two other useful functions: it serves to collect and retain all the liquid matter that may be condensed in the pipe a from the spot at which it was originally level or was given a fall to the seal, as well as that condensing in c as far as the spot where c dips again; and it equally acts as a washer to the gas, especially if the orifice g of the gas-inlet pipe is not left with a plain mouth as represented in the figure, but terminates in a large number of small holes, the pipe being then preferably prolonged horizontally, with minute holes in it so as to distribute the gas throughout the entire vessel. Such an apparatus requires very little attention. It may with advantage be provided with the automatic arrangement for setting the water-level shown at d and e. d is a tunnel tube extending almost to the bottom of the vessel, and e is a curved run-off pipe of the form shown. The lower part of the upper curve in e is above the level f, being higher than f by a distance equal to that of the gas pressure in the pipes; and therefore when water is poured into the funnel it fills the vessel till the internal level reaches f, when the surplus overflows of itself. The operation thus not only adjusts the quantity of water present to the desired level so that a cannot become unsealed, but it also renews the liquid when it has become foul and nearly saturated with dissolved and condensed impurities from the acetylene. It would be a desirable refinement to give the bottom of the vessel a slope to the mouth of e, or to some other spot where a large-bore draw-off cock could be fitted for the purpose of extracting any sludge of lime, &c., that may collect. By having such a water-seal, or one simpler in construction, between the generator and the holder, the former may be safely opened at any time for repairs, inspection, or the insertion of a fresh charge of carbide while the holder is full of gas, and the delivery of acetylene to the burners at a specified pressure will not be interrupted. If a cock worked by hand were employed for the separation of the holder from the generator, and the attendant were to forget to close it, part or all of the acetylene in the holder would escape from the generator when it was opened or disconnected.
Especially when a combined washer and non-return valve follows immediately after a generator belonging to the shoot type, and the mouth of the shoot is open to the air in the plant-house, it is highly desirable that the washer shall be fitted with some arrangement of an automatic kind for preventing the water level rising much above its proper position. The liquid in a closed washer tends to rise as the apparatus remains in use, water vapour being condensed within it and liquid water, or froth of lime, being mechanically carried forward by the stream of acetylene coming from the decomposing chamber. In course of time, therefore, the vertical depth to which the gas-inlet pipe in the washer is sealed by the liquid increases; and it may well be that eventually the depth in question, plus the pressure thrown by the holder bell, may become greater than the pressure which can be set up inside the generator without danger of gas slipping under the lower edge of the shoot. Should this state of things arise, the acetylene can no longer force its way through the washer into the holder bell, but will escape from the mouth of the shoot; filling the apparatus-house with gas, and offering every opportunity for an explosion if the attendant disobeys orders and takes a naked light with him to inspect the plant.
It is indispensable that every acetylene apparatus shall be fitted with a safety-valve, or more correctly speaking a vent-pipe. The generator must have a vent-pipe in case the gas-main leading to the holder should become blocked at any time, and the acetylene which continues to be evolved in all water-to-carbide apparatus, even after the supply of water has been cut off be unable to pass away. Theoretically a non-automatic apparatus does not require a vent-pipe in its generator because all the gas enters the holder immediately, and is, or should be, unable to return through the intermediate water seal; practically such a safeguard is absolutely necessary for the reason given. The holder must have a safety-valve in case the cutting-off mechanism of the generator fails to act, and more gas passes into it than it can store. Manifestly the pressure of the gas in a water-sealed holder or in any generator fitted with a water-sealed lid cannot rise above that corresponding with the depth of water in the seal; for immediately the pressure, measured in inches of water, equals the depth of the sealing liquid, the seal will be blown out, and the gas will escape. Such an occurrence, however, as the blowing of a seal must never be possible in any item of an acetylene plant, more especially in those items that are under cover, for the danger that the issuing gas might be fired or might produce suffocation would be extremely great. Typical simple forms of vent-pipe suitable for acetylene apparatus are shown in Fig. 7. In each case the pipe marked "vent" is the so-called safety-valve; it is open at its base for the entry of gas, and open at its top for the escape of the acetylene into the atmosphere, such top being in all instances carried through the roof of the generator-house into the open air, and to a spot distant from any windows of that house or of the residence, where it can prove neither dangerous nor a nuisance by reason of its odour. At A is represented the vent-pipe of a displacement vessel, which may either be part of a displacement holder or of a generator working on the displacement principle. The vent-pipe is rigidly fixed to the apparatus. If gas is generated within the closed portion of the holder or passes through it, and if the pressure so set up remains less than that which is needed to move the water from the level l to the levels l' and l", the mouth of the pipe is under water, and acetylene cannot enter it; but immediately such an amount of gas is collected, or such pressure is produced that the interior level sinks below l", which is that of the mouth of the pipe, it becomes unsealed, and the surplus gas freely escapes. There are two minor points in connexion with this form of vent-pipe often overlooked. At the moment when the water arrives at l" in the closed half of the apparatus, its level in the interior of the vent-pipe stands at l', identical with that in the open hall of the apparatus (for the mouth of the vent-pipe and the water in the open hall of the apparatus are alike exposed to the pressure of the atmosphere only). When the water, then, descends just below l" there is an amount of water inside the pipe equal in height to the distance between l' and l"; and before the acetylene can escape, it must either force this water as a compact mass out of the upper mouth of the vent-pipe (which it is clearly not in a position to do), drive it out of the upper mouth a little at a time, or bubble through it till the water is gradually able to run downwards out of the pipe as its lower opening is more fully unsealed. In practice the acetylene partly bubbles through this water and partly drives it out of the mouth of the pipe; on some occasions temporarily yielding irregular pressures at the burners which cause them to jump, and always producing a gurgling noise in the vent- pipe which in calculated to alarm the attendant. If the pipe is too small in diameter, and especially if its lower orifice is cut off perfectly horizontal and constricted slightly, the water may refuse to escape from the bottom altogether, and the pipe will fail to perform its allotted task. It is better therefore to employ a wide tube, and to cut off its mouth obliquely, or to give its lower extremity the shape of an inverted funnel. At the half of the central divided drawing marked B (Fig. 7) is shown a precisely similar vent-pipe affixed to the bell of a rising holder, which behaves in an identical fashion when by the rising of the bell its lower end is lifted out of the water in the tank. The features described above as attendant, upon the act of unsealing of the displacement-holder vent-pipe occur here also, but to a less degree; for the water remaining in the pipe at the moment of unsealing is only that which corresponds with the vertical distance between l' and l", and in a rising holder this is only a height always equal to the pressure given by the bell. Nevertheless this form of vent-pipe produces a gurgling noise, and would be better for a trumpet-shaped mouth. A special feature of the pipe in B is that unless it is placed symmetrically about the centre of the bell its weight tends to throw the bell out of the vertical, and it may have to be supported at its upper part; conversely, if the pipe is arranged concentrically in the bell, it may be employed as part of the guiding arrangement of the bell itself. Manifestly, as the pipe must be long enough to extend through the roof of the generator-house, its weight materially increases the weight of the bell, and consequently the gas pressure in the service; this fact is not objectionable provided due allowance is made for it. So tall a vent-pipe, however, seriously raises the centre of gravity of the bell and may make it top-heavy. To work well the centre of gravity of a holder bell should be as low as possible, any necessary weighting being provided symmetrically about its circumference and close to its bottom edge. The whole length of an ascending vent-pipe need not be carried by the rising bell, because the lower portion, which must be supported by the bell, can be arranged to slide inside a wider length of pipe which is fixed to the roof of the generator-house at the point where it passes into the open air.
A refinement upon this vent-pipe is represented at C, where it is rigidly fastened to the tank of the holder, and has its internal aperture always above the level of the water in the apparatus. Rigidly fixed to the crown of the bell is a tube of wider diameter, h, which is closed at its upper end. h is always full of gas, and its mouth is normally beneath the level of the water in the seal; but when the bell rises to its highest permissible position, the mouth of h comes above the water, and communication is opened between the holder and the outer atmosphere. No water enters the vent-pipe from the holder, and therefore no gurgling or irregular pressure is produced. Another excellent arrangement of a vent-pipe, suggested by Klinger of Gumpoldskirchen, is shown at D, a drawing which has already been partly considered as a washer and water-seal. For the present purpose the main vessel and its various pipes are so dimensioned that the vertical height g to f is always appreciably greater than the gas pressure in the service or in the generator or gasholder to which it is connected. In these circumstances the gas entering at a depresses the water in the pipe below the level f to an extent equal to the pressure at which it enters that pipe—an extent normally less than the distance f to g; and therefore gas never passes into the body of the vessel, but travels away by the side tube b (which in former references to this drawing was supposed to be absent). If, however, the pressure at a exceeds that of the vertical height f to g, gas escapes at g through the water, and is then free to reach the atmosphere by means of the vent c. As before, d serves to charge the apparatus with water, and e to ensure a proper amount being added. Clearly no liquid can enter the vent-pipe in this device. Safety-valves such as are added to steam-boilers and the like, which consist of a weighted lever holding a conical valve down against its seat, are not required in acetylene apparatus, for the simpler hydraulic seals discussed above can always be fitted wherever they may be needed. It should be noticed that these vent-pipes only come into operation in emergencies, when they are required to act promptly. No economy is to be effected by making them small in diameter. For obvious reasons the vent-pipe of a holder should have a diameter equal to that of the gas-inlet tube, and the vent-pipe of a generator be equal in size to the gas-leading tube.
FROTHING IN GENERATORS.—A very annoying trouble which crops up every now and then during the evolution of acetylene consists in the production of large masses of froth within the generator. In the ordinary way, decomposition of carbide is accompanied by a species of effervescence, but the bubbles should break smartly and leave the surface of the liquid reasonably free from foam. Sometimes, however, the bubbles do not break, but a persistent "head" of considerable height is formed. Further production of gas only increases the thickness of the froth until it rises so high that it is carried forward through the gas-main into the next item of the plant. The froth disappears gradually in the pipes, but leaves in them a deposit of lime which sooner or later causes obstructions by accumulating at the angles and dips; while during its presence in the main the steady passage of gas to the holder is interrupted and the burners may even be made to jump. Manifestly the defect is chiefly, if not always, to be noticed in the working of carbide-to-water generators. The phenomenon has been examined by Mauricheau-Beaupre, who finds that frothing is not characteristic of pure carbide and that it cannot be attributed to any of the impurities normally present in commercial carbide. If, however, the carbide contains calcium chloride, frothing is liable to occur. A 0.1 per cent. solution of calcium chloride appears to yield some foam when carbide is decomposed in it, and a 1 per cent. solution to foam in a pronounced manner. In the absence of calcium chloride, the main cause of frothing seems to be the presence in the generator of new paint or tar. If a generator is taken into use before the paint in any part of it which becomes moistened by warm lime-water has had opportunity of drying thoroughly hard, frothing is certain to occur; and even if the carbide has been stored for only a short time in a tin or drum which has been freshly painted, a production of froth will follow when it is decomposed in water. The products of the polymerisation of acetylene also tend to produce frothing, but not to such an extent as the turpentine in paint and the lighter constituents of coal-tar. Carbide stored even temporarily in a newly painted tin froths on decomposition because it has absorbed among its pores some of the volatile matter given off by the paint during the process of desiccation.
THE "DRY" PROCESS OF GENERATION.—A process for generating acetylene, totally different in principle from those hitherto considered, has been introduced in this country. According to the original patents of G. J. Atkins, the process consisted in bringing small or powdered carbide into mechanical contact with some solid material containing water, the water being either mixed with the solid reagent or attached to it as water of crystallisation. Such reagents indeed were claimed as crude starch and the like, the idea being to recover a by-product of pecuniary value. Now the process seems to be known only in that particular form in which granulated carbide is treated with crystallised sodium carbonate, i.e., common washing soda. Assuming the carbide employed to be chemically pure and the reaction between it and the water of crystallisation contained in ordinary soda crystals to proceed quantitatively, the production of acetylene by the dry process should be represented by the following chemical equation:
5CaC_2 + Na_2CO_3.10H_2O = 5C_2H_2 + 5Ca(OH)_2 + Na_2CO_3.
On calculating out the molecular weights, it will be seen that 286 parts of washing soda should suffice for the decomposition of 320 parts of pure calcium carbide, or in round numbers 9 parts of soda should decompose 10 parts of carbide. In practice, however, it seems to be found that from 1 to 1.5 parts of soda are needed for every part of carbide.
The apparatus employed is a metal drum supported on a hollow horizontal spindle, one end of which is closed and carries a winch handle, and the other end of which serves to withdraw the gas generated in the plant. The drum is divided into three compartments by means of two vertical partitions so designed that when rotation proceeds in one particular direction portions of the two reagents stored in one end compartment pass into the centre compartment; whereas when rotation proceeds in the opposite direction, the material in the centre compartment is merely mixed together, partly by the revolution of the drum, partly with the assistance of a stationary agitator slung loosely from the central spindle. The other end compartment contains coke or sawdust or other dry material through which the gas passes for the removal of lime or other dust carried in suspension as it issues from the generating compartment. The gas then passes through perforations into the central spindle, one end of which is connected by a packed joint with a fixed pipe, which leads to a seal or washer containing petroleum. Approached from a theoretical standpoint, it will be seen that this method of generation entirely sacrifices the advantages otherwise accruing from the use of liquid water as a means for dissipating the heat of the chemical reaction, but on the other hand, inasmuch as the substances are both solid, the reaction presumably occurs more slowly than it would in the presence of liquid water; and moreover the fact that the water employed to act upon the carbide is in the solid state and also more or less combined with the rest of the sodium carbonate molecule, means that, per unit of weight, the water decomposed must render latent a larger amount of heat than it would were it liquid. Experiments made by one of the authors of this book tend to show that the gas evolved from carbide by the dry process contains rather less phosphorus than it might in other conditions of generation, and as a fact gas made by the dry process is ordinarily consumed without previous passage through any chemical purifying agent. It is obvious, however, that the use of the churn described above greatly increases the labour attached to the production of the gas; while it is not clear that the yield per unit weight of carbide decomposed should be as high as that obtained in wet generation. The inventor has claimed that his by-product should be valuable and saleable, apparently partly on the ground that it should contain caustic soda. Evidence, however, that a reaction between the calcium oxide or hydroxide and the sodium carbonate takes place in the prevailing conditions is not yet forthcoming, and the probabilities are that such decomposition would not occur unless the residue were largely diluted with water. [Footnote: The oldest process employed for manufacturing caustic soda consisted in mixing a solution of sodium carbonate with quick or slaked lime, and it has been well established that the causticisation of the soda will not proceed when the concentration of the liquid is greater than that corresponding with a specific gravity of about 1-10, i.e., when the liquid contains more than some 8 to 10 per cent, of sodium hydroxide.] Conversely there are some grounds for believing that the dry residue is less useful than an ordinary wet residue for horticultural purposes, and also for the production of whitewash. From a financial standpoint, the dry process suffers owing to the expense involved in the purchase of a second raw material, for which but little compensation can be discovered unless it is proved that the residue is intrinsically more valuable than common acetylene-lime and can be sold or used advantageously by the ordinary owner of an installation. The discarding of the chemical purifier at the present day is a move of which the advantage may well be overrated.
ARTIFICIAL LIGHTING OF GENERATOR SHEDS.—It has already been argued that all normal or abnormal operations in connexion with an acetylene generating plant should be carried out, if possible, by daylight; and it has been shown that on no account must a naked light ever be taken inside the house containing such a plant. It will occasionally happen, however, that the installation must be recharged or inspected after nightfall. In order to do this in safety, a double window, incapable of being opened, should be fitted in one wall of the house, as far as possible from the door, and in such a position that the light may fall on to all the necessary places. Outside this window may be suspended an ordinary hand- lantern burning oil or paraffin; or, preferably, round this window may be built a closed lantern into which some source of artificial light may be brought. If the acetylene plant has an isolated holder of considerable size, there is no reason at all why a connexion should not be made with the service-pipes, and an acetylene flame be used inside this lantern; but with generators of the automatic variety, an acetylene light is not so suitable, because of the fear that gas may not be available precisely at the moment when it is necessary to have light in the shed. It would, however, be a simple matter to erect an acetylene burner inside the lantern in such a way that when needed an oil-lamp or candle could be used instead. Artificial internal light of any kind is best avoided; the only kind permissible being an electric glow-lamp. If this is employed, it should be surrounded by a second bulb or gas-tight glass jacket, and preferably by a wire cage as well; the wires leading to it must be carefully insulated, and all switches or cut-outs (which may produce a spark) must be out of doors. The well-known Davy safety or miner's lamp is not a trustworthy instrument for use with acetylene because of (a) the low igniting-point of acetylene; (b) the high temperature of its flame; and (c) the enormous speed at which the explosive wave travels through a mixture of acetylene and air. For these reasons the metallic gauze of the Davy lamp is not so efficient a protector of the flame as it is in cases of coal-gas, methane, &c. Moreover, in practice, the Davy lamp gives a poor light, and unless in constant use is liable to be found out of order when required. It should, however, be added that modern forms of the safety lamp, in which the light is surrounded by a stout glass chimney and only sufficient gauze is used for the admission of fresh air and for the escape of the combustion products, appear quite satisfactory when employed in an atmosphere containing some free acetylene.
THE SELECTION OF AN ACETYLENE GENERATOR
In Chapter II. an attempt has been made to explain the physical and chemical phenomena which accompany the interaction of calcium carbide and water, and to show what features in the reaction are useful and what inconvenient in the evolution of acetylene on a domestic or larger scale. Similarly in Chapter III. have been described the various typical devices which may be employed in the construction of different portions of acetylene plant, so that the gas may be generated and stored under the best conditions, whether it is evolved by the automatic or by the non- automatic system. This having been done, it seemed of doubtful utility to include in the first edition of this work a long series of illustrations of such generators as had been placed on the markets by British, French, German, and American makers. It would have been difficult within reasonable limits to have reproduced diagrams of all the generators that had been offered for sale, and absolutely impossible within the limits of a single hand-book to picture those which had been suggested or patented. Moreover, some generating apparatus appeared on the market ephemerally; some was constantly being modified in detail so as to alter parts which experience or greater knowledge had shown the makers to be in need of alteration, while other new apparatus was constantly being brought out. On these and other grounds it did not appear that much good purpose would have been served by describing the particular apparatus which at that time would have been offered to prospective purchasers. It seemed best that the latter should estimate the value and trustworthiness of apparatus by studying a section of it in the light of the general principles of construction of a satisfactory generator as enunciated in the book. While the position thus taken by the authors in 1903 would still not be incorrect, it has been represented to them that it would scarcely be inconsistent with it to give brief descriptions of some of the generators which are now being sold in Great Britain and a few other countries. Six more years' experience in the design and manufacture of acetylene plant has enabled the older firms of manufacturers to fix upon certain standard patterns for their apparatus, and it may confidently be anticipated that many of these will survive a longer period. Faulty devices and designs have been weeded out, and there are lessons of the past as well as theoretical considerations to guide the inventor of a new type of generator. On those grounds, therefore, an attempt has now been made to give brief descriptions, with sectional views, of a number of the generators now on the market in Great Britain. Moreover, as the first edition of this book found many readers in other countries, in several of which there is greater scope for the use of acetylene, it has been decided to describe also a few typical or widely used foreign generators. All the generators described must stand or fall on their merits, which cannot be affected by any opinion expressed by the authors. In the descriptions, which in the first instance have generally been furnished by the manufacturers of the apparatus, no attempt has therefore been made to appraise the particular generators, and comparisons and eulogistic comments have been excluded. The descriptions, however, would nevertheless have been somewhat out of place in the body of this book; they have therefore been relegated to a special Appendix. It has, of course, been impossible to include the generators of all even of the English manufacturers, and doubtless many trustworthy ones have remained unnoticed. Many firms also make other types of generators in addition to those described. It must not be assumed that because a particular make of generator is not mentioned it is necessarily faulty. The apparatus described may be regarded as typical or well known, and workable, but it is not by reason of its inclusion vouched for in any other respect by the authors. The Appendix is intended, not to bias or modify the judgment of the would-be purchaser of a generator, but merely to assist him in ascertaining what generators there are now on the market.
The observations on the selection of a generator which follow, as well as any references in other chapters to the same matter, have been made without regard to particular apparatus of which a description may (or may not) appear in the Appendix. With this premise, it may be stated that the intending purchaser should regard the mechanism of a generator as shown in a sectional view or on inspection of the apparatus itself. If the generator is simple in construction, he should be able to understand its method of working at a glance, and by referring it to the type (vide Chapter III.) to which it belongs, be able to appraise its utility from a chemical and physical aspect from what has already been said. If the generator is too complicated for ready understanding of its mode of working, it is not unlikely to prove too complicated to behave well in practice. Not less important than the mechanism of a generator is good construction from the mechanical point of view, i.e., whether stout metal has been employed, whether the seams and joints are well finished, and whether the whole apparatus has been built in the workman- like fashion which alone can give satisfaction in any kind of plant. Bearing these points in mind, the intending purchaser may find assistance in estimating the mechanical value of an apparatus by perusing the remainder of this chapter, which will be devoted to elaborating at length the so-called scientific principles underlying the construction of a satisfactory generator, and to giving information on the mechanical and practical points involved.
It is perhaps desirable to remark that there is scarcely any feature in the generation of acetylene from calcium carbide and water—certainly no important feature—which introduces into practice principles not already known to chemists and engineers. Once the gas is set free it ranks simply as an inflammable, moisture-laden, somewhat impure, illuminating and heat-giving gas, which has to be dried, purified, stored, and led to the place of combustion; it is in this respect precisely analogous to coal- gas. Even the actual generation is only an exothermic, or heat-producing, reaction between a solid and a liquid, in which rise of temperature and pressure must be prevented as far as possible. Accordingly there is no fundamental or indispensable portion of an acetylene apparatus which lends itself to the protection of the patent laws; and even the details (it may be said truthfully, if somewhat cynically) stand in patentability in inverse ratio to their simplicity and utility.
During the early part of 1901 a Committee appointed by the British Home Office, "to advise as to the conditions of safety to which acetylene generators should conform, and to carry out tests of generators in the market in order to ascertain how far those conform with such conditions," issued a circular to the trade suggesting that apparatus should be sent them for examination. In response, forty-six British generators were submitted for trial, and were examined in a fashion which somewhat exceeded the instructions given to the Committee, who finally reported to the Explosives Department of the Home Office in a Blue Book, No. Cd. 952, which can be purchased through any bookseller. This report comprises an appendix in which most of the apparatus are illustrated, and it includes the result of the particular test which the Committee decided to apply. Qualitatively the test was useful, as it was identical in all instances, and only lacks full utility inasmuch as the trustworthiness of the automatic mechanism applied to such generators as were intended to work on the automatic system was not estimated. Naturally, a complete valuation of the efficiency of automatic mechanism cannot be obtained from one or even several tests, it demands long-continued watching; but a general notion of reliability might have been obtained. Quantitatively, however, the test applied by the Committee is not so free from reproach, for, from the information given, it would appear to have been less fair to some makers of apparatus than to others. Nevertheless the report is valuable, and indicates the general character of the most important apparatus which were being offered for sale in the United Kingdom in 1900-1901.
It is not possible to give a direct answer to the question as to which is the best type of acetylene generator. There are no generators made by responsible firms at the present time which are not safe. Some may be easier to charge and clean than others; some require more frequent attention than others; some have moving parts less likely to fail, when handled carelessly, than others; some have no moving mechanism to fail. For the illumination of a large institution or district where one man can be fully occupied in attending to the plant, cleaning, lighting, and extinguishing the lamps, or where other work can be found for him so as to leave him an hour or so every day to look after the apparatus, the hand-fed carbide-to-water generator L (Fig. 6) has many advantages, and is probably the best of all. In smaller installations choice must be made first between the automatic and the non-automatic principle—the advantages most frequently lying with the latter. If a non-automatic generator is decided upon, the hand carbide-feed or the flooded- compartment apparatus is almost equally good; and if automatism is desired, either a flooded-compartment machine or one of the most trustworthy types of carbide-feed apparatus may be taken. There are contact apparatus on the markets which appear never to have given trouble, and those are worthy of attention. Some builders advocate their own apparatus because the residue is solid and not a cream. If there is any advantage in this arising from greater ease in cleaning and recharging the generator and in disposing of the waste, that advantage is usually neutralised by the fear that the carbide may not have been wholly decomposed within the apparatus; and whereas any danger arising from imperfectly spent carbide being thrown into a closed drain may be prevented by flooding the residue with plenty of water in an open vessel, imperfect decomposition in the generator means a deficiency in the amount of gas evolved from a unit weight of solid taken or purchased. In fact, setting on one side apparatus which belong to a notoriously defective system and such as are constructed in large sizes on a system that is only free from overheating, &c., in small sizes; setting aside all generators which are provided with only one decomposing chamber when they are of a capacity to require two or more smaller ones that can more efficiently be cooled with water jackets; and setting aside any form of plant which on examination is likely to exhibit any of the more serious objections indicated in this and the previous chapters, there is comparatively little to choose, from the chemical and physical points of view, between the different types of generators now on the markets. A selection may rather be made on mechanical grounds. The generator must be well able to produce gas as rapidly as it will ever be required during the longest or coldest evening; it must be so large that several more brackets or burners can be added to the service after the installation is complete. It must be so strong that it will bear careless handling and the frequent rough manipulation of its parts. It must be built of stout enough material not to rust out in a few years. Each and all of its parts must be accessible and its exterior visible. Its pipes, both for gas and sludge, must be of large bore (say 1 inch), and fitted at every dip with an arrangement for withdrawing into some closed vessel the moisture, &c., that may condense. The number of cocks, valves, and moving parts must be reduced to a minimum; cocks which require to be shut by hand before recharging must give way to water-seals. It must be simple in all its parts, and its action intelligible at a glance. It must be easy to charge—preferably even by the sense of touch in darkness. It must be easy to clean. The waste lime must be easily removed. It must be so fitted with vent-pipes that the pressure can never rise above that at which it is supposed to work. Nevertheless, a generator in which these vent-pipes are often brought into use is badly constructed and wasteful, and must be avoided. The water of the holder seal should be distinct from that used for decomposing the carbide; and those apparatus where the holder is entirely separated from the generator are preferable to such as are built all in one, even if water-seals are fitted to prevent return of gas. Apparatus which is supposed to be automatic should be made perfectly automatic, the water or the carbide-feed being locked automatically before the carbide store, the decomposing chamber, or the sludge-cock can be opened. The generating chamber must always be in communication with the atmosphere through a water-sealed vent-pipe, the seal of which, if necessary, the gas can blow at any time. All apparatus should be fitted with rising holders, the larger the better. Duplicate copies of printed instructions should be demanded of the maker, one copy being kept in the generator-house, and the other elsewhere for reference in emergencies. These instructions must give simple and precise information as to what should be done in the event of a breakdown as well as in the normal manipulation of the plant. Technical expressions and descriptions of parts understood only by the maker must be absent from these rules.
BRITISH AND FOREIGN REGULATIONS FOR THE CONSTRUCTION AND INSTALLATION OF ACETYLENE GENERATING PLANT
Dealing with the "conditions which a generator should fulfil before it can be considered as being safe," the HOME OFFICE COMMITTEE of 1901 before mentioned write as follows:
1. The temperature in any part of the generator, when run at the maximum rate for which it is designed, for a prolonged period, should not exceed 130 deg. C. This may be ascertained by placing short lengths of wire, drawn from fusible metal, in those parts of the apparatus in which heat is liable to be generated.
2. The generator should have an efficiency of not less than 90 per cent., which, with carbide yielding 5 cubic feet per pound, would imply a yield of 4.5 cubic feet for each pound of carbide used.
3. The size of the pipes carrying the gas should be proportioned to the maximum rate of generation, so that undue back pressure from throttling may not occur.
4. The carbide should be completely decomposed in the apparatus, so that lime sludge discharged from the generator shall not be capable of generating more gas.
5. The pressure in any part of the apparatus, on the generator side of the holder, should not exceed that of 20 inches of water, and on the service side of same, or where no gasholder is provided, should not exceed that of 5 inches of water.
6. The apparatus should give no tarry or other heavy condensation products from the decomposition of the carbide.
7. In the use of a generator regard should be had to the danger of stoppage of passage of the gas and resulting increase of pressure which may arise from the freezing of the water. Where freezing may be anticipated, steps should be taken to prevent it.
8. The apparatus should be so constructed that no lime sludge can gain access to any pipes intended for the passage of gas or circulation of water.
9. The use of glass gauges should be avoided as far as possible, and, where absolutely necessary, they should be effectively protected against breakage.
10. The air space in a generator before charging should be as small as possible.
11. The use of copper should be avoided in such parts of the apparatus as are liable to come in contact with acetylene.
The BRITISH ACETYLENE ASSOCIATION has drawn up the following list of regulations which, it suggests, shall govern the construction of generators and the installation of piping and fittings:
1. Generators shall be so constructed that, when used in accordance with printed instructions, it shall not he possible for any undecomposed carbide to remain in the sludge removed therefrom.
2. The limit of pressure in any part of the generator shall not exceed that of 20 inches of water, subject to the exception that if it be shown to the satisfaction of the Executive of the Acetylene Association that higher pressures up to 50 inches of water are necessary in certain generators, and are without danger, the Executive may, with the approval of the Home Office, grant exemption for such generators, with or without conditions.
3. The limit of pressure in service-pipes, within the house, shall not exceed 10 inches of water.
4. Except when used for special industrial purposes, such as oxy- acetylene welding, factories, lighthouses, portable apparatus containing not more than four pounds of carbide, and other special conditions as approved by the Association, the acetylene plant, such as generators, storage-holders, purifiers, scrubbers, and for washers, shall be in a suitable and well-ventilated outhouse, in the open, or in a lean-to, having no direct communication with a dwelling-house. A blow-off pipe or safety outlet shall be arranged in such a manner as to carry off into the open air any overmake of gas and to open automatically if pressure be increased beyond 20 inches water column in the generating chamber or beyond 10 inches in the gasholder, or beyond the depth of any fluid seal on the apparatus.
5. Generators shall have sufficient storage capacity to make a serious blow-off impossible.
6. Generators and apparatus shall be made of sufficiently strong material and be of good workmanship, and shall not in any part be constructed of unalloyed copper.
7. It shall not be possible under any conditions, even by wrong manipulation of cocks, to seal the generating chamber hermetically.
8. It shall not be possible for the lime sludge to choke any of the gas- pipes in the apparatus, nor water-pipes if such be alternately used as safety-valves.
9. In the use of a generator, regard shall be had to the danger of stoppage of passage of the gas, and resulting increase of pressure, which may arise from the freezing of the water. Where freezing may be anticipated, steps shall be taken to prevent it.
10. The use of glass gauges shall be avoided as far as possible, and where absolutely necessary they shall be effectively protected against breakage.
11. The air space in the generator before charging shall be as small as possible, i.e., the gas in the generating chamber shall not contain more than 8 per cent. of air half a minute after commencement of generation. A sample of the contents, drawn from the holder any time after generation has commenced, shall not contain an explosive mixture, i.e., more than 18 per cent, of air. This shall not apply to the initial charges of the gasholder, when reasonable precautions are taken.
12. The apparatus shall produce no tarry or other heavy condensation products from the decomposition of the carbide.
13. The temperature of the gas, immediately on leaving the charge, shall not exceed 212 deg. F. (100 deg. C.)
14. No generator shall be sold without a card of instructions suitable for hanging up in some convenient place. Such instructions shall be of the most detailed nature, and shall not presuppose any expert knowledge whatever on the part of the operator.
15. Notice to be fixed on Generator House Door, "NO LIGHTS OR SMOKING ALLOWED."
16. Every generator shall have marked clearly upon the outside a statement of the maximum number of half cubic foot burners and the charge of carbide for which it is designed.
17. The Association strongly advise the use of an efficient purifier with generating plant for indoor lighting.
18. No composition piping shall be used in any part of a permanent installation.
19. Before being covered in, all pipe-work (main and branches) shall be tested in the following manner: A special acetylene generator, giving a pressure of at least 10 inches water column in a gauge fixed on the furthest point from the generator, shall be connected to the pipe-work. All points shall be opened until gas reaches them, when they shall be plugged and the main cock on the permanent generator turned off, but all intermediate main cocks shall be open in order to test underground main and all connexions. The gauge must not show a loss after generator has been turned off for at least two hours.
20. After the fittings (pendants, brackets, &c.) have been fixed and all burners lighted, the gas shall be turned off at the burners and the whole installation shall be re-tested, but a pressure of 5 inches shall be deemed sufficient, which shall not drop lower than to 4-1/2 inches on the gauge during one hour's test.
21. No repairs to, or alterations in, any part of a generator, purifier, or other vessel which has contained acetylene shall be commenced, nor, except for recharging, shall any such part or vessel be cleaned out until it has been completely filled with water, so as to expel any acetylene or mixture of acetylene and air which may remain in the vessel, and may cause a risk of explosion.
Recommendation.—It being the general practice to store carbide in the generator-house, the Association recommend that the carbide shall be placed on a slightly raised platform above the floor level.
THE BRITISH FIRE OFFICES COMMITTEE in the latest revision, dated July 15, 1907, of its Rules and Regulations re artificial lighting on insured premises, includes the following stipulations applicable to acetylene:
Any apparatus, except as below, for generating, purifying, enriching, compressing or storing gas, must be either in the open or in a building used for such purposes only, not communicating directly with any building otherwise occupied.
An acetylene portable apparatus is allowed, provided it holds a charge of not more than 2 lb. of carbide.
A cylinder containing not more than 20 cubic feet of acetylene compressed and (or) dissolved in accordance with an Order of Secretary of State under the Explosives Act, 1875, is allowed.
The use of portable acetylene lamps containing charges of carbide exceeding the limit of 2 lb. allowed under these Rules (the average charge being about 18 lb.) is allowed in the open or in buildings in course of erection.
Liquid acetylene must not be used or stored on the premises.
The pipe, whether flexible or not, connecting an incandescent gas lamp to the gas-supply must be of metal with metal connexions.
(The reference in these Rules to the storage of carbide has been quoted in Chapter II. (page 19).)
These rules are liable to revision from time to time.
The GERMAN ACETYLENE VEREIN has drawn up (December 1904) the following code of rules for the construction, erection, and manipulation of acetylene apparatus:
I. Rules for Construction.
1. All apparatus for the generation, purification, and storage of acetylene must be constructed of sheet or cast iron. Holder tanks may be built of brick.
2. When bare, galvanised, or lead-coated sheet-iron is used, the sides of generators, purifiers, condensers, holder tanks, and (if present) washers and driers must be built with the following gauges as minima:
Holder bells. All other apparatus.
Up to 7 cubic feet capacity 0.75 mm. 1.00 mm. From 7 to 18 " 1.00 1.25 From 18 to 53 " 1.25 1.50 Above 53 " 1.50 2.00
When not constructed of cast-iron, the bottoms, covers, and "manhole" lids must be 0.5 mm. thicker in each respective size.
In all circumstances, the thickness of the walls—especially in the case of apparatus not circular in horizontal section—must be such that alteration in shape appears impossible, unless deformation is guarded against in other ways.
Generators must be so constructed that when they are being charged the carbide cannot fall into the residue which has already been gasified; and the residues must always be capable of easy, complete, and safe removal.
3. Generators, purifiers, and holders must be welded, riveted or folded at the seams; soft solder is only permissible as a tightening material.
4. Pipes delivering acetylene, or uniting the apparatus, must be cast- or wrought-iron. Unions, cocks, and valves must not be made of copper; but the use of brass and bronze is permitted.
5. When cast-iron is employed, the rules of the German Gas and Water Engineers are to be followed.
6. In generators where the whole amount of carbide introduced is not gasified at one time, it must be possible to add fresh water or carbide in safety, without interfering with the action of the apparatus. In such generators the size of the gasholder space is to be calculated according to the quantity of carbide which can be put into the generator. For every 1 kilogramme of carbide the available gasholder space must be: for the first 50 kilos., 20 litres; for the next 50 kilos., 15 litres; for amounts above 100 kilos., 10 litres per kilo. [One kilogramme may be taken as 2.2 lb., and 28 litres as 1 cubic foot.]
The generator must be large enough to supply the full number of normal (10-litre) burners with gas for 5 hours; the yield of acetylene being taken at 290 litres per kilo. [4.65 cubic feet per lb.]
The gasholder space of apparatus where carbide is not stored must be at least 30 litres for every normal (10-litre) flame.
7. The gasholder must be fitted with an appliance for removing any gas which may be generated (especially when the apparatus is first brought into action) after the available space is full. This vent must have a diameter at least equal to the inlet pipe of the holder.
8. Acetylene plant must be provided with purifying apparatus which contains a proper purifying material in a suitable condition.
9. The dimensions of subsidiary apparatus, such as washers, purifiers, condensers, pipes, and cocks must correspond with the capacity of the plant.
10. Purifiers and washers must be constructed of materials capable of resisting the attack of the substances in them.
11. Every generator must bear a plate giving the name of the maker, or the seller, and the maximum number of l0-litre lights it is intended to supply. If all the carbide put into the generator is not gasified at one time, the plate must also state the maximum weight of carbide in the charge. The gasholder must also bear a plate recording the maker's or seller's name, as well as its storage capacity.
12. Rules 1 to 11 do not apply to portable apparatus serving up to two lights, or to portable apparatus used only out of doors for the lighting of vehicles or open spaces.
II. Rules for Erection
1. Acetylene apparatus must not be erected in or under rooms occupied or frequented (passages, covered courts, &c.) by human beings. Generators and holders must only be erected in apartments covered with light roofs, and separated from occupied rooms, barns, and stables by a fire-proof wall, or by a distance of 15 feet. Any wall is to be considered fire- proof which is built of solid brick, without openings, and one side of which is "quite free." Apparatus may be erected in barns and stables, provided the space required is partitioned off from the remainder by a fire-proof wall.
2. The doors of apparatus sheds must open outwards, and must not communicate directly with rooms where fires and artificial lights are used.
3. Apparatus for the illumination of showmen's booths, "merry-go-rounds," shooting galleries, and the like must be erected outside the tents, and be inaccessible to the public.
4. Permanent apparatus erected in the open air must be at least 15 feet from an occupied building.
5. Apparatus sheds must be fitted at their highest points with outlet ventilators of sufficient size; the ventilators leading straight through the roof into the open air. They must be so arranged that the escaping gases and vapours cannot enter rooms or chimneys.
6. The contacts of any electrical warning devices must be outside the apparatus shed.
7. Acetylene plants must be prevented from freezing by erection in frost- free rooms, or by the employment of a heating apparatus or other suitable appliance. The heat must only be that of warm water or steam. Furnaces for the heating appliance must be outside the rooms containing generators, their subsidiary apparatus, or holders; and must be separated from such rooms by fire-proof walls.
8. In one of the walls of the apparatus shed—if possible not that having a door—a window must be fitted which cannot be opened; and outside that window an artificial light is to be placed. In the usual way acetylene lighting may be employed; but a lamp burning paraffin or oil, or a lantern enclosing a candle, must always be kept ready for use in emergencies. In all circumstances internal lighting is forbidden.
9. Every acetylene installation must be provided with a main cock, placed in a conveniently accessible position so that the whole of the service may be cut off from the plant.
10. The seller of an apparatus must provide his customer with a sectional drawing, a description of the apparatus, and a set of rules for attending to it. These are to be supplied in duplicate, and one set is to be kept hanging up in the apparatus shed.
III. Rules for Working the Apparatus.
1. The apparatus must only be opened by daylight for addition of water. If the generator is one of those in which the entire charge of carbide is not gasified at once, addition of fresh carbide must only be made by daylight.
2. All work required by the plant, or by any portion of it, and all ordinary attendance needed must be performed by daylight.
3. All water-seals must be carefully kept full.
4. When any part of an acetylene apparatus or a gas-meter freezes, notwithstanding the precautions specified in II., 7, it must be thawed only by pouring hot water into or over it; flames, burning fuel, or red- hot iron bars must not be used.
5. Alterations to any part of an apparatus which involve the operations of soldering or riveting, &c., i.e., in which a fire must be used, or a spark may be produced by the impact of hammer on metal, must only be carried out by daylight in the open air after the apparatus has been taken to pieces. First of all the plant must be freed from gas. This is to be done by filling every part with water till the liquid overflows, leaving the water in it for at least five minutes before emptying it again.
6. The apparatus house must not be used for any other operation, nor employed for the storage of combustible articles. It must be efficiently ventilated, and always kept closed. A notice must be put upon the door that unauthorised persons are not permitted to enter.
7. It in forbidden to enter the house with a burning lantern or lamp, to strike matches, or to smoke therein.
8. A search for leaks in the pipes must not be made with the aid of a light.
9. Alterations to the service must not be made while the pipes are under pressure, but only after the main cock has been shut.
10. If portable apparatus, such as described in I., 12, are connected to the burners with rubber tube, the tube must be fortified with an internal or external spiral of wire. The tube must be fastened at both ends to the cocks with thread, copper wire, or with ring clamps.
11. The preparation, storage, and use of compressed or liquefied acetylene is forbidden. By compressed acetylene, however, is only to be understood gas compressed to a pressure exceeding one effective atmosphere. Acetylene compressed into porous matter, with or without acetone, is excepted from this prohibition.
12. In the case of plants serving 50 lights or less, not more than 100 kilos. of carbide in closed vessels may be kept in the apparatus house besides the drum actually in use.
A fresh drum is not to be opened before the previous one has been two- thirds emptied. Opened drums must be closed with an iron watertight lid covering the entire top of the vessel.
In the case of apparatus supplying over 500 lights, only one day's consumption of carbide must be kept in the generator house. In other respects the store of carbide for such installations is to be treated as a regular carbide store.
13. Carbide drums must not be opened with the aid of a flame or a red-hot iron instrument.
14. Acetylene apparatus must only be attended to by trustworthy and responsible persons.
The rules issued by the AUSTRIAN GOVERNMENT in 1905 for the installation of acetylene plant and the use of acetylene are divided into general enactments relating to acetylene, and into special enactments in regard to the apparatus and installation. The general enactments state that:
1. The preparation and use of liquid acetylene is forbidden.
2. Gaseous acetylene, alone, in admixture, or in solution, must not be compressed above 2 atmospheres absolute except under special permission.
3. The storage of mixtures of acetylene with air or other gases containing or evolving free oxygen is forbidden.
4. A description of every private plant about to be installed must be submitted to the local authorities, who, according to its size and character, may give permission for it to be installed and brought into use either forthwith or after special inspection. Important alterations to existing plant must be similarly notified.
5. The firms and fitters undertaking the installation of acetylene plant must be licensed.
The special enactments fall under four headings, viz., (a) apparatus; (b) plant houses; (c) pipes; (d) residues.
In regard to apparatus it is enacted that:
1. The type of apparatus to be employed must be one which has been approved by one of certain public authorities in the country.
2. A drawing and description of the construction of the apparatus and a short explanation of the method of working it must be fixed in a conspicuous position under cover in the apparatus house. The notice must also contain approved general information as to the properties of calcium carbide and acetylene, precautions that must be observed to guard against possible danger, and a statement of how often the purifier will require to be recharged.
3. The apparatus must be marked with the name of the maker, the year of its construction, the available capacity of the gasholder, and the maximum generating capacity per hour.
4. Each constituent of the plant must be proportioned to the maximum hourly output of gas and in particular the available capacity of the holder must be 75 per cent. of the latter. The apparatus must not be driven above its nominal productive capacity.
5. The productive capacity of generators in which the gasholder has to be opened or the bell removed before recharging, or for the removal of sludge, must not exceed 50 litres per hour, nor may the charge of carbide exceed 1 kilo.
6. Generators exceeding 50 litres per hour productive capacity must be arranged so that they can be freed from air before use.
7. Generators exceeding 1500 litres per hour capacity must be arranged so that the acetylene, contained in the parts of the apparatus which have to be opened for recharging or for the removal of sludge, can be removed before they are opened.
8. Automatic generators of which the decomposing chambers are built inside the gasholder must not exceed 300 litres per hour productive capacity.
9. Generators must be arranged so that after-generation cannot produce objectionable results.
10. The holder of carbide-to-water generators must be large enough to take all the gas which may be produced by the introduction of one charge of carbide without undue pressure ensuing.
11. The maximum pressure permissible in any part of the apparatus is 1.1 atmosphere absolute.
12. The temperature in the gas space of a generator must never exceed 80 deg. C.
13. Generating apparatus, &c., must be constructed in a workmanlike manner of metal capable of resisting rust and distortion, and, where the metal comes in contact with carbide or acetylene, it must not be one (copper in particular) which forms an explosive compound with the gas. Cocks and screw connexions, &c., of brass, bronze, &c., must always be kept clean. Joints exposed to acetylene under pressure must be made by riveting or welding except that in apparatus not exceeding 100 litres per hour productive capacity double bending may be used.
14. Every apparatus must be fitted with a safety-valve or vent-pipe terminating in a safe place in the open, and of adequate size.
15. Every apparatus must be provided with an efficient purifier so fitted that it may be isolated from the rest of the plant and with due consideration of the possible action of the purifying material upon the metal used.
16. Mercury pressure gauges are prohibited. Liquid gauges, if used must be double the length normally needed, and with a cock which in automatic apparatus must be kept shut while it is in action.
17. Proper steps must always be taken to prevent the apparatus freezing. In the absence of other precautions water-seals and pressure-gauges must be filled with liquid having a sufficiently low freezing-point and without action on acetylene or the containing vessel.
18. Signal devices to show the position of the gasholder bell must not be capable of producing sparks inside the apparatus house.
19. Leaks must not be sought for with an open flame and repairs requiring the use of a blow-pipe, &c., must only be carried out after the apparatus has been taken to pieces or freed from gas by flooding.
20. Apparatus must only be attended to by trustworthy and responsible adults.
21. Portable apparatus holding not more than 1 kilo. of carbide and of not more than 50 litres per hour productive capacity, and apparatus fixed and used out of doors are exempt from the foregoing regulations except Nos. 11 and 12, and the first part of 13.