W. J. Atkinson Butterfield

“ Water is clearly, therefore, the proper substance to employ for the dissipation of the heat generated, although it is strictly speaking almost devoid of heat-conducting power; for not only is the specific heat of water much greater than that of any other material present, but it possesses in a high degree the faculty of absorbing heat throughout its mass, by virtue of the action known as convection, provided that heat is communicated to it at or near the bottom, and not too near its upper surface. ”

“ It is not too much to say that if ignorant and short-sighted makers in the earliest days of the acetylene industry had not recommended and supplied to their customers lightly built apparatus which has in many instances already begun to give trouble, to need repairs, and to fail by thorough corrosion--apparatus which frequently had nothing but cheapness in its favour--the use of the gas would have spread more rapidly than it has done, and the public would not now be hearing of partial or complete failures of acetylene installations. ”

“ Just as, by an immutable law of chemistry, a given weight of calcium carbide yields a given weight of acetylene, and by no amount of ingenuity can be made to produce either more or less; so, by an equally immutable law of physics, the decomposition of a given weight of calcium carbide by water, or the decomposition of a given weight of water by calcium carbide, yields a perfectly definite quantity of heat--a quantity of heat which cannot be reduced or increased by any artifice whatever. ”

“ All the mechanical advantages are in favour, as just indicated, of making water the moving substance; and accordingly, when classified in the present manner, a great majority of the generators now on the markets are termed water-to-carbide apparatus. Their disadvantages are twofold, though these may be avoided or circumvented: in all types save one the carbide is in excess at the immediate place and time of decomposition; and in all types without exception the carbide in the whole of the generator is in excess, so that the phenomenon of "after- generation" occurs with more or less severity. ”

“ Looked at from one aspect the holder of a fixed apparatus is merely an economical substitute for the wasteful vent- pipe, because it is a place in which acetylene can be held in reserve whenever the make exceeds the consumption in speed. It is perhaps possible to conceive of a large table acetylene lamp fitted with a water- sealed rising holder; but for vehicular purposes the displacement holder is practically the only one available, and in small apparatus it becomes too minute in size to be of much service as a store for the gas produced by after-generation. ”

“ In the presence of a meter, the installation can conveniently be tested for soundness by throwing into it, through the meter, a pressure of 12 inches or so of water from the weighted holder, then leaving the inlet cock open, and observing whether the index hand on the lowest dial remains perfectly stationary for a quarter of an hour--movement of the linger again indicating a leak. The search for leaks must never be made with a light; if the pipes are full of air this is useless, if full of gas, criminal in its stupidity. ”

“ The argument is sometimes advanced that inasmuch as for the same, or a smaller, capital outlay as is required to instal a non-automatic apparatus large enough to supply at one charging the maximum amount of light and heat that can ever be needed on the longest winter's night, an automatic plant adequate to make gas for two or three evenings can be laid down, the latter must be preferable, because the attendant, in the latter case, will only need to enter the generator-house two or three times a week. Such an argument is defective because it ignores the influence of habit upon the human being. ”

“ During the operation of an acetylene generator a large amount of heat is produced, the quantity of which is beyond human control. It is desirable, for various reasons, that the temperature shall be kept as low as possible. There are three substances present to which the heat may be compelled to transfer itself until it has opportunity to pass into the surrounding atmosphere: the material of which the apparatus is constructed, the gas which is in process of evolution, and whichever of the two bodies-- calcium carbide or water--is in excess in the generator. ”

“ One peculiar and noteworthy feature of acetylene, often overlooked, is that the apparatus is constructed by men who may have been accustomed to gas-making plant all their lives, and who may understand by mere habit how to superintend a chemical operation; but the same apparatus is used by persons who generally have no special acquaintance with such subjects, and who, very possibly, have not even burnt coal-gas at any period of their lives. ”

“ It was shown in Chapter II that overheating is one of the chief troubles to be guarded against in acetylene generators, and that the temperature attained is a function of the speed at which generation proceeds. Seeing that in an automatic apparatus the rate of decomposition depends on the rate at which gas is being burnt, while in a non-automatic generator it is, or may be, under no control, the critic may urge that the reaction must take place more slowly and regularly, and the maximum temperature therefore be lower, when the plant works automatically. ”

“ Acetylene is not an economical source of power, partly for the theoretical reason that it is a richer fuel even than coal-gas, and gas-engines would appear usually to be more efficient as the fuel they burn is poorer in calorific intensity, i.e., in heating power (which is explosive power) per unit of volume. The richer, or more concentrated, any fuel in, the more rapidly does the explosion in a mixture of that fuel with air proceed, because a rich fuel contains a smaller proportion of non-inflammable gases which tend to retard explosion than a poor one ”

“ The black mark on a ceiling over a source of light is caused by a rising current of hot air and combustion products set up by the heat accompanying the light, which current of hot gas carries with it the dust and dirt always present in the atmosphere of an inhabited room. As this current of air and burnt gas travels in a fairly concentrated vertical stream, and as the ceiling is comparatively cool and exhibits a rough surface, that dust and dirt are deposited on the ceiling above the flame, but the stain is seldom or never composed of soot from the illuminant itself. ”

“ The standard of illumination adopted for the table is one which is only gaining general recognition where incandescent gas or acetylene lighting is available, though in exceptional cases it has doubtless been attained by means of oil-lamps or flat-flame gas-burners, but very rarely if ever by means of carbon-filament electric glow-lamps, or candles. It assumes that the occupants of a room do not wish to be troubled to bring work or book "to the light," but wish to be able to work or read wheresoever in the room they will, without consideration of the whereabouts of the light or lights. ”

“ This last assertion requires substantiation; for it is at least a grave theoretical error to add a non-inflammable gas to a combustible one, as is seen in the lower efficiency of all flames when burning in common air in comparison with that which they exhibit in oxygen; while from the practical aspect, so harmful is carbon dioxide in an illuminating gas, that coal-gas and carburetted water-gas are frequently most rigorously freed from it, because a certain gain in illuminating power may often thus be achieved more cheaply than by direct enrichment of the gas by addition of hydrocarbons. ”

“ Regarding somewhat more closely the relative convenience and safety of acetylene and paraffin for the illumination of country residences, it may be remarked that an extraordinarily great amount of care must be bestowed upon each separate lamp if the whole house is to be kept free from an odour which is very offensive to the nostrils; and the time occupied in this process, which of itself is a disagreeable one, reaches several hours every day. Habit has taught the country dweller to accept as inevitable this waste of time, and largely to ignore the odour of petroleum in his abode ”

“ Since of the substances in or about a generator water is the one which has by far the largest capacity for absorbing heat, and since it is the only substance to which any necessary quantity of heat can be safely or conveniently transmitted, it follows that the larger in size an acetylene generator is, or the more rapidly that generator is made to deliver gas, the more desirable is it to use water as the means for dissipating the surplus heat, and the more necessary is it to employ an apparatus in which water is in large chemical excess at the actual place of decomposition. ”

“ It is easy to imagine that the carbide container of a small generator might be so large, or loaded with so small a quantity of carbide, or that the apparatus might in other respects be so badly designed, that the gas evolved might contain a sufficient proportion of air to render it liable to explode in presence of a naked light, or of a temperature superior to its inflaming-point. ”

“ 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 ”

“ As acetylene can easily be burnt in a portable apparatus, and as the burners can be supplied with gas at such comparatively high pressure that the flames are capable of withstanding sharp gusts of wind even when not protected by glass, the brilliant light given by acetylene forms an excellent method of destroying the insects before they have had time to lay their eggs. Two methods of using the light have been tried with astonishing success: in one a naked flame is supported within some receptacle, such as a barrel with one end knocked out, the interior of which is painted heavily with treacle ”

“ As calcium carbide evolves an inflammable gas when it merely comes into contact with water, it becomes possible to throw into the sea or river, by hand or by ejection from a mortar, a species of bomb or portable generator which is capable of emitting a powerful beam of light if only facilities are present for inflaming the acetylene generated; and it is quite easy so to arrange the interior of such apparatus that they can be kept ready for instant use for long periods of time without sensible deterioration, and that they can be recharged after employment. ”

“ But the amount of heat liberated when a certain weight (or volume) of a particular fuel combines with a sufficient quantity of oxygen to oxidise it wholly is absolutely fixed, and is exactly the same whether that fuel is made to give a luminous or a non-luminous flame. Nevertheless the atmospheric flame given by a certain fuel may be appreciably hotter than its luminous flame, because the former is usually smaller than the latter. Unless the luminous flame of a rich fuel is made to expose a wide surface to the air, part of its carbon may escape ultimate combustion ”

“ Perfect purification by means of fluid reagents unattended by too great a consumption of pressure is only to be effected by a mechanical scrubber such as is used on coal-gas works, wherein, by the agency of external power, the gas comes in contact with large numbers of solid surfaces kept constantly wetted; or by the adoption of a tall tower filled with porous matter or hollow balls over which a continuous or intermittent stream of the liquid purifying reagent is made to trickle, and neither of these devices is exactly suited to the requirements of a domestic acetylene installation. ”

“ Carbide cannot well be crushed by the consumer of acetylene. It is a difficult operation, and fraught with the production of dust which is harmful to the eyes and throat, and if done in open vessels the carbide deteriorates in gas- making power by its exposure to the moisture of the atmosphere. True dust in carbide is objectionable, and practically useless for the generation of acetylene in any form of apparatus, but carbide exceeding 1 inch in mesh is usually sold to satisfy the suggestions of the British Acetylene Association, which prescribes 5 per cent, of dust as the maximum. ”

“ Gaseous carbon, on the other hand, emits more heat than an equivalent quantity of hydrogen, [Footnote: In a blowpipe flame hydrogen can only burn to gaseous, not liquid, water.] even when it is only converted into the monoxide. In other words, a gaseous fuel which consists of hydrogen alone can only yield that temperature as a maximum at which the speed of the dissociation of the water vapour reaches that of the oxidation of the hydrogen; and were carbon dioxide the only oxide of carbon, a similar state of affairs would be ultimately reached in the flame of a carbonaceous gas. ”

“ 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. ”

“ The gas, indeed, is a powerful heating gas, but owing to the amount consumed being so small in proportion to the light developed, the heat arising from acetylene lighting in a room is less than that from most other illuminating agents, if the latter are employed to the extent required to afford equally good illumination. The ratio of the heat developed in acetylene lighting to that developed in, e.g., lighting by ordinary coal-gas, varies considerably according to the degree of efficiency of the burners, or, in other words, of the methods by which light is obtained from the gases. ”

“ It must be remembered also that only a gas yields a flame when it is burnt; the flame of a paraffin lamp and of a candle is due to the combustion of the vaporised fuel. Methods of burning acetylene under the mantle are discussed in Chapter IX.; here only self-luminous flames are being considered, but the theoretical question of heat economy applies to both processes.
Heat may be lost from a flame in three several ways: by direct radiation and conduction into the surrounding air, among the products of combustion, and by conduction into the body of the burner. ”

“ Still, by properly designing the ports of a gas-engine cylinder, so that the normal amount of compression of the charge and of expansion of the exploded mixture which best suit coal-gas are modified to suit acetylene, satisfactory engines can be constructed; and wherever an acetylene installation for light exists, it becomes a mere question of expediency whether the same fuel shall not be used to develop power, say, for pumping up the water required in a large country house, instead of employing hand labour, or the cheaper hot-air or petroleum motor. ”

“ The light petroleum, benzol, or other suitable volatile hydrocarbon is volatilised, where necessary, by the application of gentle heat, while air is driven over or through it by means of a small motor, which in some cases is a hot-air engine operated by heat supplied by a flame of the air-gas produced. These air-gas producers, or at least the reservoir of volatile hydrocarbon, may be placed in an outbuilding, so that the risk of fire in the house itself is minimised. They require, however, as much attention as an acetylene generator, usually more. ”

“ Well built, such plant will stand much heat and fire without failure; if it is non-automatic, and of combustible materials contains nothing but gas in the holder, the worst that could happen in times of fire would be the unsealing of the bell or its fracture, and this would be followed, not at all by any explosion, but by a fairly quiet burning of the escaping gas, which would be over in a very short time, and would not add to the severity of the conflagration unless the generator-house were so close to the residence that the large flame of burning gas could ignite part of the main building. ”

“ When a large carbide-to-water generator is worked systematically so as to avoid more loss of acetylene by solution in the excess of liquid than is absolutely necessary, the liquid residues coming from it will be collected in some ventilated closed tank where they can settle quietly. The clear lime-water will then be pumped back into the generator for further use, and the almost solid sludge will be ready to be carried to the pit where it is to be buried. Special care must be taken in disposing of the residues from a generator in which oil is used to control evolution of gas. ”

“ No other gas which can be produced on a commercial scale is capable of giving, volume for volume, so great a yield of light as acetylene. Hence, apart from the advantages accruing to it from its mode of production and the nature of the raw material from which it is produced, it possesses an inherent advantage over other illuminating gases in the smaller storage accommodation and smaller mains and service-pipes requisite for the maintenance of a given supply of artificial light. ”

“ There is one respect in which acetylene and other flame illuminants are superior to electric lighting, viz., that they sterilise a larger volume of air. All the air which is needed to support combustion, as well as the excess of air which actually passes through the burner tube and flame in incandescent burners, is obviously sterilised; but so also is the much larger volume of air which, by virtue of the up-current due to the heat of the flame, is brought into anything like close proximity with the light. ”

“ But owing to the irregular habits engendered by modern life it is often difficult to know, during any given day, how much gas will be required in the ensuing evening; and it therefore becomes necessary always to have, as ready-made acetylene, or as carbide in a proper position for instant decomposition, a patent or latent store of gas more than sufficient in quantity to meet all possible requirements. Now, as already stated, a non-automatic apparatus has its store of material in the form of gas in a holder ”

“ For example, in a district to which coal and oil must be brought great distances, the freight on them may be so heavy that--regarding the question as simply one of obtaining light in the cheapest manner--it may be more economical to bring calcium carbide an equal or even greater distance and generate acetylene from it on the spot, than to use oil or make coal-gas for lighting purposes, notwithstanding that acetylene may not be able to compete on equal terms with oil--or coal-gas at the place from which the carbide is brought. ”

“ Electric lighting is as superior to other modes of lighting in respect of direct vitiation as of exhaustion of the air, because it does not depend on combustion. Putting it aside, however, light is obtainable by means of acetylene with less attendant vitiation of the air than by means of any other gas or of oil or candles. The principal vitiating factor in all cases is the carbonic acid produced by the combustion. Now one volume of acetylene on combustion yields two volumes of carbonic acid, whereas one volume of coal-gas yields about 0.6 volume of carbonic acid. ”

“ CHAPTER VIII COMBUSTION OF ACETYLENE IN LUMINOUS BURNERS--THEIR DISPOSITION
NATURE OF LUMINOUS FLAMES.--When referring to methods of obtaining artificial light by means of processes involving combustion or oxidation, the term "incandescence" is usually limited to those forms of burner in which some extraneous substance, such as a "mantle," is raised to a brilliant white heat. Though convenient, the phrase is a mere convention, for all artificial illuminants, even including the electric light, which exhibit a useful degree of intensity depend on the same principle of incandescence. ”

“ Any fluid combustible which burns with a flame can be made to give light on the incandescent system, for all such materials either burn naturally, or can be made to burn with a non- luminous flame, which can be employed to raise the temperature of some mantle; but only those fuels can be burnt on the self-luminous system which contain some ingredient that is liberated in the elemental state in the flame, the said ingredient being one which combines energetically with oxygen so as to liberate much local heat. ”

“ From a well-constructed installation no acetylene escapes unconsumed: the gas remains wholly within the pipes until it is burnt, and whatever odour it may have fails to reach the human nostrils. A house properly piped for acetylene will be no more conspicuous by its odour than a house properly piped for coal-gas. On the contrary, the fact that the carbide impurities of acetylene, which, in the absolutely pure state, is a gas of somewhat faint, hardly disagreeable, odour, do confer upon that gas a persistent and unpleasant smell, is distinctly advantageous ”

“ 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. ”

“ The British Association requires the test to be made on carbide parcels ranging between 1 and 2-1/2 inches or larger, because that is the "standard" size for this country, and because no guarantee is to be had or expected from the makers as to the gas-producing capacity of smaller material. Manifestly, if a consumer employs such a form of generator that he is obliged to use carbide below "standard" size, analyses may be made on his behalf in the ordinary way; but he will have no redress if the yield of acetylene is less than the normal. ”

“ Moreover, the nitrogen and the excess of oxygen occupy much space in the flame, making it larger, and distributing that fixed quantity of heat which it is capable of generating over an unnecessarily large area. It is for this reason that any gas gives so much brighter a light when burnt in pure oxygen than in air, (1) because the flame is smaller and its heat more concentrated, and (2) because part of its heat is not being wasted in raising the temperature of a large mass of inert nitrogen. ”