Illuminating power. 896° F., which is somewhat below that of the visible red heat of iron, and is considerably lower than the igniting point of coal-gas or petroleum vapour. The temperature necessary to produce an explosion of compressed acetylene is, however, considerably higher, being about 1436° F. In the smaller percentage which is necessary to form an explosive mixture, and in the lower temperature of ignition, acetylene is somewhat more dangerous in case of leakage than coal-gas; while, on the other hand, the very small size of the burner for the former gas allows it to escape much more slowly in the event of the flame being blown out or the burner being accidentally left turned on. The illuminating power of acetylene as compared with coal-gas varies with the type of burner employed. In a suitable burner 5 cubic feet of acetylene per hour will give 240 candle-power, while the same quantity of coal-gas gives 16 candle-power. Acetylene is, however, generally burnt in much smaller burners, consuming fromto 1 cubic foot per hour. Under these conditions the illuminating power of acetylene is from six times to ten times as great as that of coal-gas. Generators. It would be impossible, within the limits of this chapter, to give a detailed description of the numerous forms of acetylene generator which have been devised. The fact that it is only necessary to bring water into contact with carbide of calcium in order to generate the gas makes the designing of a generator apparently so simple a matter that many inventors have been tempted to devote their energies to the subject. The matter is really not so simple as it seems, and it is upon the many important details of design that the success, and even the safety, of the apparatus depend. In the report of the Committee on the Exhibition of Acetylene Generators at the Imperial Institute in June 1898, the various forms of apparatus are classified as follows: (1) Those in which the gas is generated by water being allowed to These are again subdivided into: AUTOMATIC. By automatic generators are meant those which have a storage capacity for gas less than the total volume which the charge of carbide is capable of generating, and which depend upon special contrivance for stopping contact between the water and carbide. some NON-AUTOMATIC. Non-automatic generators are This report gives a detailed description of the various forms of generator tested by the committee, together with much other useful information on the subject. Since it was written, many new forms of apparatus have been placed on the market, all of which, however, fall within the above-mentioned classification. Soon after the introduction of carbide of calcium as Legislation. an article of commerce into this country, it became evident that unless this substance were placed under some restrictions, serious accidents might arise. Notwithstanding the great difference between carbide and petroleum, it was recognised that the danger attending the storage of the two substances is much the same, since it arises from the liability of both to create an explosive atmosphere by giving off inflammable gas or vapour. *This report was issued by the Society of Arts, and may be obtained from William Trounce, 10 Gough Square, Fleet Street, London. Licences. Consequently it was decided that the best method of dealing with the danger was to take advantage of the power provided in Section 14 of the Petroleum Act, 1871, of bringing other substances within the scope of that Act, and to subject carbide of calcium to such of the provisions of the Petroleum Acts as were applicable. An Order in Council to this effect was accordingly made on February 26, 1897. This Order will be found in Appendix XII. together with a subsequent Order in Council dated July 7, 1897, by which a quantity up to 5 lbs., when kept in hermetically closed metal vessels containing not more than 1 lb., is exempted from the necessity of licence. It is not therefore lawful for any person to keep more than 5 lbs. of carbide of calcium, whether for sale or for use without a licence from the local authority under the Petroleum Acts. The conditions to be attached to such licence rest entirely with the local authority, and will vary somewhat in different places; but it is usual to attach such conditions as will afford protection not only in the storage, but also in the use of carbide on the licensed premises. The power to attach conditions in regard to the construction and position of the generator in which the carbide is to be used has not, as far as the authors are aware, ever been questioned; and though there may be some doubt on the matter, it is probable that a Court of Law would hold that such conditions come within the wording of Section 9 of the Petroleum Act, 1871. Certainly these conditions do come within the wording of that section if it is held, as it very well may be, that carbide, even when in the generator, is being "kept " on the premises until the whole of it has been decomposed in the formation of acetylene gas. In preparing licences for carbide of calcium, local authorities will probably be guided in some measure by the forms adopted by the London County Council, who have had the advantage of the assistance of the Home Office and of competent scientific advisers in framing their regulations. The forms of licence adopted by this body, together with a memorandum issued by them, will be found in Appendix VI. In dealing with the dangers which have to be Precautions. guarded against in keeping carbide of calcium, it should be clearly understood that the material by itself is wholly inexplosive and incombustible, and is absolutely safe so long as no water or moisture can reach it. The carbide should be kept, therefore, in hermetically sealed metal vessels, which should be protected from the weather and stored in a dry place. As some gas may be formed from contact with the moisture of the atmosphere whenever the carbide vessels are opened or are not perfectly air-tight, it is desirable that the place of storage should be thoroughly ventilated, and that precautions should be taken to prevent the ignition of any gas which may be so formed. Thus a naked light* should never be brought into close proximity to an open vessel containing, or which has contained, carbide, nor should such light be used in any building where large quantities of carbide are stored. Another danger may arise in the case of a fire from some other cause, which may damage the carbide vessels. In attempting to extinguish the fire, water may then come in contact with the carbide, giving rise to a copious evolution of gas, which will add to the confla gration, even if it does not cause a disastrous explosion. For this reason no large amount of carbide should be allowed to be stored in a shop or dwelling-house, or in any highly inflammable building; and when a fire does occur in a large carbide store, the Fire Brigade should * See remarks on Safety Lamps (p. 159). N Quantity. Safety of generator. be warned not to attempt to extinguish it in the usual manner. It has been usual in licences to require that carbide should be kept in vessels containing not more than 112 lbs., but owing to the smaller size to which the material is now broken, the vessels originally designed to hold a hundredweight will now contain 140 lbs., and there is no special objection to the larger amount being allowed. With regard to the quantity to be kept on any one premises, it must be remembered that in the case of large stores the danger is measured, not by the quantity of carbide, but by the amount of water which can gain access to it at any one time. Consequently it is not usual to limit the amount of carbide which may be kept in a large store. In the special cases where licences are granted for the keeping of carbide in a shop or dwelling-house, the quantity should be strictly limited. As some guide in fixing the limit, it should be remembered that as one pound of carbide will produce 5 cubic feet of gas, and as an atmosphere of acetylene and air commences to be explosive when the proportion of the former reaches 3 per cent., therefore 3 lbs. of carbide, if all converted into gas at once, would render a space of 500 cubic feet explosive. It would be necessary, however, in order to convert the whole of the carbide into gas, that there should be nearly an equal weight of water in contact with the material. Where the evolution of gas is rapid, an explosive atmosphere may form in a portion of the space with a less quantity of gas than would be necessary to render the whole space capable of explosion. As already stated, it is usual where carbide of calcium is required for use on the premises to attach to the licence conditions in regard to the situation, construction, and method of employment of the generator. |