This section is from the book "Welding And Cutting Metals By Aid Of Gases Or Electricity", by L. A. Groth. Also available from Amazon: Welding and cutting metals by aid of gases or electricity.
Acetylene (C2H2) was first obtained by Davy in 1837 from the black mass which he obtained when making potassium. Berthelot in 1858-59 produced acetylene by passing hydrogen between the poles of an electric arc, and established the more important properties of the gas and its compounds. Wohler in 1862 produced calcium carbide by raising a mixture of lime, zinc, and carbon to a white heat. He obtained acetylene by bringing the carbide into contact with water. Acetylene was first liquefied by Cailletet in 1877, and repeated by Ansdell in 1879, whose method was criticised by Villard, Willson, and Suckert. The method of using compressed acetylene was discovered by Claude and Hess.
Acetylene is a colourless gas of disagreeable odour, which is to a great extent due to impurities, and can be easily liquefied. It is an endothermic compound the formation of which is attended by the absorption or storing up of heat, in contradiction to those exothermic bodies which evolve heat in their formation.
Great care is evidently required in its use, as on account of its endothermic property its decomposition is easily effected when under pressure and takes place with explosive violence.
As acetylene forms an explosive compound with copper, the use of this metal is to be avoided.
Another danger arises from the use of impure calcium carbide, in that phosphuretted hydrogen may be generated along with the acetylene.
Unfortunately, however, calcium carbide continues to evolve acetylene after the removal of the water on account of the presence of aqueous vapour, and the gas so generated, whilst the apparatus is not in use, accumulates until sufficient pressure is generated to force the water seal.
Dr. Frank Clowes has shown that the range of explosibility of acetylene mixed with air is greater than that of any other gas; escape of the gas must therefore be strictly avoided.
The Royal Society of Arts appointed a committee to report upon the exhibition of acetylene generators at the Imperial Institute in 1898, and the conditions laid down by the said committee form, so to say, the foundation stone upon which the construction of acetylene generators is based. It will therefore be of interest here to give the results obtained from the tests as kindly permitted by the said Society.
The committee have, for convenience in classification, divided the generators into three groups: -
1. Those in which water is by various devices allowed to drip or flow in a thin stream on to a mass of carbide, the evolution of the gas being regulated by the stopping of the water-feed.
2. Those in which water in volume is allowed to rise in contact with the carbide, the evolution of the gas being regulated by the water being driven back from the carbide by the increase of pressure in the generating chamber.
3. Those in which the carbide is dropped or plunged into an excess of water.
These are again subdivided into :
(a) Automatic generators, or 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 some special contrivance for stopping contact between the water and carbide.
(b) Non-automatic generators, or those in which a holder of sufficient capacity is provided to receive the whole of the gas made from the largest charge of carbide which the apparatus is capable of taking.
The following are the conditions, laid down by the committee, which the generators admitted to the exhibition at the Imperial Institute were required to fulfil: -