80 PKACTICAL PHOTO-MICROGRAPHY 



disadvantage that with such an arrangement the moisture 

 that rises from the water-chamber reaches the carbide, and so 

 causes deterioration. Further, there is usually not sufficient 

 depth of water to wash the acetylene gas thoroughly before 

 it passes into the container. From experience the writer is 

 convinced that this type is not the most desirable, and that a 

 generator of the second type is much to be preferred. In the 

 latter the carbide is contained in a receptacle which is sub- 

 divided into small sections. The water is allowed to reach each 

 chamber successively ; so that a small charge of carbide is only 

 acted on at a time, and the remainder is quite out of the way 

 of the influence of water at all. Further, the gas rises through 

 a considerable body of water, which fulfils the double purpose 

 of cleansing it from impurities, and what is even more important, 

 of cooling it before use. The carbide container is so arranged that 

 the material is thoroughly saturated with water ; consequently 

 complete decomposition takes place, the whole of the gas is 

 extracted, and little or no waste results. The container is also 

 surrounded by water, and, therefore, a minimum of heat is set 

 up in the process of decomposition. A regular pressure upon 

 the gas is essential. 



The generator made by the Thorn & Hoddle Acetylene Co., 

 for lantern and projection work, fulfils these requirements, and 

 will be found to be a good example of the type now described. 

 A burner consuming about three-quarters of a foot of gas 

 per hour, approximating to fifty- candle power, will be found 

 the most useful. A larger burner only results in a larger flame, 

 and this is not desirable. 



Acetylene bicycle lamps have been recommended by some 

 for this purpose, but there appears to be little to recommend 

 them. Excepting in the very best make, they are not entirely 

 free from the danger of explosion, and, owing to there being 

 no cooling arrangement, the gas, which is usually unpurified, 

 passes into the burner in a heated condition, so that rapid 

 carbonising of the burner may result. 



A very convenient, although somewhat expensive, method 

 of using acetylene has lately been introduced by the Acetylene 

 Illuminating Company, and is called by them ' dissolved 

 acetylene.' In this arrangement the gas is dissolved in acetone, 

 and is supplied to purchasers in cylinders from which it can be 



