THE USE OF ACETYLENE. 



345 



center of the mass of carbide, the acetylene generated has to pass 

 through the external layers, which, as shown, may be at high tem- 

 peratures, above that at which acetylene decomposes; thus a con- 

 siderable amount of gas is lost, and the tar formed may distill into 



CAS 



Type II, A. 



Type II, B. 

 TTPKB OF GENERATORS. 



Type III. 



the generator and tubes, clogging the tubes. A more serious evil 

 is the deterioration in the illuminating quality of the gas. Samples 

 of the gas were taken as the maximum temperature was approached, 

 and analyzed with this average result: Acetylene, seventy per cent; 

 other hydrocarbons, eleven per cent; hydrogen, nineteen per cent. 

 This reduces the illuminating value from two hundred and forty to 

 one hundred and twenty-six candles. The hydrocarbons consist 

 largely of benzene, which requires three times as much air for com- 

 plete combustion as acetylene does. The best possible acetylene 

 burner smokes when the acetylene contains benzene. 



At first sight these experiments would seem absolutely to con- 

 demn generators of class II, yet the fact remains that some excellent 

 generators are of this type. Under certain conditions excessive over- 

 heating may be avoided. The rising bell shown in II, B should be 

 discarded. Generators in which the water rises from below, and 

 slowly attacks the carbide, can be made safe if the water is never 

 driven back from the carbide, and the carbide is in separated layers 

 as in II, A. Under these conditions the water is always in excess at 

 the point where it attacks the carbide, so that the evaporation, by 

 rendering heat latent, keeps the temperature down, the temperature 



VOL. LT. 26 



