332 Mixter — Partial non-explosive Combination of 



Two grams and 2 volumes of hydrogen burn with 1 volume of 

 oxygen, with a thermal result of 58,700 calories, the product 

 gaseous ; and 2 volumes of the mixture, therefore, give 39,134 c. 

 Likewise, 2 volumes of carbonic oxide and oxygen give 45,312 

 c. ; 1 volume of hydrogen and 1 of chlorine give 22,000 c. ; 

 and 24 grams of solid carbon and 2 of hydrogen unite with 

 an absorption of 48,170 c. to form 2 volumes of acetylene, 

 which evolves this amount of heat when resolved into its 

 elements. In the same way, we have for cyanogen 65,700 c, 

 for nitrous oxide 17,470 c, and for nitric oxide 21,575 c. set 

 free when these compounds are decomposed into their elements. 

 The following table gives the resultant heat of the combina- 

 tion of equal volumes of three mixtures, and of the decompo- 

 sition of four endothermic gases : 



Resultant heat. Nature of product. 



Hydrogen and oxygen .. 39134 Gaseous 



Hydrogen and chlorine 22000 " 



Carbonic oxide and oxygen . _ 45312 " 



Acetylene 48170 12/13 solid 



Cyanogen 65700 12/21 " 



N itrous oxide _ 17470 Gaseous 



Nitric oxide ._ 21575 . " 



The molecular heats at constant volume of H 2 , 2 , N a , CO, 

 NO, and HOI are 4-2 to 5, and of N 2 0, H 2 0, and C0 2 , about 

 one-half larger. Those of C 2 H 2 and C 2 N 2 do not appear to 

 have been determined, but they are probably not greater than 

 10. Evidently the molecular heats have little influence in 

 determining the temperature at which explosion occurs, and 

 the resultant heat does not account for the fact that the igni- 

 tion temperature of chlorine and hydrogen is much lower than 

 that of hydrogen and oxygen, or of carbonic oxide and oxygen. 



Acetylene requires a pressure 20 times greater than detonat- 

 ing gas for explosion, while the heat of decomposition of the 

 former exceeds that of chemical union of the latter. At 

 temperatures not high enough to cause acetylene to separate 

 completely into its elements or cause detonating gas to explode, 

 the two gases exhibit similar deportment in this respect, 

 namely, that the change is one of slow combination. Acety- 

 lene polymerizes to form C 6 H 6 , C 8 H 8 , and other condensation 

 products, and detonating gas forms water. But acetylene, 

 when sparked under sufficient pressure, decomposes completely 

 into carbon and hydrogen. The impacts of acetylene mole- 

 cules with a certain velocity causes them to combine with each 

 other, but when they have a higher velocity complete decom- 

 position results. The change started by a spark in dense acety- 



