vin THE BURNING OF INFLAMMABLE GASES 139 



was separated from it, was of a very remarkable kind, being 

 quite as heavy as common air" (Experiments and Observa- 

 tions, 1786, VI. 109). 



This observation attracted a great deal of attention. 

 According to Lavoisier's theory the reduction of an oxide 

 with charcoal should give rise to the metal and fixed air ; in 

 this experiment hydrogen appeared to be produced instead. 

 The only explanation that the French chemists were able to 

 give of the production of the inflammable gas was that the 

 charcoal, even when strongly heated, retained a certain 

 amount of hydrogen, which it released only when burnt 

 with the help of a suitable oxide. 



Cruikshank (1801) recognises an inflammable oxide 

 of carbon. The real nature of this inflammable gas was 

 discovered in 1801 by W. Cruikshank of Woolwich 

 (Nicholson 1 s Journal, April 1801, 5, 1-9), who proved it 

 to be an oxide of carbon. This was generally regarded as 

 an impossible view, on account of the low density of the 

 gas. The French chemist, C. L. Berthollet (17481822), 

 for instance, in 1809 (Mem. Soc. Arcueil, 1809, II., 68 93, 

 p. 85), pointed out that this oxide would be " the only 

 example that one can quote, in which the gaseous compound 

 would be lighter than the lightest of its component 

 elements " and argued that the gas must contain hydrogen. 



Cruikshank examined the gases formed by reducing the 

 black oxide of iron and the white oxide of zinc, and then 

 proceeded to study the reduction of the red oxide of copper, 

 of litharge, and of the black oxide of manganese described 

 by Scheele (p. 210). He found : 



(1) "That all metallic oxides capable of enduring a red 

 heat, will, when mixed with charcoal, not only yield carbonic 

 acid, but also a very considerable quantity of an inflammable 

 gas. 



(2) " That those oxides which retain their oxygen most 

 obstinately, yield the greatest quantity of inflammable gas ; 



