vi THE COMPOSITION OF FIXED AIR 97 



production of fixed air during the reduction of the calx 

 was thus clearly proved ; but it was not until Priestley had 

 discovered oxygen, as described in Chapter III, that 

 Lavoisier was able to give a satisfactory explanation of 

 what had occurred in this reduction, 



Lavoisier (1774) proves that fixed air is an oxide of 

 carbon. The crucial experiments by which fixed air was 

 proved to be an oxide of carbon were made by Lavoisier in 

 November, 1774, after Priestley had demonstrated to him 

 the method of making oxygen from the red calx of mercury. 



By heating an ounce of this calx with forty-eight grains of 

 charcoal in a tiny glass retort he was able to collect, in a 

 bell jar over water, 64 cubic inches of gas. This gas dis- 

 solved in water, communicating to it the properties of the 

 natural acidulated waters, destroyed animals brought into it, 

 at once extinguished candles and other burning substances, 

 precipitated lime-water, and combined readily with the 

 alkalis, removing their causticity and enabling them to 

 crystallise. " All these properties are exactly those of the 

 kind of air known as fixed air." 



Lavoisier found that the red precipitate heated alone 

 gave 78 cubic inches of a gas which did not dissolve in 

 water, did not precipitate lime-water, did not unite with 

 alkalis or diminish their caustic qualities, but which could be 

 used again for the calcination of metals. " In conclusion, 

 it had none of the properties of fixed air ; far from being 

 fatal, like it, to animals, it seemed, on the contrary, more 

 proper for the purposes of respiration ; candles and burning 

 bodies not only were not extinguished by it, but burned 

 with an enlarged flame in a very remarkable manner ; the 

 light they gave was much greater and clearer than in 

 common air ; charcoal burned in it with a brilliancy 

 almost like that of phosphorus, and all combustible sub- 

 stances were consumed in it with surprising rapiaity. All 

 these circumstances convinced me that this air, far from 



H 



