2oa HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



in atmospheric " nitrogen " the principle from which the 

 acid is derived. Lavoisier's experiments were therefore 

 restricted to measuring the proportions in which nitrous air 

 (nitric oxide) and oxygen are united in the acid. 



Lavoisier's analysis of nitric acid. Lavoisier first 

 attempted to analyse nitric acid by acting upon it with 

 mercury in such a way that the mercury was recovered 

 unchanged, whilst the acid was resolved into a series of 

 gaseous constituents. For this purpose two ounces of acid 

 of density i '316 were heated with two ounces of mercury and 

 the gaseous products were collected as they were set free, 



(1) during the dissolution of the mercury in the acid, 



(2) during the decomposition of the nitrate to oxide 

 (red precipitate), 



(3) during the decomposition of the oxide into mercury 

 and oxygen. 



At the end of the experiments 226 cubic inches of nitrous 

 air and 238 cubic inches of oxygen had been collected, in 

 addition to a considerable quantity of water, whilst the 

 mercury was recovered intact. The experiment failed to 

 give correct results because nitrous fumes, produced at 

 various stages of the action, were absorbed and lost in the 

 water over which the gases were collected ; but the method 

 was so ingenious as to be well worthy of notice. 



Lavoisier's synthesis of nitric acid. Lavoisier also 

 attempted in 1776 to synthesise nitric acid by combining 

 together known quantities of nitrous air and oxygen in 

 presence of water. He found that 7 J measures of nitrous air, 



mixed with 4 measures of oxygen over water, 



- 



" were reduced to about J of a measure, that is to say to ^ of 

 their original volume." 



" The water in the tube was acid at the end of this 

 operation, or rather was nothing but a weak [nitric] acid ; 

 on saturating it with an alkali, I obtained from it by evapora- 

 tion a true saltpetre " ( Works, II. 135). 



