x NITRE, NITRIC ACID, AND NITROGEN 199 



(oxygen) set free during this action, Scheele noted 

 that : 



" Nitre maintained in red-hot fusion in a glass retort for 

 half an hour, becomes moist in the open air, and deliquesces 

 after cooling, and still does not show any trace of alkali." 



"This liquefied nitre permits its volatile acid to escape 

 immediately, when rubbed or mixed with the vegetable 

 acids"(A.C.R. VIII. 28-29). 



A further distinction was discovered by Cavendish, who 

 found that nitre after heating in an earthenware retort 

 acquired the property of forming a precipitate when 

 mixed with nitrate of silver (A.C.R. III. 46), the silver salt 

 of the " phlogisticated " acid being almost insoluble in water 

 (see above, p. 191). 



The name NITRIC ACID was given to the acid of common 

 nitre by the French chemists in 1787. The traditional 

 name of NITROUS ACID was transferred by them to the 

 "phlogisticated" or deoxidised acid of Scheele's ignited 

 salt. 1 Thus they write : 



" We have not hesitated to make the authority of the rule 

 prevail over that of custom, by naming for example, nitric 

 add that in which the azote is impregnated with all the 

 oxygen it is capable of containing,, and reserving the 

 appellation of nitrous acid for that much weaker acid where 

 the same base is mixed to a much less quantity of oxygen " 

 (Chemical Nomenclature, tr. 1788, p. 35). 



The salts of nitric acid were called NITRATES, whilst those 

 derived from nitrous acid were called NITRITES. 



Composition of nitric and nitrous acids. The first 

 attempts to determine the composition of nitric acid were 

 made by Lavoisier in 1776 (Mem. Acad. Sci., 1776, 671; 

 Works, II. 129) eight years before Cavendish had discovered 



1 Saltpetre which has been heated with metallic lead consists almost 

 entirely of potassium nitrite, the potassium salt of nitrous acid, but the 

 red fuming " acid of nitre " contains both nitric and nitrous acids. 



