282 Experiments on the Nature of [Oct. 



least the difference between them, have been hitherto un- 

 known to chemists, I shall here give a sketch of their proper- 

 ties and composition. 



1. The First Subnitrate, or Subniirote at a Minimum, is 

 produced when nitrate of lead is precipitated by a smaller 

 quantity of ammonia than is sufficient to neutralize one half of 

 the nitric acid. It is composed of such proportions that the 

 acid contains three times as much oxygen as the oxide. It 

 contains no water of combination. When decomposed by 

 heat it leaves its oxide in an agglutinated and reddish coloured 

 mass, just as happens when the neutral nitrate is treated in the 

 =ame way- It is very soluble in water, and boiling water dis- 

 solves a much greater quantity of it than cold water. On 

 cooling it deposites the salt in small transparent crystals, which 

 decrepitate strongly when heated. 



2. The Second, or Intermediate Sulnitraie, is formed when 

 the neutral nitrate of lead is mixed with a quantity of ammonia 

 exactly sufficient to neutralise f. of the nitric acid. When more 

 or less of the alkali is employed there is formed a mixture of the 

 intermediate subnitrate with one or other of the two other sub- 

 nitrat.es. The intermediate subnitrate is composed in such a 

 manner that the acid contains twice as much oxygen as the base, 

 while the water of combination contains halt as much oxygen as 

 the base. When heated it loses its water and becomes yellowish, 

 but recovers its white colour again on cooling; so that it con- 

 tains enough of acid to conceal the colour of the oxide. It is 

 feebly soluble in pure water; but the addition of any other salt, 

 even nitrate of lead, precipitates it again. When heated to red- 

 ness it is decomposed, leaving the oxide of lead in the state of 

 a very minute powder, and of a very fine yellow colour. 



3. The Third Sul 'nitrate, or Subnitrate at a Maximum, is 

 obtained when nitrate of lead is mixed with a considerable 

 excess of concentrated ammonia. It is so constituted that the 

 acid and oxide contain equal quantities of oxygen. It contains 

 water of combination, the oxygen of which is J. of that of the 

 oxide. It loses its water at a moderate heat, and becomes of a 

 deep yellow colour, which it retains when cold. It is scarcely 

 soluble in water. When decomposed by heat it leaves its oxide 

 in a fine powder and yellow colour, like the preceding subnitrate. 



The anomaly in my first experiments having disappeared, 

 iuid the onlv circumstance in which these experiments did not 

 coincide with those of Davy and Dalton being removed, it re- 

 mains only to verify by direct experiment their determination 

 of the quantity of azote contained in nitric acid. My method 

 of proceeding was as follows : — 



I dissolved in water in a convenient apparatus 12"05 parts of 

 nitrate of barytes, previously reduced to powder and strongly 



