362 Experiments on the Nature of [Nov. 



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with the determination of Davy. Hence it follows that the 

 ditterence between nitrous and nitric acids must be greater than 

 between Az + 4 O and Az + 5 O. 



But if we suppose nitric acid to be N + 6 O, and nitrous 

 acid to be i\ + 4 O, we shall find that it will afford a satisfac- 

 tory explanation of all the phenomena. 



To understand completely the experiment in question, we 

 must divide the operation into three periods. The Jirsl period 

 continues till one-half of the nitric acid is decomposed by a 

 second quantity of lead dissolved. There is formed at first some 

 first subnitrate and some neutral nitrite ; then the subnitrate 

 begins to be decomposed, and to be converted into subnitrite. 

 At the end of this period the liquor contains first subnitrate 



(NO + 2PO) and first subnitrite (NO + 2 P O). The 

 second period terminates when two-thirds of the nitric acid are 

 converted into nitrous acid, and one-third remains still unde- 

 eomposed. The nitrate has then dissolved 14/ as much lead as it 

 contained at first; that is to say, JS parts. The solution while 



cooling, deposites second subnitrate (N O + 3 P O) mixed 



4 



with a great quantity of the first subnitrite (N O 4- 2 P O). 

 It is to be understood that I suppose no nitrous gas to be disen- 

 gaged. This disengagement produces no effect upon the ulti- 

 mate results of this operation ; but when it takes place the quan- 

 tity of subnitrite at the end f the second period is diminished 

 in consequence, while at the same time that of the subnitrate is 

 increased. The third period terminates when the whole of the 

 nitric acid is decomposed. The nitrous acid is then united with 

 a maximum of oxide, and forms a subsalt, which may be repre- 



4 



sented by this symbol, NO 4- 4 P O ; that is to say, that the 

 nitrous acid and base contain equal quantities of oxygen. The 

 nitrate lias now dissolved 24 as much lead as it contained before 

 the commencement of the experiment; that is to say, 1374,: 

 but it is very difficult to carry the experiment so far, and that 

 from two causes : the subnitrite at a maximum covers the lead 

 with a crust, and that prevents the mutual action between the 

 metal and the liquid ; and if we add new lead, the subnitrite at 

 a minimum which is in the solution being too dilute, and being 

 mixed with a great quantity of subnitrite at a maximum, acts 

 only very weakly upon the metal. In several of my experi- 

 ments, 1 have without difficulty dissolved 127 or 130 parts of 

 lead by 100 of nitrate of lead. M. Chevreul, who has repeated 

 apart of my experiments, has succeeded in dissolving 135 parts 

 of lead in 100 of nitrate in two successive experiments. (Ann. 

 de Chim. Jtdy, 1812.*) This approaches pretty nearly to the 



* M. Chevreul made a set of experiments on the formation of nitrite of 

 lead, it would appear, without am knowledge of my experiments; and he 

 / 



