the Laws of Affinity. 205 



an efficacious agent : i. Becaufe the fulphate of lead is much 

 lefs foluble than the muriate; 2. Becaufe the fulphuric acid 

 is much lefs volatile than the muriatic acid. 



Muriate of filver being much more infoluble than muriate 

 of lead, filver is much better than lead for retaining the mu- 

 riatic acid which happens to be in the nitric acid. Velter 

 and Bonjour obferved, however, that muriatic acid always 

 came over in diftillation, if the operation was made without 

 the precautions indicated by thofe learned chemifts. To. 

 obtain a pure nitric acid immediately, it is neceflary to make 

 the operation upon an acid little concentrated, that it may 

 not hold in folution any muriate of filver, and to feparate 

 the muriate of filver which precipitates before the liquid is 

 fubjected to the action of heat, or, which is better, to pre- 

 cipitate, by a folution of filver, the muriatic acid from the 

 nitrate of potafh ; after which, by decompofing this nitrate, 

 the nitric acid is obtained perfectly free from muriatic acid. 



When muriate of filver remains in the folution, a very 

 pure nitric acid may neverthelefs be obtained by diftillation, 

 by fetting afide the firft portion which diftils over, till it is 

 feen by the teft that no more muriatic acid is afforded. For, 

 as the chemifts I have juft quoted obferved, the muriatic 

 acid in this procefs affumes the nature of oxygenated muri- 

 atic acid, and is difengaged in this ftate at the beginning of 

 the operation. 



P. Sulphate of potafh having been treated with the acetite 

 of lead in the fame manner as the muriate of potafh, ful- 

 phate of lead was precipitated. The liquid retained only a 

 fmall quantity of oxide of lead. By the progrefs of evapora- 

 tion fome cryftals of fulphate of potafh were obtained, though 

 before the evaporation the acetite of lead produced no more 

 precipitate; and, laftly, the acetite of potafh, which retained 

 a fmall quantity of oxide of lead. The decompofition of the 

 fulphate of potafh was much more complete than that of the 

 muriate of foda. 



In the experiments I have juft defcribed, we fee, then, that 

 the decompofitions, or exchange of bafes, alfo follow the 

 order of the folubilities of the combinations which may be 

 formed; and that the only difference obferved in moft of the 

 preceding experiments, arifes from the propertv poffefled by 

 the oxide of lead of forming triple combinations, which 

 ibmetimes again feparate in combinations of different degrees 

 of folubility, as happens with the muriate of foda and of 

 lead. (Experiment O.) 



II. The following experiment will confirm the truth that 



the 



