1^6 Inquiry into the Laws b/ j^^tiiiy. 



and nitric acid. The oxide of lead divides its aftion upon the two acids, and both are fub- 

 jcfted to the aftion of expanfibility produced by heat. 



If the fulphuric acid were to be retained, lead would be an efficacious medium ; i. be- 

 caufe the fulphate of lead is much lefs foluble than the muriate ; 2. becaufe the fulphuric 

 acid is much lefs volatile than the muriatic acid. 



The muriate of filver being much lefs foluble than the muriate of lead, filver is much 

 better than lead for retaining the muriatic acid which is found mixed with nitric acid. 

 Velter and Bonjour have nevcrthelefs obferved that muriatic acid always came over in 

 diftillation, when the operation was made without the precautions pointed out by thofc 

 learned chemifts. To obtain a pure nitric acid immediately, it is neceflary to make the 

 operation upon an acid little concentrated, in order that it may not hold in folution any 

 muriate of filver, and to feparate the muriate of filver which precipitates before the liquid 

 is fubjeded to the adlion of heat, or which is preferable, to precipitate by thefolution of 

 filver, the muriatic acid from the nitrate of pot-afh ; after which, by decompoling 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 nevcrthelefs 

 be obtained by diftillation, by fetting afide the firft portion which diftils over, till it is feen 

 by the left that no more muriatic acid is afforded. For as the chemifts I have juft quoted 

 cbferved, the muriatic acid in this procefs afllimes the nature of oxigenated muriatic acid^ 

 and is difengaged in this ftate at the beginning of the operation-. 



Experiment P. Sulphate of pot-afh having been treated with the acetite of lead, in the 

 fame manner as the muriate of pot-afh, fulphate of lead was precipitated. The liquid re- 

 tained only a fmall quantity of oxide of lead. By the progrefs of evaporation fome cryftals 

 of fulphate of pot-afh were obtained, though before the evaporation the acetite of lead pro- 

 duced no more precipitate 5 and, laftly, the acetite of pot-afh, which retained a fmall 

 quantity of oxide of lead. The decompofition of the fulphate of pot-afh was much more 

 complete than that of the muriate of foda. 



In the experiments I have jufl defcribed, we fee, then, that the decompofitions, or ex- 

 change 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 arif*,.- 

 from the property poffefTed by the oxide of lead of forming triple combinations, which 

 fometimes again feparate in combinations of different degrees of folubility, as happens with 

 the muriate of foda and of lead Experiment O. 



1 1. The following experiment will confirm the truth that the force of cohefion produces; 

 a different effefti according to the properties of the folvent. 



Experiment Q^ I mixed an aqueous folution of plombate of foda with the water of 

 fulphate of foda, a flight pre.cipitate only was produced, though the fulphuric and muriatic 

 acids, if added, would have produced an abundant precipitate : when the experiment was 

 made with the muriate of iJuUa, the precipitate was much more abundant than with the 

 fulphate of foda.. 



4 On 



