The Tendencies of Chemistry 



mine the formation of a new quantity of potas- 

 sium sulphate and of free nitric acid, the latter 

 will evaporate, and the process will thus continue 

 until all the nitric acid has been eliminated 

 and nothing remains in the liquid except potas- 

 sium sulphate and sulphuric acid, if an excess 

 of the latter was originally present. 



This example, one of a thousand, sums up 

 the doctrine of Berthollet. It presented, at 

 least, the advantage of great practical interest 

 as it enables us to foretell, with practical certainty, 

 the course of reactions, according to the in- 

 solubility or volatility of one of their possible 

 products ; it explains, for example, why calcium 

 sulphate and ammonium carbonate produce, 

 by their reaction when cold, insoluble calcium 

 carbonate and ammonium sulphate, whereas 

 when hot the inverse reaction takes place, 

 in consequence of the volatility of the ammonium 

 carbonate. But the high priests of classical 

 chemistry continued for years to regard 

 Berthollet's laws as beneath their contempt, 

 calling them empirical rules. No qualification 

 could have been less justified, because Berthollet 

 saw in these rules, and we are to-day compelled 



49 



