The Evolution of the Sciences 



into the thick of the fight, count the combatants, 

 follow their hand-to-hand struggle and judge 

 the result on the ground. The honour of this 

 new method belongs to Berthollet. 



When sulphuric acid is poured into a solution 

 of potassium nitrate no visible phenomenon is 

 manifested, and many people might say that 

 the two liquids have mixed without any chemical 

 reaction. Berthollet saw that a reaction does 

 take place, and that in reality the base is divided 

 between the two acids, so that the liquid now 

 contains four bodies: potassium nitrate, potas- 

 sium sulphate, sulphuric acid and nitric acid; 

 a state of equilibrium has been established 

 between these bodies, capable of persisting 

 indefinitely. 



Now supposing something happens to elimin- 

 ate one of the four antagonists, the equilibrium 

 will be destroyed, then re-established by a new 

 chemical transformation, and the reaction will 

 advance accordingly step by step. If, for 

 example, the mixture is warmed, the nitric 

 acid, being more volatile than its competitors, 

 will escape; then the influence of the sulphuric 

 acid, being no longer held in check, will deter- 



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