298 DISCOURSE ON THE STUDY 



search. Yet this does not hinder us from regarding 

 such a compound as still a mere mixture, and its 

 properties are accordingly intermediate between 

 those of the liquids mixed. But this is far from 

 being the case with all liquids. When a solution of 

 potash, for example, and another of tartaric acid, 

 each perfectly liquid, are mixed together in proper 

 proportions, a great quantity of a solid saline sub- 

 stance falls to the bottom of the containing vessel, 

 which is quite different from either potash or tar- 

 taric acid, and the liquid from which it subsided 

 offers no indications by its taste or other sensible 

 qualities of the ingredients mixed, but of something 

 totally different from either. It is evident that this 

 is a phenomenon widely different from that of mere 

 mixture ; there has taken place a great and radical 

 change in the intimate nature of the ingredients, by 

 which a new substance is produced which had no 

 existence before. And it has been produced by the 

 union of the ingredients presented to each other ; for 

 when examined it is found that nothing has been 

 lost, the weight of the whole mixture being the 

 sum of the weights mixed. Yet the potash and 

 tartaric acid have disappeared entirely, and the 

 weight of the new product is found to be exactly 

 equal to that of the tartaric acid and potash em- 

 ployed, taken together, abating a small portion held 

 in solution in the liquid, which may be obtained 

 however by evaporation. They have therefore com- 

 bined, and adhere to one another with a cohesive 

 force sufficient to form a solid out of a liquid ; a force 

 which has thus been called into action by merely 

 presenting them to each other in a state of solution. 



