INFLUENCE OF INSOLUBILITY. I s'j 



position depending upon volatility, and affected by changes in 

 the nature of the atmosphere into which evaporation takes 

 place. Alcohol or the hydrate of ether is added in a gradual 

 manner to sulphuric acid somewhat diluted, and heated to 

 280. In these circumstances, the double sulphate of ether 

 and water is formed ; water, which was previously com- 

 bined as base to the acid, being displaced by ether, and 

 evolved together with the water of the alcohol. The first 

 effect of the reaction therefore, is the disengagement of 

 watery vapour, and the creation of an atmosphere of that 

 substance which tends to check its farther evolution. But 

 the existence of such an atmosphere offers a facility for 

 the evaporation of ether, which accordingly escapes from 

 combination with the acid and continues to be replaced by 

 water, the affinity of sulphuric acid for water and for ether 

 being nearly equal, till ether forms such a proportion of the 

 gaseous atmosphere as to check its own evolution, and to fa- 

 vour the evolution of watery vapour. Then again alcohol is 

 decomposed, and more of the double sulphate of water and 

 ether formed as at first ; the sulphate of ether of which comes 

 in its turn to be decomposed as before, and ether evolved. 

 Hence, both ether and water distil over in this process, the 

 evolution of one of these bodies favouring the separation and 

 disengagement of the other. In this description, the evolution 

 of water and ether are for the sake of perspicuity supposed to 

 alternate, but it is evident that the result of such an action 

 will be the simultaneous evolution of the two vapours in a 

 certain constant relation to each other. 



Influence of insolubility. The - great proportion of chemical 

 reactions which we witness are exhibited by bodies dissolved in 

 water or some other menstruum, and are affected to a great 

 extent by the relations of themselves and their products to their 

 solvent. Thus carbonate of potash dissolved in water is decom- 

 posed by acetic acid, and carbonic acid evolved, the affinity of 

 the acetic acid prevailing over that of the carbonic acid for 

 potash. But if a stream of carbonic acid gas be sent through 

 acetate of potash dissolved in alcohol, acetic acid is displaced, 

 or the carbonic acid prevails, apparently from the insolubility 

 of the carbonate of potash in alcohol. The insolubility of a 

 body appears to depend upon the cohesive attraction of its 

 particles, and such decompositions may therefore be ascribed to 

 the prevalence of that force. 



