30 PRECIPITATIONS BY ETHER, ETC. 



of the liquid which is added (such as aqua potassse, 

 alcohol, &c.), but in many other cases there is re- 

 quired only a slight alteration in the quality of the 

 solvent to effect separations of this kind, 

 of ferrocy- When hydrochloric acid is added to a solution of 



anic acid by i P 



ether; ferrocyamde of potassium, ferrocyamc acid is set 

 free, and remains dissolved in the liquid. If now 

 the vapour of boiling ether be passed through the 

 mixture, there occurs, after a few moments, a com- 

 plete separation. The whole of the ferrocyamc 

 acid is deposited from the liquid in the form of 

 white or bluish-white crystalline scales, which 

 generally appear in such quantity as to render the 

 whole mass semisolid. In proportion as the vapour 

 of ether is dissolved by the water, the latter fluid 

 loses entirely its solvent power (its affinity) for the 

 ferrocyanic acid. The coagulation of albumen by 

 ether depends on a similar cause. 



The capacity of solids to become moistened by 

 liquids, and, in short, all phenomena connected with 

 chemical affinity, are affected, altered, increased, or 

 destroyed, by causes quite analogous. 



of sus- After heavy rains, the water of many rivers be- 



mudby comes turbid and opaque from the presence of a fine 

 clay. These suspended particles of clay are so fine 

 as to pass through the finest filters ; and their adhe- 

 sion to the water is so great, that such water does 

 not clear after standing for weeks. The water of 

 the Yellow River, in China, possesses, during the 

 greater part of the year, this character ; and from 



