TECHNICAL CHEMISTRY. 



337 



COMPOSITION OF BLACK-ASH. 



1 and 2, German Ash, analysed by tinker and Stohmann. 

 3, English Ash, analysed by Brown and Kynaston. 



The next operation consists in the separation of the 

 carbonate of soda from the insoluble calcium mono-sulphide, 

 and the other impurities. This is easily effected by the 

 process of lixiviation, or washing out the soluble carbonate 

 of soda, leaving the mono-sulphide of calcium and the 

 excess of lime and carbonate of lime as insoluble powders 

 behind. In this process the object aimed at is to dissolve 

 as large a quantity of the carbonate of soda with as small 

 a quantity of water as possible. The arrangement of lixi- 

 viating vats for effecting this is the invention of the late 

 Mr. Shanks of St. Helens. A series of vats is employed 

 in which the broken black-ash is placed ; pure water is 

 allowed to flow on to the ash, which has already been nearly 

 exhausted, and the solution then passes on until the nearly 



VOL. II. Z 



