222 JAMES SHANKS 



if this difference is only caused by that 

 in the specific gravities of the solutions. 

 In the connecting tubes, &c., a certain 

 amount of friction has to be overcome by 

 a corresponding pressure, the tanks must 

 be made higher, and those openings from 

 which the strong liquor issues must be made 

 low enough to satisfy not merely the difference 

 of level between the water and the strong 

 liquor, but also the pressure required for 

 overcoming the friction. The head of water 

 between the top of the tank and the lateral 

 exit opening is the real moving principle ; if it 

 is made too low, or, if by a partial obstruction 

 of the connecting pipes the friction is increased, 

 the weak tank will run over before the strong 

 ones begins to run." 



Dr. Hofmann concludes his remarks on 

 this subject by observing : " It is not only in 

 the manufacture of soda that the process of 

 methodical lixiviation is applicable. It is 

 available in all branches of arts and manu- 

 factures, for the economical collection and 

 concentration of all kinds of soluble matter, 

 whenever such matter is diffused in small 

 proportion throughout the substance of bulky, 

 porous, insoluble masses. 



Considered, then in its general bearings, 



