1826.] as carried on in Germani/. 201 



an inch square. The coarse parts fall into moveable boxes ; the 

 fine particles, or what passes through the screen, fall into the 

 cases, the opening to which is on the opposite side to the stairs. 

 This machine is inclosed in a wooden case, and is surmounted 

 by a funnel or chimney, which communicates with a receiving 

 chamber immediately under the roof of the building. By this 

 means, any fine particles that fly off during the operation are 

 collected, and the workmen are not inconvenienced. 



The coarse stuff from the upper screen is broken on a table 

 placed near it, and being mixed with two per cent, of salt is 

 again calcined. The finer parts that pass through the riddles 

 fall into a hopper placed over a moveable screen on the under 

 floor. 



The holes in the grating of the screen are of two sizes ; those 

 in the upper part being somewhat smaller than those in the 

 lower. The calcined ore falling upon the higher part of the 

 screen, the finer particles pass through ; those that are coarser 

 roll down, and some pass the larger apertures of the lower part 

 of the screen ; whilst that portion which is too large for either, 

 and which is trifling in quantity, rolls entirely over the screen, 

 and falls off" at the bottom. Thus three sizes of stuff are 

 obtained. The coarsest part, which does not pass through the 

 screen, is treated in the same way as the coarse stuff' from the 

 upper riddle. The finer parts are passed through wooden pipes 

 to the lower floor, and are there ground in granite mills which 

 are precisely similar in construction to those used for grinding 

 corn. The ore which passes through each part of the screen is 

 ground separately, the particles being of an uniform size. 



After being ground, the ore is passed through a fine sieve; 

 and being now reduced to an impalpable powder, is fit for the 

 process of amalgamation. 



The object in reducing the ore to so fine a powder is, that the 

 mercury may act on every portion of it, so as to extract the 

 smallest particles of silver it may contain. The calcination of 

 the ore renders it more frangible, and therefore facilitates the 

 operations necessary to bring it to the state just described. 

 The Freyberg works contain two coarse and two fine screens, 

 and 14 pair of grinding stones. 



{To le continued.) 



