262 Mr. Vivian on the Process of Amalgamation [April, 



then be lowered a little to bring the beam horizontal, and the 

 mark cut by the water noted for specific gravity ?/. 



In the same manner, by simply adding weights to the scale, 

 as many other specific gravities may be found as are thought 

 necessary ; when the scale is to be withdrawn and laid flat, and 

 the intervals measured with a pair of compasses, and transferred 

 to a new scale, the true specific gravities wiitten opposite their 

 proper marks, and the scale put in its place. The instrument 

 may be loaded a few grains heavy, and nicely adjusted in seal- 

 ing. It will show true specific gravities without referring to a 

 table, temperature being attended to. 



If it is desired to adjust a hydrometer for spirits, or fluids 

 lighter than water, then the scale will begin at the lower part of 

 the stem, and the differences of weight being taken from the 

 counterpoise, the instrument will sink. 



If it is wished to begin at a specific gravity different from 

 water, suppose at 1*2, for heavy solutions, the only difference 

 will be in loading the instrument. Thus a hydrometer that 

 displaces 300 grains of water must be loaded to weigh 360 

 grains, that it may stand at the same mark in a fluid whose 

 specific gravity is 1'2. The specific gravity of a body is equal 



to its weight divided by its volume r^ = 1*2, then to find any 



other specific gravity, suppose 1-25, - — -r^ — "^^^f ^^^ ^^^ 

 — 288 = 12. Twelve grains being added to the counterpoise, 

 the instrument will displace only 288, and— = r25. 



Article VII. 



Description of the Process of Amalgamation as carried on in 

 Germany. Extracted from a Letter to John Taylor, Esq. 

 from John Henry Vivian, Esq. 



{Concluded from p. 201.) 



Having thus traced the ore through various mechanical 

 operations, I come to the actual process of amalgamation, or the 

 extraction of the silver by mercury. It will be recollected, that 

 after calcination the ore is raised to the upper floor of the building 

 by means of a shaft and windlass, which is conveniently situated 

 near the division wall between the calcining house and the mills. 

 By its progress through the different sets of screens, mills, and 

 sieves, the ore again reaches the bottom floor, and the same 

 apparatus is employed for raising it to the third story, which is 

 a httle below the top of the shaft, where the boxes containing 

 the ore are placed in large iron barrows, and conveyed across 



