SILVER 



809 



combine with the particles of ore ; and if too thin, they fall and rest at the bottom. 

 In the first case some water must be added; in the second, ore. During the 

 rotation, the temperature rises, so that even in winter it sometimes stands so high as 

 104 Fahr. 



The chemical changes which occur in the casks are the following : The metallic 

 chlorides present in the roasted ore are decomposed by the iron, whence results 

 chloride of iron, whilst the protochloride of copper is reduced partly to subchloride, 

 and partly to metallic copper, which throw down metallic silver. The mercury 

 dissolves the silver, copper, lead, antimony, in a complex amalgam. If the iron is 

 not present in sufficient quantity, or if it has not been worked with the ore long 

 enough to convert the cupric chloride into a cuprous chloride, previously to the 

 addition of the mercury, more or less of the last metal will be wasted by its con- 

 version into protochloride (calomel). The water holds in solution sulphate of soda, 

 undecomposed sea-salt, with chlorides of iron, manganese, &c. 



As soon as the revivification is complete, the casks must be filled with water, set to 

 revolve slowly (about 6 or 8 times in the minute), by which in the course of an hour, 

 or an hour and a half at most, a great part of the amalgam will have collected at the 

 bottom ; and in consequence of the dilution, the portion of horn-silver held in solu- 

 tion by the sea-salt will fall down and be decomposed. Into the small plug in tho 

 centre of the bung, a tube with a stopcock is now to be inserted, to discharge the 

 amalgam into its appropriate chamber. The cock must be stopped whenever the 

 brown muddy residuum begins to flow. The main bung being then opened, the 

 remaining contents of the casks arc emptied into the wash-tun, while the pieces of 

 iron are kept back. The residuary ore is found to be deprived of its silver to within 

 sis OT 5o f an ounce per cwt. The emptying of all the casks, and charging them 

 again, 'takes 2 hours; and the whole process is finished within 18 or 20 hours; 

 namely, 1 hour for charging ; 14 to 16 hours for amalgamating ; ll hour for diluting ; 

 1 hour for emptying. In 14 days 3,200 cwts. of ore are amalgamated. For working 

 100 cwts. of ore, 14^ Ibs. of iron are required ; and for every pound of silver obtained, 

 3 ozs. of mercury are consumed. 



Trials have been made to conduct the amalgamation-process in iron casks, heatod 

 to 150 or 160 Fahrenheit, over a fire ; but although the desilvering was more com- 

 plete, the loss of mercury was so much greater as to more than counterbalance that 

 advantage. 



Treatment of the Amalgam. It is first received in a moist canvas bag, through 

 which the thin uncombined quicksilver spontaneously passes. The bag is then tied 

 up and subjected to pressure. Out of 20 casks, from 3 to 3^ cwts. of solid amalgam 

 are thus procured, which usually consist of 1 part of an alloy, containing silver of 12 

 or 13 loths (in 16), and 6 parts of quicksilver. The foreign metals in that alloy are 

 copper, lead, gold, antimony, cobalt, nickel, bismuth, zinc, arsenic, and iron. The 

 filtered quicksilver contains moreover 2 to 3 loths of silver in the cwt. 



Fig. 1798 represents the ap- 

 paratus formerly used for dis- 

 tilling the amalgam in the Hals- 

 briicke works, a is the wooden 

 drawer, sliding in grooves upon 

 the basis, q ; B is an open basin 

 or box of cast iron, laid in the 

 wooden drawer ; y is a kind of 

 iron candelabrum, supported upon 

 four feet, and set in the basin, 

 B; under d are five dishes or 

 plates, of wrought iron, with a 

 hole in the centre of each, by 

 which they are fitted upon the 

 stem of the candelabrum, 3 inches 

 apart, each plate being successively smaller than the one below it. 3 indicates a 

 cast-iron bell, furnished with a wrought-iron frame and hook, for raising it by means 

 of a pulley and cord, s is a sheet-iron door for closing the stove, whenever the bell 

 has been set in its place. 



The box, a, and the basin, B, above it, are filled with water, which must be con- 

 tinually renewed, through a pipe in the side of the wooden box, so that the iron basin 

 may be kept always submersed and cool. The drawer, a, being properly placed, and 

 the plates under d being charged with balls of amalgam (weighing altogether 3 cwts.). 

 the bell, 3, is to be let down into the water, as at y, and rested upon the lower part of 

 the candelabrum. Upon the ledge, 1, which defines the bottom of the fireplace, a 

 circular plate of iron is laid, having a hole in its middle for the bell to pass through. 



1798 



