806 SILVER 



stirring it with their feet, while at the same time a stream of water is made to pass 

 through. By this means the lighter particles of the mud flow out into canals 

 furnished with basins, called apuros, to catch all stray amalgam and quicksilver, and 

 the great body of the amalgam remains at the bottom of the vat. 



In Guanaxuato, the process of washing is more perfect. They have three circular 

 vats called tinas, in which the ore is stirred by means of long wooden teeth fixed in 

 cross bars attached to a vertical shaft, the whole turned by a simple machine, worked 

 by mules. The slime has to pass through the third vat before being carried entirely 

 away, so that a very small portion indeed of the amalgam escapes. The process 

 of washing is somewhat similar in Zacatecas, but there they use but one tina or vat. 



The amalgam is carried in bowls into the azogueria, where it is subjected to strain- 

 ing through the strong canvas bottom of a leathern bag. The hard mass left in the 



bag is moulded into wedge-shaped 



1795 j- 1796 (| masses of 30 Ibs., which are arranged 



in the burning house (fig. 1795), to 

 the number of 11, upon a solid copper 

 stand, called baso, having a round 

 hole in its centre. Over this row of 

 wedges several others are built ; and 

 the whole pile is called pina. Each 

 circular range is firmly bound round 

 with a rope. The base is placed 

 over a pipe which leads to a small 

 tank of water for condensing the quicksilver ; a cylindrical space being left in the 

 middle of the pina, to give free egress to the mercurial vapours. 



A large bell-shaped cover, called capdlina, is now hoisted up, and carefully lowered 

 over the pina, by means of pulleys. A strong lute of ashes, saltierra, and lama is 

 applied to its lower edge, and made to fit very closely to the plate on which the 

 base stands. A wall of fire-bricks is then built loosely round the capellina, and this 

 space is filled with burning charcoal, which is thrice replenished, to keep it burning 

 all night. After the heat has been applied 20 hours, the bricks and ashes are re- 

 moved, the luting broken, and the capellina hoisted up. The burned silver is then 

 found in a hard mass, which is broken up, weighed, and carried to the casting-house, 

 to be formed into bars. 



It will be observed that quicksilver performs a very important part in the process 

 of amalgamation, the silver being through its agency collected from the ore : but this 

 is only done by an enormous loss of its own bulk, occasioned in part mechanically 

 from its minute subdivision through such an immense mass of matter, but principally 

 from the chemical action upon it during the reducing process. The consumption of 

 quicksilver varies in different districts, according to the nature of the ores, the climate, 

 and the practical skill attained by the operator. 



In some places and on some ore the loss of quicksilver is as low as ten ounces for 

 every marc of silver produced, while in others it exceeds 20 ounces ; the average 

 loss may, however, be taken to be a pound of quicksilver for every half-pound of silver 

 extracted. 



Gay-Lussac, Boussingault, Karsten, and several other chemists of note have offered 

 solutions of the amalgamation enigma of Mexico and Peru. The following seems 

 to be the most probable rationale of the successive steps of the process : 



The addition of the magistral (powder of the roasted copper pyrites), is not for the 

 purpose of disengaging hydrochloric acid from the sea-salt (saltierra), as has been 

 supposed, since nothing of the kind actually takes place ; but, by reciprocal or com- 

 pound affinity, it serves to form chloride of copper and chloride of iron, upon the 

 one hand, and sulphate of soda, upon the other. Were sulphuric acid to be used 

 instead of the magistral, as certain novices have prescribed, it would certainly prove 

 injurious, by causing muriatic acid to exhale. Since the ores contain only at times 

 oxide of silver, but always a great abundance of oxide of iron, the acid would partly 

 carry off both, but leave the chloride of silver in a freer state. A magistral, such as 

 sulphate of iron, which is not in a condition to generate the chlorides, will not suit 

 the present purpose ; only such metallic sulphates are useful as are ready to be trans- 

 formed into chlorides by the saltierra. This is peculiarly the case with sulphate of 

 copper. Its proto-chloride gives up chlorine to the silver, becomes in consequence a 

 subchloride, while the chloride of silver, thus formed, is revived, and amalgamated 

 with the quicksilver present, by electro-chemical agency which is excited by the 

 saline menstruum; just as the voltaic pile of copper and silver is rendered active by 

 a solution of sea-salt. A portion of chloride of mercury will be simultaneously 

 formed, to be decomposed in its turn by the sulphate of silver resulting from the 

 mutual action of the acidified pyrites, and the silver or its oxide in the ore. An 



