140 Commentaries on the 



litharge or copperas should not be roasted, until they have been 

 washed and thoroughly agitated in tubs of water, so as to separate 

 the copperas ; for unless this precaution be taken, it will be increased 

 in quantity by the action of the fire, instead of being driven off, and 

 it will have the effect of destroying the quicksilver, and preventing* 

 its uniting with the silver. It is sometimes proper to roast the ore 

 after grinding, and sometimes while in the rough. But the most 

 usual course, in the mining districts of New Spain, is not to roast 

 the ore at all, on account of the injurious effect of the operation, in 

 rendering it dry, in diminishing its richness, and in augmenting its 

 bad qualities. 



* Fifth, the ore being ground, is thrown into heaps or montons, 

 usually of 30 quintals ; but in some places of 18 quintals: and the 

 montons are sometimes placed beneath a roof, but most frequently 

 in a well-flagged yard or patio, whence this mode of reduction is 

 called the reduction by the patio. 



* Sixth, with each monton of 18 quintals, are mixed two barrels 

 of brine, from impure salt; six, eight, or ten pounds of magistral, 

 as the nature of the ore may require, and from ten to twelve pounds 

 of quicksilver. The monton thus prepared, is stirred and trodden, 

 which is called repasar. After two or three days, the stirring and 

 treading are repeated, and if it require more quicksilver, a further 

 charge is thrown in, and it is again stirred, until found to require 

 no more : and it is to be observed, that the more quicksilver it 

 requires the better, as a proportionate quantity of silver may be 

 expected. 



* Seventh, the quicksilver must be added at different times, and 

 not be thrown in all at once, so that it may by degrees take up the 

 whole of the silver. The first stirrings must be performed with 

 softness and gentleness, lest the quicksilver should become too 

 minutely divided and form Us, which is the term applied when it 

 divides into almost imperceptible particles. From the varying na- 

 ture of the ore, and the diversity of circumstances which arise, no 

 certain rules can be laid down for the course to be pursued in 

 stirring in the quicksilver and magistral, and it will therefore be 

 found, that it is sometimes necessary to excite heat by stirring, and 

 at others to apply moisture. Neither is it possible to determine the 

 precise moment at which the montons are in a state for washing, 

 for though they may not make any Us of silver, nor require any 

 more quicksilver, yet the quicksilver may be dispersed. The only 

 rule is, to ascertain whether the proportion of silver taken up, cor- 

 responds with the result of the assay made at the commencement 

 of the process ; and there is no way of ascertaining this, but by 

 making a further trial, in a small way, whether the monton is in 

 want of any addition, which in such case may be supplied, or whe- 

 ther it is complete, in which latter case the monton may be washed. 



4 Eight, the monton being ready for washing, is thrown into 

 wooden Vats of very large size, within each of which is contained a 



