50 MEXICAN RESOURCES. 



noon. On the very clay the stirring is made, the cake is overturned, so as to have 

 the whole mass perfectly mixed up. This operation is made with shovels handled 

 by men ; its purpose being to cause the mud to be equally affected by the mules, the 

 combination of the substances added, and the action of the sun. 



The quantity of magistral used depends upon several circumstances, the main one 

 being the amount of sulphate of copper it contains, as it is a well-known fact that 

 said ingredient is a double sulphur of copper and iron, which by calcination assumes 

 the condition of sulphate of the same metals, but mixed with variable quantities of 

 metallic oxides. The kind of the ore to be reduced, and the atmospherical tempera- 

 ture, are also to be taken into consideration when stating the proportion. With 

 regard to the first influence, it is obvious, that, the richer in sulphate of copper the 

 magistral is, the smaller the quantity required. As a general rule, we may say that 

 pure crystallized sulphate of copper is added at the rate of seven or eight pounds to a 

 monton of ore having from five to eight marks of silver. As regards the second 

 influence, — that is to say, the kind of ore to be reduced, — nothing but practice can 

 ascertain it, and suggest the quantity of magistral to be used. Regarding the third 

 influence, — viz., atmospherical temperature, — we can only state, that, under similar 

 circumstances, ]ess,magistral is required in winter than in summer time. Quicksilver 

 is in general put at the rate of four pounds to each mark of silver in the cake, as 

 per the assay made before salting it, better still, as per the result of the assay made 

 with the grama, deducting the metal which has remained in the arrastres. The 

 quicksilver is put in smaller quantity than the one above mentioned ; but, in the 

 course of the reduction, small portions are gradually fed, when the assay hereafter 

 alluded to shows that the amalgamation wants quicksilver. 



After the cake has been incorporated and stirred, another experiment is made, 

 called tentadura, in order to ascertain the effects the ingredients are producing. 

 Said assay is practised every day, in the morning (also at noon, when the cake has 

 been stirred), taking about half a pound of mud from different parts of the cake, 

 — now from the superficies, now from the bottom, or from both, according to the pur- 

 pose in view. The mud is dissolved in water contained in a dark-bottomed vessel, 

 which is a small tray made of a gourd called gttaje ; then the mud is washed (taking 

 care not to rub it either against the vessel or between the fingers) by a rotary move- 

 ment, the water carrying away the earth and other useless parts ; then, putting in clean 

 water, the vessel is lightly shaken, so that the different components of the remaining 

 sediment may take their respective places, according to their different densities, in 

 order to be inspected; finally, a few drops of water are skilfully sprinkled with 

 the fingers into the gourd, a little over the place occupied by the ore. 



The characteristics of the ore are offal or refuse (called lis de azogiie), limature, 

 metallic sediment or fine powder, and a globule formed by the detached quicksilver. 

 Offal, so called because it is the somewhat modified and greatly subdivided quick- 

 silver, forms a white and tarnished stripe on the upper part of the ore, — a reason why 

 it is also called caheza (head), — and on being rubbed between the fingers forms 

 small globules of quicksilver. Limature is a white and shining stripe, which on 

 being rubbed with the thumb becomes a thin sheet of amalgam, called /(?«7/tz. The 

 metallic sediment, also called body of the hard cake, is composed of the unreduced 

 ore and some of the substances accompanying it. 



The quicksilver globule at the bottom gives, when strongly compressed with the 

 thumb, a certain amount of amalgam, which increases as the reduction advances. 



