The Patio and Oazo Process. 45 



tory furnace built of adobes, and heated with wood, which receives 

 a charge of 300 kilos, of the crude bullion. This charge is refined 

 iu four hours. A little litharge and lead are added to remove 

 the impurities, which are generally sulphur, arsenic, lead, iron, 

 and sometimes zinc. Borax and carbonate of soda are used as a 

 flux. The loss is seven per cent, of the crude bullion, and con- 

 sists mostly of quicksilver, but to some extent of silver. 



The silver obtained is quite pure: it contains at San Dimas.994 

 of silver, .0033 of gold, leaving only .0026 for base metals. At 

 Chihuahua it is .998 from the arrastra, and .990 from the treat- 

 ment of the tails.* The bars weigh 35 kilos. The slags from 

 the refining furnace, with the tails from the tanks for washing 

 amalgam, and other products, are occasionally smelted in a shaft 

 furnace with the addition of galena, and the lead is used in refining 

 retort silver. 



The loss of mercury in retorting varies from two to six kilograms 

 per ton. The total loss of mercury in Mexico has been for many 

 years calculated on the supposition that it requires a loss of a 

 unit of mercury for every unit of silver obtained. This 

 being a fixed amount, is called consumido. Any amount a- 

 bove this which is not recovered is called perdlda, or loss, 

 and is always attributed either to carelessness on the part 

 of the workmen, or to mechanical losses during the operation. 

 The losses, both the fixed and the variable, are always referred 

 to the Mexican mark, which is equal to 248.83 grams. 



Consumido, - 248.83 grams. 



Perdida, - 124.42 



Total loss, 373.25 



The loss of mercury for sulphuretted ores of from $G0 to $100 

 will be, under the most careful management, not less than four to 

 five kilograms. In some exceptional cases it has been three kilo- 

 grams for every kilogram of silver extracted. The richer the 

 ore the greater the loss. It may be averaged at one and a half 

 kilograms for every kilogram of silver produced. With ores 

 containing large amounts of native silver, the loss is proportion- 

 ately much less, and sometimes even less iu amount. The loss in 



* Mining Commissioners' Report for 1S72, p. 488, Washington, D. C, 1873. 



