4S MEXICAX RESOURCES. 



The arrastrc is divided by the runners in four equal parts: when a trial is to be 

 made, the runners are placed in a given position, which is to be changed at the 

 moment of effecting the trial. One of the four compartments of the ar7-ast)-e is 

 emptied; and, when the bottom is exposed to view, small quantities of mud are 

 taken from the interstices, forming with them balls, which are placed in an orderly 

 manner in a box with compartments, numbered as the compartments of the arrastre, 

 in order to avoid confusion. 



I'he balls are washed ; and from the appearance of the sediment the condition 

 of the mud is ascertained. If the sediment appear compact, or divided in large 

 ]3ieces, it proves that the mud is well saturated with quicksilver, and the operation 

 can go on; but should the mud be too much pulverized, almost powdered, then 

 it is too dry, and wants more quicksilver, until it becomes as fluid as at the begin- 

 ning of the operation. In the former case, the pressure of the mud with the 

 finger forms a white and shining surface : in the latter instance, it forms a dark and 

 opaque one. An accurate account of the quantity of quicksilver put into each 

 arrastre is kept, so as to know at any moment the total amount employed in the 

 galera: hence the approximate quantity of silver in all the arrastres. From ores 

 without pure silver, ten or twelve per cent of the alloy contained in the whole 

 grinding is gathered; but the best way to ascertain it is to assay the amalgam, 

 taking small quantities from each trial in order to estimate the condition of the 

 galera. Said assays show very accurately the amount of gold and silver contained 

 in all the arrastres. 



When the amalgam is considered rich enough, or when it is thought that its 

 quantity at the bottom of the arrastre is too large (which would be detrimental to 

 the grinding operation), the scraping o[)eration is commenced. This consists in 

 taking out the flags forming the bottom of the an-astre, extracting with hooks from 

 the interstices all the earth which may contain amalgam. The operation ends, 

 when, assaying the earth taken from the interstices, no amalgam is found in it. 

 It would be no inconvenience, however, to leave a small quantity of amalgam in 

 the earth, as it will be picked out when putting new bottom to the an-astre. The 

 earth is washed, adding to it a suitable amount of quicksilver, and putting it into 

 large trays, where the amalgam settles, containing about eighteen to twenty-two 

 pounds of mixed silver for a hundred pounds of quicksilver used in ihe galeras. 



Patio {yard). — The /atia is a large yard paved with flags very well adjusted to 

 each other, so as to prevent as much as possible the escaping of the quicksilver, 

 and with declivity enough to allow the running of the rain-water without carrying 

 the mud of the cakes which are to be placed over the flags. The cakes are formed 

 with the ground ore which is to be worked upon. Whenever there is in the lamero 

 (reservoir) mud enough to form a cake (about a hundred inontones, though they are 

 sometimes larger), the mud is tlirown in the yard, taking care of dailv taking out 

 from the lamero any excess of water that may be there. The mud is received into 

 another provisional reservoir, constructed over the yard in the space to be occupied 

 by the cake, which reservoir is called cajete ; and its size is such as to allow the 

 mud to form a cake c" 25 to oni 30 thick. The cake is allowed to settle itself, 

 being perforated now and then, to make the water on its surface gradually flow out. 

 This operation, together with the spontaneous evaporation, prepares the cake for 

 salting within four or six days. Before salting the mud, it must be assayed, taking 

 from different points in the reservoir small quantities of mud by means of a wooden 



