MINING. 279 



the size of a pigeon's egg, are called a " charge" for an arastra 

 ten feet in diameter, and are put in at a time. Tiie mule is 

 started and in four or five hours the quartz is pulverized. 

 Water is now poured in until the powder is thoroughly mixed 

 with it, and the mass has the consistence of thick cream. Care 

 is taken that the mixture be not too thin, for the thickness 

 of it is important to the amalgamation. The paste being all 

 right, some quicksilver (an ounce and a quarter of it for every 

 ounce of gold in the quartz, and the amount of gold is guessed 

 at from the appearance of the rock) is scattered over the aras- 

 tra. The grinding continues for about two hours more, dur- 

 ing which time it is supposed the quicksilver is divided up into 

 very fine globules and mixed all through the paste (which is so 

 stift'that the metal does not sink in it to the bottom), and that 

 all the particles of gold are caught and amalgamated. The 

 amalgamation having been completed, some water is let in 

 three or four inches deep over the paste, and the mule is made 

 to move slowly. The paste is thus dissolved in the water, and 

 the gold, quicksilver, and amalgam have an opportunity to fall 

 to the bottom. At the end of half an hour, or sooner, the 

 thin mud of the arastra is allowed to run off, leaving the pre- 

 cious material at the bottom. Another charge of broken 

 quartz is now put in and the process is repeated, and so on. 

 The length of a "run," or the period from one cleaning up to 

 another, varies much in different places. In the rude arastra 

 a run is seldom less than a week, and sometimes three or four. 

 The amalgam having settled down between the paving stones, 

 the bed must be dug up and all the dirt between them carefully 

 washed. In the improved arastra the paving fits so closely 

 together, that the quicksilver and amalgam do not get down 

 between them, but remain on the surface, and can readily be 

 brushed up into a little pan, and therefore cleaning up is much 

 less troublesome and is more frequently repeated than in the 

 rude arastras ; besides there is a greater need of frequent 

 cleaning up in the improved arastras, because the amount of 

 work done within a given time is usually greater. 



