10 The Patio and Cazo Process. 



drags. When new, all the stones together weigh from 300 to 800 

 kilos. The arms are sometimes niched so as to allow of chang- 

 ing the position of the stones at will. There are usually four of 

 these mullers, but sometimes only two, and in very rude arrastras 

 only one is used. They do not last much over a month, and are 

 sometimes worn out before that time. When they are worn 

 down to about 200 kilos they are replaced one at a time, so that 

 there are always old and new stones in the mill at the same time. 

 The arrangement of the arms differs according as animal or 

 water-power is to be used. When mules are used, one of the 

 arms is made to project over the side of the arrastra, and to it 

 one and sometimes two mules are hitched. Such arrastras are 

 called arrastra cle inula, or when they are of large size, arrastra 

 de marca. When water power is to be used, all the horizontal 

 arms project beyond the rim. From these arms rods descend, 

 which support a horizontal wheel, which revolves around outside 

 of the arrastra a few centimeters above the pit. In the circum- 

 ference of this wheel, at intervals of 0.15 m., rectangular floats, 

 slightly concave, and set edgewise, are placed. These are called 

 spoons, cucharas, and these arrastras are distinguished as spoon 

 arrastras, taliona or arrastra de cucliara, in distinction from the 

 arrastra de mala. The men in charge of the grinding are called 

 tahoneros. The water strikes these paddles, the power being ac- 

 quired Avhile descending through a tapering shoot which has a fall 

 of 0.20 m. in every 3.5 m. to 4.5m. This horizontal water -wheel 

 runs in a channel a few centimeters deep on the outside of the ar- 

 rastra, as shown in the plate. * If the central space, called tosa, 

 which is the arrastra proper, is three meters in diameter, it is 

 usually not more, and about 0.50 m. deep, the wheel six meters 

 in diameter with a width of from 0.60 m. to 0.70 m., the out- 

 side diameter of the ditch would be about 7 m. Such an 

 arrastra would treat between 400 to 600 kilos of soft ore in 

 twenty-four hours, or if it is hard, 700 and 800 kilos in about 

 three days. This is a wasteful appliance, but there is a super- 

 abundance of water, so that it makes little difference. These 

 arrastras are constantly employed when water-power can be 



*' I am indebted to Dr. Drown, the obliging Secretary of the Am. Inst. 

 of Min. Eng., for the cliches taken from Mr. E. Chism's paper. 



