TEEATMENT OF THE COMSTOCK GEES. 217 



different lieads are used in different places. Generally, however, in Califor- 

 nia the aperture is made two inches deep and as long as need be in order to 

 furnish the requisite number of inches, and the water in the measuring box, 

 which is at one side of the supplying flume, is allowed to attain a height of 

 six inches above the center of the orifice. 



The quantity of water that will pass through an orifice of one inch 

 square in the side of the box, under a head of six inches, determined by 

 multiplying the area of the orifice by the theoretical velocity yj 2gli, and taking 

 two-thirds of the product as effective discharge, is .02633 cubic feet per sec- 

 ond, 1.578 cubic feet per minute, and 94.68 cubic feet per hour. The miU 

 just referred to uses five inches of water. Assuming that its measurement is 

 uniformly in accordance with the above conditions, the amount dehvered in 

 twenty-four hours is 11,361 cubic feet; equal to about 206^ cubic feet per 

 ton of rock treated. Taking the operation of this mill as a criterion, one inch 

 jf water is a supply for five stamps, including the quantity required for amal- 

 gamation as well as for crushing. 



The mills of Virginia City and Gold Ilill, that have no springs or other 

 tjources of water of their own, are supplied by the Virginia and Gold Hill 

 Water Company. This company obtain water by means of tunnels driven 

 into the hillside for the purpose, and by purchase from mining companies, 

 whose works furnish considerable quantities. Under ordinary circumstances 

 the supply of water, derived from sources above Virginia City and available 

 for use there, is sufficient to meet all demands at that place ; in addition to 

 which there are more sources below the city, in the mines and lower tunnels. 

 In seasons of drought some inconvenience is experienced. 



Pans. — The common features of the grinding and amalgamating pans 

 have already been described on a foregoing page. There are, however, 

 various kinds of pans which, although resembling each other in general char- 

 acter, present some important differences in the details of construction. 

 These differences have been gradually developed since the first inti'oduction 

 of the common pan, each aiming especially to meet some one or more of the 

 various requirements of an efficient machine. 



The main objects sought for by inventors have been to produce grinding 



surfaces of most efiective form, securing the greatest uniformity of wear with 

 28 



