132 MINING INDUSTRY. 



very efficient and has given much satisfaction to the mining companies that 

 employ it on the Comstock. It is made of various sizes. At the Ophir 

 works a No. 5 machine is used, the drum being 4 feet long. It is driven by 

 a small engine provided especially for the purpose, but capable of doing addi- 

 tional work. The machine is calculated to run at 300 revolutions per minute, 

 but running at 130 revolutions fully performs the present required duty, forcing 

 the air down 700 feet in the shaft and thence to the end of the drift, several 

 hundred feet more. 



For conveying the air down the shaft and along the drift a square, 

 wooden box-pipe is used. When these blowers were first introduced the con- 

 veying pipes were made of galvanized iron, but this material was not proof 

 against the corroding influences of the water in the shafts, and very soon 

 became useless in that part of the work, though better adapted to the drier 

 levels. Air-boxes of common pine wood were used next, but the tendency of 

 this wood to split and crack caused them to leak very badly. The best and 

 most satisfactory material now in use for this purpose is the redwood of Cali- 

 fornia, which seems to be less affected than any other by the changes of tem- 

 perature and different degrees of moisture in the mine. The air-box or 

 convey ing-pipe is made of dressed lumber 1^ inch thick, and is about 12 

 inches square in horizontal section. The four sides of the box are tightly 

 joined together with a tongue and groove, as shown in Fig. 3, Plate VI, at a, 

 and the ends of the sections of pipe are connected by letting the lower end of 

 the upper section into the upper end of the lower section as shown in same 

 figure at h. An iron band is put round this joint which is v^ell packed and 

 then covered with a thick coat of paint. The pipe is supported in the shaft 

 by clamps, c, c. Fig. 2, which secure it to the timber-sets. It is fixed snugly 

 in the corner, usually of the pump-compartment, the clamps securing it as 

 shown in the figure. The cost of this air-pipe, finished and placed in the 

 shaft, is about $1 50 per foot. The cost of the blower of the size used at the 

 Ophir (the largest made) is $700. It may, of course, be driven by the same 

 power that is employed for hoisting or pumping, but as the work is continuous 

 and cannot be interrupted while men are working in the mine, a small engine, 

 devoted exclusively to this duty, is preferred and generally provided by the 

 Comstock mines. 



