64 Assaying Ores of the Precious Metals. 



which the tank can be quickly emptied. The arrangement 

 of this tank, except in one noticeable feature, does not es- 

 sentially differ from others already well known. 



The regulator by which the pressure is steadied and 

 controlled is peculiar and efficient. It consists of a small 

 sized vessel with three openings in the top, each supplied 

 with a tube which reaches nearly to the bottom of the ves- 

 sel. One of these tubes receives water from the hydrant, 

 another delivers it into the tank, while the third carries a 

 valve which regulates the pressure. The water entering 

 the vessel through the first tube until it covers their lower 

 ends will, of course, be driven up the other two with equal 

 force. Let the top of the valve tube be covered closely and 

 the pressure needed to lift the cover will be the pressure ex- 

 erted to push the water into the tank, and will also repre- 

 sent the force of the issuing air-jet. The cover or valve is 

 simply a small tin cup, with its bottom lined with rubber, 

 inverted over the smooth open end of the tube. It is fas- 

 tened to an arm hinged upon some permanent part of the 

 apparatus by which a free vertical motion is secured and 

 any other prevented. Upon the flat top of this valve 

 weights of any denomination may be placed, and the force 

 of the blast correspondingly increased, limited only by the 

 power of the stream from the hydrant. Any variation of 

 these weights will be quickly followed by a corresponding 

 variation in the pressure, which afterwards remains con- 

 stant. The valve tube should be considerably larger than 

 the supply pipe, that the relief may the more easily adjust 

 itself to the supply. Its upper end passes through the bot- 

 tom of a vessel by which the water may be caught and car- 

 ried off by a tube into the waste. With this arrangement 

 it is found that however variable the pressure of the water 

 from the hydrant, the steadiness of the air current, after 

 the first few moments, is not affected by it, and that how- 

 ever powerful the stream may be, the force of the blast 



