636 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



To make a specific gravity determination the eye is placed in front of the mirror 

 in such a position that the pupil of the eye, the upper part of the ivory index, the 

 graduation on the mirror, and the image of the pupil in the mirror are brought into 

 line. The number of divisions at this point is x. A small piece of slag is then placed 

 in the pan P ; the division to which the ivory index is lowered is then carefully 

 noted; let this be called x 1 ; then x'x represents the weight of the slag in the 

 air, expressed in divisions. The stand S is then raised until the slag dips into the 

 water and the index rises. The number of divisions is once more carefully noted ; 

 let it be expressed by*"; x' x" represents the weight of the volume of the water 

 displaced by the slag, consequently the specific gravity will be given by the formula 



... A little correction is necessary with this instrument; x" should in reality be 



x x 



x" + x" 1 ; x'" being the number of divisions lost by the pan when immersed in water. 

 The writer has devised a little instrument, easy to carry, easy to construct, and 

 self correcting, for the determination of specific gravity. It consists of a test-tube 

 ballasted with distilled water and floating in a proof-glass filled with distilled water (see 

 Fig. 7, Plate XLIH. The test-tube is carefully graduated ; the level of the water ./, 

 outside of the tube, is noted, as well as the level o'f the water !/, inside of the tube. 

 A small piece of slag or mineral is introduced into the tube, which sinks a certain 

 number of divisions x 1 ; x 1 represents its weight. The water is raised inside of 



the tube a certain nnmber of divisions y 1 ; y' represents its volume;^ gives its spe- 

 cific gravity corrected for temperature. One of the great advantages of this instru- 

 ment is that specific gravity determinations can be made with almost as much accu- 

 racy with common water as with distilled, the weight and volume of water being self- 

 correcting. 



SECTION II. 



MATERIALS USED IN SMELTING. 



GENERAL CONSIDERATIONS. 



Smelting is conducted ou exactly the same principle by all the smelters through- 

 out the camp. Ab uno disce omues. The ore is invariably smelted in blast furnaces 

 lined with fire-brick, and provided with water jackets at the zones of agglomeration 

 and fusion ; dolomite, hematite, and old slag being used as fluxes, and a mixture 

 of charcoal and coke as fuel. In one smelter only a little metallic iroii (old horse- 

 shoes) is used for the reduction of galena when present in certain proportions in the 

 ore, but even at this smelter it is an accidental rather than a normal operation. The 

 facilities afforded to the smelters by nature in the Leadville region are really very 

 great; there smelting is practically reduced to its elementary principles. The ore 

 is, so to speak, " roasted by nature," since cerussite is evidently iii all cases the 

 result of the oxidation of galena; it requires no preliminary preparation save crush- 

 ing, and for about one-fifth of the ore, which comes out of the mine in the state of 

 sand, this is, of course, dispensed with; the quantity of matte and speiss foimed is 

 small; a good quality of hematite is found on Breece Hill, though it is used but in 



