1896 THE MICROSCOPE. 1 



tage that you can renew it at any time in a few moments. 



In the examination of rocks the specimen selected should 

 have a good, fresh surface of fracture, of a size about 3 by 

 5 inches, and IJ inches thick. With a trimming hammer 

 prepare the narrow face or edge, so that by rubbing it on 

 emery blocks you can get an even surface or polish on it. 

 Then heat the specimen so you can hardly handle it. 

 AVhen in tliat condition rub Canada balsam onhalf of the 

 polished surface. When cold it will harden so that you 

 can handle it without injury. By this method the differ- 

 ent constituents of the rock are much better seen, and the 

 insj)ection of the outer surface, viewed as an opaque object 

 with a common magnifier, say of three diameters, set in 

 a spectacle frame, gives all the information ordinarily 

 required by the mining engineer. The even surface not 

 covered by the balsam can then have the hardness of the 

 different crystallized minerals to be seen on it easily deter- 

 mined, and also treated with acids, applying the same 

 with a pointed glass rod dipped in the acid. The action, 

 if any, can be seen, and also the smallest scratch, when 

 testing for hardness, will be made visible. 



The use of the lenses mounted in a spectacle frame is 

 recommended to the miner or geologist in the field, as it 

 is scarcely possible to examine the streaks of minerals 

 when they occur in very minute crystals and keep the lens 

 in focus when holding it in one hand and working for the 

 scale of hardness with the other. 



There was sliown under the microscope a small frag- 

 ment of what is called " carbonate," or diamond carbon. 

 Bahia, Brazil, produced at one time large quantities of the 

 carbonate. Its hardness is identical with the white dia- 

 mond, and in structure it is porous, so much so that it 

 resemble pumice stone. This fragment was taken from 

 the Yellow Jacket diamond drill, at Virginia City, Nev. 

 The drill penetrated the rock 1)elow the gold and silver 



