304 JOSEPH STRUTHERS 



improved their methods, and new concentrating processes 

 are being tested. 



There are two common methods of concentrating crystal- 

 line graphite from its ore — the wet and the dry. The wet 

 or water method has been developed to a marked degree 

 of efficiency, and is the one now generally used. The mode 

 of procedure is to crush the ore wet, and separate coarsely 

 by stationary buddies, the concentrates being dried and fur- 

 ther treated with buhrstones and screens. No mill, however, 

 has adopted either method in its entirety, because the specific 

 gravities of the constituents of the ore vary so little. Several 

 pneumatic processes have lately proved a partial success, but 

 they have been of limited application, on account of the im- 

 possibility of removing the small scales of mica which occur 

 in some of the deposits. 



Two new features in concentration practice, in both 

 of which the older method of complete submersion beneath 

 the surface is replaced by flotation, are worthy of note — 

 first, the use of petroleum vapor, which, being readily ab- 

 sorbed by graphite, permits the flakes to be more readily 

 separated from the gangue material by flotation ; and, second, 

 the heating of the ground product before separation, which 

 makes the flakes of graphite so light that they float on the 

 surface of the water, whence they are removed. 



The incentive to develop properties containing amorphous 

 graphite is much less than in the case of the crystalline variety. 

 On account of the limited use of the former, the value of the 

 crude product is only from one eighth to one tenth of that 

 of the latter. For the manufacture of graphite crucibles 

 and for many electrical purposes no satisfactory substitute 

 for crystalline graphite has been discovered, while in the 

 case of amorphous graphite there are many other materials 

 of equal suitability for its various uses. 



The mining of amorphous graphite in the United States 

 has been of comparatively recent development. During 

 1902 the product was obtained chiefly from Wisconsin, fol- 

 lowed by Michigan, Rhode Island, South Dakota, Wyoming, 

 and New Mexico, in the order named. There are numerous 



