140 THE AMERICAN MONTHLY [April 



a spirit lamp melt some lapidary's cement into the vacant 

 space ; with a small pair of plyers take the fragaraents of 

 minerals, heat one end, and insert it into the cement. 

 While the cement is warm, hy wetting yonr finger, yon 

 can mold it into any shape yon please and when cold, if 

 properly done, it will harden and answer just as well as 

 if set in metal, with the advantage 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 hy 5 inches, and Ig inches thick. With a trim- 

 ming hammer prepare the narrow face or edge, so that 

 by rubbing it on emery blocks you can get an even sur- 

 face or polish on it. Then heat the specimen so you can 

 hardly handle it. When in that condition rub Canada 

 balsam on half the polished surface. When cold it will 

 harden so that you can handle it without injury. By 

 this method the different constituents of the rock are 

 much better seen, and the inspection 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 crystalized minerals to 

 be seen on it easily determined, and also tested 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, Avill be 

 made visible. 



The use of the lenses mounted in a spectacle frame Mr. 

 Attwood strongly 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 cry- 

 tals and keep the lens in focus when holding it in one 

 hand and working for the scale of hardness with the 

 other. 



