76 H. J. Grai/son : 



powder into the smoothly turned ed^e of the soft iron slicer, 

 gives a very satisfactory re<tum for the small amount of time 

 and trouble it requires to prepare. A hundred sections, each 

 of which involves two cuts, at a cost of little more than a 

 shilling, leaves nothing to complain of in the matter of expense. 

 In slicing I use kerosene for lubrication, that is, if the rocks 

 are compact and hard ; for such rocks it is more effective than 

 a soap emulsion, which of course must be used for soft and 

 porous rocks. Any good soap makes an effective lubricant if 

 properly dissolved. It need not be castile soap, which, like 

 many other things, is not always what it is claimed to be. 



B. Grinding Powders. — For this purpose only the finest 

 graded carborundum is used. I also regrade Avhat is ordinarily 

 sold as graded material by the manufacturer. For example, FFF 

 grade of the Niagara Falls Coy. can well be further separated 

 into two or three grades. The coarsest of these is used upon 

 the finest of the two machine laps ; the remaining liner irrades 

 are used for finishing purposes by hand. 



For the coarse lap, I find a fine but well graded powder 

 is more effective than one that is coarse; indeed, the latter is 

 simply thrown off a rapidly revolving lap. T%\o hundred and 

 twenty grade carborundum is the coarsest I use for rough 

 work. Ordinarily the series of laps comprises one coarse, one 

 fine and one finishing: — lap of slate for hand use only. 



C Canada Balsam and Mounting Methods. — ^Many people 

 fail in their first attempts to cut and prepare sections satis- 

 factorily, not through lack of perseverance or skill, but because 

 they do not carefully prepare their balsamed slips beforehand. 

 Good clean natural Canada balsam alone, if carefully prepared, 

 will hold almost any rock securely to the end of the process 

 of its preparation. The tenacity and range of hardness of the 

 balsam may, however, be extended if a small quantity, not 

 more than 1 to 3 per cent., of some clear and colourless organic 

 oil is added to it. Poppy oil. Castor oil. Clove oil — even Linseed 

 oil — are all suitable if used in the right proportions, and here 

 experience alone is the best guide. Those who have not tried 

 the addition of one of these oils, or something similar, will ap- 

 preciate the improvement effected by them, if the addition is 

 judiciously made. 



