ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 707 



would be the case if the diamond were only ground to an almost impalp- 

 able powder in oil, as is frequently done ; the former method is more 

 effective as well as more economical. 



Every sheer should be made to run 'dead' true, and should be main- 

 tained in that condition. The greater the speed at which it is run, the 

 more important it becomes that it should run truly. A slicer is always 

 ineffective in proportion to its eccentricity. Too often the slicer is made 

 to cut as long as it will cut ; this is unsound, both in theory and practice. 



With regard to charging a slicer, I find a chilled steel roller by far 

 the most effective instrument for this purpose. It is better than any 

 glass or agate implement, and, if properly made, is almost everlasting. 



I have tried notching the slicers and charging the notches ; it takes 

 a long time to do this well — and it must be well done, or not at all. I 

 was certainly rewarded with a slicer which cut well for a long time. 

 Usually, however, I find a slicer charged in the ordinary way, that is by 

 pressure of the diamond powder into the smoothly turned edge of the 

 soft iron slicer, gives a very satisfactory return 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 kero- 

 sene 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 lubri- 

 cant 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 car- 

 borundum is used. I also re-grade what is ordinarily sold as graded 

 material by the manufacturer. For example, FFF grade of the Niagara 

 Falls Company 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 finer grades 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. Two 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 satisfactorily, 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 hard- 

 ness of the balsam may, however, be extended if a small quantity, not 

 more than 1 to 3 p.c, 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 appreciate the improvement effected by them, if 

 the addition is judiciously made. 



