The Microscope. 41 



This may be better understood if we say that under a pocket- 

 lens a piece of rock or mineral lies in strata or la3^ers. Now 

 imagine these layers to be leaves of a book ; a leaf from the 

 book is not to be removed for a section, as every other leaf ma}'- 

 be different, and the whole will not be represented, bat cut down 

 the edge of the book and 3^ou have a shaving from every leaf, 

 which is what is needed in rock sections. This clip is then (in 

 company with its numbered glass) to be ground perfectly flat 

 and smooth. This is accomplished on an emery-wheel followed 

 by buffers of emery and rough cloth, until as high a polish as 

 possible is given it. Very good work may be done with an 

 ordinary grind-stone, followed by cloths saturated with oil, and 

 coarse and fine grades of emery, finishing with a rouge cloth. 



The ground surface should be, as nearly as possible, flat. This 

 surface is cemented to the numbered heavy glass slip with a 

 cement prepared by melting together over a gentle heat 16 parts 

 of thick Canada balsam and 5.50 parts gum shellac. The at- 

 tached clip is then to be ground thin, either by first sawing as 

 thin as possible with a diamond saw (if one has no diamond saw, 

 it may be worked down with files varying from coarse to fine, 

 then grinding on a stone), finally grinding with emery. The 

 emery can be made uniformly fine by rubbing between two 

 plates of glass or metal, or by floating in a jar of water, collect- 

 ing the sediment as one grade and the floating particles on 

 filter-paper as another. The section is ground until printed 

 matter can easily be read through it. In doing this work by 

 hand in a small way it will be found that one stone will often 

 grind another, and that a razor-hone and strop serve as good 

 polishers. 



A regular microscope slide is then numbered correspondingly 

 to the section, a drop of thick balsam put on it and heated to 

 expel the turpentine, until it is as hard as molasses candy. The 

 thick plate holding the ground section is then heated until the 

 latter will move easily. It is then removed with a thin knife to 

 the slide. The latter is gently heated, but the balsam is not 

 allowed to boil. While heated the section is covered with a 

 little balsam, the cover glass is heated and dropped on the still 

 warm slide in the usual manner. It should be allowed to settle 

 by its own weight, as in this manner the air bubbles are ex- 

 pelled without drawing off too much of the mounting medium. 



