INTRODUCTION. 7 



are easily accessible to all, it will be here detailed ; and it will be seen 

 that, although the cutting of them is often thought to be difficult, it is in 

 reality quite easy, and, with a little patience, can be done with no appa- 

 ratus ; — therefore this beautiful way of studying rocks and minerals is 

 within the reach of all who have access to a microscope. 



With a small hammer knock off from the mineral or stone to be examined a fragment 

 nearly an inch in diameter, and as flat and thin as possible. Place some coarse emery 

 (No. 60) upon a flat iron plate ; moisten it with water, and then grind a flat surface 

 upon one side of the fragment of stone. When a surface covering the whole extent 

 of the piece has been obtained, grind it further upon another plate with fine emery 

 (No. 120), and finally make the surface still smoother by grinding it with emery dust 

 upon a glass plate ; then wash and dry it. Take a piece of glass an inch and a half 

 square and an eighth of an inch thick, and place in the middle of it a large drop of 

 Canada balsam ; heat it gently over the smokeless flame of a lamp or a Bunsen burner, 

 taking care that it does not inflame and become blackened by separated carbon. The 

 balsam must be heated till so much of its volatile constituent is driven out, that, when 

 cool, it will be so hard that an impression can be made in it with the thumb-nail with 

 much difficulty. If heated less, it will yield to the subsequent pressure ; if heated 

 more, it will be brittle, and break. When the balsam has been sufficiently heated, 

 allow it to cool until it begins to get gummy about the outside edges, then quickly 

 scrape it up into a pile in the middle, and place the dry ground surface of the stone 

 directly upon it, and press it down as firmly as possible against the glass, so that the 

 surface of the stone and the glass may be as nearly in contact as possible. Then allow 

 it to cool. No bubbles of air should be included between the stone and glass ; and, if 

 any of considerable size are seen, the operation should be repeated. Now, holding 

 the stone against the iron plate by means of the glass, with coarse emery grind it until 

 it is quite thin, so thin that you fear that the coarse emery will rend it ; then grind it 

 still thinner with fine emery, and then with emery dust upon a glass plate grind it as 

 thin as possible, the rule being, that one should be able to read the type of a news- 

 paper through the section. Sometimes, to attain this end with very opaque stones, the 

 size of the fragment will be much diminished, and close watch must be kept upon it 

 during the final grinding, else it might disappear before one expected it. The section 

 is now made and ready to mount. 



The most convenient size of a glass slide to mount mineral sections on is 50 m. m. 

 long and 28 m. m. wide. The long glass slides that are commonly used are very incon- 

 venient to revolve upon the table of the microscope. In the middle of such a slide 

 place some Canada balsam, and heat it till it begins to smoke. Having washed and 

 dried the section, place a small drop of Canada balsam upon it, and heat it till it is 

 loosened from the glass ; then place on it a very thin glass cover, and with the point 

 of a knife gently push the specimen and glass cover along together over the edge on to 



