~~ a. pe ee a” eS Ee ee ere . 
mks Pte ar : a re A Re fle Yo 
é 3 J ~ > “ 2 - arn * 2%, » k 
=< ’ Par - ‘ re oe ce Apa, Te he - ae . mal: 
ra - > t= te sii tala al 5 - - an 
9. Some oblong pieces of common flat window-glass; 2 x 1 inches is 
a convenient size. 
10. Glasses with ground edges for mounting the slices upon. They 
may be had at any chemical instrument maker’s in different sizes, the 
commonest in this country being 3 x 1 inches. 
11. Thin covering-glasses, square or round. These are sold by the 
ounce ; 4 oz. will be sufficient to begin with. 
12. A small bottle of spirits of wine. 
The first part of the process consists in rubbing down and polish- 
ing one side of the chip or slice, if this has not already been done in 
cutting off a slice affixed to glass, as above mentioned. We place the 
chip upon the wheel of the grinding-machine, or, failimg that, upon 
the iron plate, with a little coarse emery and water. If the chip is 
so shaped that it can be conveniently pressed by the finger against _ 
the plate and kept there in regular horizontal movement, we may 
proceed at once to rub it down. If, however, we find a difficulty, 
from its small size or otherwise, in holding the chip, one side of it 
may be fastened to the end of a bobbin or other convenient bit of wood 
by means of a cement formed of three-parts of rosin and one of bees- 
wax, which is easily softened by heating. A little practice will show 
that a slow, equable motion with a certain steady pressure is most 
effectual in producing the desired flatness of surface. When all the 
roughnesses have been removed, which can be told after the chip has 
been dipped in water so as to remove the mud and emery, we place 
the specimen upon the square of plate-glass, and with flour emery and 
water continue to rub it down until all the scratches caused by the 
coarse emery have been removed and a smooth polished surface has 
been produced.* Care should be taken to wash the chip entirely 
free of any grains of coarse emery before the polishing on glass is 
begun. It is desirable also to reserve the glass for polishing only. 
The emery gets finer and finer the longer it is used, so that by re- 
maining on the plate it may be used many times in succession. Of 
course the glass itself is worn down, but by using alternately every 
portion of its surface and on both sides, one plate may be made to last _ 
a considerable time. If after drying and examining it carefully we 
find the surface of the chip to be polished and free from scratches, we 
may advance to the next part of the process. But it will often happen 
that the surface is still finely scratched. In this case we may place 
the chip upon the Water of Ayr stone and with a little water gently 
rub it to and fro, It should be held quite flat. The Water of Ayr 
stone too should not be allowed to get worn into a hollow, but should 
also be kept quite flat, otherwise we shall lose part of the chip. Some 
soft rocks, however, will not take an unscratched surface even with 
 Exceedingly impalpable emery powder may be obtained by stirring some of the 
finest emery in water, and after the coarse particles have subsided, pouring off the liquid - 
and allowing the fine suspended dust gradually to subside, Filtered and dried, the 
residue can be kept for the more delicate parts of the polishing, 
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184 “  S@HOGNOSY, . = ja) Baeaeeeea 

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