144 PREPARATION AND MOUNTING 
solution of carbonate of potash; at the end of that time it 
is possible to cut tolerably thin slices with a razor. These 
slices are then placed in a watch-glass with strong nitric 
acid, covered, and gently heated; they soon turn brownish, 
then yellow, when the process must be arrested by dropping 
the whole into a saucer of cold water, else the coal would 
be dissolved. The slices thus treated appear of a darkish 
amber colour, very transparent, and exhibit the structure, 
when existing, most clearly. We have obtained longitudinal 
and transverse sections of coniferous wood from various 
coals in this way. The specimens are best preserved in 
glycerine in cells; we find that spirit renders them opaque, 
and even Canada balsam has the same defect. Schultze 
states that he has brought out the cellulose reaction with 
iodine in coal treated with nitric acid and chlorate of 
potash.” Now and then in coal we meet with a half- 
formed carbon-looking substance which is no more difficnlt 
to work with than ordinary charcoal. From this it is an 
easy thing to procure interesting slides. 
Cannel-coal is so close and firm in its structure as to be 
much used instead of jet in the manufacture of ornaments: 
it takes a beautiful polish, and consequently presents the 
student with none but ordinary difficulties in getting 
sections of it. Its formation is somewhat different from 
that of coal, sometimes showing the transition very clearly. 
Fossil Wood.—This is very often brittle and requires 
great care in cutting. There are, however, different kinds 
of fossil wood, but to obtain anything like certainty and 
perform much work a lathe is necessary. I know of no 
method better than that given by Mr. Butterworth, and 
shall therefore make use of his words. First, I will begin 
with the cutting. To the framework of an ordinary foot- 
lathe I attach an upright spindle (see engraving). On this 
upright spindle I drive by a band passing over “ carry- 
pulleys” from the wheel below. On the top of this spindle 
I fix my cutting-disc, which is made from a very thin 
piece of sheet iron, and is about six inches in diameter. 
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