140 PREPARATION AND MOUNTING 
&c., are of no avail. Most of these require no particular 
care in mounting, but are placed in balsam like the other 
objects noticed in Chapter IV.: where, however, any special 
treatment is necessary it will be commented upon as we 
proceed. 
Suetis, &c.—It is seldom, if ever, necessary to possess 
apparatus for this process except a small thin saw made 
with a steel blade, for which a piece of watch-spring serves 
very well; a fine stone such as is used for sharpening pen- 
knives; and two smooth leather strops, one of which is to 
be used with putty-powder to polish the section after grind- 
ing, and the other dry, to give the final surface. It is, how- 
ever, very convenient to have three or four files of different 
degrees of fineness. A very useful implement in this process 
is, the Corundum file or rubber, sold by most dealers in 
watchmakers’ tools. It may be procured of almost any size 
or grain, either circular or flat, and will cut almost any- 
thing. They possess the very great advantage of not carry- 
ing much, if any, impurity into the texture of the object 
upon which they are used. The shell, if very thick, may be 
divided by using the watch-spring saw; and this section 
may then with ordinary care be rubbed down with water on 
the stone until one side of it is perfectly flat. When this is 
accomplished it must be rubbed with putty-powder upon 
the strop, and finally upon the other strop without the 
powder. This surface will then be finished, and must be 
firmly united to the slide in the position it is intended to 
occupy. To do this a small quantity of Canada balsam may 
be dropped upon the middle of the slide and heated over 
the lamp until on cooling it becomes hard; but this must 
be stopped before it is rendered brittle. Upon this the 
polished surface must be laid, and sufficient heat applied to 
allow the object to fall closely upon the slide, when slight 
pressure may be used to force aside all bubbles, &e. On 
cooling, the adherence will be complete enough to allow the 
same grinding and polishing upon the upper surface which 
the lower received. Whilst undergoing this, the section 
