OF MICROSCOPIC OBJECTS. 45 
and other fine work. It is very liquid, and is thought by 
some to be more easily worked than Canada balsam. 
-Dammar may be easily dissolved in benzole to any extent. 
The lumps should previously be scraped until they are freed 
from dust and other impurities, and then roughly crushed. 
AspHALTuM.—This substance is dissolved in linseed oil, 
turpentine, or naphtha, and is often termed “ Brunswick 
black.” It is easily worked, but is not generally deemed a 
trustworthy cement, as after a time it is readily loosened 
from its ground. It is, however, very useful for some pur- 
poses (such as “ finishing” the slides), as it dries quickly. 
I shall, however, mention a modification of this cement a 
little farther on. 
Marine Guiuz.—No cement is more useful or trustworthy 
for certain purposes than this. It is made in various pro- 
portions; but one really good mixture is—equal parts of 
india-rubber and gum shellac: these are dissolved in mineral 
naphtha with heat. It is, however, much better to get it 
from the opticians or others who keep it. It requires heat 
in the application, as will be explained in Chapter V.; but 
is soluble in few, if any of the liquids used by the microscopist, 
and for that reason is serviceable in the manufacture of 
cells, &c. Where two pieces of glass are to be firmly 
cemented together, it is almost always employed; and in all 
glass troughs, plates with ledges, &c., the beginner may find 
examples of its use. 
Gotp Sizz.—This substance may always be procured at 
any colourman’s shop. ‘The process of its preparation is 
long and tedious. It is therefore not necessary to describe 
it here. Dr. Carpenter says that it is very durable, and 
may be used with almost any preservative liquids, as it is 
acted upon by very few of them, turpentine being its only 
true solvent. If too thin, it may be exposed for awhile to 
the open air, which by evaporation gradually thickens it. 
Care must be taken, however, not to render it too thick, as 
it will then be useless. A small quantity should be kept on 
hand, as it is much more adhesive when old. 
Gum Dammar Crement.—An excellent cement may be 
