MICRO-CHEMICAL REAGENTS. 279 
the salt in three parts of water). These two liquids, particularly 
the first-named, leave most preparations unchanged, even after 
many years. Starch, however, is dissolved by calcium chloride, 
even when it is neutral. 
For firmer objects, sections of more compact drugs, for 
Lycopodium, and also for diatoms (provided they will bear some 
warming) Canada balsam may be employed as the mounting 
medium. The preparations must, however, have previously 
been repeatedly washed with alcohol. The section is then placed 
in Canada balsam which has been liquefied with a little warm 
chloroform, and finally in the slightly warmed balsam itself. 
A solution of gelatin in glycerin is also adapted for delicate, as 
well as.for coarse preparations. This is obtained by gently - 
warming one part of colorless gelatin with six parts of water 
and seven parts of glycerin. When used, the mixture is lique- 
fied by warming. 
When Canada balsam or glycerin-gelatin are used, it is not 
absolutely necessary to specially cement the cover-glass, since 
the solidifying mounting medium holds the cover-glass firmly; 
but if glycerin or calcium chloride solutions are used as mount- 
ing media, it is necessary to cement the cover-glass. As varnish, 
either the ordinary black asphalt varnish or the yellow “‘ pre- 
pared gold-size ” are employed. 
