OF MICROSCOPIC OBJECTS. 188 
the air-pump and exhausted, It may then be transferred 
to the ceil, and will probably cause the liquid to overflow a 
little. The cover with the gold-size applied to the edge 
must then be carefully laid upon the cell, and slightly 
pressed down, so that all air-bubbles may be displaced. The 
two portions of gold-size will now be found to adhere 
wherever the liquid does not remain, although the whole 
ring may have been previously wet. The outer edge of the 
thin glass and cell must now be perfectly dried, and a 
coating of gold-size applied. When this is dry, the process 
must be repeated until the cement has body enough to pro- 
tect the cell from all danger of leakage. When some pre- 
servative liquids are used, a scum is frequently found upon 
the surface when it is placed in the cell, and this must 
be removed immediately before the cover is laid upon it. 
I believe this method to be perfectly secure against 
leakage when carefally performed; and some of my friends 
have told me that their experience (that of some years) has 
been equally satisfactory. 
In using some of the particular kinds of preservative 
liquids, it will be found necessary to make a slight change 
in the manipulation. This will be best explained by mention- 
ing a few objects, and the treatment they require. 
For the preservation of the Mosses, Algw, &c., Deane’s 
compound is much used, and considered one of the best 
media. ‘T'he specimen to be mounted should be immersed 
in the compound, which must be kept fluid by the vessel 
containing it being placed in hot water. In this state the 
whole should be submitted to the action of the air-pump, as 
it is not an easy matter to get rid of the bubbles which form 
in and around the objects. The cell and slide must be 
warmed; and heat will also be necessary to render the 
gelatine, &c., fluid enough to flow from the stock-bottle. 
The cell may then be filled with the compound, and the 
Specimen immersed in it. A thin glass cover must then be 
warmed, or gently breathed upon, and gradually lowered 
upon the cell, taking care, as with all liquids, that no 
