OF MICROSCOPIC OBJECTS. 133 



the air-pump and exhausted. It may then be transferred 

 to the cell, and will probably cause the liquid to overflow a 

 little. The cover with the gold-size applied to the ed<re 

 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 \vhen 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 carefully 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, Algse, &c., Deane's 

 compound is much used, and considered one of the best 

 media. The 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 



