OF MICROSCOPIC OBJECTS. LSI 



to be perfect. This method has the advantage of requiring 

 no heat, but the gold-size must be perfectly dry, and the 

 ring must have been fixed upon the slide some time before 

 use. Canada balsam has also been used for the same 

 purpose, but cannot be recommended, as, when it is perfectly 

 dry, it becomes so brittle as to bear no shock to which the 

 slide may be ordinarily exposed. 



IRON RINGS. Many have worked with these, having 

 taken care to varnish thoroughly before using with any 

 preservative liquid; but they are always untrustworthy, as 

 they can never be guaranteed against the action of some salt 

 in the liquid used. They can be procured beautifully made, 

 and for dry cells cannot be surpassed. Zinc and pure tin 

 rings may also be procured, and are excellent, especially the 

 latter. 



VULCANITE. This substance is a great favourite with 

 some of our working microscopists, as it is very slightly in- 

 fluenced by change of temperature. But my own opinion is 

 that a glass cell is the safest and most satisfactory re- 

 ceptacle for any object in liquid, and if carefully prepared 

 will not deceive the operator. 



These are the cells which are mostly used in this branch 

 of microscopic mounting. The mode of using them, and the 

 different treatment which certain objects require when in- 

 tended to be preserved in the before-mentioned liquids, may 

 now be inquired into. 



I may mention, however, . that this class of objects is 

 looked upon by many with great mistrust, owing to the 

 danger there is of bubbles arising in the cells after the 

 mounting has been completed, even for years. I know some 

 excellent microscopists who exclude all objects in cells and 

 preservative liquids from their cabinets, because they say 

 that eventually almost all become dry and worthless ; and 

 this is no matter of surprise, for many of them do really 

 become so. Perhaps this is owing to the slides being sold 

 before they could possibly be thoroughly dry. As to the 

 air-bubbles, I shall have something to say presently. 



