208 THE MICROSCOPE. 
table with the clip and a gentle heat, and if level and centered 
when cold, they will remain so, if not neglected too long in ringing 
them with a strong cement. 
CEMENTS. 
A good cement to protect balsam, damar and all media 
which are soluble in oil solvents, is made out of a thick solution of 
gum senegal and gum arabic, equal parts dissolved, separately, in 
cold water, pure as possible, and strained} through closely woven 
muslin, and thoroughly mixed. To one ounce of this cement add 
three drops of carbolic acid dissolved in ten or fifteen drops of 
glycerin, chemically pure. Then add some more glycerin, without 
acid, and mix thoroughly with the cement, and in ten or fifteen 
minutes try some on a slide. In ten or fifteen minutes try it with a 
sharp-point knife; if it is hard and brittle, like hard balsam, add 
glycerin until it hardens in twenty or thirty minutes without brittle- 
ness, so that when you push the point of a knife through it, it will 
separate without breaking and flying away. It might be better to 
add glycerin till it takes a day to harden like cold beeswax. 
Unless a sufficient quantity of glycerin is thoroughly mixed 
and incorporated with this cement, it will crack and separate from 
the slide. This cement should not be applied to balsam and damar 
mounts until they are sufficiently hardened to hold the covers. A 
second coat of this cement may be spun around the mount colored 
with anilin colors and ornamented with gold bronze, if desirable, 
after the first coat has thoroughly hardened, as well as the second 
coating. Too little time between each coating makes bad work—a 
painful experience, the result of trying to rush the mounts when 
pressed with too much other business. Green mounts ringed with 
this, or any aqueous cement, will soon be found full of little air 
chambers. 
A beautiful pearl white cement is made out of this transparent 
cement, in the following manner: Pour a small quantity of the 
cement into a small mortar, and add sufficient Chinese-white (moist 
in tubes) and grind them thoroughly fine, and pack into a large- 
mouth bottle. Repeat this process until you have as much as you 
desire. This white cement, as well as the anilin cements just 
described, will not run in and ruin balsam or damar mounts, as 
white zinc or anilin cements soluble in oily solvents; 7. e., if the 
following rules are enforced: 
First—The mount must be hardened so as to hold the covers 
without care. 
+If too thick to use, thin with water. 
