ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 581 



the solution of phosphorus and allow it to run under the cover just 

 sufficient to float it. See that there are no air-cells, if so, gently move 

 the cover backwards and forwards to the mounted needles, when all the 

 air-cells will disappear. Take the small brush, load it with the 

 warmed cement, and touch the edge of the cover-glass at right angles 

 in four places, then gently revolve the turntable, keeping the brush 

 close to the edge of the cover until the cement ring is complete, then 

 absorb the remainder of the phosphorus solution on the slide with the 

 strips of blotting-paper, putting the paper into the basin of water so 

 that it can do no harm. As long as the blotting-paper saturated with 

 a solution of phosphorus is wet, no combustion will ensue. Hence 

 the necessity of seeing that all which has touched the solution of 

 phosphorus has either undergone combustion or been placed in the 

 fire before leaving off work. 



" The mounted slide may be again touched with the cement, when 

 it can be put away until the following day. A ring of solution of 

 sealing-wax or shellac may then be used to finish it off. If by acci- 

 dent more of the cement has got on the slide than is required, when 

 the ring of sealing-wax is hard, the cement can be washed off with a 

 small brush dipped in water and applied gently. When dry it can 

 then be finished off as the mounter may fancy. 



" Always wash the pipette in the carbon bisulphide before and after 

 using the solution of phosphorus. Latterly I have discarded the 

 soft cell and always mount as described, because I found that the 

 solution of phosphorus is very liable to form air-cells ; or, in other 

 words, there is a want of affinity between the glass and the medium, 

 and if it is a valuable preparation it may be completely spoiled on 

 account of the air-cells ; whereas by doing away with the soft cell and 

 mounting as I have described, the air-cells can always be got rid of 

 before applying the ring of cement. 



" Diatoms are easily resolved in this medium, which in a dry or 

 balsam mount are unresolvable." 



Vacuum-bubbles in Canada Balsam.* — Mr. W. M. Bale says, 

 " One of the first difficulties which a novice in mounting meets with 

 arises from the formation of air-bubbles in Canada balsam, but experi- 

 ence shows him that if the balsam be used in not too thick a state, 

 any bubbles that may form in it will, unless they are excessively 

 large, gradually disappear in the course of a few days at most, and. 

 henceforth air-bubbles in the balsam cease to be a source of trouble. 



It is otherwise, however, with vacuum-bubbles, which are apt to 

 appear in any closed cavities of an object at the moment of applying 

 the balsam, even though every cell may have previously been perfectly 

 filled with turpentine or carbolic acid. The cause appears to lie in 

 the different densities of the fluid and the balsam, the former finding 

 its way out of the cell to mix with the balsam, while the latter, owing 

 to its greater density, is unable to enter the cell and supply its place. 

 A vacuum is therefore left, which has all the appearance of an air- 

 bubble, and which may either take a globular form or expand till it 



* Journ. Micr. Soc. Victoria, i. (1882) pp. 103-4. 



