226 SELECTION AND tst 



do this see that the cover is hot, and that it is lowered on the 

 balsam slowly, and from one side. If in any case there should 

 be a vacant space under the cover as at a Fig. 74, and it should 

 be desired to fill it, do not apply the fresh balsam directly at a. 

 To do so would certainly be to inclose a large air bubble. Drop 

 the balsam at b, warm the slide, and the balsam will creep in by 

 capillary attraction, and expel the air. 



> 



Fig. 74. 



Let us now suppose that we have some small insect which 

 we have prepared by soaking in potash, and which we desire 

 to mount in balsam. Such a preparation if immersed directly 

 in balsam, would be spoilt, since the balsam and watery solu- 

 tion would not mix. Therefore, proceed as follows: Wash the 

 insect in pure water, and drain off the water; wash with strong 

 alcohol, drain off the alcohol, and soak for twenty-four hours 

 in the strongest alcohol you can get. Pour off the alcohol and 

 soak for twenty-four hours in turpentine. The object may 

 now be ijnmersed in balsam without difficulty. 



Air pumps and similar contrivances are generally recom- 

 mended as the best means for removing air bubbles, but we 

 never use them. If the object be dry, we soak it in alcohol 

 until all the air has been expelled, then transfer to turpentine, 

 and finally to balsam. This requires time, it is true but it does not 

 occupy the time of the microscopist. The soaking process 

 goes on without any attention from him, and while it involves 

 far less labor, with us it has always given far better results, 

 though we have used very fine air pumps, and followed the 

 best published directions. Take the case of a dry shaving of 

 wood, many of which are well worth mounting. It wouli be 



