14 MOUNTING. 



its surface, and the two slides gently pressed together, 

 the two slides fixed at the ends by sealing-wax, and 

 the whole allowed to cool and dry. If requisite, more 

 balsam is added to fill up any vacuities. When the 

 balsam has become hard, the excess is cleaned away 

 with a knife and turpentine, and the object is per- 

 manently mounted. 



If the object should be spoiled by the presence of air- 

 bubbles, the slides and object should be immersed in 

 turpentine or methylated alcohol, until the whole of 

 the balsam is dissolved ; the remounting may then 

 be proceeded with as at first. If the slides have 

 been immersed in the alcohol (which is the quickest 

 method), the object must be soaked in turpentine 

 before the balsam is reapplied. 



If, after an object has been mounted in balsam, on 

 applying heat, bubbles resembling air-bubbles should 

 be formed, the object must not be considered as 

 spoiled ; for these are merely bubbles of the vapour of 

 turpentine, and will disappear spontaneously after a 

 little time. 



A quick way of mounting in balsam is to drop the 

 melted balsam at once upon the dried object ; but as 

 air-bubbles are very apt to be produced in this way, 

 the beginner had better previously apply the tur- 

 pentine. 



As balsam is very viscid, and adheres firmly to 

 everything with which it comes in contact, some 

 care is required in its use. Young microscopists 

 very generally manage to soil the microscope, tables, 

 chairs, papers, books, and even their clothes with it. 

 It may be easily cleaned off, however, with turpentine 

 or benzole. 



Moist objects are best preserved, whenever prac- 

 ticable, in glycerine. There are, however, two im- 

 portant objections to its use : one is, that it makes 

 objects very transparent; the other is, that it often 

 -wrinkles and distorts them, by withdrawing their 



