212 MOUNTING OBJECTS IN CANADA BALSAM. 



and preserving them ; and consequently it may be almost always 

 had recourse-to in the case of such transparent objects as do not 

 need to be preserved in fluid, save where, in virtue of the action 

 just described, it impairs the distinctness of surface-markings, or 

 obliterates internal cavities or canals, which constitute the most 

 important features of the object. 



158. Canada Balsam, being nothing else than a very pure 

 Turpentine, is a natural combination of Resin with the Essential 

 Oil of turpentine. In its fresh state it is a viscid liquid, easily 

 poured out, but capable of being drawn into fine threads ; and 

 this is the condition in which the Microscopist will find it most 

 desirable to use it for the mounting of objects generally. The 

 Balsam may be conveniently kept in a glass bottle or jar with a 

 wide mouth, being taken up as required with a small glass rod 

 drawn to a blunt point, such as is used by Chemists as a 'stirrer ;' 

 and if, instead of a cork or stopper, this bottle should be provided 

 with a tall hollow 'cap,' the glass rod may always stand in the 

 balsam with its upper end projecting into the cap. In taking out 

 the Balsam, care should be taken not to drop it prematurely from 

 the rod, and not to let it come into contact with the interior of 

 the neck or with the mouth of the jar : both these mischances may 

 be avoided by not attempting to take-up on the rod more than it 

 will properly carry, and by holding it in a horizontal position 

 after drawing it out from the bottle, until the slip on which it is 

 to deposit the balsam is just beneath its point. Some recommend 

 that the Balsam should be kept in the Tin tubes used for Artists' 

 colours ; but the screw- caps of these are liable to be fixed by the 

 hardening of the contents : and the Author has himself been in the 

 habit of employing in preference a Syringe, resembling that repre- 

 sented in Fig. 83, but with a freer opening. This is most readily 

 filled with Balsam, in the first instance, by drawing out the piston 

 and pouring-in balsam previously rendered more liquid by gentle 

 warmth ; and nothing else is required to enable the operator at any 

 time to expel precisely the amount of balsam he may require, than 

 to warm the point of the syringe, if the balsam shoxild have hardened 

 in it, and to apply a very gentle heat to the syringe generally, if 

 the piston should not then be readily pressed down. When a 

 number of Balsam-Objects are being mounted at one time, the 

 advantage of this plan in regard to facility and cleanliness (no 

 superfluous balsam being deposited on the slide) will make itself 

 sensibly felt. It has, moreover, the further recommendation of 

 keeping the balsam almost perfectly excluded from the air ; the only 

 contact between them being at its point, where the balsam soon 

 hardens so as to protect what is within. — When Balsam has been 

 kept too long, it becomes, through the loss of part of its volatile 

 oil, too stiff for convenient use, and may be thinned by mixing it 

 at a gentle heat with pure Oil of turpentine; this mixture, how- 

 ever, does not produce that thorough incorporation of the consti- 



