OF MICROSCOPIC OBJECTS. 113 



rather difficult process, and will not, on that account, be de- 

 scribed here ; but when possessed, a small quantity of a 

 strong solution in water must be made, and a little placed 

 on the slide, and evaporated slowly. Part of the salt will 

 then be deposited in circles with the needle-like crystals 

 extending from common centres. They should then be 

 mounted in pure Canada balsam ; and, when the best colours 

 are wanted, used with the selenite plate. Of this class of 

 crystal, salicine is a universal favourite, and can be easily 

 procured of most chemists. The crystals may be produced 

 in two ways : A small portion of the salt must be placed 

 upon the slide, and a strong heat applied underneath until 

 fusion ensues ; the matter should then be evenly and thinly 

 spread over the surface. In a short time the crystals will 

 form, and are generally larger than those procured by the 

 following process ; but the uncertainty is increased a little 

 when fusion is used, which, however, is desirable with many 

 salts. Secondly, make a saturated solution of salicine, 

 which is effected by boiling one part of the salt in eighteen 

 of water, and allowing it to cool. Place a little upon the 

 slide, and let it evaporate spontaneously, or with the aid of 

 gentle heat. The crystals are generally uniform, and with 

 ordinary powers quite large enough to make a beautiful 

 object. Their circular shape and gorgeous colours even 

 without a selenite plate have made them such great 

 favourites that there are few cabinets without them. 



There are also some salts which are crystallized in a some- 

 what different manner from those before mentioned. San- 

 tonine is one of the most beautiful, and will illustrate my 

 meaning. Place a small portion upon a slide, and heat over 

 a lamp until it is fused. With a hot needle spread the salt 

 over the surface required. As the slide cools, the formation 

 of crystals takes place, until it becomes one mass. This 

 salt is slightly soluble in the ordinary balsam, and should 

 be mounted in castor oil. If, however, the slide is well 

 covered under the thin glass, the balsam soon becomes; 

 saturated, and very little injury results. According to the 



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