302 MANIPULATION. 



time laid between glasses to dry. A more common plan before 

 mounting them in the balsam, especially if they should be 

 very opaque, is to allow them to soak for a time in turpentine, 

 and as this is perfectly miscible with the balsam, they may be 

 taken from one and put into the other, at the couvenlence of 

 th(J operator, without the trouble of drying. The turpentine 

 renders every part of them more transparent in two ways ; 

 in the first by lessening refraction, and in the second by 

 dissolving fluids and substances of a greasy nature and taking 

 their places. 



When veiy thin and transparent objects are required to be 

 mounted in balsam, they become so indistinct that their true 

 structure cannot be made out, hence some mode of giving 

 them a dark colour becomes necessary, which may be effected 

 either by charring or dyeing. In the case of vegetable 

 matter, the charring is readily done by placing the specimen 

 between two plates of glass, and holding them over- the 

 flame of an argand or spirit lamp until the specimen assumes 

 the proper tinge ; it may then be taken out, placed in 

 balsam and mounted in the usual manner. Some structures, 

 especially those of an animal nature, will not bear the 

 charring process ; to these the dyeing only is applicable, and 

 may be effected by soaking them for a time in a decoction 

 of fustic or logwood, after which they may be taken out and 

 dried. A weak tincture of iodine may be employed for the 

 same purpose. 



Necessary Apparatus. — The things necessary for mounting 

 preparations in Canada balsam are as follows : — 



Some clear and tolerably fluid balsam, the whiter the better ; 

 also, some that is older and thicker. 



A pair of wooden forceps to hold the glass slides. 



A pair of fine-pointed forceps. 



A pointed instrument, or, what will answer the purpose, a 

 needle fastened into a wooden handle. 



Glass slides, with covers of thin glass of the required size. 



A small solar oil or a spirit lamp. 



Canada Balsam. — This excellent material, first suggested 

 by Mr. J. T. Cooper, was employed about the year 1832, by 



