MOUNTING OBJECTS IN CANADA BALSAM. 31 1 



cellular parts of the objects, and to occupy the place the air 

 originally did. Should aU the air not be got rid of by the 

 first exhaustion of the receiver, the operation may be repeated 

 until the desired eifect is produced. The air-pump is also 

 extremely useful for mounting objects on a large scale without 

 air bubbles; several of these being placed between glasses, and 

 secured in their proper places by string or fine wire,. may be 

 placed upright in a tin vessel containing balsam liquefied by 

 heat ; the vessel (as soon as the objects are adjusted) is to be 

 placed under the receiver and exhausted, the air confined 

 between the glasses, as weU as that from all parts of the object, 

 will escape, and the hot balsam occupy its place. When the 

 balsam has penetrated every part, the slides may be taken out 

 and laid in a horizontal position, and when cold are ready to 

 be cleaned off as follows : — 



Cleaning Balsam from the Slides. — For this purpose an old 

 knife, some rags, together with turpentine or alcohol, and a 

 small quantity of ether, will be required. If the balsam be 

 very fluid, it may be wiped off" with a rag dipped occasionally 

 in turpentine; but if rather hard, the flat-bladed knife, warmed 

 in the spirit-lamp, wiU readily remove the greater portion, 

 whilst the turpentine rag and a thin sharp knife will clean off 

 the remainder. Some persons scrape away every particle of 

 balsam from the edges of the cover; the author, however, 

 prefers leaving a little there, which he cuts in a sloping direc- 

 tion, at an angle of about 45", as he considers that a little em- 

 bankment of this material tends to secure the cover more 

 firmly to the slide, and prevent the ingress of air. Objects 

 that have been mounted for some time in balsam should be 

 handled with care, as they are very easily damaged, even in 

 being wiped, and a sudden blow or jar is nearly always 

 attended with a partial separation of the balsam; this is known 

 by the appearance of coloured bands or rings from the thin 

 film of air which has gained entrance between the glasses. 

 When this has happened, heat should be applied both to the 

 cover and slide, and as soon as the balsam is melted, the cover 

 should be firmly pressed down until the rings have entirely 

 disappeared. The risk of this accident will be materially 



