10 



THE AMERICAN MOKTHLY 



[January, 



pentine it should be mounted in bal- 

 sam. An object that is to be mount- 

 ed in balsam must be free from any 

 trace of water, for water and balsam 

 do not mix. If the object has a ten- 

 dency to retain air within its pores it 

 will be necessary to replace the air 

 with some fluid which will mix 

 with balsam, before proceeding to 

 add' the latter medium, otherwise the 

 air-bubbles will appear as dark spots 

 in the mount. The fluid usually em- 

 ployed for this purpose is spirits of 

 turpentine ; in fact, it may be laid 

 down as a general rule that any ob- 

 ject that is to be mounted in pure 

 balsam should first be freed from 

 water and then thoroughly permeated 

 by turpentine, after which the balsam 

 may be applied. Some objects may 

 be dried, placed for a few moments 

 in turpentine and then mounted in bal- 

 sam, but there are many others which 

 cannot be dried without distortion, 

 and others which, when once dried, 

 retain the air so tenaciously that it is 

 almost impossible to remove it. In 

 such cases one has to resort to some 

 other process for the removal of the 

 water. This is readily done as fol- 

 lows : Place the object in alcohol for 

 a short time, then transfer it to abso- 

 lute alcohol and then to the turpen- 

 tine. When an already dry object 

 retains air, place it in turpentine and 

 boil it a number of times. From tur- 

 pentine the object should be trans- 

 ferred to the slide, a drop of balsam 

 added, and the slide warmed until 

 the balsam flows and penetrates the 

 object. The cover-glass is then ap- 

 plied, and if necessary this is held in 

 place by means of spring clips. The 

 mount is then dried slowly, either in a 

 drying oven, over a stove, or on the 

 brass mounting plate. The writer 

 usually follows the above process, 

 using the ordinary balsam of the 

 shops, which has become somewhat 

 hardened by long keeping. In this 

 matter his practice is somewhat at 

 variance from that of a large number 

 of the best mounters, for the process 

 which is described below, owing to 



the rapidity with which it can be con- ,11 

 ducted, is in great favor. 



However, the above process pos- 

 sesses certain advantages over any 

 other, which the beginner will not be 

 slow to appreciate ; for in case a few 

 minute air-bubbles are left under the 

 cover, they will be absorbed by the 

 balsam, and in laounting certain dia- 

 toms, from which it is difficult to re- 

 move the air, it will be found that 

 pure balsam will absorb every trace 

 of it in a short time. Moreover, 

 it is possible to llnish a slide in a few 

 minutes by hardening the balsam over 

 a spirit-lamp, but care must be exer- 

 cised not to heat too much, or the 

 balsam will turn yellow. When the 

 balsam is sufficiently hardened, it can 

 be readily scraped off from around 

 the cover by a knife-blade, and the 

 last traces cleaned off by means of a 

 cloth dipped in turpentine, alcohol or 

 ammonia. The mount is then finish- 

 ed and ready to be labelled. 



Mounting in Dissolved Balsam. 

 The benzole-balsam (Vol. I, p. 65), 

 is most useful for this purpose, but the 

 other solutions are also employed. 

 To mount in this medium it is best 

 to substitute benzole for turpentine, 

 but otherwise the process is conduct- 

 ed in the same manner as described 

 above. The only difference is in the 

 application of the balsam which is 

 quite thin, and must therefore be 

 used in larger quantity. When the 

 cover is applied heat gently until 

 bubbles appear, and in a few minutes 

 the balsam will be hardened so that 

 the slide may be cleaned. A balsam- 

 mount is greatly improved in appear- 

 ance if the edge of the cover-glass is 

 covered with a ring of benzole- 

 balsam, applied on the turn-table. 

 Some special processes will be given 

 next month. 



Extract from ^*Le Microscope." 



BY H. PH. ADAN. 

 Published in Brussels : 1873. 



[We are indebted to Mr. Charles 

 Stodder for the following interesting 



