62 PREPARATION AND MOUNTING 



This mode of employing the balsam, however, will not be always 

 applicable, as chloroform acts upon some substances which balsam 

 alone does not. Some salts are even soluble in it, the crystals 

 disappearing after a few days or weeks, whereas in the balsam 

 alone they are quite permanent. Experience is the only guide in 

 some cases, whilst in others a little forethought will be all that is 

 required. 



The particular methods used for certain objects may be now 

 entered upon. Many of the Diatomacese and fossil Infusoria, as 

 they are sometimes termed, are mounted dry, and cleaned in the 

 way described in Chapter II. Others are almost always placed in 

 balsam, except where they are intended to be used with the lieber- 

 kuhn and dark background, by which means some of them are 

 rendered exquisitely beautiful. The usual way of mounting them 

 in balsam is as follows : Take a drop of the water containing 

 them, place it upon the slide, and evaporate over the lamp, whilst 

 with a needle they may be dispersed over any space desired. 

 When they are thoroughly dry, drop a little balsam on one side, 

 and exclude the bubbles. The slide may then be warmed to such 

 a degree that the balsam, by lifting the glass at one end, will be 

 carried over the specimens, which may then be covered with thin 

 glass, made warm as before described. Where the objects are 

 quite dry, and loose upon the glass, it requires great care in plac- 

 ing the cover upon them, otherwise they are forced to one edge, 

 or altogether from under it, in the wave of the balsam. For this 

 reason, Professor Williamson adds a few drops of gum-water to 

 the last washing, which causes them to adhere sufficiently to the 

 glass to prevent any such mishap. 



Mr. T. G. Rylands' method differs in some degree from the 

 above, and is, to use his own words, as follows : Thick balsam is 

 preferable, and the burnt covers (see Chapter II.) to be mounted 

 are laid in a convenient position with the diatoms upwards. The 

 slides required having been carefully cleaned and marked on the 

 under side with a ring of ink, by the aid of a turntable about half 

 an inch in diameter to point out the centre, a drop of benzole is 

 applied by a large pin to the diatoms on the cover, so as to exclude 

 the air from the valves and frustules. The slide is then held over 

 the lamp, and when warm, a sufficiently large drop of balsam is 



