96 PREPARATION AND MOUNTING 



cleaned in the ordinary way. Sometimes the balsam isr 

 dissolved in the chloroform without being first hardened; 

 but this is only to render it more fluid, and so give the 

 operator less chance of leaving bubbles in the finished slide, 

 as, the thicker the medium is, the more difficult is it to get 

 rid of these intruders. 



It has been before noticed that some have objected to 

 chloroform and balsam, believing that it became clouded 

 after a certain time. Perhaps this may be accounted for 

 in part by the fact that almost all objects have a certain 

 amount of dampness in them. Others are kept in some 

 preservative liquid until the time of mounting, and these 

 liquids generally contain certain salts (Chapter V.). If 

 this dampness, as well as all traces of these salts, however 

 small, are not totally removed the former by drying, the 

 latter by repeated washings the addition of chloroform 

 will render the balsam much more liable to cloudiness than 

 when balsam alone was used. It may safely be affirmed that 

 benzole will be found in all cases a more valuable solvent for 

 Canada balsam than chloroform. 



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

 always applicable, as chloroform acts upon some substances 

 on which balsam alone does not. Some salts are even soluble 

 in it, the crystals appearing after a few days or weeks, 

 whereas in balsam alone they are quite permanent. Ex- 

 perience 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 now 

 be 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 III. Others 

 are almost always placed in balsam, except where they are 

 intended to be used with the lieberkuhn and dark back- 

 ground, by which means some of them are beautifully shown. 

 The usual way of mounting them in balsam is as follows : 

 Take a drop of the water containing them, place it upon 

 tiie slide, and evaporate over the lamp, whilst with a needle 



