60 PREPARATION AND MOUNTING 



syringe generally, if the piston should not then be readily pressed 

 down. When a number of balsam objects are being mounted at 

 one time, the advantage of this plan in regard to facility and 

 cleanliness (no superfluous balsam being deposited on the slide) 

 will make itself sensibly felt." 



When the "mounting" is thus far accomplished, the outer 

 " wall " of balsam may be roughly removed after a few hours have 

 elapsed ; but great care is necessary lest the cover be moved or 

 interfered with in any way. In this state it may be left for the 

 final cleansing until the balsam becomes hard, which takes place 

 sooner or later, according to the degree of warmth it has been 

 subjected to. A mantel-piece, or some place about equal to it in 

 temperature, is the best suited to this purpose ; and when the 

 requisite hardness is attained, it may be proceeded with as follows : 

 With a pointed knife the balsam must be scraped away, taking 

 care that the thin glass be not cracked by the point getting under 

 it. If used carefully, the knife will render the slide almost clean ; 

 but any minute portions which still adhere to the' glass must be 

 rubbed with linen dipped in turpentine or spirit. If the balsam 

 is not very hard, these small fragments are readily removed by 

 folding a piece of paper tightly in a triangular form with many folds, 

 and damping the point with which the glass is rubbed. As the 

 paper becomes worn with the friction, the balsam will be carried 

 off' with it. In some cases I have found this simple expedient 

 very useful. 



Sometimes the object to be mounted is of such a thickness as 

 to require a cell. For this purpose glass rings are used (as de- 

 scribed in Chapter IV.), and filled with balsam. The best mode 

 of doing this is thus described by Mr. T. S. Ralph in the Micro- 

 scopic Journal: "The question was asked me when I was in 

 England, if I knew how to fill a cell with Canada balsam and 

 leave behind no air-bubbles ? I replied in the negative ; but now 

 I can state how to accomplish this. Fill the cell with clear spirit 

 of turpentine, place the specimen in it, have ready some balsam 

 just fluid enough to flow out of the bottle when warmed by the 

 hand ; pour this on the object at one end, and, gradually inclin- 

 ing the slide, allow the spirit of turpentine to flow out on the 

 opposite side of the cell till it is full of balsam ; then take up the 



