MOUNTING OBJECTS IN CANADA BALSAM. 219 



a transfer will often be found advantageous before the final com- 

 pletion of the reducing-process ; for it will occasionally happen that 

 ■we r find something in the structure of the specimen, •which will be 

 best displayed by rubbing it down afresh on the side first attached 

 to the glass ; and, when a number of small sections are being made 

 at once (which it is often very convenient to do, not only in the 

 case already mentioned, § 138, but in many others), it not only 

 saves time, but ensures the accurate flattening of the surface in 

 grinding, to fix several upon the same slip, and to work them down 

 together until the requisite thinness has been nearly attained, when 

 they must be transferred to separate slips, and finished one by one. 

 In either case, the re-attachment must of course be made, like the ori- 

 ginal attachment, with Balsam which has been first hardened(§ 139). 

 162. When the Balsam employed in mounting has remained in 

 the liquid condition here recommended, the glass cover will not be 

 secure from displacement until the balsam has become harder. 

 This change it will require a long time to undergo, unless the aid 

 of a gentle continuous warmth be afforded. Nothing is more 

 suitable for this purpose than the warmth of a Chimney-piece im- 

 mediately above the fire-place ; as it is quite sufficient to produce 

 the effect in the course of a few days, whilst there is no danger of 

 its becoming excessive ; but in default of this convenience, an 

 oven carefully regulated, or (still better) a water-bath, may be 

 employed. Whether either of these means be adopted, or the 

 slides be put aside for the Balsam to be hardened by time, they 

 should always be laid in the horizontal position, that their covers 

 may not be caused by gravitation to slip down from their places. — 

 It may be better, before submitting the slides to this hardening 

 process, to scrape from their surface any superfluous Balsam that 

 does not immediately surround the glass-cover ; but the knit'e 

 should never be carried so near to the edge of this, as to run any 

 risk of displacing it ; and it is much better to defer the final 

 cleaning of the slide, until the attachment of the cover has become 

 firm. The remaining Balsam may then be scraped away with a 

 knife or small chisel, the implement being warmed if the balsam 

 be very stiff ; the slide shoidd be rubbed with a rag dipped in Oil 

 of Turpentine until every perceptible soil of balsam is removed, 

 especial care being taken to cleanse the surface and edges of the 

 glass-cover : and as this will itself leave a certain resinous film, it 

 is better to give the slide a final cleansing with Methylated Spirit. 

 If its surface should have been considerably smeared with balsam, 

 it is very convenient, after scraping away all that can be removed 

 in that manner, to scrub it with a soft tooth-brush or an old nail- 

 brush, first letting fall on it a few drops of Turpentine or Methylated 

 Spirit ; and there is less risk of displacing the glass-cover in this 

 mode, than in rubbing it any other way. — The menstrua which 

 serve thus to cleanse the slides, of course answer equally well for 

 cleansing the hands. The most ready solvents for Balsam are 



