206 CEMENTING WITH MAKINE GLUE. 



which it has been attached. Hence, if employed at all for affixing 

 Cells to Glass Slides, its use should be limited to those which 

 afford a large surface of attachment (§§ 167, 168), or to those very 

 thin Tube-cells (§ 169) which cannot be so conveniently attached 

 with marine glue, and of which the cover may be secured to the 

 slide by spreading the ring of gold-size round the margin of the 

 cell itself (§ 171). Care should be taken in applying the Canada 

 Balsam, that it be sufficiently hardened by heat, but that it be not 

 so heated as to become brittle (§ 139). The general method of 

 using it for this purpose, is the same as that which must be prac- 

 tised in the case of Marine Glue. The superfluous balsam left after 

 pressing down the cell is to be removed, first by scraping with a 

 heated knife, and then by a rag dipped in oil of turpentine, after 

 which it is desirable to give the glass surface a final cleansing with 

 alcohol. — For all kinds of Cells (§§ 167-170) except those just 

 mentioned, the proper cement is Marine Glue, which is a mixture 

 of shell-lac, caoutchouc, and naphtha, now extensively employed ; 

 being distinguished by its extraordinary tenacity, and by its power 

 of resisting solvents of almost every kind. Different qualities of 

 this substance are made for the several purposes to which it is 

 applied ; that which is the most suitable to the wants of the Micro- 

 scopist is known in commerce as GK 4. As this cement can only be 

 applied hot, and as it is a great saving of trouble to attach a con- 

 siderable number of cells at the same time, a Mounting -Plate 

 should be provided, which will furnish the requisite heat to several 

 slides at once. Such a surface may be afforded by the top of a 

 stove ; but it is better to have one which can be used at all seasons, 

 and the heat of which can be precisely regulated at pleasure. A 

 very simple apparatus much used for this purpose, consists of a 

 small table of brass or iron plate, about 6 inches long and 2 broad, 

 with legs about 4 inches high, either screwed into its four corners, 

 or so jointed to them as to fold down ; this is set over a small Spirit 

 Lamp, the flame of which is regulated to give the heat required.* 

 The Author has found it much preferable, however, to lay the plate 

 on one of the rings of a small ' retort-stand ' (used in Chemical 

 operations), which admits of being shifted to any height that may 

 be desired, so that the heat applied may be precisely graduated ; 

 or, if a Gas-lamp be applied for the ordinary purposes of illumina- 

 tion, its stem may be fitted with a sliding-ring, which will carry 

 either a hot plate or a water-bath. + It is convenient, moreover', to 

 have two such plates laid on two rings ; one being allowed to cool 

 with the slides upon it, whilst the other is being heated. The 

 Glass Slides and Cells which are to be attached to each other must 



* An improvement on the ordinary form of Mounting- Plate has been 

 described by Mr. Freestone in " Transact, of Microsc. Society," Vol. xii. 

 p. 46. 



t Both these fittings are adapted to the Gas-lamp supplied for the use 

 of Microscopists by Mr. S. Highley (§ 105). 



