220 MOUNTING OF OBJECTS. 



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 wliich 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 pre- 

 cisely graduated ; or, if a gas lamp be employed for the ordinary 

 purposes of illumination, its stem may be fitted with a sliding- 

 ring, which will carry either a hot plate or a water-bath.' It is 

 more convenient, however, 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 first be heated on the mount- 

 ing-plate ; and some small cuttings of marine-glue are then to 

 he placed, either upon that surface of the cell which is to be at- 

 tached, or upon that portion of the slide on which it is to lie, 

 the former being perhaps preferable. "WTien they begin to melt, 

 they may be worked over the surface of attachment by means of 

 a needle-point ; and in this manner, the melted glue may be uni- 

 formly spread, care being taken to pick out any of the small 

 gritty particles which this cement sometimes contains. When 

 the surface of attachment is thus completely covered with lique- 

 fied glue, the cell is to be taken up with a pair of forceps, turned 

 over and deposited in its proper place on the slide ; and it is 

 then to be firmly pressed down with a stick (such as the handle 

 of the needle) or with a piece of flat wood, so as to squeeze out 

 any superfluous glue from beneath. If any air-bubbles should 

 be seen between the cell and the slide, these should if possible 

 be got rid of by pressure, or by slightly moving the cell from 

 side to side ; but if their presence results, as is sometimes the 

 case, from deficiency of cement at that point, the cell must be 

 lifted off again, and more glue applied at the required spot. 

 Sometimes, in spite of care, the glue becomes hardened and 

 blackened by overheating ; and as, in this ease, it will not stick 

 well to the glass, it is preferable not to attempt to proceed, but 

 to lift off" the cell from the slide, to let it cool, and then to repeat 

 the process. "When the cementing has been satisfactorily accom- 

 plished, the slides should be allowed to cool gradually, in order 

 to secure the firm adhesion of the glue ; and this is readily ac- 

 complished, in the first instance, by pushing each, as it is finished, 

 towards one of the extremities of the plate, which is of course 

 cooler than the centre. If two plates are in use, the heated plate 

 may then be readily moved away upon the ring which supports 



' Bolli these fittinjis arr adapted to the Gas lamp supplied for the use of Mioroscopists 

 by Mr. S. Higliiey (§ 75). 



