PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS. 181 



for use. If the surface of any ring should not be sufficiently level for a 

 covering-glass to lie flat upon it, a slight rubbing upon a piece of fine 

 emery-paper laid upon a flat table (the ring being held downwards) will 

 make it so. 



171. Ring-cells. For mounting objects of greater thickness, it is de- 

 sirable to use cells made by cenenting rings, either of glass or metal, to 

 the glass slides, with marine glue. Glass-rings of any size, diameter, 

 thickness, and breadth are made by cutting transverse sections of thick 

 walled tubes; the surfaces of these sections being ground flat and parallel. 

 Not only may round cells (Fig. 120 A, B) of various sizes be made by 

 this simple method, but, by flattening the tube (when hot) from which 

 they are cut, the sections may be made quadrangular or square, or oblong 

 (c, D). For intermediate thicknesses between cement-cells and glass ring- 

 cells, the Author has found no kind so convenient as the rings (sold by 

 Mr. Collins) stamped out of tin, of various thicknesses. These, after 

 being cemented to the slides, should have their surfaces made perfectly 

 flat by rubbing ^on a piece of fine grit or a corundum-file, and then 

 smoothed on a Water of Ayr stone; to such surfaces the glass covers 

 will be found to adhere with great tenacity. 



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

 heated on the Mounting plate; and some small cuttings of Marine glue are then 

 to be placed either upon that surface of the cell which is to be attached, or upon 

 that portion of the slide on which it is to lie, the former being perhaps prefer- 

 able. When they begin to melt, they may be worked over the surface of attach- 

 ment by means of a needle point; and in this manner the melted glue may be 

 uniformly 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 liquefied 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 pos- 

 sible 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 black- 

 ened by overheating; and as it will not then stick well to the glass, it is prefera- 

 able not to attempt to proceed, but to lift off the cell from the slide, to let it cool, 

 scrape off the overheated glue, and then repeat the process. When the cement- 

 ing has been satisfactorily accomplished, 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. If two plates are in use, the heated plate may 

 then be readily moved away upon the ring which supports it, the other being 

 brought down in its place, and as the heated plate will be some little time in 

 cooling, the firm attachment of the cells will be secured. If, on the other hand, 

 there be only a single plate, and the operator desire to proceed at once in mount- 

 ing more cells, the slides already completed should be carefully removed from it, 

 and laid upon a wooden surface, the slow conduction of which will prevent them 

 from cooling too fast. Before they are quite cold, the superfluous glue should be 

 scraped from the glass with a small chisel or awl; and the surface should then be 

 carefully cleansed with a solution of potash, which may be rubbed upon it with a 

 piece of rag covering a stick shaped like a chisel. The cells should next be 

 washed with a hard brush and soap and water, and may be finally cleansed by 

 rubbing with a little weak spirit and a soft cloth. In cases in which appearance 

 is not of much consequence, and especially in those in which the cell is to be 

 used for mounting large opaque objects, it is decidedly preferable not to scrape 

 off the glue too closely round the edges of attachment; as the 'hold' is much 

 firmer, and the probability of the penetration of air or fluid much less, if the im- 

 mediate margin of glue be left both outside and inside the cell. To those to 

 whom time is of value, it is recommended that all cells which require Marine- 

 glue cementing be purchased from the dealers in Microscopic apparatus. 



