170 ANNUAL OF SCIENTIFIC DISCOVEKY. 



The principle of the process depends upon the fact, that a crack 

 will not extend across any part of a piece of thin glass which is fixed 

 by marine glue to any firm surface to which it is capable of adhering. 

 The edges of the thin glass may be broken in all directions, but the 

 crack will extend only up to the marine glue and no farther. If a 

 piece of thin glass be fixed by marine glue to one of the thick sec- 

 tions of tube used for making cells in which injections are mounted, 

 and allowed to cool, a hole may be made in the centre with a file, 

 which may then be carried round the edges, and a thin glass cell ex- 

 actly the size of the thick one is produced. It is removed by heating 

 the glass, and may then be transferred to a slide and fixed at once, or 

 the glue adhering to it can easily be removed by soaking it for a short 

 time in potash. The surfaces may be roughened, or the cell may be 

 ground thinner by rubbing it on a flat surface with emery powder in 

 the usual way. All that is requisite, then, to make thin glass cells of 

 any required form and dimensions, is to obtain a perfectly flat, thick 

 ring, to which the glass may be cemented, and in a few minutes sev- 

 eral thin cells of large size may be made, and at very trifling cost. 



The usual plan of constructing the deep glass cells, by joining to- 

 gether several slips of thick plate glass, the edges of which have been 

 ground perfectly flat, and cementing them at the angles with marine 

 glue, is a process of considerable labor. For some time past I have 

 been endeavoring to devise a method by which these cells could be 

 more readily made, as their advantage over bottles for mounting many 

 preparations is obviously great. The process about to be detailed 

 requires some practice, but, when this is acquired, cells may be made 

 much more rapidly than by the old method, and have the advantage 

 of possessing fewer joins. 



A slip of plate glass, of the required depth, of about the eighth of 

 an inch in thickness, and of sufficient length to make all four 

 sides of the cell, is taken. The length of each side is to be accu- 

 rately marked upon it with a spot of ink, and in these situations the 

 glass is to be carefully and very gradually raised to a red heat 

 in the blow-pipe flame, and then bent so as to form a good angle ; 

 care being taken not to twist the glass in the slightest degree. The 

 other angles are formed in the same manner, each being cooled as 

 gradually as it wss heated. The ends are to be afterwards cemented 

 together by heating in the blow-pipe. If the last side when bent 

 round should be ibund to be too long, a small portion can be cut off 

 by aid of the diamond, and, with a little care in heating the ends and 

 pressing the glass together when in a softened state by a small piece 

 of wire, an excellent juncture may be made; or, if preferred, the 

 join may be effected in the centre of one of the sides. In this way 

 cells may be made of half an inch in depth, or rather more, and of any 

 required size. The great difficulty in constructing cells in this way 

 arises from the glass cracking in the process of heating or cooling, and 

 from the tendency of the sides to twist when the glass is softened in the 

 position of the angles. The latter difficulty is soon overcome by prac- 

 tice ; the former would be avoided if, instead of the ordinary plate 



