74 Laboratory Arts 



liquid is that of preventing shattering or chipping of the glass, 

 and though it is difficult to understand the reason, there is no 

 question as to the fact, and, curiously enough, larger quantities 

 of camphor and impure turpentine destroy the virtue of the 

 liquid almost entirely. It should, therefore, be prepared in 

 small quantities frequently, rather than in bulk, and the solution, 

 as well as the turpentine, kept in the dark. 



Having moistened the emery-paper with the solution, rub 

 the glass along in the direction of its length never across 

 backwards and forwards until the edge is smooth, though it 

 presents a " ground " surface. By slightly inclining the glass 

 the sharp edges may be removed. 



All four edges should be so treated, and if required to be 

 polished and transparent instead of ground, some brown paper 

 should be spread upon a yellow pine or bass wood board, and 

 flour emery sprinkled upon this, with a little camphor solution 

 to moisten it, and the process repeated. The finest " matt " 

 possible having been produced by this means, the edges are 

 subsequently rendered transparent by a similar polishing or 

 rubbing upon brown paper smeared with rouge and water, rouge 

 and oil, or powdered rotten stone and oil. Microscope slips 

 may be prepared in this way, several being treated at the 

 same time. 



When glass cells are being made, it is frequently of advan- 

 tage to grind the edges of contiguous sheets at an angle of 45 

 in order to produce a mitred joint instead of a lapped joint (see 

 Fig. 62). A mitred joint is much stronger than a lapped one, as 

 a larger cemented surface joins the two sheets of glass, conse- 

 quently a firmer hold is obtained, while, in addition, four mitred 

 corners key each other into place, so that on holding the cell 

 together, there is one position the true square or rectangle 

 which the plates assume by preference, hence cementing is 

 a much more easily performed operation. 



The mitred corners are, however, more difficult to make, 

 the grinding being rather tedious. The best method is to pre- 

 pare a wooden block with an angle of 45 cut on one end. 

 The plate is temporarily cemented with Chatterton's compound 

 to the sloping surface of this block (see Fig. 63), with the edge 



