218 MOUNTING OF OBJECTS. 



prevented by employing very liquid Gold-size, and by using it in 

 extremely small quantity in the first instance ; since whenever 

 the glass cover lies perfectly flat on its bed, and the fluid be- 

 neath extends to the edges, the thin layer of this varnish dries 

 very quickly, without any tendency to run in. When this has 

 completely set, a second layer shovild be applied ; and a layer of 

 Asphalte over the whole will add to its security, and improve 

 the appearance of the mounting. The danger of running in 

 appears to the Author to be the greatest, when, in consequence 

 of the use of old and viscid gold-size, the layer is too thick, 

 and is long in drying. His experience leads him to distrust 

 Asphalte when used alone, as being liable to admit air after a 

 lengthened period of drying. He has recently learned from 

 Mr. Tomes, that he finds saturated solution of arsenious acid to 

 be a very good medium for mounting delicate preparations of 

 animal structures. If it be allowed to become so thick, how- 

 ever, as not to be easily worked by the brush, it is quite unfit 

 for use. There are few preservative liquids with which gold- 

 size may not be employed ; since it is not acted on by any aque- 

 ous solution, and resists moderately diluted spirit ; oil of turpen- 

 tine being its only true solvent.' Many Microscopists prefer the 

 solution of shell-lac in naphtha, which is sold under the name 

 of Liquid Gflue ; this dries more quickly than gold-size, but is 

 more brittle when completely hardened, and does not, in the 

 Author's opinion, adhere so firmly and enduringly to glass ; and 

 it is, moreover, more easily acted on by diluted alcohol than the 

 preceding. Of late, a solution of Asphalte in drying-oil or tur- 

 pentine, sometimes known under the name of " Brunswick- 

 black," has come much into use. It is extremely easy and 

 pleasant to work with, and dries quickly ; but it is brittle when 

 dry, and is disposed to crack, not merely when subject to any 

 "jar," but also (after some time) spontaneously. This evil may 

 be corrected, according to Mr. Brooke, by adding to it a little 

 solution of Caoutchouc in mineral naphtha. Oil of turpentine 

 is the solvent for this varnish, as for gold-size ; and brushes 

 which have been used with either, may be cleansed by that 

 menstruum ; those which have been used Avith liquid glue, may 

 be cleansed with naphtha. For mounting objects dry (§ 122), or 

 for giving a finished appearance to mountings which have been 

 made by one or other of the foregoing cements, varnishes may 

 be used, which, from containing coloring particles, or from being 

 acted on by the preservative liquids employed, could not be safely 

 laid on in the first instance. Among the most convenient of 

 this kind, are varnishes made by dissolving red or black or any 

 other colored Sealing-wax in strong alcohol ; these are more to 

 be recommended for their appearance, however, than for their 



' The Author has preparations mounted witli gold-size as ranch as twelve years ago, 

 which have remained perfectly free from leakage; the precaution having been taken, 

 to lay on a thin coat of varnish every two or three years. 



