CEMENTS. 



CEMENTS. 



A large number of compositions have been pro- 

 posed for use as cements for mounting prepara- 

 tions. As only a few of these appear to me 

 deserving of attention, I do not hesitate to add a 

 few words on this subject to the digression already 

 made in behalf of mounting media. 



Cements should adhere to glass strongly, so as 

 to be both air and water-tight. They should be 

 unaffected by the mounting fluid, and should not 

 crack with age. 



Those which I would recommend, from my own 

 experience, are asphalt varnish (Brunswick black), 

 which can be bought ready for use, and is made by 

 dissolving asphalt in linseed oil or turpentine ; pre- 

 pared gold-size (a sort of Copal varnish) ; and an 

 alcoholic solution of Holmblad's best sealing wax. 

 All these substances should have a rather ropy 

 consistency, and must not harden too quickly. 

 They are applied with a small camel's-hair pencil. 

 The safest sealing is effected by applying a layer 

 of asphalt first, and covering this with the sealing- 

 wax solution when it is half-hard. 



In my opinion the following new composition is 

 to be recommended. We have tried it in the 

 Copenhagen laboratory, and so far are pleased with 

 it. 50 gm. Canada balsam ; 50 gm. shellac ; 50 

 gm. absolute alcohol, and 100 gm. ether are mixed, 



