182 MOSSES AND LIVERWORTS 



mind, is Copal varnish (" picture copal varnish," 

 to give it its full name), to be obtained from any 

 artists' colourman ; this may be thinned, when 

 necessary, with a little benzol, which I prefer to 

 turpentine for this purpose, This varnish adheres 

 very closely to the glass, and as it does not dry too 

 hard it does not easily chip off ; moreover, it has 

 this further advantage, that if part of the object 

 in the cell has located itself a little too near to the 

 margin of the cover-glass, and is thus covered by 

 the varnish, it may nevertheless be seen through 

 this practically colourless coating. 



Where an object of any considerable thickness 

 is mounted, a cement of a thicker consistency is 

 needed, in order to form more of a wall to the sides 

 of the cell, and here nothing could serve the pur- 

 pose better than Marine glue. The best form in 

 which to apply it is that of a moderately thin 

 solution in benzol, and any one who has had an 

 intimate acquaintance with this most adhesive sub- 

 stance will readily believe that it is far better to 

 purchase the preparation ready-made rather than 

 attempt its manufacture oneself. This is at all 

 times a very safe cement, though, owing partly to 

 its light brown colour, and partly to the fact that 

 it does not dry with a very good surface, it does 

 not impart the same finish to a slide that other 

 sealing media do. These defects can, however, 

 always be remedied by a final coat of asphalt 

 varnish. 



