01' MICROSCOPIC OBJECTS. 4-5 



and other fine work. It is very liquid, and is thought by 

 some to be more easily worked than Canada balsam. 

 Dammar may be easily dissolved in benzole to any extent. 

 The lumps should previously be scraped until they are freed 

 from dust and other impurities, and then roughly crushed. 



ASPHALTUM. This substance is dissolved in linseed oil, 

 turpentine, or naphtha, and is often termed " Brunswick 

 black." It is easily worked, but is not generally deemed a 

 trustworthy cement, as after a time it is readily loosened 

 from its ground. It is, however, very useful for some pur- 

 poses (such as " finishing " the slides), as it dries quickly. 

 I shall, however, mention a modification of this cement a 

 little farther on. 



MARINE GLUE. No cement is more useful or trustworthy 

 for certain purposes than this. It is made in various pro- 

 portions; but one really good mixture is equal parts of 

 india-rubber and gum shellac: these are dissolved in mineral 

 naphtha with heat. It is, however, much better to get it 

 from the opticians or others who keep it. It requires heat 

 in the application, as will be explained in Chapter Y. ; but 

 is soluble in few, if any of the liquids used by the microscopist, 

 and for that reason is serviceable in the manufacture of 

 cells, &c. Where two pieces of glass are to be firmly 

 cemented together, it is almost always employed ; and in all 

 glass troughs, plates with ledges, &c., the beginner may find 

 examples of its use. 



GOLD SIZE. This substance may always be procured at 

 any colourman's shop. The process of its preparation is 

 long and tedious. It is therefore not necessary to describe 

 it here. Dr. Carpenter says that it is very durable, and 

 may be used with almost any preservative liquids, as it is 

 acted upon by very few of them, turpentine being its only 

 true solvent. If too thin, it may be exposed for awhile to 

 the open air, which by evaporation gradually thickens it. 

 Care must be taken, however, not to render it too thick, as 

 it will then be useless. A small quantity should be kept on 

 hand, as it is much more adhesive when old. 



GUM DAMMAR CEMENT. An excellent cement may be 



