96 PREPARATION AND MOUNTING 



of potash ; at the end of that time it is possible to cut tolerably 

 thin slices with a razor. These slices are then placed in a watch- 

 glass with strong nitric acid, covered and gently heated; they 

 soon turn brownish, then yellow, when the process must be ar- 

 rested by dropping the whole into a saucer of cold water, else the 

 coal would be dissolved. The slices thus treated appear of a 

 darkish amber colour, very transparent, and exhibit the structure, 

 when existing, most clearly. We have obtained longitudinal 

 and transverse sections of coniferous wood from various coals in 

 this way. The specimens are best preserved in glycerine in cells ; 

 we find that spirit renders them opaque, and even Canada balsam 

 has the same defect. Schulz states that he has brought out the 

 cellulose reaction with iodine, in coal treated with nitric acid and 

 chlorate of potash." 



Cannel-coal is so close and firm in its structure as to be much 

 used instead of jet in the manufacture of ornaments ; it takes a 

 beautiful polish, and consequently presents the student with none 

 but ordinary difficulties in getting sections of it. Its formation is 

 somewhat different from that of coal, sometimes showing the transi- 

 tion very clearly. 



In flint there are often found remains of sponges, shell, Dia- 

 tomacese, &c. ; but to show these well, sections must be cut and 

 polished by the lathe and wheel of the lapidary, which the micro- 

 scopic student seldom possesses. Thin chippings may, however, 

 be made, which when steeped in turpentine and mounted in bal- 

 sam, will frequently show these remains very well. 



Teeth are very interesting objects to all microscopists, more 

 especially to those who give much study to them ; as the class 

 of animal may very frequently be known from one solitary re- 

 maining tooth. To examine them thoroughly, it is necessary to 

 cut sections of them ; but this is rather difficult to perform well, 

 and needs some experience. Some instructions, however, will at 

 least lessen. these difficulties, and we will now endeavour to give 

 them. 



It is generally thought that Canada balsam injures the finer 

 markings of these sections, consequently they are almost invariably 

 mounted dry. A thin piece is first cut from the tooth with, the 

 saw of watch-spring before mentioned, if possible ; but should the 



