78 THE AMERICAN MONTHLY [Mar 



gum solution is to prevent the balsam running into the 

 structure of the tooth, and so rendering it too transparent. 

 When dry, add balsam and benzole until it is well cover- 

 ed. Set aside in a place free from dust and mount by the 

 exposure method. 



Sections of seed-shells may be treated in just the same 

 way as described for rocks, with this exception, that some 

 of them are best soaked in spirits of turpentine before 

 mounting, instead of the second benzole. 



Where round cover glasses are used, it is best to run a 

 ring of cement round before putting the finishing varnish 

 on. This prevents all chance of its running under, and 

 thus disfiguring or spoiling a specimen. 



How to Clean Thin Glass Covers. — Always keep 

 your glasses in a solution of nitric acid and water, about 

 two parts water to one of acid. This will take any marks 

 off that may be on the surface of the glass. The best way 

 is to have them in a glass or porcelain vessel. Take them 

 out as required, or clean a number together, immerse 

 them in methylated spirits. Have a block of wood, about 

 6 in. by 4 in, tack a piece of American cloth over the top, 

 fasten at the ends and sides, take your covers one at a 

 time, and breathe on one surface and place on the block. 

 A dozen may be placed in a row the damp-side down. 

 Gently press them. All air being out from between them 

 and the cloth on the block, they will hold. You can now 

 clean them all together. When one side is done, take 

 your forceps or something with a point and gently lift up 

 one edge of each cover. Take them up in the forceps, re- 

 peating the operation of breathing. Your second surface 

 will be clean. Should the other show any signs of con- 

 tact with the cloth, this will easily clean off when the 

 cover is used and fixed in its place, but this will be noth- 

 ing to speak of if the block is cleaned occasionally. By 

 this method, all cover glasses may be easily cleaned with- 

 out breakage. 



