MICROSCOPIC OBJECTS. 135 



Having thus mounted your object, it must be slowly 

 dried in a warm situation. This will take one or two 

 days ; after which the slide is to be cleaned by scraping 

 off the surplus balsam with a strip of plate brass (iron is 

 liable to scratch the glass, and therefore is objectionable). 

 Finally, wipe it clean, using first a linen rag moistened 

 with turpentine, and then a piece of dry clean leather. 



On Preparing Woods for making thin sections. — This 

 process will vary with different kinds of wood. When 

 the specimens are hard woods, which usually contain gums, 

 resins, &c., the first operation wiU be to immerse the 

 specimen in some essential oil, and keep it in a closed 

 vessel at a moderate heat for a few days. This is 

 necessary for the purpose of slowly dissolving out the 

 resins, &c. ; otherwise a clean section cannot be made. 

 Various solvents must be tried, such as oil of turpentine, 

 oil of lavender, spirits of wine, sulphuric ether, &c. 

 When the wood has been freed fi'om resin and gum, it 

 wiU be ready to be cut into thin sections. Specimens 

 thus prepared should be kept in closed bottles with 

 alcohol. 



In soft w^oods the chief difficulty to be overcome in the 

 preparation is in the drying. This must be slowly and 

 uniformly done. The heat must never exceed the tem- 

 perature of boihng water. The specimen^ when quite 

 dry are ready to be cut. It is usual to cut soft woods 

 dry, but some artists prefer immersing them in spirits. 



In the preparation of woods great care must be taken 

 not to rupture the different vessels or break the fibres 



