68 THE MICROSCOPIST. 



solution of gelatine, &c., upon a slide, put into it a drop of 

 some strong solution of salts, as Epsom salts, hydrochlorate of 

 ammonia, tartaric acid, &c. Hold the slide over the spirit- 

 lamp until evaporation is perceived, when it should be removed 

 and placed under the microscope. If the evaporation is too 

 rapid, the crystals will not be well formed. They may be 

 mounted dry, or in balsam. A power of 30 diameters is 

 generally sufficient. Crystals of salts form interesting and 

 splendid objects under polarized light. 



Ice. A plan for observing the crystallization of water is as 

 follows. Mix some water with a little charcoal, chalk, &c., in 

 such a manner that a number of fine particles may be mechani- 

 cally suspended in it; then take a glass slide, place it on a 

 cold night in an exposed situation, as outside of a window-sill ; 

 pour upon it as much water as it will support without running 

 over the edge, and let it remain all night. The next morning, 

 if the weather has been sufficiently cold and the atmosphere 

 dry, neither water nor ice will be seen on the slide ; but the 

 particles of charcoal will be found arranged in the various 

 forms which they assumed while the water crystallized. The 

 slide may be carefully prepared with Canada balsam for pre- 

 servation. 



Crystals of Iron Pyrites and other substances ; Oolites ; and 

 various sorts of sand; are interesting objects. The sand from 

 Turkey sponge, and from the sea, often contains minute shells 

 of various kinds, as iheforaminifera, &c., corallines, and other 

 zoophytes. 



.Sections of Granite, Limestone, &c., are also of considerable 

 interest ; but sections of coal, made very thin, so as to be viewed 

 by transmitted light, develope clearly its vegetable origin, and 

 are therefore of special importance. 



Deut-Ioduret of Mercury. The change of color in this salt 

 is a beautiful object. If a little of it be placed in a watch- 



