THE MICROSCOPE IN CHEMISTRY. 99 



may then be examined with the microscope. If there is 

 no precipitate, let it stand several hours and examine again. 

 Dr. Beale prefers a flat or concave slide, and suggests that 

 if a glass rod be used for carrying the reagent, it must be 

 washed each time, or a portion may be transferred' from 

 the slide to the bottle. He also advises the use of small 

 bottles with capillary orifices for reagents. Dr. Lawrence 

 Smith uses small pipettes with the open end covered by 

 india-rubber. 



If heat be required, the drop may be boiled on the slide 

 over a spirit-lamp, or a strip of platinum-foil or mica may 

 be held with forceps so as to get a red or white heat from 

 the lamp or a Bunsen burner. This is especially needed 

 to get rid of organic matters. 



For the examination of earthy materials, as carbonate 

 or phosphate of lime, phosphate of ammonia and magne- 

 sia, sulphates or chlorides, a small fragment may be placed 

 on a slide and covered with thin glass. A drop of nitric 

 acid is then put near the edge of the cover. If bubbles 

 escape a carbonate is indicated. Neutralize the acid with 

 ammonia ; let the flocculent precipitate stand awhile ; 

 cover and examine with the microscope. After a time, 

 amorphous granules and prisms will show phosphates of 

 ammonia, magnesia, and lime. Sulphates are shown by 

 adding to the nitric acid solution nitrate of barytes, and 

 chlorides by nitrate of silver. 



Dr. Beale recommends adding glycerin to the test solu- 

 tions. The reactions are slower but more perfect, and the 

 crystalline forms resulting are more complete. 



If a sublimate be desired, a watch-glass can be inverted 

 over another, and the lower one containing the material, 

 as biniodide of mercury, etc., heated over a spirit-lamp, 

 or the sublimation may be made in a reduction-tube. 



Preparation of Crystals for the Polariscope. Many speci- 

 mens may be prepared by concentrating the solution with 

 heat and allowing it to cool. It should not be evaporated 



