CHAPTER XII. 



METHODS FOR THE HANDLING OF SMALL AMOUNTS OF 



MATERIAL. 



Microchemical Methods. By microchemical methods we 

 generally mean the application of chemical operations to the 

 examination and study of very small quantities of material. The 

 chief chemical operations with which we have to deal are: i. 

 Solution; 2. Decantation; 3. Filtration; 4. Sublimation; 5. 

 Distillation; 6. Precipitation; 7. Ignition, Fusion, and Mis- 

 cellaneous Treatments. 



Since success in chemical microscopy requires skill in the 

 technique of these operations each one will be discussed at 

 length. 



i. Solution. Testing for Solubility. At the corner of a 

 perfectly clean object slide of glass, quartz, or celluloid, place a 

 small drop of water (or other solvent) ; the drop should be 3 to 4 

 millimeters in diameter and about i millimeter deep. Place 

 close to this drop a tiny fragment of the material whose solu- 

 bility is to be tested. Transfer the glass slip to the stage of the 

 microscope and focus with a low power objective upon the edge 

 of the drop nearest the fragment. See that the illumination, 

 using an Abbe condenser, is carefully adjusted, and that the iris 

 diaphragm is at least two-thirds closed. By means of a glass 

 rod drawn out fine, a platinum wire or a stiff hair, slowly push 

 the fragment into the drop, at the same time looking into the 

 instrument so as to be able to note the phenomena which may 

 take place the instant the material enters the solvent; for ex- 

 ample, the substance may merely "melt" away, or it may de- 

 crepitate, or give off bubbles of gas, or it may dissolve with 

 decomposition (hydrolise), etc. A little practice is often neces- 

 sary to enable the beginner to push substances into drops of 

 solvent while looking into the instrument. It is of course 



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