THE MICROSCOPE IN CHEMISTRY. 101 



The Use of the Microspectroscope. We have already de- 

 scribed this accessory in Chapter III. It promises im- 

 portant results in chemical analysis, but requires delicate 

 observation and exact measurements, together with a 

 careful and systematic study of a large number of colored 

 substances. 



In using the microspectroscope, much depends on the 

 regulation of the slit. It should be just wide enough to 

 give a clear spectrum without irregular shading. As a 

 general rule, it should be just wide enough to show Frau- 

 enhofer's lines indistinctly in daylight. The slit in the 

 side stage should be such that the two spectra are of 

 equal brilliancy. Xo light should pass up the microscope 

 but such as has passed through the object under exam- 

 ination. This sometimes requires a cap over the object- 

 glass, perforated with an opening of about one-sixteenth 

 of an inch for a one and a half inch objective. 



The number, position, width, and intensity of the ab- 

 sorption-bands are the data on which to form an opinion 

 as to the nature of the object observed, and Mr. Sorby 

 has invented a set of symbols for recording such observa- 

 tions. (See Dr. Beale's How to Work with the Microscope.) 

 These bands, however, do not relate so much to the ele- 

 mentary constitution as to the physical condition of the 

 substance, and vary according to the nature of the solvent, 

 etc., yet many structures give such positive effects as to 

 enable us to decide with confidence what they are. 



Colored beads obtained by ordinary blowpipe testing, 

 sections of crystals, etc., cut wedge-shaped so as to vary 

 their thickness, often give satisfactory results. But 

 minute quantities of animal and vegetable substances, as 

 blood-stains, etc., dissolved and placed in short tubes 

 fastened endwise on glass slides, or in some other conve- 

 nient apparatus, offer the most valuable objects of re- 

 search. 



To measure the exact position of the absorption-bands, 



