6 3 8 



EMISSION SPECTRA 



[Cn. XV 



Didymium salts, such as crude didymium nitrate or the pure 

 neodidymium, praseodidymium, erbinum, and other rare earth salts. 



The following substances will show general absorption at one 

 end of the spectrum and should be shown in comparison with the 

 spectrum of white light : 



Amber glass, green glass. 



Copper sulphate, Ferric chloride, Nickel nitrate, Potassium 

 chromate and dichrorrate, Chrome alum. 



FIG. 366. COMPARISON OF SPECTRA. 

 C Condenser. 



Specimen This covers only a part of the slit. 

 Slit Longitudinal view of slit. 



Through the rest of the slit passes white light or light traversing another 

 specimen. The two spectra then appear side by side. 



EMISSION SPECTRA 



903. Besides the projection of absorption spectra, the optical 

 system as described above will serve also for the projection of 

 emission spectra. In this case the arc is both the specimen and 

 the source of light. 



We will suppose that it is desired to project the spectrum of a 

 "yellow flame" carbon, this being about the easiest and most 

 satisfactory to begin with. The apparatus is set up as shown in 

 fig. 367. L is a vertical arc, the lower electrode of which is a yellow 

 flame arc carbon or a hollow carbon filled with a sodium, potassium 

 or other salt. The upper electrode is a carbon about 13 mm. (% 

 inch) in diameter. The carbon holder may be of the hand-feed 

 type or an automatic lamp may be used. 



904. Automatic lamp for use in projection of spectra. 



When using certain materials in the arc, the arc goes out frequently 



