8 



A STUDY OF THE ABSORPTION SPECTRA. 



preted his results from the point of view of hydration. Houstoun investi- 

 gated the bands of glasses containing uranium and neodymium but found 

 no shifts of the bands. 



Very important papers on this subject have been published by Becque- 

 rel, Ritz, Retschinsky, Stark, Bois and Elias, Konigsberger and Kilchling, 

 Page, Laub, Voigt, and others. 



A METHOD OF CHEMICAL ANALYSIS. 



The stimulus to research along many lines in science is often very much 

 augmented by the requirements of technology. This is especially true in 

 connection with many branches of organic chemistry. A good example is 

 the case of the pure food laws. In regulating the use of various coloring and 

 preserving matters added to foods, it is necessary that the examiners shall 

 be able to recognize various compounds easily and quickly. Many organic 

 compounds possess very characteristic colors, and it has often been asked 

 whether the absorption spectra of these compounds would aid in their 

 detection. Our present knowledge of absorption spectra is limited chiefly 

 to the visible region of the spectrum. Before this method of analysis can 

 be satisfactorily used by chemists it will be necessary to measure the absorp- 

 tion throughout the region of the infra-red. At present a few potassium 

 salts have been studied in the regions of wave-lengths as long as 0.1 mm. 

 (The shortest electromagnetic waves that are produced by mechanical 

 apparatus are about 6 mm. in length.) 



The analysis of inorganic compounds by means of their spectra is 

 probably less hopeful, although the absorption or reflection spectra would 

 often be very useful. A great many of the inorganic cations show charac- 

 teristic absorption in the visible portion of the spectrum, and practically 

 all have bands in the infra-red. J. Formanek x has suggested that the absorp- 

 tion spectra of metallic compounds of alkannin would serve to indicate 

 the presence of the metals. 



The following measurements of the absorption bands of different com- 

 pounds of alkannin show the effect of the metal upon the position of the bands. 



Uranium . . 



Iron 



Potassium . 

 Cobalt .... 

 Sodium . . . 

 Barium . . . 



6870 

 6545 

 6387 

 6370 

 6337 

 6281 



6315 



6030 



5910 



5845 5405 



5857 



5805 5395 



Lithium 



Nickel 



Calcium 



Copper 



Aluminium . 



X 

 6210 

 6192 

 6147 

 5953 

 5857 



5745 5340 



5725 5320 



5682 5276 



5515 5128 



5425 5048 



The use of absorption and emission spectra has been most successful 

 in separating the rare earths. The method has been used by Crookes, 

 Becquerel, Exner, Demarcay, and many others. A very good account of 

 this work has been given by Bohm. 2 Recently Urbain 3 has used the phos- 

 phorescent spectra to purify compounds of europium, gadolinium, terbium, 

 dysprosium, neoytterbium, and lutecium. 



1 Die Qualitative Spectralanalyse anorganischer Korper. 



2 Die Darstellung der seltenen Erden, Leipzig (1905). 

 8 Le Radium, June (1909). 



