50 



A STUDY OF THE ABSORPTION SPECTRA. 



nitric acid causes the uranyl nitrate bands to shift still further towards 



the violet. 



Bois and Elias ' have investigated the effect of low temperature and 

 a magnetic field on several chromium salts, and have made an especially- 

 detailed study of the ruby. 



Chrome alum crystals (KCr(SO) 2 .12H 2 0) at 18 give a strong band 

 from X 669cS to X 6716. At 190 this band has become smaller, X 6684 to 

 X 6694, and is shifted about 17 Angstrom units to the violet. A strong line 

 appears at X 6702 and about twenty bands occur between X 6190 and X 7160. 

 The band X 6686 to X 6694 was slightly affected by a magnetic field. An 

 aqueous solution shows bands at XX 6627, 6723 and 6875, 7275. 



Potassium chromium oxalate (K 6 Cr 2 (C 2 O 4 ) .6H 2 O) at 18 gives a band 

 from X 6980 to X 7032; at - 180 X 6965 to X 7012, a shift of 16 Angstrom 

 units. An aqueous solution gives bands at XX 6953 to 6990 and 7084 to 

 7110. At 18 a glycerol solution gives a band at XX 6946 to 6990. At - 130 

 bands appear at XX 6947, 6976; 6597, 6654; 6694, 6716; 6752, 6772. 



The band X 6925 of potassium chromium oxalate (K 2 Cr 2 (C 2 < ) 4 .a;H 2 0) 

 is slightly broadened by a magnetic field. Chromium fluoride mixed with 

 borax gave at 18 two bands XX 6734, 6810, and 6947, 7390; at -190 

 XX 6724, 6805 and 6923, 7476; the first band thus shifting about 8 Angstrom 

 units to the violet. 



The most important chromium compound investigated by Bois and 

 Elias was the ruby, a solid solution of a small amount of Cr 2 3 in aluminium 

 oxide, A1 2 3 . Miethe 2 has found the absorption and fluorescent bands to 

 occupy the same positions. The following data are taken from the paper 

 of Bois and Elias. 



Ordinary absorption spectra of the ruby. 



The extraordinary absorption spectra give considerable relative dif- 

 ferences in the relative intensities of the absorption bands, but very little 

 if any difference in the wave-lengths of the finer bands. The fluorescent 

 bands excited either by arc or sunlight occupied the same positions as the 

 absorption bands. A detailed account is given of the effect of magnetic 

 fields of different strengths upon B 2 , B x , R 2 , and R v The effect of a mag- 



1 Ann. Phys., 27, 12, 247 (1908). 



2 Verh. d. deutsch. physik. Gesell., 9, 715 (1907). 



