8 THE ABSORPTION SPECTRA OF SOLUTIONS. 



The phosphorescence of several organic compounds has been studied by 

 Kowalski. 1 Phosphorescence was found to appear in many cases at about 

 150 C, depending on the substance dissolved in the alcohol. When phos- 

 phorescence first appears it only lasts a few hundredths of a second, but as 

 the temperature is lowered the duration of the phosphorescent light increases 

 very appreciably. If the time of excitation is short, an "instantaneous" phos- 

 phorescence results which resembles the fluorescence of the solution. If the 

 time of excitation is increased, fine bands are superimposed upon the broad 

 fluorescent bands, and these increase in intensity as the time of excitation is 

 increased. The time required to reach a maximum intensity is different for 

 different bands. The duration of these bands is much longer than that of the 

 "instantaneous" phosphorescence, and is called by Kowalski "progressive 

 phosphorescence . ' ' 



Kowalski and Dzierzbicki give the following wave-lengths for the pro- 

 gressive phosphorescent bands in ethyl alcohol: 



(1) Benzene, 0.05 normal solution in alcohol : XX 3390, 3460, 3520, 3570, 

 3650, 3710, 3800, 3850, 3970, 4020, 4130, 4190, 4290, 4350. 



(2) Toluene, ethylbenzene, and propylbenzene, 0.05 normal solution 

 in alcohol. The introduction of the methyl group into the benzene nucleus 

 transforms the 14 benzene doublets into 7 broad bands, occupying almost the 

 same position in the spectrum. An introduction of a methyl group in a 

 side chain produces very little effect. The toluene bands are at XX 3460, 3580, 

 3650, 3800, 3890, 4060, and 4120. The ethylbenzene bands are at XX 3450, 

 3580, 3640, 3780; 3870, 4050, and 4120. The propylbenzene bands are at 

 XX 3440, 3580, 3650, 3790, 3890, 4050, and 4130. 



(3) The bands of a 0.05 normal solution of o-xylene, C 6 H 4 (CH 3 )2, are at 

 XX 3480, 3560, 3610, 3670, 3780, 3830, 3900, 4000, 4070, and 4130; m-xylene, 

 C 6 H 4 (CH 3 ) 2 , at 3540, 3610, 3670, 3730, 3820, 3880, 3970, 4090, 4160, and 4230; 

 and p-xylene, C 6 H 4 (CH 3 ) 2 , at 3550, 3650, 3700, 3770, 3890, 3950. 4010, 4120, 

 4190, and 4270. 



(4) Pseudocumene, mesitylene, and cymene all show bands at XX 3560, 

 3650, 3770, 3880, 4000, 4120, and 4270. 



(5) Phenol shows bands at XX 3510, 3610, 3710, 3830, 3960, and 4080. 



(6) o-cresole has bands at XX 3530, 3630, 3740, 3850, and 3970; ra-cresole 

 at 3540, 3620, 3730, 3850, 3970, and 4080; p-cresole at 3630, 3730. 3850, 3980, 

 and 4110. 



THE ABSORPTION SPECTRA OF ORGANIC COMPOUNDS. 



The Unit of this Absorption. 

 In discussions concerning the color of organic compounds it is customary 

 to speak of the selective absorption as being due to certain ions or molecules. 

 This is probably true in the infra-red, the electric charges absorbing these long 

 wave-length radiations being probably associated with masses of molecular 

 size. However, in the visible and ultra-violet portions of the spectrum the 

 value e/m of the absorbers is invariably of the same magnitude as that of the 

 electron. Drude 2 has investigated a large number of organic compounds, 



1 Compt. Rend.. 151, S10 (1910). 



2 Ann. (1. Phys., 14, 677, 726, 936, 961 (1904). 



