34 INFRA-RED ABSORPTION SPECTRA. 



at 12 fji, which would make it appear that the lack of large absorption 

 bands in this region is due to the absence of ions whose free periods 

 coincide with that of the heat waves transmitted. The photographs 

 obtained by Abney and Festing usually show only fine lines, which can 

 not be resolved with the radiometer. The characteristic band found 

 by them at 0.867 fx is represented in the present investigation by a small 

 band whose maximum oscillates between the values 0.83 fx and 0.86 (i. 

 This band occurs in nearly every compound studied, and is the most 

 marked in eucalyptol, at 0.83 /x, and in ethyl succinate, at 0.85 /x. It has 

 been found so frequently that one can hardly doubt its existence. 



The hand at /./ fi. — ^Beyond 0.85 //. the bands are more variable in 

 their occurrence, and in their depth, until we approach 1.7 fx. This band 

 is found in all the carbohydrates studied, which agrees with Puccianti. 

 Of course, it is slightly shifted at times, which does not always appear 

 to be due to lack of precision in the apparatus. This is especially 

 noticeable in thiophene, where the maximum occurs at 1.66 /a, which 

 is just double the 0.83 fx band, and in ethyl succinate, where these two 

 bands are shifted to 0.85 /x and 1.73 /x, respectively. In noticing the 

 constant occurrence of bands in these two regions, one begins to inquire 

 into their significance, and, after finding similar conditions at 3.43 /x, 

 6.86 /x, and 13.8 /<., this becomes still more urgent. The question of the 

 importance to be attached to these facts must be reserved for a later 

 discussion. 



The hand at 2.08 ix. — This shallow band in Puccianti's curve of the 

 alcohols was found at 2.14 fx for a sample of de Haen's bidistilled glyc- 

 erin. On adding a drop of water the band was broadened out, extend- 

 ing from 2.08 IX to 2.1 fx, as in ethyl alcohol. The gradual increase in 

 the general absorption beyond 2 fx is very marked in contrast to its 

 almost complete transparency from 0.8 /t to 1.2 fx. 



The bands at 2.18 fx and 2.4Q fx. — In the present study of the simpler 

 benzene derivatives, these two bands always occur, which substantiates 

 the work of Puccianti. In the very complex derivatives, like pinene, 

 eucalyptol, eugenol, and safrol, the bands are wanting or shifted to 

 entirely new positions, which agrees with the observations farther in 

 the infra-red. 



As a whole, the curves form an interesting study by themselves. In 

 comparing them with the curves obtained with the rock-salt prism, for 

 this region of the spectrum, we can see how useless it would have been 

 to explore it thoroughly with the rock-salt prism and the small spectro- 

 meter. Only in the chloroform curve do we find the marked bands 

 resolved and in their proper places. With the larger spectrometer, 

 however, the agreement in the location of the maxima with those 

 obtained with the quartz prism is very close. 



