CHAPTER VI. 



ABSORPTION SPECTRA OF A NUMBER OF SALTS AS MEASURED 

 BY MEANS OF THE RADIOMICROMETER. 



The results tabulated and discussed in Chapters IV and V, which are con- 

 cerned with the energy measurements of the absorption spectra of solutions 

 by means of the radiomicrometer, were made by comparing the intensity of a 

 given source of light (after passing through the solution) with the intensity 

 of the same source of light after passing through an equal depth of water. 

 In a word, the depths of cells in each case were the same. As has already 

 been stated, a cell whose depth was 1 cm. was filled with the solution and 

 placed in the path of the beam of light and the deflection of the instrument 

 noted; then a cell of the same depth was filled with the solvent and interposed 

 in exactly the same position as the former cell, and the deflection of the 

 instrument again noted. Denoting the former by I and the latter by 7 we 

 get the ratio I/h, which represents the percentage transmission of the solu- 

 tion as compared with water. Such a procedure was repeated at frequent 

 intervals throughout the spectrum, locating a series of points through 

 which the transmission curves could be drawn. 



Certain phenomena presented themselves throughout the course of this 

 investigation, which suggested a more careful study of some of the absorp- 

 tion bands located in the infra-red portion of the spectrum ; and at the same 

 time it was thought advisable to map the absorption spectra of some of the 

 more common salts of cobalt, nickel, etc., in terms of Beer's law; since up to 

 the time of this investigation no satisfactory quantitative study of the 

 infra-red spectrum of these salts had appeared. 



In order to make a careful study of the exact intensity of the various por- 

 tions of any given bands, it is clear that we are dealing with a much more 

 complex and intricate problem than simply with the location of the band; 

 and on this account it was necessary to improve our apparatus and at the 

 same time to exert more care, if possible, in carrying out any given operation. 



It was early found that if we desired to study that region of the infra-red 

 spectrum in which water had considerable absorption, we must not compare 

 our solutions with an equal depth of layer of water, as noted above ; but with 

 a depth of layer equal to the water in the solution, which in the most con- 

 centrated solutions was much less than the actual depth of the cell containing 

 the solution a part of the cell's depth being occupied by the dissolved sub- 

 stance. Even when such a correction was made, it was found that for a 

 given wave-length, in the water absorption bands, the solution gave greater 

 deflections than did the solvent, i. e., that in such regions the solution was 

 actually more transparent than an equivalent depth of water. 



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