202 HYDRATES IN AQUEOUS SOLUTION. 



The half-films were not developed simultaneously in this particular 

 case. The depth of the cell was 1.41 cm. The spectrogram* shows quali- 

 tatively the same regions of absorption for the solutions made up with 

 calcium bromide, as had been described above for the solutions containing 

 calcium chloride. The negative recorded the line at 2265.1 A. U. as trans- 

 mitted by the solution in which no dehydrating agent was present. No 

 shorter wave sensibly affected the film. The region of absorption in the 

 ultra-violet extended to longer and longer wave-lengths as the amount of 

 bromide in the solutions became greater and greater. The shortest wave 

 transmitted by the most concentrated solution, as shown by the negative, 

 had a length of 3261.2 A.U. The middle of the band in the green has approx- 

 imately the position given by 0.518. The strips pertaining to the first 

 eleven solutions show that the width of the band just mentioned varied almost 

 linearly with the like change in concentration of the calcium chloride. This 

 band, according to the negative for the most concentrated solution, possessed 

 complete absorption from 0.460/< to wave-lengths beyond the nearer end of 

 the spectrogram. The presence of general absorption in the yellow-orange 

 is clearly brought out by the photographic strips beginning with the 12th and 

 ending with the 16th. 



Eye observations on typical solutions of the set under consideration were 

 made with the aid of the double-cell, and the most important changes in 

 absorption noted were as follows: The comparison of the 1st and 6th solu- 

 tions showed no appreciable differences in the orange and red portions of the 

 parallel spectra. The data relative to the band in the green need not be 

 repeated, since they can be obtained in great detail from plate 10. 



The 6th and 9th solutions gave spectra of sensibly the same intensity, 

 except in the region of the absorption band in the green. No trace of the 

 bands in the orange and red could be seen in the preceding spectra. 



The 12th solution absorbed the extreme red a little more than the 9th. 

 More specifically, if it be said that the spectrum of the former began at 

 0.700/t, then the corresponding number for the latter would be 0.736/*. The 

 narrow bands at 6245 and 6095 (plate 8) could only be seen for the 12th 

 solution by moving the spectrumf across the field of view of the telescope. 



The bright regions of transmission were approximately of the same intensity 

 throughout. The 13th solution dimmed almost the entire spectrum a little 

 more than the 12th, and it showed faintly the band at 6405 and more dis- 

 tinctly the bands at 6610, 6245, and 6095. The former solution showed 

 almost complete absorption of all visible light of wave-length greater than 

 0.687/(. The absorption in the same region was not so intense for the 



* The slit of the spectrograph was narrower than usual, and this accounts for the par- 

 tial absence of continuous background in the ultra-violet. 



t The axes of the collimator and telescope were fixed at right angles to each other, and 

 the spectrum was moved by rotating the prism by means of the wave-length drum. 



