246 HYDRATES IN AQUEOUS SOLUTION. 



greatest and least amounts of water are contiguous, respectively, to the 

 numbered scale and to the comparison spectrum of plate 24. This spec- 

 trogram will be discussed before plate 25 (a) . The depth of the cell was 2 

 cm.* As would be expected, the same general regions and bands of absorp- 

 tion were possessed by the solutions of cobalt chloride in ethyl alcohol and 

 water, as by those in which methyl alcohol took the place of ethyl alcohol. 

 The negative strip pertaining to the solution which contained the greatest 

 amount of water barely recorded the intense zinc line of wave-length 2502.1 

 A.U. The continuous background ceased about 0.280//.. The middle of the 

 band in the green as shown by the negative was near 0.516/<. For the solu- 

 tion whose percentage of water was 2.00, the negative strip gave 0.519/< as 

 the middle of the band in the green. Hence, the photographic band w ? as 

 displaced towards the blue by about 30 A. U. as the percentage of water 

 was increased from 2.00 to 20.00. The strip corresponding to the mother- 

 solution showed transmission between the extreme limits 0.384/t and 0.508/<. 

 The last three strips, and especially the very last one, showed the existence 

 of appreciable general absorption in the yellow and orange. The negative 

 for plate 25 (a) was taken with a Cramer trichromatic plate. The solutions 

 used were the last five of the set of twelve; in other words, the five that 

 contained the smallest amounts of water. The strip pertaining to the 

 mother-solution is closest to the scale. The depth of the cell was 2 cm. 

 The exposure for the Nernst filament lasted two minutes. The negative 

 recorded the middle of the absorption band in the green as at 0.510/< for the 

 solution that contained 5 per cent of water. The five strips show dis- 

 tinctly the gradual shift of the middle of this band towards the red, as the 

 quantity of water in the solutions decreased from 5 to per cent. They 

 also showed the progress of absorption both in the violet and in the orange 

 and yellow. In fact, the strip pertaining to the mother-solution shows no 

 transmission of the yellow. The middle of the region of transmission 

 between the band in the violet and the band in the green moved towards 

 the red, whereas the center of the bright region between the band in the 

 green and the band in the orange shifted towards the blue as the percentage 

 of water decreased. 



The results obtained by eye observations with the Hilger spectroscope 

 were as follows: The depth of cell used was 2 cm. With only air in the 

 path of the beam of light, the spectrum began near0.776/<. The mother- 

 solution transmitted faintly a band of red from 0.775 /* to 0.735/<. The more 

 refrangible limit was quite well defined. An intense region of absorption 

 extended from 0.735/t to 0.575/t. Transmission began again in the blue- 

 green. This color, however, was weak. Absolutely no light of shorter 

 wave-length than 0.417, could be seen, which shows that the ultra-violet 

 region of absorption extended into the visible spectrum by at least 170 A.U. 



* As this number is given from memory, it may not be exact. 



