248 HYDRATES IN AQUEOUS SOLUTION. 



faint and then gradually increased as the amount of w^ter decreased. The 

 mother-solution had a very deep blue color. The photographic strips adja- 

 cent to the numbered scale and to the comparison spectrum correspond, 

 respectively, to the solutions that contained the greatest amount of water 

 and no water at all. The spectrogram shows the existence of a region of 

 very intense absorption in the ultra-violet, and another region in the orange. 

 No band appeared photographically in the green. The negative strip for the 

 28 per cent solution showed that the ultra-violet region of absorption ended 

 abruptly at 3250. That this limit of absorption did not vary rapidly as the 

 amount of water de-creased is shown by the fact that the strip for the 2 per 

 cent solution gave the wave-length of complete absorption as 3329 A. U. 

 In other words, this limit only moved by about 80 A. U., while the percentage 

 of water changed from 28 to 2. In addition to the abrupt limit of absorption, 

 the existence of ever-increasing, weak absorption of the extreme violet and 

 least refrangible ultra-violet is shown by the last five or six strips, which 

 correspond to the solutions that contained smaller amounts of water. For 

 the mother-solution, this general absorption was relatively strong. Although 

 the strip for the mother-solution recorded very faintly the air-line at 3331.5, 

 nevertheless the continuous background only began to grow strong near, say, 

 0.375/t. The last 8 or 9 negative strips showed distinctly the existence of 

 absorption in the orange and yellow. Also the more refrangible limit of 

 this band did not shift in direct proportion to the percentage of water in 

 the successive solutions. The strip for the mother-solutions shows that 

 transmission of sufficient intensity to affect the photographic film stepped at 

 about 0.554/t. 



The spectroscopic study of the bands in the red and orange brought out 

 the following facts: The cell depth was 2 cm. For the mother-solution 

 transmission began near 0.570, and increased to about 0.554/. The green 

 and blue regions are not very bright, and the nearest approach to trans- 

 parency seemed to be in the indigo. Visible transmission ceased at 0.424j. 

 The spectrum of the 4 per cent solution was qualitatively like that of the 

 mother-solution. The wave-lengths which corresponded to 0.570/(, 0.554/<, 

 and 0.424/1 for the mother-solution were, respectively, 0.599/(, 0.574/<, and 

 0.416,, in the case of the 4 per cent solution. The solution which contained 

 6 per cent of water was the first to show definite absorption bands. It 

 transmitted very faintly the red from 0.77 n to 0.731/t. One absorption band 

 extended from 0.731 /* to 0.630,, and another from 0.616/j to about 0.596/<. 

 Slight transmission separated these two bands of complete absorption. 



The complete spectrum for the 8 per cent solution was more complicated 

 than that of the 6 per cent solution. The red was faintly transmitted from 

 0.77// to0.721j, with the maximum of brightness near 0.741/*. Complete 

 absorption from 0.721/t to 0.651/< was succeeded by very weak transmis- 



