188 HYDRATES IN AQUEOUS SOLUTION. 







green was at about 0.515//. The general contour of the limits of ultra- 

 violet transmission can best be understood by referring to plate 2. The 

 region of absorption encroached on the shorter wave-lengths more rapidly 

 than on the longer ones. The asymmetry of the region may be due to the 

 superposition of two close, unresolved bands, of which the more refrangible 

 was the weaker. For the seventh solution (of concentration 1.409), the mid- 

 dle of the photographic region for absorption was at 0.503/>. The more 

 refrangible end of this band was at about 0.432,u for the more concentrated 

 solution. 



The absorption spectra of the five most concentrated solutions were photo- 

 graphed with a red sensitive plate, and the result is reproduced as plate 3 

 (a). The depth of cell was 0.67 cm., as before, but the exposure with the 

 Nernst filament was two minutes in length. The photographic limits of 

 absorption of the solution of concentration 1.843 were about 0.43S,u and 

 0.565//.; while those for the mother-solution were about 0.427,^ and 0.5S5,". 



The apparent displacement of the middle of the band from 0.502// to 

 0.506,, with increasing concentration, is probably due to weak photographic 

 action in the neighborhood of the less refrangible end of the absorption 

 band of the most concentrated solution. Moreover, the negative plate was 

 undeveloped. 



Plate 4 (b) shows the continuous variation with thickness of the absorption 

 of the mother-solution of cobalt chloride. The solution was placed in the 

 wedge-cell and hence the depth varied linearly. To bring out the band in 

 the blue-green, zero depth of absorbing layer could not be used. The least 

 and greatest depths of liquid were 0.53 mm. and 1.09 mm., respectively, and 

 the angle of the cell was 58.5'. As usual, the side of the spectrogram corre- 

 sponding to the least depth of the liquid lies nearest to the comparison spec- 

 trum. The band in the blue-green has its center about 0.520,^.. It seems to 

 be slightly asymmetric, but this appearance is doubtless exaggerated by the 

 great sensitivity of the Seed film to yellow light. The end of the band in 

 the extreme ultra-violet varies slightly with increasing thickness of absorbing 

 layer. Faint transmission begins about 0.245,^. 



A negative taken* with the cell set at an angle of 35.1'f and commencing 

 at zero depth, showed practically no band in the green, but it did show a 

 definite curved line of absorption in the remote ultra-violet. A general idea 

 of the course of this curve can probably be gathered from the following 

 statements: The least trace of the zinc doublet at 2062 A. V. was shown 

 at the very edge of the negative. The spectral lines of wave-length 2144.5 

 and 2194.7 jutted out from the edge of the spectrogram through distances 



* Not reproduced for publication, 

 f Greatest depth equaled 0.32 mm. 



