SALTS OF COBALT. 19 



increased depth of the layer of the solvent. The limit of transmission for 

 the 8-mm. layer falls at A 3260, and for the 24-mm. layer at about A 3320. 

 The absorption in the red is seen to be unchanged by dilution, or, as 

 it may be stated, it obeys perfectly Beer's law. In A it consists of a band 

 extending from A 5500 to A 7100, with faint transmission near A 6000; 

 thus indicating a band of absorption at A 5700. B shows three wide and 

 poorly-defined absorption bands, having their centers at A 5725, A 6200, 

 and A 6780, respectively. Of these, the last is much more intense than any 

 of the others. No breaking up of these bands into narrower ones, as ob- 

 served in solutions in the alcohols, can be noticed, although the trans- 

 mission throughout the region of absorption in B is sufficient to allow the 

 narrower bands to be seen if they existed. We must conclude, therefore, 

 that the absorption spectrum of the acetone solution differs considerably 

 from that of the alcohol solutions, which resemble each other very closely. 



COBALT CHLORIDE IN METHYL ALCOHOL WITH WATER. (See Plate 7.) 



In preparing the solutions used in making the negatives for this plate 

 a fixed amount of the mother-solution of cobalt chloride in methyl alco- 

 hol was run into a measuring-flask, then the required amount of water 

 added, and finally the flask was filled up to the mark with pure methyl 

 alcohol. The concentration of the colored salt, therefore, remained con- 

 stant throughout. Fourteen solutions were made up, the spectra of eight 

 of which were photographed on one film and the remaining six on the 

 other. Therefore, the line of separation of the two films falls between the 

 eighth and ninth strips, counting from the numbered scale. 



The concentration of cobalt chloride throughout was 0.088. The 

 percentages by volume of water added were 0, 0.5, 0.75, 1, 1.25, 1.5, 2, 

 3, 3.5, 4, 5, 6, 8, and 10, respectively. The strip corresponding to the 

 solution in pure methyl alcohol is adjacent to the numbered scale; the 

 strip corresponding to the solution containing 10 per cent of water was 

 at the top of the plate. The depth of cell was 2 cm., and the exposures 

 to the Nernst lamp and spark were 1| and 3 minutes, respectively; the 

 slit was 0.01 cm. wide. 



Two regions of absorption may be seen, one in the extreme ultra- 

 violet and one in the green. The two absorption bands in the ultra-violet 

 at A 3100 and A 3600, already described for Plate 4, were too faint to be 

 recorded with certainty, and the merest trace of the absorption in the red 

 is seen in the negative strip nearest the numbered scale. The band in the 

 extreme ultra-violet narrows regularly with addition of water, the limits 

 of transmission for the solution in pure alcohol and for the one containing 

 10 per cent of water being, respectively, A 2650 and /I 2480. 



The green band narrows markedly with increase of water. Its center 

 also shifts slightly towards the blue, being at A 5250 for the solution in 

 pure methyl alcohol, and at X 5210 for the solution containing the largest 

 percentage of water. 



The marked difference between the ultra-violet spectrum shown by 

 this plate and that shown by Plate 23 in "Hydrates in Aqueous Solution" 

 has already been mentioned. It is evident from the negatives that the 



