SALTS OF COBALT. 13 



The paper by Donnan and Bassett 1 should be especially mentioned in 

 connection with the changes in color of cobalt salts. After citing a num- 

 ber of well-known facts, and adding a fairly large number of interesting 

 new ones, they came to the conclusion that the blue color of solutions of 

 cobalt salts is due to the formation of complex anions containing cobalt. 

 Some of the evidence which they furnish merits very careful consideration 

 in this connection. 



Hartley 2 takes issue with the conclusions reached by Donnan and 

 Bassett, interpreting the facts cited or discovered by them in terms of 

 hydration and dehydration. 



COBALT CHLORIDE IN WATER BEER'S LAW. (See Plate 2 A and B.) 



In both A and B, the strip corresponding to the most concentrated 

 solution is adjacent to the numbered scale. The concentrations of the 

 solutions used in making set A were 2.5, 1.88, 1.25, 0.83, 0.58, 0.42, and 0.31, 

 respectively; the corresponding depths of cell were 3, 4, 6, 9, 13, 18, and 24 

 mm. The concentrations used in making set B were 0.83, 0.63, 0.42, 

 0.276, 0.192, 0.139, and 0.104; the depths of cell were the same as in set 

 A. The exposures to the red end of the spectrum were omitted in this 

 case, inasmuch as observations with the direct-vision spectroscope showed 

 that the solutions, at least in such thicknesses of layer as were emploj^ed, 

 were perfectly transparent from the beginning of the orange to the end of 

 the red. The most concentrated solution in layers of 2 cm. or more showed 

 faint traces of bands in the orange and red, but in layers of a few milli- 

 meters thickness these were of course quite invisible. 



The spectrogram shows three regions of absorption: One in the green, 

 middle near X 5200; one in the ultra-violet, with its middle near X 3300; 

 and one in the extreme ultra-violet. The strips corresponding to the four 

 most concentrated solutions of set A show only one absorption band in 

 the ultra-violet, but the strip corresponding to the fifth solution shows 

 transmission between X 2800 and X 3000, and absorption from X 3000 to 

 X 3500; thus making it very evident that there are two regions of absorp- 

 tion. The strips corresponding to the three most concentrated solutions 

 of set B also show very plainly the existence of the band at X 3300, al- 

 though the absorption is not complete even at the middle of the band. 

 In the fourth strip of B, corresponding to a concentration of 0.276 and 

 depth of cell equal to 9 mm., practically all trace of the band has disap- 

 peared, the spark spectrum appearing to shade off uniformly from X 3600 

 to X 2650, where it ends. 



It will be noticed that the intensity of the spark spectrum in the 

 region X 2900 is greater for the strips near the numbered scale than for 

 the fourth, fifth, and sixth strips. This is due partly to a gradual de- 

 crease in the intensity of the spark itself, while the spectrogram was made, 

 produced by a gradual fall in potential of the source of alternating cur- 

 rent operating the coil. That the effect is real, however, is shown by 

 Plate 3 B, where a similar decrease in transmission at X 2900 with dilu- 



1 Journ. Chem. Soc., 81, 939 (1902). J Ibid., 83, 401 (1903). 



