SALTS OF COBALT. 17 



3. Fairly narrow, intense band, with center at A 6240, which may be 

 seen as far as the strip corresponding to the seventh solution. 



4. Faint, rather wide band, with center at approximately A 6450, and 

 disappearing practically in the strip corresponding to the fourth solution. 

 This band is nowhere clearly separated from the larger one at A 6700. 



5. Intense, wide band, with center at A 6700, which narrows rapidly 

 with dilution, but may be seen quite plainly in the negative strip corre- 

 sponding to the most dilute solution of set A. It is also clearly visible 

 in the strips corresponding to the three most concentrated solutions of 

 set B, while the other bands are seen only with difficulty on this negative. 



The transmission from A 7000 to the end of the visible red is complete 

 for all the solutions referred to on page 245 of "Hydrates in Aqueous 

 Solution." In describing the absorption of cobalt chloride in methyl 

 alcohol, Jones and Uhler say with reference to their observations on the 

 absorption in the red: "If the solution could have been made more con- 

 centrated, or better, if the cell had been deeper, it is extremely probable 

 that all the bands observed in aqueous solutions could have been seen 

 with the alcoholic solution in question." 



The above description of the bands shown on Plate 4, in conjunction 

 with Jones and Uhler 's curves on page 197, and their description of the 

 absorption of cobalt chloride in water given on page 189, will show how 

 very different the absorption spectra in question are. Not only are the 

 locations of the centers of the bands very different, but the character of 

 the group is so changed that it is difficult to see how it can be regarded as 

 the same set of bands. Furthermore, Jones and Uhler's description on 

 page 189, and their curves on page 197, show that the absorption in the 

 concentrated cobalt chloride solution is quite different from that ob- 

 served when a large amount of calcium chloride is added to a dilute solu- 

 tion of the salt. In the first case the three absorption bands noted had 

 their centers at A 7140, A 6760, and A 6360, whereas the curves for the sec- 

 ond case show that these figures correspond to regions of maximum trans- 

 mission. It might be argued that this indicates a shift of the position of 

 the bands with addition of calcium chloride, but this is answered by Jones 

 and Uhler, who find that with the addition of more of this salt the bands 

 simply increase in intensity without change of position. The shift may, 

 however, be due to a change in the concentration of the cobalt salt, but 

 this point has yet to be investigated. 



COBALT CHLORIDE IN ETHYL ALCOHOL BEER'S LAW. (See Plate 5.) 



The concentrations of the solutions used in making the negative for A 

 were 0.15, 0.126, 0.104, 0.086, 0.071, 0.060, and 0.050; the corresponding 

 depths of cell were 8, 9.5, 11.5, 14, 17, 20, and 24 mm., respectively. For B 

 the concentrations were 0.060, 0.050, 0.042, 0.034, 0.028, 0.024, and 0.020; 

 the corresponding depths of cell being the same as used in making set A. 



The color of the solutions as seen in the bottles was deep blue for the 



most concentrated, changing to a light greenish-blue in the most dilute. 



The general absorption observed in the concentrated solutions in methyl 



alcohol was quite absent in ethyl alcohol, so that in making the negatives 



2 



