COBALT CHLORIDE. 187 



solution of the colored salt was measured out into the flask mentioned above. 

 Then a definite volume of the mother-solution of the dehydrating agent 

 was poured into the flask containing the colored liquid. The sum of the 

 two volumes just specified was less* than the fixed capacity of the flask. 

 Finally, the mixture of the mother-solutions was made up to the full volume 

 of the measuring flask by the addition of pure water. In a series of solu- 

 tions containing the same pair of salts, tw T o things were kept constant. First, 

 the mass of colored salt present, and second, the total volume of the solu- 

 tion. The chief variable was the mass of dehydrating agent in the several 

 solutions. As formerly, the color changes were the criteria governing the 

 number and respective concentrations of the solutions of any one series. 

 It was not deemed necessary to determine the specific gravities of the liquids 

 studied. The details relating to the individual salts will not be considered. 



COBALT CHLORIDE. [See plates 2, 3 (a), and 4 (6).] 



The concentrations of the solution were 0.217, 0.379; 0.542; 0.759, 0.976; 

 1.192; 1.409; 1.626; 1.843; 2.060; 2.276; 2.493, and 2.170. Therefore, the 

 first two increments of concentration were each equal to 0.1626, and each 

 of the remaining successive differences equal to 0.2168. 



The number 2.710 belongs to the mother-solution of cobalt chloride. 

 The color of the liquids increased in depth from a delicate pink or rose color 

 to a very dark red. In layers of more than about a centimeter in thick- 

 ness, the more concentrated solutions were opaque to ordinary light. The 

 solution whose concentration was 0.217 normal gave the absorption spec- 

 trum shown by the photographic strip nearest to the numbered scale of plate 

 2. The next strip corresponds to the concentration 0.379, etc., across the 

 spectrogram. Thus, the strip nearest to the comparison spectrum is asso- 

 ciated with the mother-solution. The common depth of the absorbing 

 layers of liquid was 0.67 cm. The line of separation of the half-films comes 

 between the seventh and eighth photographic strips, counting from the side 

 of the numbered scale. The spectrogram shows two regions of absorption, 

 the one in the remote ultra-violet and the other in the blue and green. 



The most dilute solution transmitted the line at 2138.3, but nothing of 

 shorter wave-length. f 



The background stops at about 2265. The most concentrated solution 

 barely transmitted the line of wave-length 2502.1, and cut out practically 

 all the continuous background which is more refrangible than 2748; due 

 regard being had for the successive increments of concentration of the solu- 

 tion. For the most dilute solution, the maximum of absorption in the 



*In special cases shrinkage in volume on mixing would make this statement slightly 

 inexact. 



t All numerical data were derived from the negatives and not from the plates. 



