198 HYDRATES IN AQUEOUS SOLUTION. 



length. In all other particulars the spectrum of this solution was qualita- 

 tively similar to the spectra of the two preceding solutions. 



The contrasts were more pronounced for the solution of concentration 

 3.128 than for any of the solutions containing smaller amounts of the dehy- 

 drating agent. The spectrum had gradually changed to the form suggested 

 by fig. 71(6). The maxima of absorption had not changed their wave-lengths. 

 The transmission between 0.72 /( and 0.66/i had become so weak that it was 

 difficult to distinguish the maximum at 0.697/*. 



The bands at 0.697/t and 0.661, had coalesced completely for the solution 

 of concentration 3.336 of the calcium chloride; in other words, the region of 

 weak transmission at c had entirely disappeared. [See fig. 71 (c).] The result- 

 ant wide band extended from 0.714/t to 0.654/ with rather abrupt boundaries. 

 The narrow bands at 6245 and 6095 had increased appreciably in depth, and 

 the regions of transmission between 6610, 6405, 6245, and 6095 were much 

 weaker, i. e., the bands were joined by strong general absorption. 



The solution which contained the largest amount of the dehydrating agent 

 showed only one intense band in the red. [See fig. 71 (d).] This band com- 

 prises the interval from 0.724/z to 0.603/z. The brightest spot of transmis- 

 sion in the red was at about 0.739^. Transmission in the yellow-green was 

 noticeably weakened, and the next region of selective absorption commenced 

 near 0.578^, increased to totality at 0.567/*, and then began to fade away 

 again at 0.465;*. All the spectra of the several solutions seemed to begin at 

 the same wave-length, namely, at 0.770/i; i.e., there was no evidence of select- 

 ive absorption in the extreme red. 



The observed lowerings of the freezing-point of aqueous solutions contain- 

 ing both cobalt chloride and calcium chloride are tabulated below. Certain 

 associated data are also given, but the interpretation of the tables will be 

 deferred to a later section, in which the general bearing of all the experi- 

 mental facts on the theory of hydrates will be discussed. 



The solutions whose concentrations are marked (2) or (3) were made up 

 respectively, on November 21 and on December 11, 1905. The freezing-point 

 lowerings indicated by (4), (5), or (6) were measured on December 7, 1905, 

 and February 16 and February 21, 1906. The arithmetical mean of the num- 

 bers in the last column, which correspond to solutions for which either 66 or 

 71 days elapsed between the times when the solutions were made up and when 

 their freezing-point lowerings were determined, is 1.48. The like mean for 

 the remaining solutions, which had stood only 15 days, is 0.655. These two 

 numbers show conclusively that the two solutions both underwent a change 

 with time, and that the number of effective particles in the solutions increased, 

 i.e., marked hydrolysis took place. Compare especially the numbers in the 

 seventh column associated with concentrations 1.950 and 2.091. 



