194 HYDRATES IN AQUEOUS SOLUTION. 



since the spectrograms of plates 3 (c) and 6 seemed to indicate a change of 

 this kind. In the spectroscope the solution of concentration 1.224 appeared 

 to transmit a spectrum which commenced at about 0.690/t, rose gradually 

 to a maximum of transmission, then decreased to about half the maximum 

 intensity near 0.500/<, and finally faded away very gradually to zero value 

 in the neighborhood of 0.447/t. This type of variation in intensity, which 

 is likewise characteristic of the solution of concentration 1.399, is shown 

 correctly by the photographic strip next to the last, both on plate 3 (c) and 

 on plate 6, only in so far as a weak penumbra is indicated for the green and 

 blue; but the eye did not detect a maximum of general absorption followed 

 by slight increase in intensity of transmission as shorter and shorter wave- 

 lengths were observed, as would be inferred from the photographic strip in 

 question. 



Furthermore, the spectrum of the most concentrated solution of the set 

 began at about 0.6SO/(, rose slowly to a maximum of transmission at 0.608/, 

 decreased gradually for a certain distance, then fell off rather abruptly near 

 0.545/s and finally faded away to invisibility in the vicinity of 0.495/ ( . The 

 colors which were transmitted clearly enough to be recognized, i. e., bright 

 red, orange, yellow, and green, were greatly weakened in intensity as compared 

 with that of the light incident upon the absorbing layer of solution. 



The region of very weak transmission between 0.545/t and 0.495 ( was 

 not shown by the negative from which plates 3 (c) and 6 were reproduced. 

 The conclusion to be drawn, then, is that there was no abrupt change in the 

 general characteristics of the regions of absorption and of transmission of 

 the several solutions of copper bromide studied, and that the lack of complete 

 agreement between the results obtained, on the one hand by the photo- 

 graphic method, and on the other by observations in the case of the two 

 solutions of greatest concentration, was due to the fact that certain parts of 

 the spectra transmitted were of too feeble intensity to affect the photographic 

 film or plate either at all or in a correct manner. Thus, the case of copper 

 bromide furnishes a good illustration of the desirability, if not of the necessity 

 in general, of supplementing photographic work by eye observations. 



COBALT CHLORIDE AND CALCIUM CHLORIDE. [See plates 8, 9 (a), and 9 (6).] 



The spectrogram of plate 8 will be first discussed. The concentration 

 of the cobalt chloride in all of the solutions is a constant 0.271. The concen- 

 trations of the calcium chloride were 0.000, 1.676, 2.514, 2.724, 2.849, 2.919, 

 3.007, 3.128, 3.336, and 3.765. These solutions were made up so as to show 

 successive color changes which, judged by the eye, were as uniform as possible. 

 The colors themselves varied from clear red to deep blue, passing through 

 intermediate shades of garnet, purple, violet, etc, 



