SALTS OF COBALT. 29 



Bands are seen having their centers at A 6160 and A 6350, with a band 

 extending from A 6650 to X 7150. In the solution containing 7 per cent 

 of water the latter band is broken up into two, with centers at A 6700 and 

 A 7000. The indications are that the band having its center at A 6350 is 

 really made up of two bands, the centers being at A 6300 and A 6430, respec- 

 tively. They are, however, very faint and the slightly greater transpar- 

 ency near A 6360 not very well marked. The three solutions containing 

 the least amount of water were examined with a small, direct-vision, 

 prism spectroscope, having a scale attached so that wave-lengths could 

 be read off directly. These solutions were all transparent in the extreme 

 red, the edge of the absorption band for the solution containing no water 

 being between A 7500 and A 7600. It seemed extremely sharp, but this 

 was undoubtedly due to the small dispersion of a prism spectroscope in 

 this region of the spectrum. 



Here again, as in the case of cobalt chloride in ethyl alcohol and water, 

 we must assume that the system of narrow absorption bands is due in 

 some way to the presence of the water, for the absorption of cobalt bro- 

 mide in acetone showed no sign of breaking up into finer bands with dilu- 

 tion. The group of bands brought out in the bromide solution is quite 

 different from that shown by the corresponding solution of the chloride, 

 a fact which must be accounted for by any theory of the cobalt solutions. 

 It will be recalled also that water added to solutions of cobalt bromide in 

 eth3 r l alcohol did not break up the absorption into finer bands, as was the 

 case with the chloride solution under similar circumstances. 



COBALT NITRATE IN WATER BEER'S LAW. (See Plate 19.) 



The concentrations of the solutions used in making the negative for 

 A, beginning with the one whose spectrum is adjacent to the numbered 

 scale, were 2.05, 1.53, 1.02, 0.683, 0.473, 0.342, and 0.256; the correspond- 

 ing depths of absorbing layer were 3, 4, 6, 9, 13, 18, and 24 mm. For set 

 B the concentrations were 0.683, 0.513, 0.342, 0.227, 0.158, 0.114, and 

 0.085; the depths of absorbing layer were the same as for A. 



The most concentrated solutions were purple in color, from which the 

 color changed to the usual pink with dilution. 



The exposures to the Nernst lamp and spark lasted 1 and 3 minutes, 

 respectively, the width of the slit used being, as usual, 0.01 cm. 



The spectrogram shows two regions of absorption, one in the ultra- 

 violet and one in the green. In A the edge of the ultra-violet band is per- 

 fectly straight and sharp, reminding one of the absorption due to acetone; 

 the limit of transmission being at A 3280, which is also the same as for ace- 

 tone. In B the corresponding edge falls at A 3200, but here we also find 

 a region of transmission located at about A 2650, increasing in width with 

 dilution. A band of absorption is thus outlined, the limits of which are 

 A 2650 and A 3200. A number of spectrograms of nitrates shows that this 

 band is always present. It is hence connected in some way with the radi- 

 cal NO 3 , but B makes it seem improbable that it is due to the free N0 3 ion, 

 since the number of these in the path of the beam of light was increasing 

 in the direction away from the numbered scale, while the absorption band 



