26 



tions, sufficient to account in a most satisfactory manner for the 

 observed color differences. As a measure of the depressions of 

 the vapor pressure we may use the lowering of the freezing 

 point. The data used in the following discussion are obtained from 

 the work of Jones and Getman/ sometimes by means of extrapola- 

 tion. When this extrapolation is carried over a considerable range 

 the number is indicated as doal)tful by the mark ±. 



The freezing-point depressions of the four bromide solutions are, 

 approximately, KBr, 12°; NH^Br, proba])ly between NaBr and 

 KBr; NaBr, 13^°; LiBr, 19°. 



Similar experiments were made with cupric chloride and solu- 

 tions of the five chlorides, KCl, NH.Cl, NaCl, LiCl, and HCl. Here 

 the colors are not so pronounced as in the previous case. All the 

 solutions are green. No difference could be detected in the first 

 three, but the LiCl solution was decidedly greener and the HCl 

 solution still more so. The freezing-point depressions are, respec- 

 tively, 11.1°, 11.7°, 12.2°, 15.0°, and 18.1°. 



Since solutions of the chlorides of the bivalent metals have 

 much lower vapor pressures than those of the univalent ones, it 

 was expected that they would have a -much greater influence on 

 the color, SrClj, CaCl,, MgCl,, BeCl^ were used. The solutions 

 were in fact much greener than in the preceding case, having an 

 olive tint. They arranged themselves by color in the order given, 

 the last being greenest, and between each solution and the next 

 there was a very marked difference in color. The freezing-point 

 depressions are, approximately, SrCl^, 30° ±; CaCl2, 40°; MgCl.^, 

 48° ±; and BeClg, unknown. Similar experiments were made 

 with one and one-half molecular-normal solutions of these sub- 

 stances, and BaCl2 was added to the list. Here the color dift'er- 

 ences were slight but the solutions could be repeatedly arranged 

 by color in the above order both by myself and by others, 

 BaClj assuming its proper place before SrCl^. The freezing-point 

 depressions are, approximately, BaClj, 9°±; SrCl^, 10°; CaCl.^, 11°; 

 MgCl, 12°. 



Of course these one and one-half normal solutions, on account 

 of less dissociation, have a smaller concentration of chloride ion 

 than the thrice-normal solutions of the chlorides of the first 

 group, but the l^n BeClj had the same color as the Sn KCl. 



Finally aluminum chloride, 3n, was tried. As was to be 



M. c. and Zcit. Phys. Chem. 46, 244 (1903). 



