142 A STUDY OF THE ABSORPTION SPECTRA. 



nitrates formed, about which we know nothing chemically, but whose 

 existence is shown by a purely physical method the action of these sub- 

 stances on light. 



Whether we shall ever be able to deal with these substances chemically, 

 it is impossible at present to predict on account of their comparative in- 

 stability; the most hopeful methods of studying them being the physical 

 chemical, which can investigate their properties while in solution in the 

 different solvents. 



Rise in temperature causes the general absorption of any salt in water 

 to increase, and also causes the bands to broaden and become more intense. 



The increase in the general absorption with rise in temperature is 

 much greater for concentrated solutions. This also holds true for bands 

 of the second type, and to a small extent for bands of the third type. 



The presence of calcium and aluminium chlorides causes the chromium 

 chloride bands to widen very unsymmetrically on the long wave-length 

 edge with rise in temperature. 



The uranyl chloride bands are shifted towards the red with rise in 

 temperature. No shift for the uranyl nitrate could be detected. Uranyl 

 nitrate, however, dissolved in strong nitric acid showed quite a large shift. 

 The uranyl acetate and sulphate bands were slightly shifted. 



No shift with rise in temperature was noticed for solutions of neodym- 

 ium or erbium salts. When calcium chloride is present the neodymium 

 chloride bands are, however, shifted, and the remarkable fact is observed 

 that the bands then become fainter with rise in temperature. This latter 

 phenomenon is considered to be very important, and it may be that the 

 abnormal Zeeman effect observed by Becquerel is due to the presence of 

 foreign compounds in the tysonite and xenotine crystals. 



BEARING OF THE SOLVATE THEORY OF SOLUTION. 



So much evidence has now been accumulated for the general correct- 

 ness of the theory of solvation in solution, or combination of solvent and 

 dissolved substance, that there can scarcely exist any reasonable doubt as 

 to it representing a great truth of nature. Such being the case, the ques- 

 tion arises whether it helps us in dealing with the phenomena presented 

 by solutions? 



When the study of the properties of solutions led to the discovery of 

 the theory of electrolytic dissociation, it was soon recognized that this 

 theory satisfied the conditions quantitatively only for very dilute solutions. 

 The laws that hold for the properties of such solutions did not hold for 

 solutions that were concentrated. Indeed, they did not apply to solutions 

 of even moderate concentration; not to those solutions with which, for the 

 most part, we actually have to deal in chemistry. If the solutions were 

 fairly concentrated, the laws of osmotic pressure, of lowering of freezing- 

 point, and lowering of vapor-tension did not hold at all. 



Why this was true was not known. It was simply said that the laws 

 of solutions do not hold for concentrated solutions, just as the laws of gases 

 do not hold for concentrated gases, which, of course, was simply an analogy 

 and explained nothing. 



