188 DISCUSSION OF EVIDENCE. 



of the salt seems to shift the absorption of the water towards the 

 larger wave-lengths. Rise in temperature and increase in concentra- 

 tion shift the absorption of the salt towards the longer wave-lengths. 

 The effect of rise in temperature and increase in concentration is to 

 simplify the hydrates existing in the solution. Simplifying the resona- 

 tor, then, shifts the absorption towards the red. 



The effect of the salt on the absorption of the water, is the same as 

 rise in temperature and increase in the concentration of the solution 

 on the absorption of the dissolved substance. It may well be that the 

 dissolved substance diminishes the association of the solvent and this 

 simplifies the solvent resonator. This may be true, especially with 

 water of hydration, which is more directly under the influence of the 

 dissolved substance than the free water. 



WORK OF JONES. SHAEFFER, AND PAULUS. 



The result obtained by Jones and Guy was regarded as of such 

 importance in its bearing on the solvate theory of solution, that it 

 was thought desirable to repeat and elaborate with improved method 

 the work which led to it. Certain details of method and manipulation 

 were carefully studied, and the degree of accuracy of the procedure 

 adopted was carefully ascertained. This has all been discussed in 

 detail in the first chapter of this monograph. The non-hydrating or 

 slightly hydrating salts, potassium chloride, ammonium bromide, and 

 sodium nitrate, were studied. The strongly hydrated calcium chloride, 

 magnesium chloride, magnesium bromide, magnesium sulphate, mag- 

 nesium nitrate, zinc sulphate, and zinc nitrate were investigated at 

 varying concentrations and depths of layers. 



Solutions of the strongly hydrated salts have in general greater 

 transparency than pure water, especially at the centers of the absorp- 

 tion bands. As the regions of intense absorption are approached in the 

 longer wave-lengths, the solution is much more transparent than the 

 pure solvent. This difference may amount to as much as 40 per cent. 



The non-hydrated or only slightly hydrated salts give results which, 

 in many respects, are exactly the opposite of those obtained with 

 hydrated salts. In the three cases studied, the solution had greater 

 absorption than the solvent at the centers of the bands. This is pre- 

 cisely the opposite of what was found for the strongly hydrated salts. 

 Regions of the spectrum, for which solutions of hydrated salts were as 

 much as 40 per cent more transparent than the solvent, show for non- 

 hydrated salts that the solution is 40 per cent less transparent. 



It was pointed out that the results obtained could be best explained 

 by the solvate theory of solution. Indeed, this evidence is of the very 

 strongest for that theory. In the solutions studied, more than half 

 of the water was shown to be combined with the dissolved substance. 

 It was shown that this would certainly alter the vibrational frequency 

 or resonance of the absorbing systems. 



