CHAPTER IX. 

 THE DISSOCIATING POWERS OF FREE AND OF COMBINED WATER. 



BY G. FRED. ORDEMAN. 



INTRODUCTION. 



One of the most interesting and important results established by 

 Jones and Guy, 1 in their work with the radiomicrometer on the absorp- 

 tion spectra of solutions, was the effect of the dissolved substance on 

 the absorption spectra of water. They noted that aqueous solutions 

 of hydrated salts were often more transparent than pure water. The 

 absorption of aqueous solutions of strongly hydrated salts was com- 

 pared by them with the absorption of a layer of water equal in depth 

 to the water in the solution. Similar experiments were carried out 

 with salts which were but slightly hydrated. The concentrated solu- 

 tions of strongly hydrated salts, e. g., 5.3-normal solution of calcium 

 chloride, were found to be more transparent than a comparable quan- 

 tity of pure water. In the case cited, the transparency was 25 per cent 

 greater from 1.05^ to 1.2/*. The solutions of slightly hydrated salts, 

 e. g., potassium chloride, ammonium chloride, and ammonium nitrate, 

 were found to have, in general, the same absorption as water having 

 the same depth as the water in the solution. To account for the facts, 

 they concluded that the combined water has less power to absorb light 

 than free or uncombined water. This is regarded by them as striking 

 evidence that some of the water in the presence of salts which by other 

 methods are shown to hydrate, is different from pure, free, uncombined 

 water. The simplest explanation seems to be that this is combined 

 water or water of hydration. 



The work of Jones and Guy has been repeated and extended by 

 Jones, Shaeffer, and Paulus. 2 Their results are of the same general 

 character. In some instances they found the aqueous solutions of 

 hydrated salts to be 40 per cent more transparent than a comparable 

 quantity of pure water. 



Believing a determination of the power of dissociation of combined 

 water might aid in explaining the above facts, Dr. Shaeffer suggested 

 the use of isochloric solutions in the manner we have adopted. The 

 object of this work has been to ascertain the difference, if any, between 

 the dissociating power of combined water or water of hydration, and the 

 dissociating power of uncombined or free water. 



Carnegie Inst. Wash. Pub. No. 190 (1913). Phys. Zeit., 14, 278 (1913). 2 Ibid., 210 (1915). 



161 



