26 HYDRATES IN AQUEOUS SOLUTION. 



A comparison of the lowerings produced by the chlorides of iron and 

 aluminium, containing 6 molecules of crystal water, with the nitrates of 

 the same metals which have a larger amount of water of crystallization, 

 will show a somewhat greater lowering, at the same concentrations, produced 

 by the nitrates. 



Thus, the relation between the lowering of the freezing-point of water produced 

 by salts and their water of crystallization comes out on every hand, whether 

 we compare the salts of a given acid with different metals, or the salts of the 

 same metal with different acids. 



This line of evidence, together with several others already pointed out 

 in earlier papers, confirms us in the belief of the correctness of the theory 

 advanced by Jones,* to account for the abnormally great depressions of the 

 freezing-point of water, produced by electrolytes, viz., that in solution the dis- 

 solved substance is in combination with a part of the solvent, the amount of the 

 solvent held in combination by the dissolved substance being a function of the con- 

 centration of the solution; in general, increasing with increase in concentration. 



It might be concluded that the facts presented on pages 18 and 19 are at 

 variance with the relations just pointed out between water of crystallization 

 and lowering of freezing-point. That this is not the case will be seen, when 

 we consider that the water of crystallization given above is the amount of 

 water with which the salt crystallizes under ordinary conditions, i. e., under 

 as nearly comparable conditions as possible. 



EXPERIMENTAL WORK. 



The experimental work consisted in measuring the freezing-point of the 

 solution; in determining its conductivity at 0, and in taking its specific 

 gravity. In many cases the refractivity of the solution was also measured. 

 The first three quantities are necessary in order to calculate even the 

 approximate composition of the hydrate formed. 



The freezing-point lowerings produced by the various substances, over 

 as wide range of dilution as was practicable, were measured. The more 

 concentrated solutions were frozen by means of a mixture of solid carbon 

 dioxide and alcohol, the freezing temperatures being determined by means 

 of alcohol thermometers. These temperatures could not be measured 

 more closely than 0.5, and we are not certain of our measurements for 

 the very low temperatures to within 1. Solutions of intermediate concen- 

 tration were frozen by means of a mixture of ice and calcium chloride. For 

 the more dilute solutions, Beckmann thermometers, covering a range of 

 5, 12, and 25, respectively, were used. When the more concentrated solu- 

 tions were frozen, they were removed from the bath of solid carbon dioxide 



*Amer. Chem. Journ., 23, 89 (1900). 



