28.6 Mr. W. C. D. Whetham on the 



of the freezing-point, and in Raoult's book on Cryoscopie 



are given the following results obtained bv Loomis for the 

 molecular depressions at a concentration of 0*01 gram-mole- 

 cule of salt in 1000 grams of water, as in themselves trust- 

 worthy and in accordance with the best of other results 

 published before the year 1901. 



Group I. 



Potassium hydrate . . . 3*71 I Nitric acid 3*73 



Hydrochloric acid ... 361 Potassium nitrate 3*46 



Potassium chloride ... 3*60 | Sodium nitrate 3*55 



Sodium chloride 3*67 Ammonium nitrate ... 3*58 



Sulphuric acid 4*49 



Sodium sulphate 5*09 



Group II. 



Calcium chloride 5*04 



Magnesium chloride... 5*08 



Group III. 

 Magnesium sulphate... 2*66 | Zinc sulphate 2*90 



In the first group are substances which are shown by their 

 electrical properties to yield in solution two monovalent ions. 

 On the dissociation theory, therefore, the osmotic pressure 

 effects should, at high dilution, have double their normal 

 value. The normal value for the molecular depression of the 

 freezing-point is 1'857, calculated from the osmotic theory, 

 and confirmed by experiments on dilute aqueous solutions 

 of non-electrolytes. Twice this value is 3*714, a number to 

 which all the observed molecular depressions of substances 

 in Group I. closely approximate. The electrical behaviour 

 of bodies in the second group similarly indicates dissociation 

 into three ions, which would produce a molecular depression 

 of 5*57. The experimental numbers differ from this value 

 by about 10 per cent., but the error is in the right direction, 

 since the electrical conductivities at the concentrations used 

 show that the ionization is still far from complete in salts 

 with divalent ions. The corresponding error is yet greater 

 in salts of the third group, which give two ions both divalent : 

 the molecular depression should be again 3*714, a number 

 exceeding the observed values by about 30 per cent. All 

 discrepancies are thus of the kind to be expected from a con- 

 sideration of the electrical phenomena ; and the salts of the 

 first group, which are about 95 per cent, ionized at the con- 

 centration used in the cryoscopie experiments, yield very 

 concordant results. 



Since the date of BaoulPs book, the most important and 



