of Water from Salt- Solutions. 511 



salt into two groups — A, for temperatures 70°, 75°, and 80°; 

 B, for 85°, 90°, and 95° — and add together all the figures in 

 group A and group B, then we find that, in the case of Nad, 

 group A exceeds group B by 20, with KG A = B, and with 

 NaN0 3 and KN0 3 group B exceeds group A by 30 and 

 91 respectively; thus showing that the net result for all 

 strengths of solutions of the salts is that rise of temperature 

 diminishes the restraining effect of the salt in the case of 

 NaCl, does not affect it in the case of KG/ but increases it in 

 the case of NaN0 3 and KN0 3 , and more so with the latter 

 than with the former. I am fully aware of the danger of 

 drawing conclusions from differences so small as these; still 

 the number of experiments in each of the groups (eighteen 

 being the minimum) is probably sufficiently great to justify 

 my doing so. In any case, the accuracy of the results is at 

 least as great as those attainable by the barometric method; 

 and I fail to see that more accurate results can be in any way 

 obtained. 



Comparing now the weak solutions with the strong ones at 

 the low and high temperatures, we find that, taking the 

 figures in Tables II. to V., and subdividing the groups A and 

 B at the dotted lines, and calling these subgroups A w and A,, 



A B 



B w and B s respectively, then the ratio of -r 2 to ^ is : — 



For NaCl, 1:0-983; for KC1, 1 :0'990; for NaN0 3 , 1 : 0*999; 

 for KN0 3 , 1 : T018; that is (in words), concentration in- 

 creasing and temperature rising, the result is diminution of 

 the restraining effect of the salt — considerable in the case of 

 NaCl, appreciable with KG, little or none with NaN0 3 , and, 

 on the contrary, a considerable increase in the restraining 

 effect of KN0 3 . 



Turning now to the results of Tammann (loc. cit.), we find 

 general confirmation of the conclusions arrived at above. 

 Tables IX. and X. contain his results compared with mine 

 for the four salts examined by me. Tammann made his 

 determinations at no definite temperatures, but at irregular 

 intervals on the temperature-scale, and he employed the 

 vapour-pressure of water observed at the same time with the 

 salt-solutions as his temperature-indicator ; nor did he use mo- 

 lecular solutions. The quantity of salt present is expressed 

 in parts per 100 of w^ater; and he gives the observed values 

 of T— T', i. e. {p—p f ) and also what he terms "die relative 

 Spann-kraftserniederungen," or relative diminution of vapour- 



... . (T-T')xlOOO , „ ; 



pressure; this is v ffr , where m= parts of salt per 



