and its bearing on the Nature of Solutions. 497 



Such numbers can certainly not be accepted as constants, 

 and the values are certainly largely dependent on the nature 

 of the solvent*. 



In the present instance the variation cannot always be 

 taken as a proof of the incorrectness of the osmotic-pressure 

 theory, for it may be perfectly legitimate to attribute it some- 

 times to the various complexity of the molecules of the solvent. 

 But we cannot, however, do so in all cases, as for instance 

 that of formic &c. acids in benzene and acetic acid, where 

 the two solvents have been proved to act normally with 

 the majority of dissolved substances. Yet, in any case, the 

 absence of constancy means the absence of what would have 

 been a strong argument in favour of the theory, and this 

 absence must be felt all the more because there appears to be 

 no simple numerical relationship between the very different 

 values given above. 



Influence of Proportions taken with very Weak Solutions. 



My own recently published results (Chem. Soc. Trans. 1890, 

 p. 331) with sulphuric-acid solutions form, I believe, the only 

 series of determinations as yet made which would, from their 

 number and precision, be at all likely to settle whether the 

 molecular depression is really constant or not with very weak 

 solutions ; and the results here can leave little doubt but that 

 it is not so. 



Between and 9 per cent, solutions the results are repre- 

 sented by what would with rough determinations appear to be 

 a single line of typical straightness. The deviations from 

 straightness in regions below 4 per cent, (about 0*8 H 2 S0 4 to 

 100 H 2 0) are less than o, 02, and would, therefore, not have 

 been revealed by determinations such as have been made by 

 other investigators. From 4 per cent, to the determinations 

 (each being the mean of several observations) which I made 

 show mean error of o, 0008 at most, and the number of points 

 determined is about 80 ; and the results obtained leave no 

 doubt but that the apparently straight line is really composed 

 of four distinct lines, three of which are straight, meeting at 

 (generally) w T ell marked angles at the percentages of 1*0, 

 0'35, and 0*07 respectively. 



The relative magnitude of these changes is best illustrated 

 by drawing a straight line from the freezing-point of water 



* Combining the variations due to different solvents with those due to 

 different dissolved substances, we get a variation of 153,000 per cent. 

 (4°-6 to 0°-003). 



