DEPRESSIONS FOR ELECTROLYTES MACGREGOR. 225 



So do Ponsot's, and probably Wildermann's (not plotted), and I 

 gather from Ponsot's diagrams of Pickering's observations, to 

 which I have not access, that Pickering's also have the leftward 

 tendency. Archibald's and Barnes' curves show less tendency to 

 diverge than those of any other observers. And although this 

 may be partially, it is not wholly, due to their having worked at 

 moderate dilutions only. For in several cases, pointed out below, 

 the curves of other observers start on a divergent course within 

 their limit of dilution. But the fact that their curves usually 

 agree with Loomis's, would lead one to suspect them of a left- 

 ward tendency. 



The divergence, as shown on the diagram, is most marked in 

 the case of highly dissociated electrolytes (NaCl, HC1, etc.) in 

 which, at great dilution, the rate of increase of ionization with 

 dilution is small, the curves being crushed up, therefore, into a 

 small space. But it is obvious also, in the K 9 S0 4 curves (espec- 

 ially Abegg's) and the BaCl 2 curves (including Ponsot's, not 

 shown). And although for MgSO 4 and H 8 P0 4 , whose ionization 

 increases rapidly with dilution, the single curves do not reveal it, 

 the relative positions of the two curves in each case are what 

 they might be expected to be, if they were tending unduly, 

 Jones's to the right, and Loomis's to the left. 



This tendency is explicable at once, when we reflect that as 

 it is equivalent depression that is plotted, the errors of the obser- 

 vations are brought into greater and greater prominence as 

 dilution increases. According, therefore, as the characteristic 

 error of an observer's method of measuring total depression is 

 positive or negative, will his curves of equivalent depression 

 diverge at great dilution to the right or left of their true 

 course. And they must diverge even if the error is very 

 small. 



The equivalent depression curves of single observers are 

 therefore open to grave suspicion at high dilutions ; and since one 

 can never be sure that the errors of different methods will even 

 approximately neutralise one another, mean curves are, at high 



PROC. & TRANS. N. S. INST. Sci., VOL. X. TRANS. O. 



