514 Prof. J . G. MacGregor on a Diagram of 



It would be difficult to draw a mean curve with confidence; 

 but any such curve would run about midway between the 1-2 

 and 2-4 (1'85) lines, would have a slight rightward bending 

 at its upper end, and if produced with diminishing curvature 

 would run out to a point a little to the right of the 1 -2 (1*85) 

 intersection. 



If this intersection were the starting-point of the curve 

 and if there were no association, the curve should lie wholly 

 to the right of the 1—2 (1'85) line. If, as dilution diminished, 

 sufficient doubling of molecules with unchanged mode of 

 ionization should occur, the curve, after first bending away 

 from that line to the right, would change its curvature, bend 

 towards the line and cross it, and then run towards and 

 finally away from the 2-4 line, as the mean curve appears 

 to do. 



As the 2-2 line is far to the left, the mean curve might be 

 accounted for also on the assumption of a very slight forma- 

 tion of double molecules dissociating into two ions — a 

 formation of such molecules so slight as probably to involve 

 no greater variation of the migration numbers with concen- 

 tration than has been observed. 



If the 1-2 (1*86) intersection be assumed as the starting- 

 point of the curve, the mean curve would cut the 2-4 (1'86) 

 line. If, therefore, association in molecules with unchanged 

 mode of ionization were assumed, some formation of triple 

 molecules would be indicated, and if the associated molecules 

 were assumed to dissociate into two free ions, a greater 

 extent of such association would be indicated. Thus with 

 this starting-point less probable assumptions as to association 

 must be made to account for the observations. 



If the 1-2 (1-84), or even the 1-2 (1'845) intersection 

 were taken as the starting-point, the curve must bend con- 

 siderably to the left before running out, of which bending 

 none of the experimental curves give any indication what- 

 ever. 



The most probable conclusion then that we can draw from 

 the observations is that the depression-constant is 1*85, with 

 a limit of error of *01 or perhaps "005, that the electrolyte 

 has single molecules at great dilution, and that as dilution 

 diminishes either double' molecules with unchanged mode of 

 ionization form to a considerable extent, or double molecules 

 dissociating into two ions, to a small extent. 



Loomis's and Barnes's observations on which the NaCl 

 (LB-B) curve is mainly based are also in close agreement; 

 but as Loomis's curve for slightly greater dilution bends 

 slightly to the right, the upper part of the LB-B curve 



