On the Physical Properties of Aqueous Solutions. 99 



attain to that of the indications of the M'Leod gauge. Thus 

 there is strong evidence that in the investigations of highly 

 rarefied gases in glass vessels there is always an unremoved 

 trace of water which exercises a perturbing influence in- 

 creasing with the rarefaction, and becoming serious in 

 Crookes's experiments at about a millionth of an atmo. In 

 investigating the highest vacua it would seem to be desirable 

 to dispense with glass or to ascertain if glass can be obtained 

 which does not exercise a special " dissolving " action on 

 water-vapour. 



Melbourne, August 1896. 



XV. On the Relation of the Physical Properties of Aqueous 

 Solutions to their state of Ionization. By Prof, J. Gr. Mao 

 GrREGOK, Dalhousie College, Halifax, N.&.* 



[Concluded from p. 55.] 



Relative Values of a Property for a Mixture and for its 

 Constituents. " Corresponding " Solutions. 



AS change of ionization in general occurs on mixing two 

 solutions, it follows from (3; and (4) that the value of 

 a property for a mixture of two solutions having one common 

 ion will differ from the volume-mean, (i'iPi + i , 2 P 2 )/(V L + v 2 ), 

 of its values for the constituents by the amount 



&-*») ,7^7 (*'-«*) + 6-**) ~r («•'-%)• • (5) 



v l ~T V 2 v l~i~ v 2 



The name of " corresponding " solutions has been given to 

 solutions for which this quantity vanishes. In general it 

 will obviously have a value, though that value may be small. 

 In most cases this conclusion is borne out by experience. 

 But Rother has concluded from his observations that, in the 

 case of surface-tension, throughout a wide range of concen- 

 tration, solutions of all concentrations are "corresponding." 

 Were this the case it would throw serious doubt on the pos- 

 sibility of expressing surface-tension in terms of state of 

 ionization. If, however, with the aid of the constants for 

 surface-tension determined above, we compute, in the case of 

 Sodium and Potassium Chlorides, the difference between the 

 value for a mixture and the volume-mean of the values for its 

 constituents, we find it to be beyond the limit of Rother's 

 power of observation. Thus, in the case of his first mixture 

 calculated above, the difference amounts to only OOslo. His 

 * Communicated bv the Author. 



