SUKFACE TEIS 7 SION OF AQUEOUS SOLUTIONS. BARNES. 61 



salts up to an average concentration of 0.8 gramme-equivalent 

 per litre at least, can be predicted within the limit of error of 

 tny observations. 



Specific Gravity and Surface Tension. 



Prof. MacGregor 1 has proposed, in the case of simple solutions 

 of electrolytes, so dilute that the ions and the undissociated 

 molecules may be regarded as without mutual action, to express 

 any of their physical properties, such as specific gravity, surface 

 tension, &c , by the following formula : 



P=P W +k (l-) n + l>i n, 



where P is the numerical value of the property for the solution, 

 P w that of the same property for water under the same physical 

 conditions, n the concentration expressed in gramme-equivalents 

 per unit volume, the ionization coefficient of the electrolyte 

 in the solution, and k and I constants, called ionization constants. 



He has also shown how to predict the value of any such 

 property for a mixture of simple solutions, by the aid of the 

 ionization constants determined for the simple solutions. 2 



1 Trans. N. S. Inst. Sci , 9, 219, 1896. 



2 Note by the communicator of the paper. The fact that values of k and I in the 

 above formula can be found which make the formula represent the observed values of 

 a property for simple solutions of an electrolyte has of course little theoretical interest. 

 The ionization coefficient, a, is a complex function of the concentration, n. If expressed 

 in terms of powers of n the expression would involve several powers. (See Trans. N. S. 

 I. S., 9, 112). The above expression for P is thus equivalent to an expression in terms 

 of three or more powers of n with coefficients which are functions of constants deter- 

 mined by the electrical character of the electrolyte and of two additional arbitrary 

 constants. As the concentration curves of specific gravity and surface tension for 

 solutions are but slightly curved, it is thus to be expected that the above expression 

 would represent them. It is of theoretical interest, however, to find whether, when the 

 ionization constants for any property have been determined for simple solutions of 

 two electrolytes, it is possible to predict the value of the property for mixtures by the 

 method referred to. For (1) there are no arbitrary constants in the expression by 

 which the prediction is made, (2) the expression itself is derived from the dissociation 

 theory, and (3) the ionization coefficients of the electrolytes in the mixture, involved in 

 the expression, are determined by a direct application of that theory. I think it well to 

 make this remark because several reviewers of former papers have written under the 

 apprehension that the k's and I's of the expression for the value of a property for a 

 mixture (see p. 65 of this paper) were arbitrary constants determined by the observa- 

 tions on the mixtures. They are, however, the ionization constants .already determined 

 by observations on simple solutions. J. G. M. 



