The determination of the ionisation of an aqueous solution
Transactions of the Faraday Society
read a paper oti " T h e Determination of the Tonisation of an Aqueous Solution." I . Introduction. 2. The relation of mobility to ionisation. 3. hutolytic ionisation. 4. -4n ionisation law for dilute solutions. 5 . An ionisation law for concentrated soliitions. k. ~e w vapour-pressure measurement., . 7. The vapour-pressure formula. S. Relation between ionisation and combined water. 9. Test of results by ionic sizes. 10. The idiosyncrasies of potassium nitrate. I I . General observations on
... observations on vapour pressure. I 2 . Partial difiercn tials o f vapour-pressure lowering. 13. Kectilication to meet the case ol KNO,. 14. Conclusions. I . Introductzmt.-To determine the ionisation of a dilute aqueous solution from conductivity data is not a matter of difficulty, and the approximate agreement of the values derived from conductivity, freezingpoint, and V.P. measurements * is now a familiar matter. But even in half-normal solutions the agreement is only approximate, and beyond this point the margin of error becomes large. To obtain accurate values at higher concentrations, not only must the chanxing mobilities of the ions and the amount of their water combination be brought into the account, but also the changes in the composition of the solvent water produced by the solute and the idiosyncrasies oi the solute and of its reactions with the solvent. The group of salts t o which most attenticn has been given in the past is that of the chlorides of potassium, sodium, and lithium, but even in this small group there are marked idiosyncrasies. When we pass t o an allied group-the nitrates-we are met by a phenomenon which introduces new idiosyncrasies, the study of which will help t o elucidate the general problem. The goal which is the aim of physicists is a general ionisation law in which, by giving appropriate values t o the constants, the idiosyncrasies of the various electrolytes can be expressed. The considerations which have been advanced in former papers, together with the further reasons contained in this paper, lead t o the view t h a t * The words " vapour pressure " occur so many times in this paper, that much space will be saved by using the abbreviation V.