334 CARNEGIE INSTITUTION OF WASHINGTON. 



mass-action and thermodynamic relations; that this activity varies 

 with the concentration differently in the case of different substances; 

 and that for the present it can be determined only empirically for each 

 substance, with the aid of measurements of chemical equilibrium, 

 electromotive force, or freezing-point. 



These results, combined with a consideration of other known facts, 

 make it probable that the behavior of largely ionized substances can 

 be most simply accounted for by the hypothesis that these substances 

 are in reality nearly completely ionized, at any rate up to moderate 

 concentrations, such as 1.0 molal. Correspondingly, the decrease in 

 the conductance-ratio would then be due mainly to a decrease in the 

 mobility of the ions (rather than to a decrease in their number) ; and 

 the decrease in the ion-activity would be due mainly to a physical devi- 

 ation from the laws of perfect solutes, these two physical effects becom- 

 ing large in solutions of ions, in virtue of their large electric charges, 

 at much lower concentrations than in solutions of ordinary un-ionized 

 substances. 



Researches to test more fully the adequacy of this hypothesis of 

 complete ionization are being continued, not only by the electro- 

 motive-force method, but by a more thorough study of the effect of salts 

 on the solubilities of one another. 



During the past year the investigations on electrode potentials or 

 reduction potentials in aqueous solution have been continued. These 

 are the fundamental constants which determine the equilibrium condi- 

 tions of reactions of oxidation and reduction. A research by Dr. 

 Ernest W. Wescott on the reduction potential of plumbous and plumbic 

 compounds has been published, and one by Dr. Charles E. Ruby on 

 that of manganates and permanganates has been completed. Work 

 in this direction on other combinations is still under way. 



Progress has also been made on the other line of research carried on 

 wath the aid of the grants from the Carnegie Institution of Washing- 

 ton — that on the determination of the atomic structure of crystalline 

 substances by X-rays. This work has been pursued by Dr. Duncan 

 Maclnnes at the Massachusetts Institute of Technology and by Dr. 

 Roscoe G. Dickinson at the California Institute of Technology. The 

 former is studying especially the influence of the atomic w^eight or 

 atomic number on the intensity of the reflection, and the latter has 

 been applying the X-ray method to the determination of the structure 

 of substances of somewhat greater crystallographic complexity than 

 most of those previously investigated. Dr. Dickinson has published 

 a research on the structure of wulfenite and scheelite (PbMo04 and 

 CaW04), and has carried on an investigation on the structures of 

 sodium chlorate and bromate (NaClOs and NaBrOs). This work has 

 brought into prominence the great difficulty of locating the atoms 

 w^hose positions are not determined by the crystallographic symmetry. 



