636 



SCIENCE 



[N. S. Vol. XLVII. No. 1226 



Minnesota. He has been granted a leave of 

 absence for a year in order to take charge of 

 the Research Division of the Gas Offensive 

 at the American University in Washington. 

 Dr. Harry S. Fry, associate professor, has 

 been appointed acting head of the department 

 of chemistry in the University of Cincinnati. 



John F. Guberlet, A.M. ('11, Illinois), 

 Ph.D., '14 (zoology), -wtho since 1915 has been 

 professor of biology at Carroll College, "Wau- 

 kesha, Wisconsin, has recently accepted the 

 position of assistant parasitologist at the 

 Oklahoma Agricultural and Mechanical Col- 

 lege and Experiment Station, at Stillwater, 

 Oklahoma. He will take up his work in Okla- 

 homa on July first. 



Herbert Ruckes, in charge of the dei>art- 

 ment of biology at Grove City College, has re- 

 signed to accept a position in the department 

 of biology at the Agricultural and Mechanical 

 College of Texas. For the past year Mr. 

 Euckes has been carrying on a botanical sur- 

 vey of Mercer county. Pa. 



Professor H. V. Tartar, who for the first 

 five years has been station chemist and asso- 

 ciate professor of agricultural chemistry at the 

 Oregon Agricultural College, has accepted a 

 position in the department of chemistry of the 

 University of Washington at Seattle. 



DISCUSSION AND CORRESPONDENCE 



SOLUTION TENSION AND INDUCTIVITY 



To THE Editor of Science: In Science of 

 May 3, Professor Fernando Sanford, of Stan- 

 ford University, describes a concentration cell 

 in which the direction of deposition is the re- 

 verse of what would be expected if it were 

 previously assumed that the solution tension 

 of the metal is constant for both solvents. 

 He offers an explanation connecting the phe- 

 nomenon with the dielectric property of the 

 solvent. 



In the absence of quantitative data, the 

 great difference known to exist between the 

 solution tensions of a metal in different sol- 

 vents would seem a sufficient explanation. It 

 is true that in the Nemst theory of the con- 

 centration cell prior to 1894 it was supposed 

 that the solution tension of a metal was a con- 



stant property of the metal at a given tempera- 

 ture ; but the supposition was short lived, as it 

 involved a difficulty exactly like the one in 

 question, and led to measurements of solution 

 tension in water and in alcohol,^ so that ap- 

 parently a difficulty has been raised which does 

 not exist. 



It may well be, as Professor Sanford sug- 

 gests, that there is a relation between solution 

 tension and the inductivity of the solvent, 

 just as there must be a relation between in- 

 ductivity and dissociating power, since the 

 forces between charged bodies vary inversely as 

 was remarked by J. J. Thomson and by Nernst. 

 The same consideration would indicate a re- 

 lation between the effective solution pressiu-e 

 of a metal and inductivity, since there could 

 hardly be a more typical condenser than the 

 Helmholtz " double layer." Certainly the 

 quantitative investigation of the matter is 

 greatly to be desired. 



An assumption of constancy of solution 

 tension of a metal in contact with varying con- 

 centrations of its ions in the same solvent is 

 not warranted; although the results of com- 

 putations using the equation for electromotive 

 force. 



RT 

 nF 



\ Pi-piJ 



in which the solution tensions, P^ and P„, are 

 assumed to cancel, and the ionic concentra- 

 tions, m^o.^ and m„a^, are substituted for the 

 osmotic pressures, p^ and p,, would indicate 

 that the simplified equation is at least approxi- 

 mately true. 



On a priori grounds, the assumption is con- 

 tradicted by the probability that the mainten- 

 ance of ionization is largely due to an associa- 

 tion of the charged particle with molecules of 

 the already associated solvent, as well as that 

 large inductivity and association certainly ac- 

 company each other, even if no simple relation- 

 ship exists. So that it seems reasonable to ex- 

 pect, as he points out, that the inductivity of a 

 solvent would change with changing concen- 

 tration of ionic solute. But the change is in 



1 H. C. Jones, Zeitschr. f. physiTc. Chem., 14, 346 

 (1894). 



