August 1, 1902.] 



SCIENCE. 



171 



other method, is still in the experimental 

 stage. 



Leonard P. Kinnicutt. 



WOKCESTEK POLTTECHNIC INSTITUTE. 



PHYSICS AT THE PITTSBURGH MEETING OF 

 THE AMERICAN ASSOCIATION. 



The meetings of Section B were held in 

 the Middle Lecture Room of the Carnegie 

 Institute. The first session of the Section 

 on Monday, June 30, at 2 :30 p.m., was 

 taken up -with the address of the retiring 

 Vice-President, Professor D. B. Brace, on 

 the subject 'The Group-Velocity and the 

 Wave-Velocity of Light.' Tuesday after- 

 noon the Section adjourned to inspect the 

 AVestinghouse works at East Pittsburgh. 

 Wednesday morning was devoted to a joint 

 session with the American Physical Society 

 and Thursday noon the Section took a final 

 adjournment for the Pittsburgh meeting. 



The Section program was an unusually 

 full one. Its forty-five titles, together with 

 the fourteen on the program of the Ameri- 

 can Physical Society in joint session with 

 Section B, may be roughly classified as 

 follows: 23 were in the domain of electi'ic- 

 ity and magnetism, 22 in optics, 7 in 

 thermodynamics, 4 in general mechanics 

 and 3 in acoustics. The titles and a num- 

 ber of abstracts of the papers presented are 

 . given below. The papers were presented by 

 the writers, except as otherwise indicated. 



Contributions to the Theory of Concentra- 

 tion Cells: Henry S. Carhaet, Univer- 

 sity of Michigan. 



The paper dealt first with concentration 

 cells of the first class, in which two elec- 

 trodes of one metal are immersed in a 

 solution of a salt of the same metal, the. 

 density of the solution being different at 

 the two electrodes. The Nernst theory re- 

 quires that the direction of the E.M.F. 

 within the cell be from the dilute to the 



concentrated solution. The author has dis- 

 covered a cell in which the E.M.F. is 

 directed the other way, viz., from the con- 

 centrated to the dilute solution. It con- 

 sists of nickel electrodes immersed in solu- 

 tions of nickel sulphate or nickel chloride. 



The explanation given depended on the 

 thermal E.M.F. 's at the two electrodes. 

 Curves were exhibited showing that these 

 E.M.F. 's increase with the density of the 

 solution. In most concentration cells the 

 thermal E.M.F. is from the metal to the 

 solution; in nickel cells it is in the other 

 direction. Hence the reverse direction of 

 the E.M.F. of these cells. Application was 

 made of these new facts to the explanation 

 of the dependency of the E.M.F. of 

 the Daniell cell on the density of the two 

 solutions, and to the reversal of the tem- 

 perature coefficient of the Daniell cell when 

 the density of the zinc sulphate solution is 

 only slightly over unity. 



The paper next took up the other class 

 of concentration cells in which the two 

 electrodes are amalgams of a metal of dif- 

 ferent densities, the two amalgams being 

 'immersed in a single solution of the same 

 metal. In these the thermal E.M.F. 's in- 

 crease when the density of the amalgams 

 decreases. The direction of the E.M.F. 

 within the cell from the concentrated to 

 the dilute amalgam is thus explained. 



Further, since the thermal E.M.F. in- 

 creases with the density of the solution, 

 and decreases with the density of the amal- 

 gam, it should be possible to make a concen- 

 tration cell with the denser amalgam in 

 the denser solution and the weaker amal- 

 gam in the weaker solution, so that the 

 E.M.F. of the cell would be zero. This has 

 been foimd to be true. 



Curves of thermal E.M.F. were shown 

 for amalgams of different densities. 



A preliminary paper will be published 

 in the Proceedings of the American Electro- 

 chemical Society. 



