January 30, 1903.] 



SCIENCE. 



77 



tention of the section as it meets in ^\'asli- 

 ington certain unique opportunities for re- 

 search afforded to the public by the Patent 

 Office and printed patents. 



The relations may be grouped under 

 three heads: 



1. The patent system, its laws, methods 

 and collections, as an organized body of 

 material. 



2. Scientific men as inventors and 

 patentees. 



3. The usefulness of printed patents to 

 scientific men. 



Why the E.M.F. of the Daniell Cell 

 changes ichen the Densities of the So- 

 lutions Change: Henry S. Carhart, 

 University of Michigan. 

 In my paper read at the Pittsburgh meet- 

 ing of the American Association for the 

 Advancement of Science I applied the in- 

 crease of thermo-electromotive force per 

 degree between a metal and a solution of 

 one of its salts with the density of the so- 

 lution to the above pi-oblem. An increase 

 in the density of the zinc sulphate solution 

 increases the back thermo-electromotive 

 force, and so decreases the E.M.F. of the 

 cell as a whole. 



The writer's explanation has been criti- 

 cised on the ground that the heat of forma- 

 tion of both zinc sulphate and copper sul- 

 phate, in aqueous solution, deei'eases as the 

 density increases. The result would ap- 

 pear to be a rational explanation of the 

 change of E.M.F. of the Daniell cell with- 

 oixt any regard to the thermo-electromotive 

 force and its variation with the density of 

 the solution. 



To test this question I have measured the 

 E.M.F. of a Daniell cell of a special form 

 set up with concentrated copper sulphate 

 solution, and, first, with 1/16jV zinc sul- 

 phate solution; and, second, with a normal 

 zinc sulphate solution. The E.M.F. in the 

 second case is less than in the former by 



0.021 volt at 20° C. The difference calcu- 

 lated from the thermo-electromotive forces 

 is 0.029 volt, without taking into account 

 the E.M.F. at the junction of the two solu- 

 tions. The thermal E.M.F. is then abund- 

 antly large enough to explain the phenom- 

 enon. 



Further, the most interesting fact about 

 this is that the observed change of E.M.F. 

 of the Daniell cell is exactly the E.M.F. of 

 a concentration cell set up with the two 

 zinc sulphate solutions. A little considera- 

 tion shows that such should be the case, but 

 I am not aware that this point has been 

 observed before. 



Preliminary Report on an Absolute Meas- 

 urement of the E.M.F. of the Cadmium 

 Cell: Henry S. Carhart and Karl E. 

 GuTHE, University of IMichigan. 

 The paper will describe the preparation 

 of the materials for the cadmium cells 

 used, will give a comparison of their 

 E.M.F. 's, will describe the new electro- 

 dynamometer built for the measurement of 

 the current which produces a fall of po- 

 tential over a known resistance, this fall 

 of potential being compared with the 

 E.M.F. of the cadmium cell. If secured in 

 time, some results of the measurement will 

 also be given. 



The Characteristic Absorption Curves of 

 the Permanganates : B. E. Moore, Uni- 

 versity of Nebraska. 

 A speetrophotometric study of solutions 

 of potassium and zinc permanganate was 

 made. These solutions were prepared 

 nearly saturated (concentration not yet 

 determined). Then solutions diluted 10, 

 100 and 1,000 times were studied. 



For all points in the spectrum the value 

 K (the thiclmess of the standard concentra- 

 tion which would absorb ninety per cent, 

 of light) is calculated. This value changes 

 from point to point in the .spectrum, but 

 should not change at any fixed point in 



