August 4, 1911] 



SCIENCE 



159 



reports, or in any journal which might not 

 come to the attention of the abstractors. 



It is expected that the publication of the 

 tables will, after three or four years, become 

 seK-supporting. In the meantime, generous 

 subscriptions have been made by governments, 

 academies, scientific societies and individ- 

 uals throughout the world; but further sub- 

 scriptions must be obtained before the con- 

 tinued success of the project is assured. The 

 general secretary. Dr. Charles Marie, 98 Rue 

 du Cherche-Midi, Paris, and the members of 

 the International Commission serve without 

 remuneration. 



Information concerning the " Annual 

 Tables " or the work of the international 

 committee will be gladly furnished by the 

 undersigned American members of the com- 

 mittee. 



G. N. Lewis, 

 Massachusetts Institute of Technology, 

 Boston, Mass. 



G. F. Hull, 

 Dartmouth College, Hanover, N. S. 

 J. Stieglitz, 

 The University of Chicago, Chicago, III. 



SPECIAL AMTICLES 



CHEMISTRY OF THE SILVER VOLTAMETER* 



Among the questions relating to the chem- 

 istry of the silver voltameter which have been 

 investigated more or less in detail are the fol- 

 lowing: (1) Effect upon electrolyte of the 

 various septa employed in the different types 

 of voltameters to separate the anode electro- 

 lyte from that of the cathode; these septa in- 

 clude (a) filter paper, (&) silk, and (c) porous 

 pots of unglazed porcelain; (2) the effect of 

 various kinds of impurities upon the weight 

 of the silver deposit and the explanation of 

 this effect; (3) the preparation and testing of 

 pure silver nitrate free from traces of im- 

 purities which produce disturbing effects in 

 the voltameter; (4) anode secondary reac- 

 tions; (5) cathode secondary reactions; 

 (6) preparation of the silver anode; (7) purity 

 of the silver deposit. 



■ Read before the Philosophical Society of 

 Washington, May 20, 1911. 



Of these, the first question has been studied 

 in greatest detail, principally because of the 

 fact that it includes the cardinal differences 

 between the various types in use by national 

 standardizing laboratories. It early became 

 evident that the different results obtained 

 with the various types was due principally to 

 the effect produced by these septa, and that 

 two of them introduced errors of much greater 

 magnitude than any ordinary variations in 

 the conditions or in the purity of different 

 samples of even commercially pure silver 

 nitrate. However desirable it might have 

 been to have devoted every energy to the 

 preparation of pure electrolyte and to its 

 protection from contamination during the 

 experiments, it was nevertheless necessary 

 first to show, if possible, just what the nature 

 of the action of the septa might be, since the 

 primary object of the work was a study of the 

 silver voltameter as actually used, and espe- 

 cially as used by the various standardizing 

 laboratories, with a view of determining a 

 uniform type if possible. The results of the 

 investigation of the effect of filter paper 

 seem to show that ordinary filter paper is 

 superficially covered with oxycellulose, which 

 can be extracted with water but which again 

 forms spontaneously when the filter paper is 

 allowed to remain in contact with the air. 

 This oxidation is probably due to fermenta- 

 tion. This oxycellulose solution (colloidal) 

 very readily reduces silver nitrate solution to 

 colloidal metallic silver, which is very similar 

 in properties to the colloidal silyer of Carey 

 Lea. Permanent colloidal solutions of silver 

 have been prepared from concentrated aque- 

 ous extracts of filter paper. This reduction 

 of silver nitrate is probably due to the inter- 

 mediate formation of fur fur aldehyde since 

 the oxycellulose solution is readily decom- 

 posed into this aldehyde by the action of ex- 

 ceedingly dil;ite nitric acid of no greater 

 concentration than that which is probably 

 present in neutral silver nitrate solution (due 

 to slight hydrolysis). Furfuraldehyde, espe- 

 cially the polymerized variety, produces all 

 the peculiar effects which have been observed 

 with filter paper, e. g., imparts to the electro- 



