An accurate value of t he faraday has bee n deter min ed by the e lectrolytic dissolution of metall ic silver in aq ueous solu tions of perchloric acid. Standards of electric curren t mass, a nd time a s maintained by t he National Bureau of Standards were utili zed in th~ determinatio ns. Th e electri c c l1l'rent was m easured in terms of th e standards of cle ctromotive force and electrical resistan ce. Silver of hi gh purity, freed fr om oxygen, was used.The value of t he faraday was found to be faraday = 96516.5 ± 2.4 coulombs gram -equival e nt-1 (physical scale). faraday = 96490.0 ± 2.4 coulombs gram -eq ui valent-1 (chemical scale) .These values were obtained usin g 107.9028 ± 0.001 3 and 107.8731 ± 0 .0013 for t h e atomic weigh t of silver on t h e phys ica l and ch e mical scales, resp ectively . ' The electrochemical eq uiva lent of sil ver was found to be electrochemical equivalent of s ilver = 1.117972 ± 0.000019 milligram coulomb-I.This value may be used in a n alternate meth od of defining t h e ampere in absolute value, llamely, t hat steady current which will d issolve 1.117972 milligrams of silver per seco nd a nd de pends only on t he standards of mass and t ime. The indicated un cer tainties are overa ll limi ts of error based on 95 percent co nfidence limi ts for t he mean an d a ll owan ces for t he effects of kn own sources of possible systematic errol'. I . IntroductionThe classic m ethod for the determination of the faraday involves the electrolytic deposition of silver on platinum from an aqueous solu tion of silve)' nitrate. This method h as been extensively studied and tmder closely sp ecified condi tions [1] 1 was used for many years in defining the international amper e. In the original work at th e National Bureau of Standards the national standards of electric current mass, and time were used, and great emphasis wa~ placed on the r eproducibility of the method as a ch eck on the stability of th e existing standards of electromotive for ce (Weston cell) and electrical r esistan ce (mercury ohm). In 1916 Rosa and Vinal [2] sum.-m arized th e work that h ad been done with the silver coulometer not only in yielding a value of the faraday but also in ftttaining conditions wherein reproducible r esults could be obtained. At th at time the consensus was th at tIl e silver coulome ter gave highly accurate as well ftS reproducible r esults and yielded a value of the faraday acc ura te to within 0.001 percent (10 ppm).However , 4 years earlier (in 1912) vVashburn and B ates [3 ] h ad proposed ftn improved 2 iodine coulom-1 F igures in brackets indicate the literature references at th e end of this paper. 2 T he iodine eoulometC!· bad bren studied earlier by H elTOtul [4]. D ann eel 15J, Kreider [6J , and Gallo l7J b ut tbese experimenters did not cla im higb aecm aey for t heir \vork .eter for which high reproducibility and accuracy wer e elaimed. In 1914 Vinal and B ates [8,9] made a direct comparison of the silver and iodine coulometer s in the labor atories of NBS and found that the two...

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The heat of reaction in a lead storage cell involves reactions a t the positive and negative plates and changes in the heat content of sulfuric-acid solutions.

New determinations of the solubility of lead sulfate in sulfuric acid solutions have been made, using diphenylthiocarbazone, commonly called dithizone, as the r eagent. This provides a very sensitive method for small quantities of lead. The eq uivalence point was detected by a simple arrangement of a photronic cell and color filter. The range of concentrations of acid extended from 0.1 to 50 percent H 2S04• Determinations of the lead could be made with an average error not exceeding 0.7 microgram (,..g). Determinations were made at 25° and 0° C, employing solutions, some of which were brought to saturation equilibriu m from undersaturation and others from supersaturation. Important maxima and minima in the solubility curves which had not been reported previously were found. Tables are given for the solubility of the salt at 25° and 0° C. Comp arison is made of the effect of H 2S0 4 on the solubility of lead and mercurous sulfates. The trend of the curves for these is strikingly similar, although the latter is more than 80 times as soluble. CONTENTS Page

A method is described for the preparation of silver‐silver oxide electrodes which are stable and reproducible. When used in cells of the type normalHgfalse(lfalse) , normalHgOfalse(normalsfalse)|normalNaOH,normalaq.|Ag2Ofalse(normalsfalse) , normalAgfalse(normalsfalse) the silver‐silver oxide electrodes give stable potentials over periods of 38 days. No evidence was found that Ag, Ag2O electrodes evolve oxygen, that Ag2O exists in different forms in aqueous solutions at normal temperatures, that Ag2O reverts to a lower oxide, or that imperfections exist in the Ag2O crystal. The free energy and entropy changes for the reaction in the above cell are −11254 cal. and −9.12 e.u., respectively, at 25°C. These values are reasonably consistent with the best available thermodynamic data. The standard electrode potential of the Ag, Ag2O electrode is found to be −0.342 v at 25°C.