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...
Distillation from perchloric or sulfuric acid solutions, during the gradual addition of hydrochloric or hydrobromic acid to the hot solution (200 0 to 220 0 C), was undertaken to obtain information on the volatility under these conditions of elements that might be encountered in chemical analysis. It was found that, if proper conditions are established, antimony, arsenic, chromium, germanium, osmium, rhenium, ruthenium, and tin can bc quantitatively distilled from perchloric acid, and germanium, arsenic, selenium, tin, antimony, and rhenium from sulfuric acid solutions. Certain others, as bismuth, boron, gold, molybdenum, tellurium, and thallium, may be lost in part from either perchloric or sulfuric acid solutions. From the information obtained, certain precautions against unintentionallosses are evident, and certain possible separations of elements are indicated. C O NTENTS
The viscosities of solutions of sodium dodecyl s ulfate of concentratio ns up to 0.8 per ce nt in distilled water and in 0.01-to 0.12-iVI sodium chloride have been measmed . By int roducing t he concept of a m onomer saturation concentration i t is possible to determi ne t he intrinsic viscosity of the micelles at each concentratio n of sodium chloride. A method for t he experiment a l determination of the monomer saturation concent ration is prese nted. The dependence of t he intrinsic viscosity on the sal t concent rat ion is disc ussed in te rms of eJectrovi sco us a nd hy dration effects . The data indicate tile presence of spherical micelles in t he solu t ions investigated. Introd u ctionSince th e early exp erimen ts of . K rafft [1]1 and McBain [2] on soap solu tions, and th e subscqucnt intcrpretaLjon of th ejr r es ults in terms of th e existence of micelles i n su ch solutions, m any r esearch es [3, 4] h ave b een under ta ken. to investigate th e size and shape of these particles . It is now generally assumed that th ere are at least two types of micelles .In th e concentration range b eL",veen th e onset of micelle formation (about 0.1 to 0.25 percent by weight) and a~out 1 to 2 p er cent! a s~all, highly charo·ed and hIghly conductll1g mlCelle I S though t t o e~ist. This typ e of micelle h as b een discussed at some len.gth by Hartley [5,6]. H e considered them as spher es, but th ere has been 1~0 general ~gree nient on th eir shape. A large mIcelle, havmg a structure discernible by X-ray diffraction, exists at high er concentrations (about 10 pOl·cen t 0:· gr eater). They h ave been diseussed and mvestigated by M cBain [2], H ess [7], Philippoff [8], and others [9]. Harkins [1 0] and his coworkers interpret th eir lat~r X-ray diffraction data for co ncentrated solutJOns III terms of cylindrical micelles. Brady [11], however, utilizing a treatment considered b y 90r1"1n [12], interprets hi~ da~a for concentrate~ sodlUm d
The methods used at the National Bureau of Standards in the analysis of the two Standard Samples of Phosphate Rock, 56a and 120, are described, and a summary of the results obtained by nine cooperating analysts is given. The usual chemical analysis is supplemented by a qualitative spectrochemical examination, and one constituent, boric oxide, has been quantitatively determined by chemical and spectrochemical methods.I. II. III.IV.
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