THE JOURNAL QP THE
merican Chemical Society with which has been incorporated the
American Chemical Journal (Founded by Ira Remsen)
REPORT OF THE INTERNATIONAL COMMITTEE ON ATOMIC WEIGHTS FOR 1920-21. Received July 2 2 , 1920.
Since the report of this commietee for the preceding year was prepared, only a few new determinations of atomic weights have been published. They may be summarized as follows. Fluorine.-Moles and Batuecas' have made 23 determinations of the density of methyl fluoride, CHBF. For the weight of a normal liter of the gas they find, in mean, I .54.542 g. From this the molecular weight, 34.024 i s deduced, and F = x 8 996. This rounded off to 19,is the value already accepted. Silicon.-Baxter, U'ea.theril1 and Holmes,2 from analyses of silicon tetrachloride, firid Si = 2 8 . I I I . This determination, however, is not regarded by the authors as final, Its acceptance, therefore, must a.wait confirmation, especially as the ,value is much lower than that given in the present table of atomic ,weights. Zead,--'l'he atomic weight of isotopic lead from thorium minerals has been determined by HGnig~chrnid.~For lead from Norwegian thorite he finds Pb = 207.88 to 2 0 7 . " ) . For lead from Ceylonese thorianite, I
3
3
1-chim. phys., s7, 538 (1919). Bnxter, Weatherill and Holmes, THIS JOURNAL, 42, xrg4 (Igza). H6nigs&rnid, 2. Elehtrochein., asa 91 (1919).
:762
F. W. CLARK€$, L'.' E. THORP€$ AND G. URBAIN.
Pb = 206.88 to 207.24. In thorianite there is evidently a mixture of isotopes, and perhaps also of normal lead. Richards and Sameshima' have examined l e d from a radioactive Japanese mineral. The values found for the atomic weight were 207. I I, 2 0 7 . 1 2 and 207.15. Por ordinary lead. the corresponding value was 207.184. The Japanese material, evidently, contained very little isotopic lead. Tin.--In two papers Brauner and Krepelka2 give new determinat3ons of the atomic weight of tin based upon a,nalyses of the tetrabromide. In the first paper, which is preliminary, they find Sn = 118.70. In the second, by Krepelka alone, the value Sn = rz8.6g9. This confirms the earlier determinations by Briscoe and by Baxter and Starkweather. The work of the last named chemists appears in full in the same number of the JOURNAL. It was noticed in our last report from a preliminary publication. Telliuwiurn.-From analyses of the hydride, TeH2, Bruylants and Michielsen3 find for tellurium the value T e = 127.73, 127.79, and 127.4. The last value they reject. As these determinations are preliminary they need no further consideration now. Scanc%ium.--Meyer and S ~ h w e i g ,after ~ a study of methods for the purification of their material, give determinations of the atomic weight of scandium by the usual sulfate method. They found Sc = 45.0345.37, in m e m 45.23, but conclude that the method is untrustworthy. Honigschmid,j with some of the same material, prepared scandium bromide and determined its ratio to silver. In 18 concordant analyses he found Sc =; 45.099, which may be rounded off to 45.1. This value is accepted by Meyer and Schweig, and should be adopted. %arnarium.--The atomic weight of samarium has been determined by Owens, Balke and Kremers6 by analyses of the anhydrous chloride. From the mean of 18 concordant analyses, Sa = 150.43, in close agreement with the determinations by Stewart and James, 150.44, which was noticed in our report of last year. Apart from the actual determination of atomic weights 3 papers relative to the reduction of the experimental data deserve attention. Guye,' in one piper, has discussed the application of Avogadro's law to this problem. In a second paperS he has examined the data relative to bro1 Richards and Sameshima, THIS JOURNAL, 42, 929 (1920).
* Brauner and Krepelka; Krepelka, ibid.,42, 9x7, 928 (1920). a
Bruylants and Michielsen, Bull. Acad. Belg., Classe des Sciences, Nos.
1x9 (19x9).
Meyer and Schweig, Z.anorg. allgem. Chem., 108,303 (19x9). Honigschmid, 2. Elektrochem., 25, 93 (1919). G Owens, Balke and Kremers, THIS JOURNAL, 42, 5 1 5 (1920). 7 Guye, J . chinz. pltys., 17,171 (1919). 8 Guye, ibid., 17, 1 q r (1919).
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2--3,
REPORT OF INTERNATIOXAI, COMMXTTEE
.
I963
mine and silver. and concludes that Br = 79.92 and Ag = 1 0 7 . 8 7 . The last figure differs from the value 107.88, as given in the table by only o .ox.which is quite within the limits of experimental uncertainty . The third paper. by Van Eaar.1 relates to the method of calculating atomic weights. INTERNATIONAL ATOMXC WEIGHTS.192I Symbol
A.1uminuI-a.......... A1
Atomic weight . 27.1 120.2
Bromine . . . . . . . . . . .Br Cadmium . . . . . . . . . .Cd Calcium ............Ca Carbon . . . . . . . . . . . .C
Chromium .......... Cr Columbium .........Cb Copper .............c u Dysprosium . . . . . . . .Dy Fluorine ............F Gadolinium ......... Gd Germanium .........Ge Glucbum . . . . . . . . . .G1 Gold ...............Au
39.9 74.96 137.37 208 . 0 10.9 79. 92 112.40 40.07 22.005 140.25 132.81 35.46 52.0 58.97 93.1 63.57 162.5 167.7 152.0 19.0
157.3 70.I
72.5 9.1 197.2 4.00 163.5 I
Lead ...............P b Lithium ............Li Lutecium ...........Lu
.008
114.8 126.92 I93 . 1 55.84 82.92 139.0 207.20 6.94 175.0
24.32 54.93 200.6
Mercury . . . . . . . . . . . H g a Van!Laar. J . chim. phys.,
.
Symbol .
Molybdenum Mo Neodymium ............... Nd Neon . . . . . . . . . . . . . . . . . . . .Ne Nickel ...................Ni Niton (radium emanation) ..N t Nitrogen .................N Osmium . . . . . . . . . . . . . . . ..Os Oxygen. .................0 Palladium ................Pd Phosphorus ..............P Platinum ................Pt Potassium ...............K Praseodymium ........... Pr . Radium . . . . . . . . . . . . . . . . Ra Rhodium . . . . . . . . . . . . . . . .R h Rubidium ................R b Ruthenium ...............R u Samarium ................Sa Scandium ................Sc Selenium .................Se Silicon...................Si Silver . . . . . . . . . . . . . . . . . .Ag . Sodium ..................Na Strontium ................Sr SulEur .................... S Tantalum ................Ta Tellurium ................Te Terbium ...... Thorium ........... Thulium .................T m Titanium . . . . . . . . . . . . . . . .Ti Tungsten . . . . . . . . . . . . . . . .W Uranium . . . . . . . . . . . . . . . . U . Vanadium . . . . . . . . . . . . . . .V Xenon ............. Stterbium (Neoytter Yttrium . . . . . . . . . . . . . . . . Y .t Zirconium ................ Zr
266 (1.919).
Atomic weight
.
96.0 144.3 20.2
58.68 222.4 14.008 190.9 16.00
106.7 31.04
195.2 39*I O 140.9 226. 0 102.9 85.45 101.7 150.4 45.1 79.2 28.3 107.88 23. 00 87.63 32.06 181. 5 127.5
159.2 204.0 232.15 168.5 118.7 48.1 184.0 238.2 51.0 130.2
173.5 89.33 6s .37 90.6
17%
MELVIN M. SMITH AND C. JAMES.
The only change in the table of atomic weights is in the case of scaxidium: from 44. x to 45. I ; which appears to be fully justified by the evidence. Signed, F. W. CLARKB,
T.E. THORPB, 6. URBAIN. .^_ [CONTRIBUTION FROM
THE CHEMlCAL LABORATORIES OB
NEW HAMPSHIRS
COLLEGS. 1
A MEW METHOD FOR THE DETERMINATION OF ZIRCONITT BY MELVINM. SMITHAND C. JAMES. Received August 16, 1919.
The increased commercial development of zirconium and its compounds during the last two or three years has called for far more accurate determinations of the dioxide than nearly all the older methods would give. Heretofore, in practically every instance the study of the quantitative separation of an element, keeps ahead of its industrial application. It seems reasonable to state, in the case of the element under discussion, that, up to the present time, there has been only one method, that employing nitroso-phenylhydroxylamine (cupferron), which has given absolutely reliable results. Sodium thiosulfate has probably been the precipitant most corninonly employed until comparatively recently. This method separates zirconium from iron very nicely when carried out under the proper conditions. However, since thorium, aluminum, titanium and phosphoric acid were precipitated by this reagent also, the results obtained were often as much as several per cent. too high. Precipitation as the phosphate by sodium phosphate in the presence of hydrogen peroxide possesses an advantage in that titanium is held up. h considerable excess of hydrogen peroxide must be present and a second precipitation is advised. Unfortunately the solubility of the phosphate is affected by sulfuric acid ; the second precipitation involves several tedious operations and the precipitate is not any too well defined. The cupferron method, which is an excellent one, precipitates both zirconium and titanium together, iron having been previously removed. The solution should have 10% of free sulfuric acid present. If the original material contains only a few per cent. of phosphoric acid, a negligible amount of the latter will be found in the precipitate. The amount of titanirtm dioxide present must be determined either colorimetrically by hydrogen peroxide or by zinc reduction and subsequent titration. Tantalum 2nd columbitim, which occur in some varieties of zirkite, are precipitated by cupferron in the presence of large amounts of conc. sulfuric acid, Tt is, therefore, necessary to make sure that these dements are absent.
