VOL.
xxx.
JANUARY,
1908.
No.
I.
T H E JOURNAL OF THE
American Chemical Society REPORT OF THE INTERNATIONAL COMMITTEE ON ATOMIC WEIGHTS. 1908. Received November 6 , 1907.
Since the preparation of our report for 1907, several important determinations of atomic weights have been published. They are, briefly, a s follows : Nitrogen.-Richards and Forbes' have redetermined the ratio between Ag and NO,, as shown in the composition of silver nitrate. The ratio found, with all corrections applied, is +4g:NO.%= 100: 57.479. Hence, if Ag = 107.930, N = 14,037; and if N = 14.008, Ag = 107.880. In short, the higher atomic weight hitherto assigned t o silver is inconsistent with the lower value for nitrogen as found in several recent investigations. .Culfihur.-Richards and Jones2 have measured the ratio between Ag,SO, and AgCl. From the data obtained, if Ag = 107.930, S = 32.113, a value much higher than that comnionly accepted. If Ag = 107.880. then S = 32.069, which is near the figure given in our former tables. Additional evidence relative t o this constant is much t o be desired, for it influences the determination of many other atomic weights, especially those of the rare-earth metals. Potassium-From the ratios Ag: KCl and AgCl: KCl, Richards and Staehler3 find K = 39.114, when Ag = 107.930 and C1 = 35.473. From the corresponding bromide ratios, with Br = 79.953, Richards and Mueller' find K = 39.1143 and 39.1135. The final result of both researches is K = 39.114, a distinct lowering of the constant in question. h1angunese.--Atomic weight redetermined by Baxter and Hines,s from This Journal, This Journal, This Journal, This Journal, This Journal,
29, 8 0 8 ; and 2 . anorg. Chem., 55, 31. 29, 826; and 2. anorg. Chem., 55, 7 2 . 29, 623; and Ber., 39, 3611. 29, 639; and 2 . anorg. Chem. 53, 423. 28, 1560; and 2. anorg. Chern., 51, 202.
COMMITTEE ON ATOMIC WEIGIITS.
2
analyses of the chloride and bromide. The mean of their very concordant determinations is hln = 54.957, when =\g = io-I ,930. Cobalt.-From new analyses of the chloride, liaxter and Coflin' find CO = 58.997, or 59 in round numbers. This confirms thc earlier determinations by Richards and Baxter. Indium.--hlathers,* from analyses of indium chloride, found I n = 114.88. From the bromide, In = 114.86. The author reconlniends the 107.93, C1 35.473, adoption of the rounded-off value, 114.9, when -4g and Br = 79.953. Tellu~ium.-Xorris,~ b y twelve concordant reductions of the lusic nitrate, zTeO,.HNC>, t o 'reo,, found the atomic weight of telluriu~iito be 127.48, when N = 14.01. With S = 14.04, 're = 127.63, which is in better agreement with other recent deterniinations. The true cause of the difference is not clear. Areodymiwn.-Holmberg4 has redetermined the atomic weight of this element by synthesis of the sulphate from the oxide. In mean, when S = 32.06, Nd = 144.08. This is higher by 0.48 than the value given in our table. DysprosiuwL.-In two series of deterniinations, based upon the ignition t o oxide of the octohydrdted sulphate, Urbain and Uenienitrous; find for the atomic weight of dysprosium, values ranging between 162.29 and 162.75. I n mean, Dy = 162.53. liudiztm.-Madame Curie,6 in a series of three nciv deterininations, has found a more precise value for the atomic weight Of radium. LYorking with material more abundant and pure than t h a t formerly analyzed, she found Ra = 226.18 when Ag = 107.8 and C1 = 35.4. With Ag = 107.93 and C1 = 35.45, Ita = 226.45. This number is higher than her earlier determination b y more than a unit. From the d a t a here given, and from those cited in previous reports, it is evident t h a t the entirc table of atomic weights is in need of revision. The values assigned t o K and Ka are too high; those given t o C1 and S are too low; and these constants affect the determinations of many others. They depend, however, upon the atomic weight of silver, which is prohably, but not certainly, as low as 107.88. I t is well known that work upon these Fundamental constants is now nearing completion in several laboratories, notably under T. L\-. Richards, UT. A . Yoyes, and probably other investigators also. &?thin a few months it should be possible to :
7
This Journal, 28, I 5 8 0 ; and 2. anorg. Cheni., 51, 1 7 1 . This Journal, 29, 485; and Der., 40, 1220. This Journal, 28, 1675. 2. anorg. Chem., 53, 83. Compt. rend., 143, j g 8 . Ibid., 145,422. The atomic weight of radium is also under investigation by Thorpe. ?
'
R E P O R T OF COMMITTEE ON ATOMIC WEIGHTS.
3
enter upon a satisfactory revision of the table, a task which would be unsatisfactory, if undertaken now. I t is true, as Brauner has suggested,' t h a t the present table contains inconsistencies, but they are small in amount, and are due t o inconsistencies in the original data from which the values are derived. In our next report we hope t o recompute the entire table; but meanwhile, awaiting the completion of the researches which we know t o be in progress, we prefer t o leave the table practically International Atomic Weights. Aluminum. . . . . . . . . . . . . . . .A1
27.I
1908.
Molybdenum. . . . . . . . . . . . . .Mo
120.2
Arsenic.. . . . . . . . . . . . . . . . .. A s Barium.. . . . . . . . . . . . . . . .. B a Bismuth.. . . . . . . . . . . . . . ..Bi .. B Boron .. Br Bromi . Cadmium.. . . . . . . . . . . . . . . Cd Carbon . . . . . . . . . . . . . . . . . .C. . . . . . . . . . .Ce Chlorine.. . . . . . . . . . . . . . . ..CI .. . .Cr .. . .co Columbium.. . . . . . . . . . . . . .Cb Copper.. . . . . . . . . . . . . . . . ..Cu Dysprosium . . . . . . . . . . . . . .. =y
Gadolinium.. . . . . . . . . . . . . .Gd
39.9 75.0 137.4 208.0 1 1 .o 79.96 112.4 132.9 40.I I 2 .oo 140.25 35.45
20.
58.7 14.01 191.o 16.00 106.5 31 .o
.................Pt Potassium.. . . . . . . . . . . . . . .K
140.5 103.0
Silver. . . . . . . . . . . . . .
70.0
127.6 159.2
9.1
Lanthanum.. . . . . . . . . . . . . .La Lead ..................... Pb Manganese., . . . . . . . . . . . . . . Mn . Mercury . . . . . . . . . . . . . . . . . Hg Chem.-Ztg., May
11,
1907.
197.2 4.0 1.008
204.I
232.5
115.
171.
126.97 I93.o 55.9 81.8 Vanadium. . . . 138.9
. . . . . . . . . .Sn
200.0
119.0 48.1 184.0 238.5 51.2
128.
206.9
7.03 24.36 55.0
85.5 101.7 150.3 44.1 79.2 28.4 107.93 23.05 87.6 32.06 181.
72.5
Helium.. . . . . . . . . . . . . . . . .. H e Hydrogen H Indium.. . . . . . . . . . . . . . . . .. I n Iodine.. . . . . . . . . . . . . . . . . . .. I Iridium. . . . . . . . . . . . . . . . .. I r
rg4.S 39.15 225.
52.1
59.0 94. 63.6 162.5 166. 152. 19.o 1j6.
96.0 143.6
Ytterbium. . . . . . . . . . . . . . . Y . b Yttrium.. . . . . . . . . . . . . . . . . Y Zinc.. . . . . . . . . . . . . . . . . . . .Zn Zirconium. . . . . . . . . . . . . . . .Zr
173.0
89.0 65.4 90.6
4.
WIL1,IAM A. NCIYES.
unchanged. X conservative policy seems t o be safer than oiie of haste, and the dela! of another !ear will do no harni. One exception to the rule ma! , however, be iliatie. Dysprosiuni, with the atomic weight 162.5, iiiav now he properl! added t o the list of the cheniical elements, and we recornniend its insertion in the table. I t is n i t h the deepest regret t h a t we record the loss, by death, in 1;ebruary last, of our distinguished coileaguc, I'rofessor AIoissan. Thc Chemical Society of I'ariq has designdtcd RIonsieur G.Vrbain a$ his successor upoii t Itis Cotiiiniision. (Signed) 1:. W. CLARKE, \V. OSTWALL), '1'.
E. THORPU,
(.;
tTTKI?.41N.
THE CHOICE OF THE MOST PROBABLE VALUE FOR AN ATOMIC WEIGHT: THE ATOMIC WEIGHT OF HYDROGEN.' B Y \VILLIADf A .
NOPBS.
Received Dersmher 6 , 190;.
.4 large amount of material has been accumulated from which the atomic wieghts of the more important elements can be calculated. X \.cry superficial examination of this material reveals t h e [act t h a t thc experimental results on which our knowledge of these constants is based, vary \.er!. greatly in their \*aluc and t h a t many of the older determinations ha1-c beeti rendered practicall!- worthless by recent work, which has been more carcful and accurate. A s some of thcsc 11cw ticsterminations affect the 1-alues for elements of such fundaniental importance that a recalculation of the whole table of atomic weights will bc necessary in the near future, it seems desirable t o fortnulatc, sonic general principles to aid in thc elirriiiiation of results which ha\-e little or no value and in t h c combination of the results which reniain. Such principles, if they meet with general acceptance, will be of value, not only for the purpose stated b u t also as setting a certain standard which must be attained by future workers in this field, if their work is t o he of permanent Yalue. The most important general principle which has been proposed for the combination of the results of different observers, is the one based on thc mathematical discussion of accidental errors of observation. In accordance with the theor!. of probabilities, these results, if subject only t o accidental errors. should be weighted in in\*erse proportion to tlic'ir I
Dec.
Presented in nhstract a t the S . Y. Meeting of the American Chemical Society, ?s, I C ~ O .
