REPORT OF COMAITTEE ON DETERMINATIONS OF ATOMIC WEIGHT, PUBLISHED DURING 1893.’ BY F W CLARKE.
To the Members of the American Chemical society: OUR committee, appointed at the last annual meeting, respectfully submits the following report, showing the advances made in our knowledge of atomic weights during 1893. T h e year has been one of reasonable activity in this branch of investigation, and it is thought that all the work actually published within its limits is here summarized and recorded. One partial exception possibly may be made to this statement. Morley’s work on oxygen, reported orally at the American Association meeting, and at the Chemical Congress in Chicago, is omitted, for only unofficial abstracts of it have yet appeared in print. That work. is of such, fundamental importance that it seems hest to await its completion, rather than to do it possible injustice by fragmentary notices which might be inexact. In the “ S t a s Memorial Lecture,” by Professor Mallet,‘ will be found a remarkably full discussion of the theory or philosophy of atomic weight determinations, which should be carefully read by all students in this domain. Taking the life and work of Stas as text and example, Mallet considers the conditions necessary to the fruitful continuation of that work, and throws out many suggestions of great practical value. H e particularly advocates the multiplication of interdependent data, in order that errors may be eliminated ; and he also recommends the establishment of a special, endowed laboratory, in which a group of trained observers may co-operate towards the attainment of the best results. T h e individual atomic weight determinations of 1893 are subjoined. Boron.-W. Ramsay and Emily Aston? redetermine the atomic weight of boron by two distinct processes, one of them being entirely new. First, with many precautions, they estimate
y
1
Read at the Baltimore meeting Dec 19 1893.
2/
Chrnt Soc , August, 1893
8J
Chem So?, 63,
207,
February, 2893
F. \V. C L A R K E .
I80
I)ETEK3IINATIOSS
the percentage of water in crystallized borax, Na,B,O,, I O H,O : all weights being reduced to vacuum standards. The same reduction is also made in their other series, but as the!. carrj. out the weights to seven decimal places, the corrections applied go farther than is necessary. 111 the subjoiiied tahleh I give the iiearest tctith iiiilligrarii. Wt. SaaB,O,, 10€1,0.
10.3582 5.3440 4.9963 5.7000 5 .3 14.; .1.997' 5,2367
\Vt. S a , H , O ,
l'cr cent H,O.
5.4784 2.8247 2.6379
47,1099
3.0 I O I
47,1912
2.8066
47.18'32
A t . W t . H. I I .04
9i
17.1-lii
10
;7.2025
ro.85 10.8; li>.SS
47.1S6j 10. 88 j 2.6392 47.1521 11.1.9j j 2.7675 Xeaii atomic weight, R=10.921, i 0.010. the second series ot experiments fused borax was distilled
In with hydrochloric acid and methyl alcohol, and the residual sodium chloride was weighed. Results as follows : Wt. Xa,R,O,.
G't. NaCI
2.7595 4.7684 5,2740 , .oj i 7'3 3.2341 1 . 8 7 2j 4.0862 2.371.; 3,4970 2.0266 Mean atomic weight, B=10.9j2,
. i t . \VI. R . 1 1I.OIj 10.92j
111.992 I 0.8 79 l0.9i'r 0.010.
T h e distillations were conducted in soft glass flasks of about cc. capacity, in which the sodium chloride was dried at about 350", and finally weighed. It was found, however, that the flasks \vere somewhat attacked during the process. with liberation of silica, consequently sorile oxygen in the alkali of the glass had been replaced by chlorine, and the weight of the vessel increased. Another set of distillations was, therefore, made with flasks of hard combustioii tubing, axid these \verc slightly attacked also. 100
W t . X:~2r%40,.
j.3118 4.7806 4.9907 4.j 2 3 1 3.3138
\Vt. S:tCI.
3.0761 2.7700 2.8930 2.7360 1.9187 Mean atomic weight, R=10.966,
,At. \v1. I3
I 0.983
10.9jj 10.936 10.968 10.992
f v.ooj.
1 Atomic w e i g h t s used in Kainsay aiid Astoti's calculatioiis : ;\g=107.9~. Sa=n;.o5, C k 3 5 . 4 5 , and B r q g . 9 5
0=16,
Ii=I.ooS,
OF ATOMIC WEIGHT.
181
As a check upon these results the sodium chloride was dissolved in water, and after filtration precipitated with silver nitrate. T h e resulting silver chloride was collected on a Gooch filter, dried a t 2m0,and weighed. Wt. AgCl.
Per cent. C1 iu NaC1.
At. Wt. B. from C1.
7.5259 6.7794 7.0801 6.6960 4.6931
60.493 11.071 60.515 I I .024 60.516 11.003 I I .Of9 60.514 60.479 11.091 Meaii atomic weight, B=II.o~z, f 0.010.
From all these results, and after discussing the supposable sources of error in them, the authors conclude that the atomic weight of boron is very nearly eleven. Still another determination of the atomic weight of boron, by an entirely independent method, is due to Rimbach.' Taking advantage of the fact that methyl orange, as an indicator, is unaffected by free boric acid, he titrated solutions of borax with standardized hydrochloric acid, thus measuring the amount of sodium in the salt and thence calculating the value to be ascertained. T h e borax was prepared in platinum vessels from carefully purified boric acid and sodium carbonate; and the hydrochloric acid used contained I .84983 per cent. of absolute HCl, deteriiiined gravimetrically as silver chloride. In the following table of results the titrated hydrochloric acid is given by weight in grams: Wt.borax.
Wt. H C l . sol
Per cent. Na.2
At. Wt. B.2
12.07081 103.1951 IO.9646 12.07138 158.I503 10.9598 12.07530 155.7271 10.9273 12.075I7 10.9298 104.5448 10.9361 12.07435 54.2571 12.07283 10.9486 155-2307 12.07448 155.2959 10.9356 12.07176 107.6602 10.9571 12.07480 52.0897 10.9330 Calculating f r o m t h e sum of all t h e weights t h e atomic weight of boron becomes 10.945,f 0.003. 10.00214 15.32772 15.08870 10.12930 5.25732 15.04324 15.04761 10.43409 5.047I3
1 Ber. d ckem. Ges., 26, 164, February, 13,&3. 2 Calculations made with O=16, Ag=107.9376.
H=x.w3z (Keiser), N a 3 3 . o g j g . C l = ~ , ~ z gand .
IS2
F
.
\VI
L,ET E K 31 I SAT I O S S
C L A K KF:.
Caibon.-L,educ' has determined the deiisitj of carbon 111011oxide, deducing thence tlie atomic \\eight of carbon. The globe used held 2.9440 of air. Fi1lt:cl with cnrlxm inonoxide the 1at t er we i g-lied 2.8J;n
2.846s 2.8461.j
Neaii, 2.84blj Hence t h e density of CO is 0 . 9 6 j 0 2 , \vlie:i air 0 2 I5.SS.
c=1
If O=16, t h e n
=I,
aiid \ v i t l i
I,(>l~j,
(:=I~.,Io,:.
In a very brief note' n'ankl!-ii :iiinounces that lie has studied a series of hydrocarbons in which the successive steps rise-not by CH,=I.+--bLlt by ( C H I ) . If these observations are
f carbon becoiiies=6. sustained, then the atoiiiic iveigl Cobalt a i d Nickd.--Atomic \\eights determined by Winkler. ' who starts with weighed quantities of nietal, electrolytically deposited. T h i s is then dissolved i n a platinum dish i n pure hydrochloric acid, and the chlorides produced are finally dried for serera1 hours at 150". In one set of experiments tlie chlorine in the chlorides is weighed gral-iiiictricall\., as silver chloride ; in another set it is titrated with a stantlard solution of silver. In the first case we have the ratio R:2XgCl, in the other, R:Ag,. Results as folloivs, for nickel : Wt.
si.
\Vt. ASCI , , , w c i v , ,
0.301 I
1..~621
A I . W t . L-i. .jS .9 I 02
0.2242
! ,089 I
j8.9418
0.5166 0.4879
2.510s
58.8j71 jS.9419 5 S . Y 304
2.3b
0.3S27
j9.s;;1
0.360,;
Mean result. Ni=58.903;. Wt. Xi.
0.1662 0.2129 0.2232 0.5082
0.6079206
0 . 7 7 7 5 2 52 0.8 I 6 2 I 08 1.8j56645 0.531joq0 Mean result. Si=j8.9104.
Cbmpt. m i d . , 1x5,roj2.
2 Phil. Ma,q.. (j)36, 552, DW2rIllbet, 1893 8
[VO!.)
0.662 I 260
0.1453 1
\Vt. A g
0.1812
Ztschv. atiovz. Chem., 4,
I O ,r893.
.It \ V t . S i
.8i.Y 25 j j 8.8665 58.9584
58.8811 j8.96S4 j8.8631
OF ATOMIC WEIGHT.
T h e following data were obtained for cobalt : Wt. co. Wt. AgCl. (grav.) 0.3458 0.3776 0.4493 0.488 0.2856 0.2648 Wt. co. 0.I77804
0.263538 0.245I 24 0.190476 0.266706 0.263538
1.6596 1.8105 2.1521 2.1520
1.3683 I. 2678 Mean result, C0=59.6834. Wt. Ag. (vol.)
0.6418284 0.9514642 0.8855780 0.6866321 0.9629146 0.9503558 Mean result, Co=59.6613.'
At. Wt. Co.
59.6044 59.6609 59.7215 59.6577 59.7dI 59.7480 At. Wt. Co.
59,6495 59.6396 59.5996 59.7311 59.6388 59.7092
I n the case of the cobalt determinations it is of course conceivable that the chloride formed might be contaminated with traces of basic compounds. This question is considered by Winkler in a supplementary communication.* The weighed, electrolytic cobalt, deposited upon the surface of a platinum dish, was treated with a solution of neutral silver sulphate. Silver was thrown down, and was washed, dried, ignited, and weighed. Thus a direct ratio was measured between silver and cobalt, involving no intervention of cobalt chloride, and consequently no error due to basic salts. Results as follows: Wt. co. Wt. As. At. Wt. Co. 0.2549
0.4069
0.9187 1.4691
59.7421 59,6377
T h e precipitated silver, as a check upon its purity, was dissolved in nitric acid, reprecipitated with hydrochloric acid as chloride, and filtered off. T h e filtrate, upon evaporation to dryness, gave traces of residue, containing cobalt. T h e amount of the latter in the first experiment was at most 0.5 milligram, and in the second not over 0.2 milligram. Correcting for these amounts the values found for the atomic weight of cobalt become 59.6356 and 59.6164, respectively. These figures fall within the limits of variation of those found in the first paper, 1 All
2
calculations with Ag=107.66 and Ck35.37
Zfschr.a w g . Chcm., 4, 462, 1893,
184
F . W. C L A R K E .
DETERMINATIONS
and show that the supposed error, if it existed, could not be large. The author admits, however, that the degree of concordance among his experiments is not so great as could be desired. Th.e iiiain purpose of his work was to show the essential constancy of the values, as opposed to tlic views of Kruss concerning the supposed composite nature of nickel and cobalt. .l~o~~bd~nz~nz.-.ltornic weight redeterniiried by Smith and Maas. Sodium molybdate was converted into chloride by heating in a current of pure, dry, gaseous hydrochloric acid. Results a s follows with weights reduced to vacuum standards : \V
