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MEMCAL SCHOOL 




SMITHSONIAN MISCELLANEOUS COLLECTIONS 

- '075 

THE CONSTANTS OF NATURE 

PART V 
A RECALCULATION 



OF 



THE ATOMIC WEIGHTS 



BY 



FRANK WIGGLESWORTH CLARKE 

Chief Chemist of the U. S. Geological Survey 



NEW EDITION, REVISED AND ENLARGED 




CITY OF WASHINGTON 

PUBLISHED BY THE SMITHSONIAN INSTITUTION 
1897 



JUDD & DETWEILER, PRINTERS 
WASHINGTON, D. C. 



ADVERTISEMENT. 



The present publication is one of a series devoted to the discussion 
and more precise determination of various u Constants of Nature; " and 
forms the Fifth contribution to that subject published by this Institution. 

The First number of the series, embracing tables of u Specific Gravi- 
ties " and of Melting and Boiling Points of Bodies, prepared by the same 
author, Prof. F. W. Clarke, was published in 1873. The Fourth part of 
the series, comprising a complete digest of the various "Atomic Weight " 
determinations of the chemical elements published since 1814, com- 
mencing with the well-known " Table of Equivalents " by Wollaston 
(given in the Philosophical Transactions for that year), compiled by 
Mr. George F. Becker, was published by the Institution in 1880. The 
present work comprises a very full discussion and recalculation of the 
"Atomic Weights" from all the existing data, and the assignment of 
the most probable value to each of the elements. 

The first edition of this work was published in 1882, and this new 
edition, revised and enlarged by Professor Clarke, contains new informa- 
tion accumulated during the past fifteen years. 

S. P. LANGLEY, 
Secretary of the Smithsonian Institution. 

WASHINGTON, January, 1897. 



13393 



TABLE OF CONTENTS 



PAGE. 

Introduction , i 

Formulae for the Calculation of Probable Error 7 

1 . Oxygen 8 

2. Silver, Potassium, Sodium, Chlorine, Bromine, and Iodine 34 

3. Nitrogen 58 

4. Carbon 72 

5. Sulphur 80 

6. Lithium 84 

7. Rubidium v 87 

8. Caesium 89 

9. Copper 91 

10. Gold 101 

1 1 . Calcium no 

12. Strontium 1 13 

13. Barium 1 18 

14. Lead 127 

15. Glucinum 132 

16. Magnesium 135 

1 7. Zinc 146 

18. Cadmium 156 

19. Mercury ., 166 

20. Boron 171 

21. Aluminum J76 

22. Gallium 181 

23. Indium 182 

24. Thallium 184 

25. Silicon 188 

26. Titanium 190 

27. Germanium 195 

28. Zirconium , 196 

29. Tin 199 

30. Thorium 204 

31. Phosphorus 209 

32. Vanadium 211 

33. Arsenic 213 

34. Antimony 4 216 

35. Bismuth 229 

36. Columbium 234 

37. Tantalum 236 

38. Chromium 238 

39. Molybdenum 250 

40. Tungsten 255 

41 . Uranium 263 

42. Selenium 268 

43. Tellurium 271 

44. Fluorine ...... 277 

(v) 



VI TABLE OF CONTENTS. 

PAGE. 

45. Manganese 282 

46. Iron . 287 

47. Nickel and Cobalt 291 

48. Ruthenium 311 

49. Rhodium , 313 

50. Palladium 315 

51. Osmium , 322 

52. Iridium 325 

53. Platinum 327 

54. Cerium 335 

55. Lanthanum.. 344 

56. The Didymiums 351 

57. Scandium 354 

58. Yttrium 355 

59. Samarium, Gadolinium, "Erbium, and Ytterbium . 359 

60. Terbium, Thulium, Holmium, Dysprosium, etc , . 362 

61. Argon and Helium 363 

Table of Atomic Weights 364 

Index . . 3 6 7 



A RECALCULATION" OF THE ATOMIC WEIGHTS. 



BY FRANK WIGGLESWORTH CLARKE. 



INTRODUCTION. 

In the autumn of 1877 the writer began collecting data relative to 
determinations of atomic weight, with the purpose of preparing a com- 
plete resume of the entire subject, and of recalculating all the estima- 
tions. The work was fairly under way, the material was collected and 
partly discussed, when I received from the Smithsonian Institution a 
manuscript by Professor George F. Becker, entitled " Atomic Weight 
Determinations: a Digest of the Investigations Published since 1814." 
This manuscript, which has since been issued as Part IV of the " Con- 
stants of Nature," covered much of the ground contemplated in my own 
undertaking. It brought together all the evidence, presenting it clearly 
and thoroughly in compact form ; in short, that portion of the task could 
not well be improved upon. Accordingly, I decided to limit my own 
labors to a critical recalculation of the data ; to combine all the figures 
upon a common mathematical basis, and to omit everything which could 
as well be found in Professor Becker's " Digest." 

In due time my work was completed, and early in 1882 it was pub- 
lished. About a year later Meyer and Seubert's recalculation appeared, 
to be followed later still by the less elaborate discussions of Sebelien and 
of Ostwald. All of these works differed from one another in various 
essential particulars, presenting the subject from different points of view, 
and with different methods of calculation. Each one, therefore, has its 
own special points of merit, and, in a sense, reinforces the others. At 
the same time, the scientific activity which they represent shows how 
widespread was the interest in the subject of atomic weights, and how 
fundamentally important these constants undoubtedly are. 

The immediate effect of all these publications was to render manifest 
the imperfections of many of the data, and to point out most emphatic- 
ally in what directions new work needed to be done. Consequently, there 
has been since 1884 an extraordinary activity in the determination of 
atomic weights, and a great mass of new material has accumulated. The 
assimilation of this material, and its combination with the old data, is 
the object of the present volume. 

(1) 



2 THE ATOMIC WEIGHTS. 

At the very beginning of my work, certain fundamental questions con- 
fronted me. Should I treat the investigations of different individuals 
separately, or should I combine. similar data together in a manner irre- 
spective of persons ? For example, ought I, in estimating the atomic 
weight of silver, to take Stas' work by itself, Marignac's work by itself, 
and so. on, and then average the results together; or should I rather 
combine all series of figures relating to the composition of potassium 
chlorate into one mean value, and all the data concerning the composi- 
tion of silver chloride into another mean, and, finally, compute from such 
general means the constant sought to be established ? The latter plan 
was finally adopted ; in fact, it was rendered necessary by the method of 
least squares, which, in a special, limited form, was chosen as the best 
method of dealing with the problem. 

The mode of discussion and combination of results was briefly as 
follows. The formula employed are given in another chapter. I began 
with the ratio between oxygen and hydrogen ; in other words, with the 
atomic weight of oxygen referred to hydrogen as unity. Each series of 
experiments was taken by itself, its arithmetical mean was found, and 
the probable error of that mean was computed. Then the several means 
were combined according to the appropriate formula, each receiving a 
weight dependent upon its probable error. The general mean thus estab- 
lished was taken as the most probable value for the atomic weight of 
oxygen, and, at the same time, its probable error was mathematically 
assigned. 

Next in order came a group of elements which were best discussed 
together, namely, silver, chlorine, potassium, sodium, bromine, and 
iodine. For these elements there were data from many experimenters. 
All similar figures were first reduced to common standards, and then 
the means of individual series were combined into general means. Thus 
all the data w r ere condensed into nineteen ratios, from which several 
independent values for the atomic weight of each element could be 
computed. The probable errors of these values, however, all involved 
the probable error of the atomic weight of oxygen, and were, therefore, 
higher than they would have been had the latter element not entered 
into consideration. Here, then, we have suggested a chief peculiarity 
of this whole revision. The atomic weight of each element involves 
the probable errors of all the other elements to which it is directly or 
indirectly referred. Accordingly, an atomic weight determined by refer- 
ence to elements whose atomic weights have been defectively ascertained 
will receive a high probable error, and its weight, when combined with 
other values, will be relatively low. For example, an atomic weight 
ascertained by direct comparison with hydrogen will, other things being 
equal, have a lower probable error than one which is referred to hydro- 
gen through the intervention of oxygen ; and a metal whose equivalent 
involves only the probable error of oxygen should be more exactly 



INTRODUCTION. 3 

/ 

known than one which depends upon the errors of silver and chlorine. 
These points will appear more clearly evident in the subsequent actual 
discussions. 

But although the discussion of atomic weights is ostensibly mathe- 
matical, it cannot be purely so. Chemical considerations are necessarily 
involved at every turn. In assigning weights to mean values I have 
been, for the most part, rigidly guided by mathematical rules ; but in 
some cases I have been compelled to reject altogether series of data 
which were mathematically excellent, but chemically worthless because 
of constant errors. In certain instances there were grave doubts as to 
whether particular figures should be included or rejected in the calcula- 
tion of means, there having been legitimate reasons for either procedure. 
Probably many chemists would differ with me upon such points of judg- 
ment. In fact, it is doubtful whether any two chemists, working inde- 
pendently, would handle all the data in precisely the same way, or 
combine them so as to produce exactly the same final results. Neither 
would any two mathematicians follow identical rules or reach identical 
conclusions. In calculating the atomic weight of any element those 
values are assigned to other elements which have been determined in 
previous chapters. Hence a variation in the order of discussion might 
lead to slight differences in the final results. 

As a matter of course the data herein combined are of very unequal 
value. In many series of experiments the weighings have been reduced 
to a vacuum standard ; but in most cases chemists have neglected this 
correction altogether. In a majority of instances the errors thus intro- 
duced are slight ; nevertheless they exist, and -interfere more or less with 
all attempts at a theoretical consideration of the results. 

Necessarily, this work omits many details relative to experimental 
methods, and particulars as to the arrangement of special forms of appa- 
ratus. For such details original memoirs must be consulted. Their in- 
clusion here would have rendered the work unwarrantably bulky. There 
is such a thing as over-exhaustiveness of treatment, which is equally 
objectionable with under-thoroughness. 

Of course, none of the results reached in this revision can be consid- 
ered as final. Every one of them is liable to repeated corrections. To 
my mind the real value of the work, great or little, lies in another direc- 
tion. The data have been brought together and reduced to common 
standards, and for each series of figures the probable error has been de- 
termined. Thus far, however much my methods of combination may 
be criticised, I feel that my labors will have been useful. The ground is 
cleared, in a measure, for future experimenters; it is possible to see more 
distinctly what remains to be done ; some clues are furnished as to the 
relative merits of different series of results. 

On the mathematical side my method of recalculation has obvious 
deficiencies. It is special, rather than general, and at some future time, 
when a sufficiently large mass of evidence has accumulated, it must 



4 THE ATOMIC WEIGHTS. 

give way to a more thorough mode of treatment. For example, the ratio 
Ag 2 : BaBr 2 has been used for computing the atomic weight of barium, 
the atomic weights of silver and bromine being supposed to be known. 
But these atomic weights are subject to small errors, and they are super- 
imposed upon that of the ratio itself in the process of calculation. Ob- 
viously, the ratio should contribute to our knowledge of all three of the 
atomic weights involved in it, its error being distributed into three parts 
instead of appearing in one only. The errors may be in part compensa- 
tory ; but that is not certainly known. 

Suppose now that for every element we had a goodly number of atomic 
weight ratios, connecting it with at least a dozen other elements, and all 
measured with reasonable accuracy. These hundreds of ratios could 
then be treated as equations of observation, reduced to linear form, and 
combined by the general method of least squares into normal equations. 
All errors would thus be distributed, never becoming cumulative ; and 
the normal equations, solved once for all, would give the atomic weights 
of all the elements simultaneously. The process would be laborious 
but the result would be the closest possible approach to accuracy. The 
data as yet are inadequate, although some small groups of ratios may 
be handled in that way ; but in time the method is sure to be applied, 
and indeed to be the only general method applicable. Even if every ratio 
was subject to some small constant error, this, balanced against the 
similar errors of other ratios, would become accidental or unsystematic 
with reference to the entire mass of material, and would practically 
vanish from the final means. 

Concerning this subject of constant and accidental errors, a word may 
be said here. My own method of discussion eliminates the latter, which 
are removable by ordinary averaging ; but the constant errors, vicious 
and untractable, remain, at least partially. Still, where many ratios 
are considered, even the systematic errors may in part compensate each 
other, and do less harm than might be expected. They have, moreover, 
a peculiarity which deserves some attention. 

In the discussion of instrumental observations, the systematic errors 
are commonly constant, both as to direction and as to magnitude. They 
are therefore independent of the accidental errors, and computation of 
means leaves them untouched. But in the measurement of chemical 
ratios the constant errors are most frequently due to an impurity in one 
of the materials investigated. If different samples of a substance are 
studied, although all may contain the same impurity, they are not likely 
to contain it in the same amount ; and so the values found for the ratio 
will vary. In other words, such errors may be constant in direction but 
variable in magnitude. That variation appears in the probable error 
computed for the series of observations, diminishes its weight when com- 
bined with other series, and so, in part, corrects itself. It is not removed 
from the result, but it is self-mitigated. The constant errors familiar to 
the physicist and astronomer are obviously of a different order. 



INTRODUCTION. 5 

That all methods of averaging are open to objections, I am of course 
perfectly aware. I also know the doubts which attach to all questions 
of probable error, and to all combinations of data which depend upon 
them. I have, however, preferred to face these objections and to recog- 
nize these doubts rather than to adopt any arbitrary scheme which per- 
mits of a loose selection of data. After all, the use of probable error as 
a means of weighting is but a means of weighting, and perhaps more 
justifiable than any other method of attaining the same result. When 
observations are weighted empirically that is, by individual judg- 
ment far greater dangers arise. Almost unconsciously, the work of a 
famous man is given greater weight than that of some obscure chemist, 
although the latter may ultimately prove to be the best. But the prob- 
able error of a series of measurements is not affected by the glamor of 
great names; and the weight which it assigns to the observations is at 
least as safe as any other. In the long run, I believe it assigns weight 
more accurately, and therefore I have trusted to its indications, not as 
if it were a mathematical fetish, but regarding it as a safe guide, even 
though sometimes fallible. 

In Meyer and Seubert's recalculation, weights are assigned in quite a 
novel manner. In each series of experiments the maximum and mini- 
mum results are given, but instead of the mean there is a value deduced 
from the sum of the weighings that is, each experiment is weighted 
proportionally to the mass of the material handled in it. For this 
method I am unable to find any complete justification. Of course, the 
errors due to the operations of weighing become proportionally smaller 
as the quantity of material increases, but these errors, with modern 
apparatus, are relatively unimportant. The real errors in atomic weight 
determinations are much larger than these, and due to different causes. 
Hence an experiment upon ten grammes of material may be a little better 
than one made upon five grammes, but it is by no means necessarily 
twice as good. The ordinary mean of a series of observations, with its 
measure of concordance, the probable error, is a better value than one 
obtained in the manner just described. If only errors of weighing were 
to be considered, Meyer and Seubert's summation method would be 
valid, but in the presence of other and greater errors it seems to have 
but little real pertinency to the problem at hand. 

In addition to the usual periodicals, the following works have been 
freely used by me in the preparation of this volume: 

BERZELIUS, J. J. Lehrbuch der Chemie. 5 Auflage. Dritter Band. 
SS. 1147-1231. 1845. 

VAN GEUNS, W. A. J. Prceve eener Geschiedenis van de ^Equivalent- 
getallen der Scheikundige Grondstoffen en van hare Soortelijke 
Gewigten in Gasvorm, voornamelijk in Betrekking tot de vier 
Grondstoffen der Bewerktuigde Natuur. Amsterdam, 1853. 



O THE ATOMIC WEIGHTS. 

MULDER, E. Historisch-Kritisch Overzigt van de Bepalingen der JEquiv- 
alent-Gewigten van 13 Eenvoudige Ligchamen. Utrecht, 1853. 

MULDER, L. Historisch-Kritisch Overzigt van de Bepalingen der JLquiv- 
alent-Gewigten van 24 Metalen. Utrecht, 1853. 

OUDEMANS, A. C., Jr. Historisch-Kritisch Overzigt van de Bepaling der 
^Equivalent-Gewigten. van Twee en Twintig Metalen. Leiden, 
1853. 

STAS, J. S. Untersuchungen iiber die Gesetze der Chemischen Propor- 
tionen iiber die Atomgewichte und ihre gegenseitigen Verhalt- 
nisse. Uebersetzt von Dr. L. Aronstein. Leipzig, 1867. 

See also his " Oeuvres Completes," 3 vols., published at Bruxelles 
in 1894. 

MEYER, L., and SEUBERT, K. Die Atomgewichte der Elemente, aus den 
Originalzahlen neu berechnet. Leipzig, 1883. 

SEBELIEN, J. Beitrage zur Geschichte der Atomgewichte. Braunschweig y 

1884. 

OSTWALD, W. Lehrbuch der allgemeinen Chemie. Zweite Aufl. I 
Band. SS. 18-138. Leipzig, 1891. 

The four Dutch monographs above cited are especially valuable. 
They represent a revision of all atomic weight data down to 1853, as 
divided between four writers. 

For the sake of completeness the peculiar volume by Hinrichs * must 
also be cited, although the methods and criticisms embodied in it have 
not been generally endorsed. Hinrichs' point of view is so radically 
different from mine that I have been unable to make use of his discus- 
sions. His objections to the researches of Stas seem to be quite un- 
founded ; and the rejoinders by Spring and by Van der Plaats are suffi- 
ciently thorough. 

* The True Atomic Weight of the Chemical Elements and the Unity of Matter. St. I^ouis, 1894. 
Compare Spring, Chem. Zeitung, Feb. 22, 1893, and Van der Plaats, Compt. Rend., 116, 1362. See 
also a paper by Vogel, with adverse criticisms by Spring and L,. Henry, in Bull. Acad. Bruxelles, 
(3), 26, 469. 



INTRODUCTION. 



FORMULAE FOR THE CALCULATION OF PROBABLE ERROR. 

The formula for the probable error of an arithmetical mean, familiar 
to all physicists, is as follows : 



Here n represents the number of observations or experiments in the 
series, and S the sum of the squares of the variations of the individual 
results from the mean. 

In combining several arithmetical means, representing several series, 
into one general mean, each receives a weight inversely proportional to 
the square of its probable error. Let A, B, C, etc., be such means, and 
a, 6, c their probable errors respectively. Then the general mean is de- 
termined by the formula : 

A JL + __. 

(2.) u = ^'-^'^- 



For the probable error of this general mean we have : 



In the calculation of atomic and molecular weights the following 
formulae are used : Taking, as before, capital letters to represent known 
quantities, and small letters for their probable errors respectively, we 
have for the probable error of the sum or difference of two quantities, 
A and B : 



For the product of A multiplied by B the probable error is 
(5.) e = 



For the product of three quantities, ABC : 



T> 

For a quotient, -T' the probable error becomes 



(7.) 



8 THE ATOMIC WEIGHTS. 

Given a proportion, A : B : : C : x, the probable error of the fourth term 
is as follows : 



This formula is used in nearly every atomic weight calculation, and 
is, therefore, exceptionally important. Rarely a more complicated case 
arises in a proportion of this kind : 



In this proportion the unknown quantity occurs in two terms. Its 
probable error is found by this expression, and is always large : 



(9.) 



When several independent values have been calculated for an atomic 
weight they are treated like means, and combined according to formulae 
(2) and (3). Each final result is, therefore, to be regarded as the general 
or weighted mean of all trustworthy determinations. This method of 
combination is not theoretically perfect, but it seems to be the one most 
available in practice. 



OXYGEN. 

The ratio between oxygen and hydrogen is the foundation upon which 
the entire system of atomic weights is sustained. Hence, the accuracy 
of its determination has, from the beginning, been recognized as of ex- 
treme importance. A trifling error here may become cumulative when 
repeated through a moderate series of other ratios. But few of the 
elements have, so far, been compared directly with th unit, hydrogen ; 
practically all of them are referred to it through the intervention of 
oxygen, and therefore the ratio in question requires discussion before 
any other can be profitably considered. 

Leaving out of account the earliest researches, which now have only 
historical value, the first determinations to be noted are those of Dulong 
and Berzelius,* who, like some of their successors, effected the synthesis 
of water over heated oxide of copper. The essential features of the 
method are in all cases the same. Hydrogen gas is passed over the hot 
oxide, and the water thus formed is collected and weighed. From this 
weight and the loss of weight which the oxide undergoes, the exact com- 

* Thomson's Annals of Philosophy, July, 1821, p. 50. 



OXYGEN. 9 

position of water is readily calculated. Dulong and Berzelius made but 
three experiments, with the following results for the percentages of 
oxygen and hydrogen in water : 

O. H. 

88.942 11.058 

88.809 11.191 

88.954 11.046 

From these figures we get, for the atomic weight of oxygen, the values 

16.124 
15-863 
16. 106 



.Mean, 16.031, db .057. 

As the weighings were not reduced to a vacuum, this correction was 
afterwards applied by Clark,* who showed that these syntheses really 
make = 15.894 ; or, in Berzelian terms, if = 100, H = 12.583. The 
value 15.894, dz .057 we may therefore take as the true result of Dulong 
and Berzelius' experiments, a result curiously close to that reached in 
the latest and best researches. 

In 1842. Dumas f published his elaborate investigation upon the com- 
position of water. The first point was to get pure hydrogen. This gas, 
evolved from zinc and sulphuric acid, might contain oxides of nitrogen ? 
sulphur dioxide, hydrosulphuric acid, and arsenic hydride. These im- 
purities were removed in a series of wash bottles; the H 2 S by a solution 
of lead nitrate, the H 3 As by silver sulphate, and the others by caustic 
potash. Finally, the gas was dried by passing through sulphuric acid, 
or, in some of the experiments, over phosphorus pentoxide. The copper 
oxide was thoroughly dried, and the bulb containing it was weighed. 
By a current of dry hydrogen all the air was expelled from the apparatus, 
and then, for ten or twelve hours, the oxide of copper was heated to dull 
redness in a constant stream of the gas. The reduced copper was allowed 
to cool in an atmosphere of hydrogen. The weighings were made with 
the bulbs exhausted of air. The following table gives the results : 

Column A contains the symbol of the drying substance ; B gives the 
weight of the bulb and copper oxide ; C, the weight of bulb and reduced 
copper ; D, the weight of the vessel used for collecting the water ; E, the 
same, plus the water ; F, the weight of oxygen ; G, the weight of water 
formed ; H, the crude equivalent of H when O = 10,000 ; I, the equiva- 
lent of H, corrected for the air contained in the sulphuric acid employed. 
This correction is not explained, and seems to be questionable. 

* Philosophical Magazine, 3d series, 20, 341. 
fCompt. Rend., 14, 537. 



10 



THE ATOMIC WEIGHTS. 



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OXYGEN. 11 

In the sum total of these nineteen experiments, 840.161 grammes of 
oxygen form 945.439 grammes of water. This gives, in percentages, for 
the composition of water oxygen, 88.864; hydrogen, 11.136. Hence 
the atomic weight of oxygen, calculated in mass, is 15.9608. In the 
following column the values are deduced from the individual data given 
under the headings F and G : 



16.014 
16.024 
15-992 
15.916 
15.916 

15.943 
16.000 

15.892 
15-995 
15-984 
15-958 
15.902 

15.987 
15.926 

15.992 
15-904 
15.900 
16.015 

Mean, 15.9607, with a probable error of .0070. 

In calculating the above column several discrepancies were noted, 
probably due to misprints in the original memoir. On comparing col- 
umns B and C with F, or D and E with G, these anomalies chiefly ap- 
pear. They were' detected and carefully considered in the course of my 
own calculations ; and, I believe, eliminated from the final result. 

The investigation of Erdmann and Marchand * followed closely after 
that of Dumas. The method of procedure was essentially that of the 
latter chemist, differing from it only in points of detail. The hydrogen 
used was prepared from zinc and sulphuric acid, and the zinc, which 
contained traces of carbon, was proved to be free from arsenic and sul- 
phur. The copper oxide was made partly from copper turnings and 
partly by the ignition of the nitrate. The results obtained are given in 
two series, in one of which the weighings were not actually made in 
vacuo, but were, nevertheless, reduced to a vacuum standard. In the 
second series the copper oxide and copper were weighed in vacuo. The 
following table contains the corrected weights of water obtained and of 
the oxygen in it, with the value found for the atomic weight of oxygen 
in a third column. The weights are given in grammes. 

* Journ. fur Prakt. Chem., 1842, bd. 26, s. 461. 



12 THE ATOMIC WEIGHTS. 

First Series. 

Wt. Water. Wt. O. At. Wt. O. 

62.980 55-95 15-917 

95.612 84.924 15.891 

94.523 84.007 15.977 

35-401 3 I -46i I5.97 



Mean, 15.939, =b .014 
Second Series. 

Wt. Water. Wt. O. At. Wt. O. 

41.664 37.34 15.996 

44.089 39-J95 16.018 

53.232 47-3 21 16.011 

55.636 49.460 16.017 

Mean, 16.010, .0036 

The effect of discussing these two series separately is somewhat start- 
ling. It gives to the four experiments in Erdmann and Marchand's 
second group a weight vastly greater than their other four and Dumas' 
nineteen taken together. For so great a superiority as this there is no 
adequate reason ; and it is highly probable that it is due almost entirely 
to fortunate coincidences, rather than to greater accuracy of work. We 
will, therefore, treat Erdmann and Marchand's experiments as one series, 
giving all equal weight, the mean now becoming = 15.975, zh .0113. 
If we take the sum of the eight experiments, 483.137 grammes water 
and 429.352 grammes oxygen, and compute from these figures, then 
O = 15.966. 

It would be easy to point out the sources of error in the foregoing sets 
of determinations, but it is hardly worth while to do so in detail. A few 
leading suggestions are enough for present purposes. First, there is an 
insignificant error due to the occlusion of hydrogen by metallic copper, 
rendering the apparent weight of the latter a trifle too high. Secondly, 
as shown by Dittmar and Henderson, hydrogen dried by passage through 
sulphuric acid becomes perceptibly contaminated with sulphur dioxide. 
In the third place, Morley * has found that hydrogen prepared from zinc 
always contains carbon compounds not removable by absorption and 
washing. Erdmann and Marchand themselves note that their zinc con- 
tained traces of carbon. Finally, copper oxide, especially when pre- 
pared by the ignition of the nitrate, is very apt to contain gaseous impuri- 
ties, and particularly occluded nitrogen. f Any or all of these sources of 
error may have vitiated the three investigations so far considered, but it 
would be useless to speculate as to the extent of their influence. They 

*Amer. Chetn. Journ., 12, 469. 1890. 

f See Richards' work cited in the chapter on copper. 



OXYGEN. 13 

amply account, however, for the differences between the older and the 
later determinations of the constant under discussion. 

Leaving out of account all measurements of the relative densities of 
hydrogen and oxygen, to be considered separately later, the next de- 
termination to be noted is that published by J. Thomsen in 1870.* 
Unfortunately this chemist has not published the details of his work, 
but only the end results. Partly by the oxidation of hydrogen over 
heated copper oxide, and partly by its direct union with oxygen, Thom- 
sen finds that at the latitude of Copenhagen, and at sea level, one litre of 
dry hydrogen at and 760 mm. pressure will form .8041 gramme of 
water. According to Regnault, at this latitude, level, temperature, and 
pressure, a litre of hydrogen weighs .08954 gramme. From these data 
O = 15.9605. It will be seen at once that Thomson's work depends in 
great part upon that of Regnault, and is therefore subject to the correc- 
tions recently applied by Crafts and others to the latter. These cor- 
rections, which will be discussed further on, reduce the value of O from 
15.9605 to 15.91. In order to combine this value with others, it is neces- 
sary to assign it weight arbitrarily, and as Thomsen made eight experi- 
ments, which are said to be concordant, it may be fair, to rank his 
determination with that of Erdmann and Marchand, and to assume for 
it the same probable error. The value 15.91, .0113 will therefore be 
taken as the outcome of Thomsen's research. 

In 1887 Cooke and Richards published the results of their elaborate 
investigation.! These chemists weighed hydrogen, burned it over copper 
oxide, and weighed the water produced. The copper oxide was prepared 
from absolutely pure electrolytic copper, and the hydrogen was obtained 
from three distinct sources, as follows : First, from pure zinc and hydro- 
chloric acid ; second, by electrolysis, in a generator containing dilute 
hydrochloric acid and zinc-mercury amalgam ; third, by the action of 
caustic potash solution upon sheet aluminum. The gas was dried ancl 
purified by passage through a system of tubes and towers containing 
potash, calcium chloride, glass beads drenched with sulphuric acid, and 
phosphorus pentoxide. No impurity could be discovered in it, and even 
nitrogen was sought for spectroscopically without being found. 

The hydrogen was weighed in a glass globe holding nearly five litres 
and weighing 570.5 grammes, which was counterpoised by a second globe 
of exactly the same external volume. Before filling, the globe was ex- 
hausted to within 1 mm. of mercury and weighed. It was then filled 
with hydrogen and weighed' again. The difference between the two 
weights gives the weight of hydrogen taken. 

In burning, the hydrogen was swept from the globe into the combus- 
tion furnace by means of a stream of air which had previously been 
passed over hot reduced copper and hot cupric oxide, then through potash 

*Berichte d. Deutsch. Chem. Gesell., 1870, s. 928. 
fProc. Amer. Acad., 23, 149. Am. Chem. Journ., 10, 81. 



14 THE ATOMIC WEIGHTS. 

bulbs, and finally through a system of driers containing successively 
calcium chloride, sulphuric acid, and phosphorus pentoxide. The water 
formed by the combustion was collected in a condensing tube connected 
with a U tube containing phosphorus pentoxide. The latter was fol- 
lowed by a safety tube containing either calcium chloride or phosphorus 
pentoxide, added to the apparatus to prevent reflex diffusion. Full 
details as to the arrangement and construction of the apparatus are 
given. The final results appear in three series, representing jthe three 
sources from which the hydrogen was obtained. All weights are cor- 
rected to a vacuum. 

First Series. Hydrogen from Zinc and Acid. 

Wt. of H. Wt. H.,0. At. Wt. O. 
.4233 3-8048 15.977 

.4136 3-7094 15.937 

.4213 3-7834 15-960 

.4163 3.7345 15.941 

.413' 3-7085 15-954 



Mean, 15.954, rh .0048 

Second Series. Electrolytic Hydrogen. 

.4112 3-6930 15.962 

.4089 3.6709 15-955 

4261 t , 3.8253 15-955 

4197 3-7651 15-942 

4H4 3.7I97 J 5-953 



Mean, 15.953, =h .0022 

Third Series. Hydrogen from Aluminum. 

.42205 3.7865 15.943 

.4284 3-8436 15-944 

.4205 3-7776 15.967 

43205 3-8748 15.937 

.4153 3-7281 15.954 

.4167 3-7435 15-967 

Mean, 15.952, .0035 
Mean of all as one series, 15.953, =t .2O 

Shortly after the appearance of this paper by Cooke and Richards 
Lord Rayleigh pointed out the fact, already noted by Agamennone, that 
a glass globe when exhausted is sensibly condensed by the pressure of 
the surrounding atmosphere. This fact involves a correction to the fore- 
going data, due to a change in the tare of the globe used, and this cor- 
rection was promptly determined and applied by the authors.* By a 

* Proc. Atner. Acad., 23, 182. Am. Chem. Journ., 10, 191. 



OXYGEN. 15 

careful series of measurements they found that the correction amounted 
to an average increase of 1.98 milligrammes to the weight of hydrogen 
taken in each experiment. Hence equals not 15.953, but 15.869, the 
probable error remaining unchanged. The final result of Cooke and 
Richards' investigation, therefore, is 

O= 15.869, .0020. 

Reiser's determinations of the atomic weight of oxygen were published 
almost simultaneously with Cooke and Richards'. He burned hydrogen 
occluded by palladium, and weighed the water so formed. In a pre- 
liminary paper * the following results are given : 

Wt. of H. Wt. of ttjO. At. Wt. O. 
.65100 5-8i777 I5-873 

.60517 5-41540 15.897 

-33733 3-00655 15.822 

Mean, 15.864, .015 

Not long after the publication of the foregoing data Reiser's full paper 
appeared. f Palladium foil, warmed to a temperature of 250, was satu- 
rated with hydrogen prepared from dilute sulphuric acid and zinc free 
from arsenic. From 100 to 140 grammes of palladium were taken, and 
it was first proved that the metal did not absorb other gases which might 
contaminate the hydrogen. Before charging, the foil was heated to bright 
redness in vacuo. After charging, the tube containing the palladium 
hydride was exhausted by means of a Geissler pump to remove any 
nitrogen which might have been present. In the preliminary investiga- 
tion cited above, the latter precaution was neglected, which may account 
for the low results. 

Between the palladium tube and the combustion tube a U tube was 
interposed, containing phosphorus pentoxide. This was to determine 
the amount of moisture in the hydrogen. The combustion tube was 
filled with granular copper oxide, prepared by reducing the commercial 
oxide in hydrogen, heating the metal so obtained to bright redness in a 
vacuum, and then reoxidizing with pure oxygen. 

Upon warming the palladium tube, which was first carefully weighed, 
hydrogen was given off and allowed to pass into the combustion tube. 
When the greater part of it had been burned, the tube was cut off by 
means of a stopcock and allowed to cool. Meanwhile a stream of nitro- 
gen was passed through the combustion tube, sweeping hydrogen before 
it. This was followed by a current of oxygen, reoxidizing the reduced 
copper; and the copper oxide was finally cooled in a stream of dry air. 
The water produced by the combustion was collected in a weighed bulb 
tube, followed by a weighed U tube containing phosphorus pentoxide. 

* Berichte, 20, 2323. 1887. 

t Amer. Chem. Journ., 10, 249. 1888. 



16 THE ATOMIC WEIGHTS. 

A second phosphorus pentoxide tube served to prevent the sucking back 
of moisture from the external air. The loss in weight of the palladium 
tube, corrected by the gain in weight of the first phosphorus pentoxide, 
gave the weight of hydrogen taken. The gain in weight of the two col- 
lecting tubes gave the weight of water formed. All weights in the follow- 
ing table of results are reduced to a vacuum : 

Wt. of H. Wt. H^O. At. Wt. O. 

.34H5 3-06338 15.943 

.68394 6.14000 15.955 

.65529 5.88200 1 5-9S 2 

.65295 5.86206 15.954 

.66664 5.98116 J 5944 

66647 5-98341 15-955 

.57967 5.20493 I5-958 

.66254 5.94758 15-952 

.87770 7.86775 I5-950 

.77215 6.93036 15.951 



Mean, 15.9514, .0011. 

In sum, 6.55880 grammes' of hydrogen gave 52.30383 of water, whence 
O = 15.9492. 

In March, 1889, Lord Rayleigh * published a few determinations of the 
atomic weight of oxygen obtained by still a new method. Pure hydrogen 
and pure oxygen were both weighed in glass globes. From these they 
passed into a mixing chamber, and thence into a eudiometer, where they 
were gradually exploded by a series of electric sparks. After explosion 
the residual gas remaining in the eudiometer was determined and meas- 
ured. The results, given without weighings or explicit details, are as 
follows : 

15.93 
15-98 

15-98 
15-93 
15.92 



Mean, 15.948, .009 

Correcting this result for shrinkage of the globes and consequent change 
of tare, it becomes = 15.89, .009. 

In the same month that Lord Rayleigh's paper appeared, Noyes f pub- 
lished his first series of determinations. His plan was to pass hydrogen 
into an apparatus containing hot copper oxide } condensing the water 
formed in the same apparatus, and from the gain in weight of the latter 
getting the weight of the hydrogen absorbed. The apparatus devised for 

*Proc. Roy. Soc., 45, 425. 

f Amer. Chem. Journ., n, 155. 1889. 



OXYGEN. 17 

this purpose consisted essentially of a glass bulb of 30 to 50 cc. capacity, 
with a stopcock tube on one side and a sealed condensing tube on the 
other. In weighing, it was counterpoised by another apparatus of nearly 
the same volume but somewhat less weight, in order to obviate reduc- 
tions to a vacuum. After filling the bulb with commercial copper oxide 
(90 to 150 grammes), the apparatus was heated in an airbath, exhausted 
by means of a Sprengel pump, cooled, and weighed. It was next re- 
placed in the airbath, again heated, and connected with an apparatus 
delivering purified hydrogen. When a suitable amount of the latter had 
been admitted, the stopcock was closed, and the heating continued long 
enough to convert all gaseous hydrogen within it into water. The appa- 
ratus was then cooled and weighed, after which it was connected with* a 
Sprengel pump, in order to extract the small quantity of nitrogen which 
was always present. The latter was pumped out into a eudiometer, 
where it was measured and examined. The gain in weight of the appa- 
ratus, less the weight of this very slight impurity, gave the weight of 
hydrogen oxidized. 

The next step in the process consisted in heating the apparatus to expel 
water, and weighing again. After this, pure oxygen was admitted and 
the heating was resumed, so as to oxidize the traces of hydrogen which 
had been retained by the copper. Again the apparatus was cooled and 
weighed, and then reheated, when the water formed was received in a 
bulb filled with phosphorus pentoxide, and the gaseous contents were 
collected in a eudiometer. On cooling and weighing the apparatus, the 
loss of weight, less the weight of gases pumped out, gave the amount of 
water produced by the traces of residual hydrogen under consideration. 
This weight, added to the loss of weight when the original water was 
expelled, gives the weight of oxygen taken away from the copper oxide. 
Having thus the weight of hydrogen and the weight of oxygen, the 
atomic weight sought for follows. Six results are given, but as they are 
repeated, with corrections, in Noyes' second paper, they need not be 
considered now. 

Noyes' methods were almost immediately criticised by Johnson,* who 
suggested several sources of error. This chemist had already shown in 
an earlier paper f that copper reduced in hydrogen persistently retains 
traces of the latter, and also that when the reduction is effected below 
700, water is retained too. The possible presence of sulphur in the 
copper oxide was furthermore mentioned. Errors from these sources 
would tend to make the apparent atomic weight of oxygen too low. 

In his second paper J Noyes replies to the foregoing criticisms, and 
shows that they carry no weight, at least so far as his work is concerned. 
He also describes a number of experiments in which oxides other than 
copper oxide were tried, but without distinct success, and he gives fuller 

*Chem. News, 59, 272. 

f Journ. Chem. Soc., May, 1879. 

jAmer. Chem. Journ., 12, 441. 1890. 



18 THE ATOMIC WEIGHTS. 

details as to manipulations and materials. His final results are in four 
series, as follows : 

First Series. Hydrogen from Zinc and Hydrochloric Acid. 

WL of H. Wt. of O. At. Wt. O. 

9443 7-5000 15.885 

.6744 5-3555 15-882 

.7866 6.2569 I 5-99 

55 21 4.3903 15.904 

.4274 3-3997 15-909 

.8265 6.5686 15-895 

Mean, 15.8973,^.0032. 
> 

This series appeared in the earlier paper, but with an error which is 
here corrected. 

Second Series. Electrolytic Hydrogen, Dried by Phosphorus Pentoxide. 

Wt. of H. Wt. of O. At. Wt. O. 

.5044 4.0095 15-898 

6325 5-0385 15-932 

.6349 5-5i7 15-913 

.55 6 4 4.4175 15-879 

7335 5-8224 15.876 

5.3181 15.885 



Mean, 15.8971,^.0064. 

Third Series. Electrolytic Hydrogen, Dried by Passage Through a Tube 

Packed with Sodium Wire. 

Wt. of H. Wt. of O. At. Wt. O. 

.9323 7.4077 15-891 

9952 7-9045 15 885 

.3268 2.5977 15.898 

.7907 6.2798 15.884 

.7762 6.1671 15.891 

1.1221 8.9131 15-887 



Mean, 15.8893, i .0014 

At the end of this series it was found that the hydrogen contained a 
trace of water, estimated to be equivalent to an excess of three milli- 
grammes in the total h}^drogen of the six experiments. Correcting for 
this, the mean becomes = 15.899. 

Fourth Series. Electrolytic Hydrogen, Dried over Freshly Sublimed Phos- 
phorus Pentoxide. 

Wt. of H. Wt. of O. At. Wt. O. 

1.0444 8.3017 15-898 

.7704 6.1233 15.896 

.8231 6.5421 15.896 

.8872 7.0490 15.890 

9993 7-9403 15-892 

1.1910 9.4595 15.885 

Mean, 15.8929, .0013 



OXYGEN. 19 

The mean of all the twenty-four determinations, taken as one series, 
with the correction to the third series included, is = 15.8966, .0017. 
In sum, there were consumed 18.5983 grammes of hydrogen and 147.8145 
of oxygen ; whence = 15.8955. 

Dittmar and Henderson,* who effected the synthesis of water over 
copper oxide by what was essentially the old method, begin their memoir 
with an exhaustive criticism of the work done by Dumas and by Erd- 
mann and Marchand. They show, as I have already mentioned, that 
hydrogen dried by sulphuric acid becomes contaminated with sulphur 
dioxide, and also that a gas passed over calcium chloride may still retain 
as much as one milligramme of water per litre. Fused caustic potash 
they found to dry a gas quite completely. 

In their first series of syntheses, Dittmar and Henderson generated 
their hydrogen from zinc and acid, sometimes hydrochloric and some- 
times sulphuric, and dried it by passage, first through cotton wool, then 
through vitrioled pumice, then over red-hot metallic copper to remove 
oxygen. In later experiments it first traversed a column of fragments 
of caustic soda to remove antimony derived from the zinc. The oxide 
of copper used was prepared by heating chemically pure copper clip- 
pings in a muffle, and was practically free from .sulphur. In weighing 
the several portions of apparatus it was tared with somewhat lighter 
similar pieces of as nearly as possible the same displacement. The re- 
sults of this series of experiments, which are vitiated by the presence, 
unsuspected at first, of sulphur dioxide in the hydrogen, are stated in 
values of H when = 16, but in the following table .have been recalcu- 
lated to the usual unit : 

Wt. of Water. Wt. of O. At. Wt. O. 

4.7980 4.26195 I5-9 01 

7.55025 6.71315 16.039 

6.2372 5-53935 15.875 

11.29325 10.03585 J 5-963 

11.6728 10.3715 I5-940 

11.8433 10.5256 15.976 

11.7317 10.4243 15-947 

19.2404 17.0926 15.916 

20.83435 18.5234 16.031 

17.40235 15.4598 I5-9I7 

19.2631 i7."485 x 5-934 

Mean, 15.949, =b .0103. 

Reducing to a vacuum, this becomes 15.843, while a correction for the 
sulphur dioxide estimated to be present in the hydrogen brings the value 

* Proc. Roy. Soc. Glasgow, 22, 33. Communicated Dec. 17, 1890. 



20 THE ATOMIC WEIGHTS. 

up again to 15.865. Still another correction is suggested, namely, that 
as the reduced copper in the combustion tube, before weighing, was ex- 
posed to a long-continued current of dry air, it may have taken up traces 
of oxygen chemically, thereby increasing its weight. As this correction, 
however, is quantitatively uncertain, it may be neglected here, and the 
result of this series will be taken as = 15.865, .0103. Its weight, 
relatively to some other series of experiments, is evidently small. 

In their second and final series Dittmar and Henderson dried their 
hydrogen, after deoxidation by red-hot copper, over caustic potash and 
subsequently phosphorus pentoxide. The copper oxide and copper of 
the combustion tube were both weighed in vacuo. The results were as 
follows, vacuum weights being given : 

Wt. Water. Wt. O. At. Wt. O. 

19.2057 17-0530 15.843 

19-5211 17-3342 [15-853] 

19.4672 17.2882 15.868 

22.9272 20.3540 15.820 

23.0080 20.4421 [15.934] 

23.4951 26.8639 15.859 

23.5612 20.9226 [15-859] 

23.7542 ^ 21.0957 15.870 

23.6568 21.8994 15.884 

23.6179 21.8593 15.848 

24.6021 21.8499 15.878 

24.3047 21.5788 15.832 

23.6172 20.9709 15.849 



Mean, 15.861,^.0052. 

The authors reject the three bracketed determinations, because of 
irregularities in the course of the experiments. The mean of the ten 
remaining determinations is 15.855, .0044. Both means, however, 
have to be corrected for the minute trace of hydrogen occluded by the 
reduced copper. This correction, experimentally measured, amounts to 
-|- .006. Hence the mean of all the experiments in the series becomes 
15.867, .0052, and of the ten accepted experiments, 15.861, .0044. 
The authors themselves select out seven experiments, giving a corrected 
mean of 15.866, which they regard as the best value. Taking all their 
evidence, their two series combine thus : 

First series 15.865, .0103 

Second series 15.867, .0052 

General mean 15.8667, .0046 

Leduc,* who also effected the synthesis of water over copper oxide, 

* Compt. Rend., 115, 41. 1892. 



OXYGEN. 21 

following Dumas' method with slight modifications, gives the results of 
only two experiments, as follows : 

Wt. Water. Wt. O. At. Wt. O. 

22.1632 19.6844 15.882 

19.7403 17.5323 15-880 



Mean, 15.881 

These experiments we may arbitrarily assign equal weight with two 
in Dittmar and Henderson's later series, when the result becomes 
15.881, =b .0132, the value to be accepted. Leduc states that his copper 
oxide, which was reduced at as low a temperature as possible, was pre- 
pared by heating clippings of electrolytic copper in a stream of oxygen. 

To E. W. Morley * we owe the first complete quantitative syntheses of 
water, in which both gases were weighed separately, and afterwards in 
combination. The hydrogen was weighed in palladium, as was done by 
Keiser, and the oxygen was weighed in compensated globes, after the 
manner of Regnault. The globes were contained in an artificial " cave," 
to protect them from moisture and from changes of temperature; being 
so arranged that they could be weighed by the method of reversals with- 
out opening either the " cave " or the balance case. For each weighing 
of hydrogen about 600 grammes of palladium were employed. After 
weighing, the gases were burnt by means of electric sparks in a suitable 
apparatus, from which the unburned residue could be withdrawn for 
examination. Finally, the apparatus containing the water produced was 
closed by fusion and also weighed. Rubber joints were avoided in the 
construction of the apparatus, and the connections were continuous 
throughout. The weights are as follows : 

H taken O taken. H^O formed. 



3-2645 


25.9*76 


29.1788 


3.2559 


25-8531 


29.1052 


3.8193 


30.3210 


34-1389 


3-8450 


3o.5 2 94 


Lost 


3.8382 


30.4700 


34.3151 


3.8523 


30.5818 


34.4327 


3.8298 


30-40 1 3 


34.2284 


3.8286 


30.3966 


34.2261 


3.8225 


30-3497 


34 1742 


3.8220 


30.3479 


34-1743 


3.7637 


29.8865 


33.6540 


3.8211 


30-3429 


34.1559 



* " On the Density of Oxygen and Hydrogen, and on the Ratio of their Atomic Weights," by 
Edward W. Morley. Smithsonian Contributions to Knowledge, 1895, 4to, xi + .117 pp., 40 cuts. 
Abstract in Am. Chem. Journ., 17, 267 (gravimetric), and Ztschr. Phys. Chem., 17, 87 (gaseous densi- 
ties) ; also note in Am. Chem. Journ., 17, 396. Preliminary notice in Proc. Amer. Association, 
1891, p. 185. 



22 THE ATOMIC WEIGHTS. 

Hence we have 

H : O Ratio H-.H^O Ratio. 

15-878 17.877 

15.881 I7 .8 7 8 

15-878 17.873 

15.880 

15.877 17.881 

15-877 17-876 

15.877 17-875 

15-878 17.879 

15-879 17.881 

15-881 17.883 

15.881 17.883 
15-882 17.878 



Mean, 15.8792, .00032 Mean, 17.8785, .00066 

Combined, these data give : 

From ratio H 2 : O . O 15.8792, .00032 

" H 2 :H 2 0^15.8785,^.00066 

General mean O 15.8790, =b .00028 

For details, Morley's fall paper must be consulted. No abstract can 
do justice to the remarkable work therein recorded. 

Two other series of determinations, by Julius Thomsen, remain to be 
noticed. In the earlier paper * he determined the ratio between HC1 
and NH 3 , and thence, using Stas' values for Cl and N, fixed by reference 
to = 16, computed the ratio H : 0. This method was so indirect as to 
be of little importance, and gave for the atomic weight of oxygen approxi- 
mately the round number 16. I shall use the data farther on in cal- 
culating the atomic weight of nitrogen. The paper has been sufficiently 
criticised by Meyer and Seubert,f who have discussed its sources of error. 

In Thomsen's later paper J a method of determination is described 
which is, like the preceding, quite novel, but more direct. First, alu- 
minum, in weighed quantities, was dissolved in, caustic potash solution. 
In one set of experiments the apparatus was so constructed that the 
hydrogen evolved was dried and then expelled. The loss of weight of 
the apparatus gave the weight of the hydrogen so liberated. In the 
second set of experiments the hydrogen passed into a combustion 
chamber in which it was burned with oxygen, the water being retained. 
The increase in weight of this apparatus gave the weight of oxygen so 
taken up. The two series, reduced to the standard of a unit weight of 
aluminum, gave the ratio between oxygen and hydrogen. 

*Zeitsch. Physikal. Chem., 13, 398. 1894. 

fBer., 27, 2770. 

I Zeitsch. Anorg. Chem., :r, 14. 1895. 



OXYGEN. 23 

The results of the two series, reduced to a vacuum and stated as ratios, 
are as follows : 

First. Second. 

Weight of H Weight of O 

Weight of Al' Weight of Al* 

o.iuSo 0.88788 

0.11175 0.88799 

0.11194 0.88774 

0.11205 0.88779 

0.11189 0.88785 

o.i i 200 0.88789 

0.11194 0.88798 

0.11175 0.88787 

0.11190 0.88773 

0.11182 0.88798 

0.11204 0.88785 

o.i 1 202 

0.11204 0.88787,^0.000018 

0.11179 

0.11178 

O.I 1202 

0.11188 
0.11186 
0.11185 
o.i 1 190 
0.11187 1 



0.11190, 0.000015 

Dividing the mean of the second column by the mean of the first, we 
have for the equivalent of oxygen : 

0.88787, 0.000018 



0.11190, 0.000015 
Hence == 15.8690, 0.0022. 



= 7-9345, 0.0011 



The details of the investigation are somewhat complicated, and involve 
various corrections which need not -be considered here. The result as 
stated includes all corrections and is evidently good. The ratios, how- 
ever, cannot be reversed and used for measuring the atomic weight of 
aluminum, because the metal employed was not absolutely pure. 

We have now before us, representing syntheses of water, thirteen series, 
as follows : 

Dulong and Berzelius O = 15.894, .057 

Dumas .. . 15.9607, .0070 

Erdmann and Marchand l 5-975, .0113 

Thomsen, 1870 15.91, .0113 

Cooke and Richards 15.869, .0020 

Reiser, 1887 15.864, .015 

1888 15.9514, .0011 



24 THE ATOMIC WKIGHTS. 

Rayleigh 15.89, .009 

Noyes 15.8966,^.0017 

Dittmar and Henderson 15.8667, .0046 

Leduc 15.881, d= .0132 

M.orley 15.8790, .00028 

Thomson, 1895 15.8690, .0022 

General mean O = 15.8837, .00026 

Rejecting Keiser 1 5. 8796, .00027 

If we reject all except the determinations of Cooke and Richards, Ray- 
leigh, Noyes, Dittmar and Henderson, Leduc, Thomsen, and Moiiey, the 
general mean of these becomes 15.8794, .00027. From this it is evi- 
dent that Reiser's determinations alone, among the higher values for 0. 
carry any appreciable weight : and it also seems clear that the rounded- 
off number, O == 15.88, .0003, cannot be very far from the truth; at 
least so far as the synthetic evidence goes. 



In discussing the relative densities of oxygen and hydrogen gases we 
need consider only the more modern determinations, beginning with 
those of Dumas and Boussingault. As the older work has some his- 
torical value, I may in passing just cite its results. For the density of 
hydrogen we have .0769, Lavoisier; .0693, Thomson; .092, Cavendish; 
.0732, Biot and Arago ; .0688, Dulong and Berzelius. For oxygen there 
are the following determinations:' 1.087, Fourcroy, Vauquelin, and Se- 
guin; 1.103, Kirwan; 1.128, Davy; 1,088, Allen and Pepys ; 1.1036, Biot 
and Arago; 1.1117, Thomson; 1.1056, De Saussure; 1.1026, Dulong and 
Berzelius; 1.106, Buff; 1.1052, Wrede.* 

In 1841 Dumas and Boussingault f published their determinations of 
gaseous densities. For hydrogen they obtained values ranging from .0691 
to .0695 ; but beyond this mere statement they give no details. For 
oxygen three determinations were made, with the following results : 

'.1055 

1.1058 



Mean, 1.10567, .00006 

If we take the two extreme values given above for hydrogen, and re- 
gard them as the entire series, they give us a mean of .0693, .00013. 
This mean hydrogen value, combined with the mean for oxygen, gives 
for the latter, when H = 1, the density ratio 15.9538, .031. 

Regnault's researches, published four years later, J were much more 

* For Wrede's work, see Berzelius' Jahresbericht for 1843. For Dulong and Berzelius, see the 
paper already cited. All the other determinations are taken from Gmelin's Handbook, Caven- 
dish edition, v. i, p. 279. 

f Compt. Rend., 12, 1005. Compare also with Dumas, Compt. Rend., 14, 537. 

J Compt. Rend., 20, 975. 



OXYGEN. 25 

elaborately executed. Indeed, they have long stood among the classics 
of physical science, and it is only recently that they have been sup- 
planted by other measurements. 

For hydrogen three determinations of density gave the following 
results : 

.06923 

.06932 

.06924 



Mean, .069263, .000019 

For oxygen four determinations were made, but in the first one the 
gas was contaminated by traces of hydrogen, and the value obtained, 
1.10525, was, therefore, rejected by Regnault as too low. The other three 
are as follows : 

1.10561 

1.10564 

1.10565 

Mean, 1.105633, .000008 

Now, combining the hydrogen and oxygen series, we have the ratio 
H : : : 1 : 15.9628, .0044. According to Le Conte,* Regnault's reduc- 
tions contain slight numerical errors, which, corrected, give for the density 
of oxygen, 1.105612, and for hydrogen, .069269. Ratio, 1 : 15.9611. 

A much weightier correction to Regnault's data has already been in- 
dicated in the discussion of Cooke and Richards' work. He assumed 
that the globes in which the gases were weighed underwent no changes 
of volume, but Agamennone,f and after him, but independently,! Lord 
Rayleigh showed that an exhausted vessel was perceptibly compressed 
by atmospheric pressure. Hence its volume when empty was less than 
its volume when filled with gas. Crafts, having access to Regnault's 
original apparatus, has determined the magnitude of the correction indi- 
cated^ Unfortunately, the globe actually used by Regnault had been 
destroyed, but another globe of the same lot was available. With this 
the amount of shrinkage during exhaustion was measured, and Reg- 
iiault's densities were thereby changed to 1.10562 for oxygen, and 
.06949 for hydrogen. Corrected ratio, 1 : 15.9105. Doubtless Dumas 
and Boussingault's data are subject to a similar correction, and if we 
assume that it is proportionally the same in amount, the ratio derived 
from their experiments becomes 1 : 15.9015. 

In the same paper, that which contained the discovery of this correc- 
tion, Lord Rayleigh gives a short series of measurements of his own. 

* Private communication. See also Phil. Mag. (4), 27, 29, 1864, and Smithsonian Report, 1878, 
p. 428. 

f Atti Rendiconti Acad. I^incei, 1885. 
t Proc. Roy. Soc., 43, 356. Feb., 1888. 
g Conipt. Rend., 106, 1662. 



26 



THE ATOMIC WEIGHTS. 



His hydrogen was prepared from zinc and sulphuric acid, and was puri- 
fied by passage over liquid potash, then through powdered mercuric 
chloride, and then through pulverized solid potash. It was dried by 
means of phosphorus pentoxide. His oxygen was derived partly from 
potassium chlorate, and partly from the mixed chlorates of sodium and 
potassium. Equal volumes of the two gases weighed as follows : 



H. 

.15811 

.15807 
.15798 
I579 2 



O. 

2.5186, 4; .00061* 



Mean, .15802, 000029. 

Corrected for shrinkage of the exhausted globe these become H, 
0.15860 ; O, 2.5192. Hence the ratio 1 : 15.884, .0048. 

In 1892 Rayleigh published a much more elaborate determination of 
this ratio. f The gases were prepared electroly tically from caustic potash , 
and dried by means of solid potash and phosphorus pentoxide. The 
hydrogen was previously passed over hot copper. The experiments, 
stated like the previous series, are in five groups ; two for oxygen and 
three for hydrogen; but for present purposes the similar sets may be 
regarded as equal in weight, and so discussable together. The weights 
of equal volumes are as follows : 



H. O. 




( -15807 2.5182 1 






_. 15816 2.5173 




First set 


.15811 2.5172 


First set. 


Mean, .15808 I .15803 2.5193 


Mean, 2.51785. 




.15801 2.5174 




L -15809 2.5177 




f .15800 2.5183 ' 




Second set '*& 2Q 2 '5 l68 


Second set. 


Mean, .15797 


.15792 25172 
.15788 2.5181 


Mean, 2.5172. 


.15783 2.5156 




r .15807 






.15801 Mean, 2.5176, 


.00019. 




.15817 




Third set j .1579 




Mean, .15804 


.15810 






.15798 






.15802 




1.15807 




Mean, .15804, .000019. 



* Arbitrarily assigned the probable error of a single experiment in Rayleigh's paper of 1892. 
tProc. Roy. Soc., 50, 448, Feb. 18, 1892. 



OXYGEN. 27 

These weights with various corrections relative to temperatures and 
pressures, and also for the compression of the exhausted globe, ulti- 
mately become for H, .158531 ; and for 0, 2.51777. Hence the ratio 
1 : 15.882, HZ .0023. For details relative to corrections the original 
memoir should be consulted. 



In his paper " On a new method of determining gas densities," * Cooke 
gives three measurements for hydrogen, referred to air as unity. They 
are : 

.06957 

.06951 

.06966 



Mean, .06958, ih .000029 

Combining this with Regnault's density for oxygen, as corrected by 
Crafts, 1.10562, .000008, we get the ratio H : : : 1 : 15.890,* .0067. 

Leduc, working by Regnault's method, somewhat modified, and cor- 
recting for shrinkage of exhausted globes, gives the following densities : t 

H. O. 

.06947 1.10501 

.06949 1.10516 
.06947 



Mean, .06948, =b .00006745 

The two oxygen measurements are the extremes of three, the mean 
being 1.10506, .0000337. Hence the ratio 1 : 15.905, .0154. 

The first two hydrogen determinations were made with gas produced 
by the electrolysis of caustic potash, while the third sample was derived 
from zinc and sulphuric acid. The oxygen was electrolytic. Both gases 
were passed over red-hot platinum sponge, and dried by phosphorus 
pentoxide. 

Much more elaborate determinations of the two gaseous densities are 
those made by Morley. J For oxygen he gives three series of data ; two 
with oxygen from potassium chlorate, and one with gas partly from the 
same source and partly electrolytic. In the first series, temperature and 
pressure were measured with a mercurial thermometer and a mano- 
barometer. In the second series they were not determined for each 
experiment, but were fixed by comparison with a standard volume of 
hydrogen by means of a differential manometer. In the third series the 
gas was kept at the temperature of melting ice, and the mano-barometer 

* Proc. Amer. Acad., 24, 202. 1889. Also Am. Chem. Journ., 11, 509. 

fCompt. Rend., 113, 186. 1891. 

I Paper already cited, under the gravimetric portion of this chapter. 



28 



THE ATOMIC WEIGHTS. 



alone was read. The results for the weight in grammes, at latitude 45' 
of one litre of oxygen are as follows : 



First Series. 



Second Series. 





.42864 


[.42952 




.42849 


.42900 




.42838 


.42863 




.42900 


.42853 




.42907 


.42858 




.42887 


.42873 




.42871 


.42913 




.42872 


.42905 




.42883 


.42896 






.42880 


Mean, 


.42875, .000051 


.42874 


Corrected,* 


.42879, zh .OOOO5I 


.42878 






.42872 






.42859 




. ] 


.42851 



Third Series. 






.42920 






.42860 






.42906 






.42957 






.42910 






.42930 






.42945 






.42932 






.42908 






.42910 






4295 1 






.42933 






.42905 






.42914 






.42849 






.42894 




.000048 


.42886 




000048 






Mean, 


.42912, zfc 


.000048 


Corrected, 


.42917, 


.000048 



Mean, 1.42882, 
Corrected, 1.42887, 



General mean of all three series, 1.42896, .000028. 

Morley himself, for experimental reasons, prefers the last series, and 
gives it double weight, getting a mean density of 1.42900. The differ- 
ence between this mean and that given above is insignificant with ref- 
erence to the atomic weight problem. 

In the case of hydrogen, Morley 's determinations fall into two groups, 
but in both the gas was prepared by the electrolysis of pure dilute sul- 
phuric acid, and was most elaborately purified. In the first group there 
are two series of measurements. Of these, the first involved the reading 
of temperature and pressure by means of a mercurial thermometer and 
mano-barometer. In the second series, the gas was delivered into the 
weighing globes after occlusion in palladium ; it was then kept at the 
temperature of melting ice, and only the syphon barometer was read. 
In this group the hydrogen was possibly contaminated with mercurial 
vapor, and the results are discarded by Morley in his final summing up. 
For present purposes, however, it is unnecessary to reject them, for they 
have confirmatory value, and do not appreciably affect the final mean. 
The weight of one litre of hydrogen at 45 latitude, as found in these two 
sets of determinations, is as follows : 



* Correction applied by Morley to all his series, for a slight error, 
standard metre bar. 



, in the length of his 



OXYGEN. 29 



First Series. Second Series. 

.089904 .089977 

.089936 .089894 

.089945 .089987 

.089993 .089948 

.089974 .089951 

.089941 .089960 

.089979 .090018 

.089936 .089909 

.089904 .089953 

.089863 .089974 

.089878 .089922 

.089920 .090093 

.089990 .090007 

.089926 .089899 

.089928 .089974 

.089900 

Mean, .089934, .000007 .089869 

Corrected, .089938, .000007 .090144 

.089984 



Mean, .089967, .000011 
Corrected, .089970, d= .000011 

In the second group of experiments, the hydrogen was weighed in 
palladium before transfer to the calibrated globe ; and in weighing, the 
palladium tube was tared by a similar apparatus of nearly equal volume 
and weight. After transfer, which was effected without the intervention 
of stopcocks, the volume and pressure of the gas were taken at the 
temperature of melting ice. A preliminary set of measurements was 
made, followed by three regular series ; of these, the first and second 
were with the same apparatus, and are different only in point of time, 
a vacation falling between them. The last series was with a different 
apparatus. The data are as follows, with the means as usual : 

Preliminary. Third Series. Fourth Series. Fifth Series. 

.089946 .089874 .089972 .089861 

.089915 .089891 .089877 .089877 

.089881 .089886 .089867 .089870 

.089901 .089866 .089916 .089867 

.089945 .089911 .089770 .089839 

.089856 .089846 .089874 

Mean, .089918, .089912 .089864 

.0000271 .089872 Mean, .089875, .089883 

Corrected, .089921 =b .0000187 .089830 

Mean, .089883, Corrected, .089880 .089877 

.0000049 .089851 

Corrected, .089886 

Mean, .089863, 
rb .0000034 
Corrected, .089866 



30 THE ATOMIC WEIGHTS. 



Now, rejecting nothing, we may combine all the series into a general 
mean, giving the weight of one litre of hydrogen as follows : 

First series 089938, .000007 

Second series 089970, .00001 1 

Preliminary series, second method 089921, .0000271 

Third series 089886, zfc .0000049 

Fourth " 089880, .0000187 

Fifth " 089866, .0000034 



General mean 089897, zfc .0000025 

Rejecting the first three 089872, .0000028 

This last mean value for hydrogen will be used in succeeding chapters 
of this work for reducing volumes of the gas to weights. Combining 
the general mean of all with the value found for the weight of a litre of 
oxygen, 1.42896, .000028, we get for the ratio H : 0, 

O = I5 8955, .0005 

If we take only the second mean for H, excluding the first three series, 

we have 

O = 15.9001, .0005 

This value is undoubtedly nearest the truth, and is preferable to all 
other determinations of this ratio. Its probable error, however, is given 
too low ; for some of the oxygen weighings involved reductions for tem- 
perature and pressure. These reductions involve, again, the coefficient of 
expansion of the gas, and its probable error should be included. Since, 
however, that factor has been disregarded elsewhere, it would be an over- 
refinement of calculation to include it here. 

In a memoir of this kind it is impossible to do full justice to so elab- 
orate an investigation as that of Morley. The details are so numerous, 
the corrections so thorough, the methods for overcoming difficulties so 
ingenious, that many pages would be needed in order to present any- 
thing like a satisfactory abstract. Hardly more than the actual results 
can be cited here; for all else the original memoir must be consulted. 

Still more recently, by a novel method, J. Thomsen has measured the 
two densities in question.* In his gravimetric research, already cited, 
he ascertained the weights of hydrogen and of oxygen equivalent to a 
unit weight of aluminum. In his later paper he describes a method of 
measuring the corresponding volumes of both gases during the same 
reactions. Then, having already the weights of the gases, the volume- 
weight ratio, or density, is in each case easily computable. From 1.0171 
to 2.3932 grammes of aluminum were used in each experiment. Omit- 
ting details, the volume of hydrogen in litres, equivalent to one gramme 
of the metal, is as follows : 

*Zeitschr. Anorg. Chern., 12, 4. 1896. 



OXYGEN. 31 

.24297 

243Q3 
.24286 
.24271 
.24283 
.24260 

243*4 
.24294 

Mean, 1.24289, .00004 

The weight of hydrogen evolved from one gramme of aluminum was 
found in Thomsen's gravimetric research to be 0.11190, zb .000015. 
Hence the weight of one litre at 0, 760 mm., and 10.6 meters above sea 
level at Copenhagen is : 

.090032, .000012; 

or at sea level in latitude 45, 

.089947, dh .000012 gramme. 

The data for oxygen are given in somewhat different form, namely, 
for the volume of one gramme of the gas at 0, 760, and at Copenhagen. 
The values are. in litres : 

.69902 

.69923 

.69912 

.69917 

.69903 

.69900 

.69901 

.69921 

.69901 

.69922 



Mean, .69910, .00002 
At sea level in latitude 45, .69976, .00002 

Hence one litre weighs 1.42906, .00004 grammes. 

Dividing this by the weight found for hydrogen, 0.089947, .000012 
we have for the ratio H : 0, 

15.8878, .0022. 



The density ratios, H : 0, now combine as follows : 

Dumas and Boussingault, corrected 15.9015, d= .031 

Regnault, corrected 15.9105, =b .0044 

Rayleigh, 1888 15.884, .0048 

" 1892 15.882, .0023 

Cooke , 15.890, .0067 

Leduc i5-95 - OI 54 

Morley, including all the data ., . . 15.8955, .0005 

Thomsen 15.8878, .0022 



General mean 15.8948, =h .00048 



32 THE ATOMIC WEIGHTS. 

If we reject all of Morley's data for the density of hydrogen except his 
third, fourth, and fifth series, the mean becomes 

O = 15.8991, .00048. 

In either case Morley's data vastly outweigh all others. 

If oxygen and hydrogen were perfect gases, uniting by volume to form 
water exactly in the ratio of one to two, then the density of the first in 
terms of the second would also express its atomic weight. But in fact, 
the two gases vary from Boyle's law in opposite directions, and the true 
composition of water by volume diverges from the theoretical ratio to a 
measurable extent. Hence, in order to deduce the atomic weight of 
oxygen from its density, a small correction must be applied to the latter? 
dependent upon the amount of this divergence. Until recently, our 
knowledge of the volumetric composition of water rested entirely upon 
the determinations made by Humboldt and Gay-Lussac* early in this 
century, which gave a ratio between H and of a little less than 2:1, 
but their data need no farther consideration here. 

In 1887 Scott t published his first series of experiments, 21 in number, 
finding as the most probable result a value for the ratio of 1.994 : 1. In 
March, 1888, J he gave four more determinations, ranging from 1.9962 to 
1.998:1; and later in the same year another four, with values from 
1.995 to 2.001. In 1893, || however, by the use of improved apparatus, 
he was able to show that his previous work was vitiated by errors, and to 
give a series of measurements of far greater value. Of these, twelve were 
especially good, being made with hydrogen from palladium hydride, 
and with oxygen from silver oxide. In mean the value found is 
2.00245, .00007, with a range from 2.0017 to 2.0030. 

In 1891 an elaborate paper by Morley^fl appeared, in which twenty 
concordant determinations of the volumetric ratio gave a mean value of 
2.00023, .000015. These measurements were made in eudiometer 
tubes, and were afterwards practically discarded by the author. In his 
later and larger paper,** however, he redetermined the ratio from the 
density of the mixed electrolytic gases, and found it to be, after applying 
all corrections, 2.00274. The probable error, roughly estimated, is .00005. 
Morley also reduces Scott's determinations, which were made at the tem- 
perature of the laboratory, to 0, when the value becomes 2.00285. The 
mean value of both series may therefore be put at 2.0028, .00004, with 
sufficient accuracy for present purposes. Leduc's ft single determination, 

* Journ. de Phys., 60, 129. 

tProc. Roy. Soc., 42, 396. 

I Nature, 37, 439. 

g British Assoc. Report, 1888, 631. 

I! Proc. Roy. Soc., 53, 130. In full in Philosophical Transactions, 184, 543. 1893. 

^ Amer. Journ. Sci. (3), 46, 220, and 276. 

** Already cited with reference to syntheses of water. 

ft Compt. Rend., 115, 311. 1892. 



OXYGEN. 33 

based upon the density of the mixed gases obtained by the electrolysis 
of water, gave 2.0037 ; but Morley shows that some corrections were 
neglected. This determination, therefore, may be left out of account. 
Now, including all data, we have a mean value for the density ratio : 

(A.) H :O: : I : 15.8948, .00048; 

or, omitting Morley's rejected series, 

(B.) H :O: : I : 15.8991, .00048. 

Correcting these by the volume ratio, 2.0028, .00004, the final result 
for the atomic weight of oxygen as determined by gaseous densities 
becomes : 

From A O 15.8726, =b .00058 

From B O = 15.8769, .00058 

Combining these with the result obtained from the syntheses of water, 
rejecting nothing, we have 

By synthesis of water O = 15.8837, .00026 

By gaseous densities O = 15.8726, .00058 

General mean O = 15.8821, .00024 

If we reject Reiser's Work under the first heading, and omit Morley's 
defective hydrogen series under the second, we get 

By synthesis of water O 15.8796, .00027 

By gaseous densities O = 15.8769, d= .00058 

General mean O = 15.8794, .00025 

Morley, discussing his own data, gets a final value of O = 15.8790, 
.00026, a result sensibly identical with the second of the means given 
above. These results cannot be far from the truth ; and accordingly, 
rounding off the last decimals, the value 

= 15.879, .0003, 
will be used in computation throughout this work. 

NOTE. A useful " short bibliography " upon the composition of water, 
by T. C. Warrington, may be found in the Chemical News, vol. 73, pp. 
137, 145, 156, 170, and 184. 



34 THE ATOMIC WEIGHTS. 



SILVER, POTASSIUM, SODIUM, CHLORINE, BROMINE, AND 

IODINE. 

The atomic weights of these six elements depend upon each other to 
so great an extent that they can hardly be considered independently. 
Indeed, chlorine, potassium, and silver have always been mutually de- 
termined. From the ratio between silver and chlorine, the ratio between 
silver and potassium chloride, and the composition of potassium chlo- 
rate, these three atomic weights were first accurately fixed. Similar 
ratios, more recently worked out by Stas and others, have rendered it 
desirable to include bromine, iodine, and sodium in the same general 
discussion. 

Several methods of determination will be left altogether out of account. 
For example, in 1842 Marignac* sought to fix the atomic weight of 
chlorine by estimating the quantity of water formed when hydrochloric 
acid gas is passed over heated oxide of copper. His results were wholly 
inaccurate, and need no further mention here. A little later Laurent f 
redetermined the same constant from the analysis of a chlorinated de- 
rivative of naphthalene. This method did not admit of extreme accu- 
racy, and it presupposed a knowledge, of the atomic weight of carbon ; 
hence it may be properly disregarded. Maumene's J analyses of the 
oxalate and acetate of silver gave good results for the atomic weight of 
that metal; but they also depend for their value upon our knowledge of 
carbon, and will, therefore, be discussed farther on with reference to that 
element. Hardin's work also, relating to the nitrate, acetate, and 
benzoate of silver, will be found in the chapters upon nitrogen and 
carbon. 

Let us now consider the ratios upon which we must rely for ascertain- 
ing the atomic weights of the six elements in question. After we have 
properly arranged our data we may then discuss their meaning. First 
in order we may conveniently take up the percentage of potassium chlo- 
ride obtainable from the chlorate. 

The first reliable series of experiments to determine this percentage 
was made by Berzelius. || All the earlier estimations were vitiated by 
the fact that when potassium chlorate is ignited under ordinary circum- 
stances a little solid material is mechanically carried away with the 
oxygen gas. Minute portions of the substance may even be actually 
volatilized. These sources of loss were avoided by Berzelius, who de- 
vised means for collecting and weighing this trace of potassium chloride. 

*Compt. Rend., 14, 570. Also, Journ. f. Prakt. Chetn., 26, 304. 
tConipt. Rend., 14, 456. Journ. f. Prakt. Chem., 26, 307. 
t Ann. d. Chim et d. Phys. (3), 18, 41. 1846. 
g Journ. Arner. Chem. Soc. 18, 990. 1896. 
j| Poggend. Annalen, 8, i. 1826. 



SILVER, POTASSIUM, ETC. 35 

All the successors of Berzelius in this work have benefited by his exam- 
ple, although for the methods by which loss has been prevented we must 
refer to the original papers of the several investigators. In short, then, 
Berzelius ignited potassium chlorate, and determined the percentage of 
chloride which remained. Four experiments gave the following results : 

60.854 
60.850 
60.850 
60.851 

Mean, 60.851, .0006 

The next series was made by Penny,* in England, who worked after 
a somewhat different method. He treated potassium chlorate with 
strong hydrochloric acid in a weighed flask, evaporated to dryness over 
a sand bath, and then found the weight of the chloride thus obtained. 
His results are as follows, in six trials : 

60.825 
60.822 
60.815 
60.820 
60.823 
60.830 



Mean, 60.8225, .0014 

In 1842 Pelouze f made three estimations by the ignition of the chlo- 
rate, with these results : 

60.843 
60.857 
60.830 

Mean, 60.843, -53 

Marignac, in 1842, J worked with several different recrystallizations of 
the commercial chlorate. He ignited the salt, with the usual precau- 
tions for collecting the material carried off mechanically, and also exam- 
ined the gas which was evolved. He found that the oxygen from 50 
grammes of chlorate contained chlorine enough to form .003 gramme of 
silver chloride. Here are the percentages found by Marignac : 

In chlorate once crystallized 60.845 

In chlorate once crystallized 60.835 

In chlorate twice crystallized 60.833 

In chlorate twice crystallized 60.844 

In chlorate three times crystallized 60.839 

In chlorate four times crystallized 60.839 

Mean, 60.8392, .0013 



* Phil. Transactions, 1839, p. 20. 

f Compt. Rend., 15, 959. 

I Ann. d. Chera. u. Pharm., 44, 18. 



36 THE ATOMIC WEIGHTS. 

In the same paper Marignac describes a similar series of experiments 
made upon potassium perchlorate, KC10 4 . In three experiments it was 
found that the salt was not quite free from chlorate, and in three more 
it contained traces of iron. A single determination upon very pure 
material gave 46.187 per cent, of oxygen and 53.813 of residue. 

In 1845 two series of experiments were published by Gerhardt. * The 
first, made in the usual way, gave these results : 

60.871 
60.881 
60.875 



Mean, 60.8757, .0020 

In the second series the oxygen was passed through a weighed tube 
containing moist cotton, and another filled with pumice stone and sul- 
phuric acid. Particles were thus collected which in the earlier series 
escaped. From these experiments we get 

60.947 
60.947 
60.952 



Mean, 60.9487, .0011 

These last results were afterwards sharply criticised by Marignac,f 
and their value seriously questioned. 

The next series, in order of time, is due to Maumene.J This chemist 
supposed that particles of chlorate, mechanically carried away, might 
continue to exist as chlorate, undecomposed ; and hence that all previous 
series of experiments might give too high a value to the residual chloride. 
In his determinations, therefore, the ignition tube, after expulsion of the 
oxygen, was uniformly heated in all its parts. Here are his percentages 

of residue : 

60.788 
60.790 
60.793 
60.791 
60.785 
60.795 
60.795 

Mean, 60.791, .0009 

The question which most naturally arises in connection with these re- 
sults is, whether portions of chloride may not have been volatilized, and 

css\ I /^a"f 



so lost 



* Compt. Rend., 21, 1280. 

} Supp. Bibl. Univ. de Geneve, Vol. I. 

I Ann. d. Chim. et d. Phys. (3), 18, 71. 1846. 



SILVER, POTASSIUM, ETC. 37 

Closely following Maumene's paper, there is a short note by Faget,* 
giving certain mean results. According to this chemist, when potassium 
chlorate is ignited slowly, we get 60.847 per cent, of residue. When the 
ignition is rapid, we get 60.942. As no detailed experiments are given, 
these figures can have 110 part in our discussion. 

Last of all we have two series determined by Stas.f In the first series 
are the results obtained by igniting the chlorate. In the second series 
the chlorate was reduced by strong hydrochloric acid, after the method 
followed by Penny : 

First Series. 
60.8380 
60.8395 
60.8440 
60.8473 
60.8450 

Mean, 60.84276, dr .OOI2 

Second Series. 
6o.8t;o 
60.853 
60.844 

Mean, 60.849, .0017 

In these experiments every conceivable precaution was taken to avoid 
error and insure accuracy. All weighings were reduced to^ a vacuum 
standard ; from 70 to 142 grammes of chlorate were used in each experi- 
ment; and the chlorine carried away with the oxygen in the first series- 
was absorbed by finely divided silver and estimated. It is difficult to 
see how any error could have occurred. 

Now, to combine these different series of experiments. 

Berzelius, mean result 60. 85 1 , dr .0006 

Penny, " 60.8225, dr .0014 

Pelouze, " 60.843, .053 

Marignac, " 60.8392, dr .0013 

Gerhardt, 1st " 60.8757, dr .0020 

" 2d V 60.9487, dr .0011 

Maumene, " 60.791, dr .0009 

.Stas, 1st " 60.8428, dr .0012 

" 2d " 60.849, .0017 



General mean from all nine series, 
representing forty experiments 60.846, db .00038 

This value is exactly that which Stas deduced from both of his own 
series combined, and gives great emphasis to his wonderfully accurate 

* Ann. d. Chim. et d. Phys. (3), 18, 80. 1846. 
f See Aronstein's translation, p. 24Q. 



38 THE ATOMIC WEIGHTS. 

work. It also finely illustrates the compensation of errors which occurs 
in combining the figures of different experimenters. 

Similar analyses of silver chlorate have been made by Marignac and 
by Stas. Marignac's data are as follows : * The third column gives the 
percentage of in AgC10 3 : 

24.5 10 grin. AgClO 3 gave 18.3616 AgCl. 25 103 

25.809 " 19-3345 " 25.086 

30.306 22.7072 " 25.074 

28.358 21.2453 " 25.082 . 

28.287 " 21.1833 " 25.113 

57.170 " 42.8366 " 25.072 



Mean, 25.088, zfc .0044 

Stas f found the following percentages in two experiments only : 

25,081 
25.078 



Mean, 25.0795, H= .0010 

Combined with Marignac's mean this gives a general mean of 25,080, 
.0010 ; that is, Marignac's series practically vanishes. 

For the direct ratio between silver and chlorine there are seven avail- 
able series of experiments. Here, as in many other ratios, the first reliable 
work was done by Berzelius. J 

He made three estimations, using each time twenty grammes of pure 
silver. This was dissolved in nitric acid. In the first experiment the 
silver chloride was precipitated and collected on a filter. In the second 
and third experiments the solution was mixed with h} T drochloric acid 
in a flask, evaporated to dry ness, and the residue then fused and weighed 
without transfer. One hundred parts of silver formed of chloride : 

132.700 
132.780 
132.790 



Mean, 132.757, .019 

Turner's work closely resembles that of Berzelius. Silver was dis- 
solved in nitric acid and precipitated as chloride. In experiments one, 
two, and three the mixture was evaporated and the residue fused. In 
experiment four the chloride was collected on a filter. A fifth experi- 
ment was made, but has been rejected as worthless. 

The results were as follows : In a third column I put the quantity of 
AgCl proportional to 100 parts of Ag. 

*Bitjl. Univ. de Gen6ve, 46, 356. 1843. 

f Aronstein's translation, p. 214. 

I Thomson's Annals of Philosophy, 1820, v. 15, 89. 

g Phil. Transactions, 1829,291. 



SILVER, POTASSIUM, ETC. 



39 



28.407 grains Ag gave 37.737 
41.917 " 55-678 

40.006 " 53.143 

30.922 " 41.070 



132.844 
132.829 
'32.837 
132.818 

Mean, 132.832, ^ .0038 



The same general method of dissolving silver in nitric acid, precipi- 
tating, evaporating, and fusing without transfer of material was also 
adopted by Penny. * His results for 100 parts of silver are as follows, in 

parts of chloride : 

132.836 
132.840 
132.830 
132.840 
132.840 
132.830 
132.838 

Mean, 132.8363, .0012 

In 1842 Marignacf found that 100 parts of silver formed 132.74 of 
chloride, but gave no available details. Later, $ in another series of de- 
terminations, he is more explicit, and gives the following data. The 
weighings were reduced to a vacuum standard : 



79.853 grm. Ag gave 106.080 AgCl. 

69.905 " 92.864 " 

64.905 " 86.210 " 

92.362 " 122.693 " 

99.653 " 132.383 " 



Ratio, 132.844 

132-843 
132.825 
132.839 
132.844 



Mean, 132.839, .0024 

The above series all represent the synthesis of silver chloride. Mau- 
mene made analyses of the compound, reducing it to metal in a current 
of hydrogen. His experiments make 100 parts of silver equivalent to 
chloride : 

132.734 

132-754 

132.724 

132.729 

132.741 



By Dumas 



Mean, 132.7364, =b .0077 

we have the following estimations : 

9.954 Ag gave 13.227 AgCl. Ratio, 132.882 



19.976 



26.542 



132.869 
Mean, 132.8755, .0044 



*Phil. Transactions, 1839, 28. 

iAnn. Chetn. Pharm., 44, 21. 

I See Berzelius' I^ehrbuch, sth Ed., Vol. 3, pp. 1192, 1193. 

J Ann. d. Chim. et d. Phys. (3), 18, 49. 1846. 

|| Ann. Chem. Pharm., 113, 21. 1860. 



40 



THE ATOMIC WEIGHTS. 



Finally, there are seven determinations by Stas,* made with his usual 
accuracy and with every precaution against error. In the first, second, 
and third, silver was heated in chlorine gas, and the synthesis of silver 
chloride thus effected directly. In the fourth and fifth silver was dis- 
solved in nitric acid, and the chloride thrown down by passing hydro- 
chloric acid gas over the surface of the solution. The whole was then 
evaporated in the same vessel, and the chloride fused, first in an atmos- 
phere of hydrochloric acid, and then in a stream of air. The sixth syn- 
thesis was similar to these, only the nitric solution was precipitated by 
hydrochloric acid in slight excess, and the chloride thrown down was 
washed by repeated decantation. All the decanted liquids were after- 
wards evaporated to dryness, and the trace of chloride thus recovered 
was estimated in addition to the main mass. The latter was fused in an 
atmosphere of HC1. The seventh experiment was like the sixth, only 
ammonium chloride was used instead of hydrochloric acid. From 98.3 
to 399.7 grammes of silver were used in each experiment, the operations 
were performed chiefly in the dark, and all weighings were reduced to 
vacuum. In every case the chloride obtained was beautifully white. 
The following are the results in chloride for 100 of silver: 

132.841 

132.843 
132.843 
132.849 
132.846 
132.848 
122.8417 



Mean, 132.8445, .0008 

We may now combine the means of these seven series, representing in 
all thirty-three experiments. One hundred parts of silver are equivalent 
to chlorine, as follows : 

Berzelius 3 2 -757, .0190 

Turner 32.832, .0038 

Penny 32.8363, .0012 

Marignac , 32.839, =b .0024 

Maumene ' 32.7364, .0077 

Dumas 3 2 -8755, =t .0044 

Stas 32.8445, dr .0008 

General mean 32.8418, .0006 

Here, again, we have a fine example of the evident compensation of 
errors among different series of experiments. We have also another 
tribute to the accuracy of Stas, since this general mean varies from the 
mean of his results only within the limits of his own variations. 

*Aronstein's translation, p. 171. 



SILVER, POTASSIUM, ETC. 41 

The ratio between silver and potassium chloride, or, in other words, 
the weight of silver in nitric acid solution which can be precipitated by 
a known weight of KC1, has been fixed by Marignac and by Stas. Ma- 
rignac,* reducing all weighings to vacuum, obtained these results. In 
the third column I give the weight of KC1 proportional to 100 parts 

ofAg: 

i 4-7 2 3 g rm - Ag = 3.2626 KG. 69.067 

22.725 " 15.001 " 69.050 

21.759 " I 5- 2 8 " 69.066 

21.909 " 15.131 " 69.063 

22.032 " 15.216 " 69.063 

25.122 " 17.350 " 69.063 

Mean, 69.062, 0017 

The work of Stas falls into several series, widely separated in point of 
time. His earlier experiments f upon this ratio may be divided into 
two sets, as follows : In the first set the silver was slightly impure, but 
the impurity was of known quantity, and corrections could therefore be 
applied. In the second series pure silver was employed. The potassium 
chloride was from several different sources, and in every case was puri- 
fied with the utmost care. From 10.3 to 32.4 grammes of silver were 
taken in each experiment, and the weighings were reduced to vacuum. 
The method of operation was, in brief, as follows : A definite weight of 
potassium chloride was taken, and the exact quantity of silver necessary, 
according to Prout's hypothesis, to balance it was also weighed out. The 
metal, with suitable precautions, was dissolved in nitric acid, and the 
solution mixed with, that of the chloride. After double decomposition 
the trifling excess of silver remaining in the liquid was determined by 
titration with a normal solution of potassium chloride. One hundred 
parts of silver required the following of KC1 : 

First Series. 
69.105 
69.104 
69.103 
69.104 

69. IO2 



Mean, 69.1036, d= .0003 

Second Series. 
69.105 
69.099 
69.107 
69.103 
69. 103 
69.105 
69.104 



*See Berzelius' I^ehrbuch, sth Ed., Vol. 3, pp. 1192-3. 
fAronstein's translation, pp. 250-257. 



42 THE ATOMIC WEIGHTS. 

69.099 

69.1034 

69.104 

69.103 

69.102 

69.104 

69.104 

69.105 

69.103 

69.101 

69.105 



Mean, 69.1033, =b .0003 

In these determinations Stas did not take into account the slight solu- 
bility of precipitated silver chloride in the menstrua employed in the 
experiments. Accordingly, in 1882* he published a. new series, in which 
by two methods he remeasured the ratio, guarding against the indicated 
error, and finding the following values : 

69.1198 
69.11965 
69.121 
69.123 

Mean, 69.1209, .0003 

Corrected for a minute trace of silica contained in the potassium 
chloride, this mean becomes 

69.11903, . 0003. f 

Still later, in order to establish the absolute constancy of the ratio in 
question, Stas made yet another series of determinations,^ in which he 
employed potassium chloride prepared from four different sources. 
One lot of silver was used throughout. The values obtained were as- 

follows : 

69.1227 
69.1236 
69.1234 
69.1244 
69.1235 
69.1228 
69.1222 
69.1211 
69.1219 
69.1249 
69.1238 
69.1225 
69.1211 

* Memoires Acad. Roy. de Beige, t. 43. 1882. 
fSee Van der Plaats, Ann. Chim. Phys. (6), 7, 15. 
I Oeuvres Posthumes, edited by W, Spring. 



SILVER, POTASSIUM, ETC. 43 

A series was also begun in which one sample of potassium chloride 
was to be balanced against silver from various sources, but only one 
result is given, namely, 69.1240. This, with the previous series, gives a 
mean of 69.1230, .0002. 

Five series of determinations are now at hand for the ratio Ag : KC1. 
They combine as follows : 

Marignac 69.062, .0017 

Stas, ist series 69. 1036, .0003 

" 2d " 69.1033, .0003 

" 3d " ...., 69. 1190, rb .0003 

" 4th " 69.1230, .0002 



General mean 69.1143, d= .00013 

The difference between the highest and the lowest of Stas' series cor- 
responds to a difference of 0.021 in the atomic weight of potassium. The 
rejection of the earlier work might be quite justifiable, but would exert 
a very slight influence upon our final result. 

The quantity of silver chloride which can be formed from a known 
weight of potassium chloride has also been determined by Berzelius, 
Marignac and Maumene. Berzelius * found that 100 parts of KC1 were 
equivalent to 194.2 of AgCl ; a value which, corrected for weighings in 
air, becomes 192.32. This experiment will not be included in our dis- 
cussion. 

In 1842 Marignac f published two determinations, with these results 
from 100 KC1 : 

192.33 
192-34 

Mean, corrected for weighing in air, 192.26, .003 

In 1846 Marignac I published another set of results, as follows. The 

weighings were reduced to vacuum, The usual ratio is in the third 
column : 

17.034 grm. KC1 gave 32.761 AgCl. 192.327 

I4-427 27.749 " 192.341 

15.028 " 28.910 " 192.374 

15.131 29.102 " 192.334 

15.216 " 29.271 " 192.370 



Mean, 192.349, .006 

Three estimations of the same ratio were also made by Maumene as 
follows : 

*Poggend. Annal., 8, i. 1826. 

f Ann. Chem. Pharm., 44, 21, 1842. 

t Berzelius' I^ehrbuch, sth E}d., Vol. 3, pp. 1192, 1193. 

Ann. d. Chim. et d. Phys. (3), 18, 41. 1846. 



44 THE ATOMIC WEIGHTS. 

10.700 grm. KC1 gave 20.627 AffCl. 192.776 

10.5195 " 20.273 " 192.716 

8.587 " 16.556 " 192.803 

Mean, 192.765, .017 

The three series of ten experiments in all foot up thus: 

Marignac, 1842 192.260, .003 

1846 192.349, .006 

Maumene 192 765, .017 



General mean 192.294, .0029 

These figures show clearly that the ratio which they represent is not 
of very high importance. It might be rejected altogether without im- 
propriety, and is only retained for the sake of completeness. It will 
obviously receive but little weight in our final discussion. 



In estimating the atomic weight of bromine the earlier experiments of 
Balard, Berzelius, Liebig, and Lowig may all be rejected. Their results 
were all far too low, probably because chlorine was present as an im- 
purity in the materials employed. Wallace's determinations, based upon 
the analysis of arsenic tribromide, are tolerably good, but need not be 
considered here. In the present state of our knowledge, Wallace's 
analyses are better fitted for fixing the atomic weight of arsenic, and 
will, therefore, be discussed with reference to that element. 

The ratios with which we now have to deal are closely similar to those 
involving chlorine. In the first place, there are the analyses of silver 
bromate by Stas.* In two careful experiments he found in this salt the 
following percentages of oxygen : 

20.351 
20.347 



Mean, 20.349, .0014 

There are also four analyses of potassium bromate by Marignac. f The 
salt was heated, and the percentage loss of oxygen determined. The 
residual bromide was feebly alkaline. We cannot place much reliance 
upon this series. The results are as follows : 

28.7016 
28.6496 
28.6050 
28.7460 



Mean, 2^.6755, .0207 



*Aronstein's translation, pp. 200-206. 

fSee E. Mulder's Overzigt, p. 117; or Berzelius' Jahresbericht, 24, 72. 



SILVER, POTASSIUM, ETC. 45 

When silver bromide is heated in chlorine gas, silver chloride is formed. 
In 1860 Dumas* employed this method for estimating the atomic weight 
of bromine. His results are as follows. In the third column I give the 
weight of AgBr equivalent to 100 parts of AgCl : 

2.028 grm. AgBr gave 1.547 AgCl. 131.092 

4.237 " 3. 2 35 " i3 -974 

5.769 4-403 " 131.024 

Mean, 131.030, .023 

This series is evidently of but little value. 

The two ratios upon which, in connection with Stas' analyses of 
silver bromate, the atomic weight of bromine chiefly depends, are those 
which connect silver with the latter element directly and silver with 
potassium bromide. 

Marignac,f to effect the synthesis of silver bromide, dissolved the 
metal in nitric acid, precipitated the solution with potassium bromide, 
washed, dried, fused, and weighed the product. The following quanti- 
ties of bromine were found proportional to 100 parts of silver : 




Mean, reduced to a vacuum standard, 74.077, dr .003 

Much more elaborate determinations of this ratio are due to Stas.J 
In one experiment a known weight of silver was converted into nitrate, 
and precipitated in the same vessel by pure hydrobromic acid. The 
resulting bromide was washed thoroughly, dried, and weighed. In four 
other estimations the silver was converted into sulphate. Then a known 
quantity of pure bromine, as nearly as possible the exact amount neces- 
sary to precipitate the silver, was transformed into hydrobromic acid. 
This was added to the dilute solution of the sulphate, and, after precip- 
itation was complete, the minute trace of an excess of silver in the clear 
supernatant fluid was determined. All weighings were reduced to a 
vacuum. From these experiments, taking both series as one, we get 
the following quantities of bromine corresponding to 100 parts of silver: 

74.0830 

74.0790 

74.0795 
74.0805 
74.0830 



Mean, 74.081, db .0006 



*Ann. Chem. Phartn., 113, 20. 

f E. Mulder's Overzigt, p. 116. Berzelius' Jahresbericht, 24, 7; 

I Aronstein's translation, pp. 154-170. 



46 THE ATOMIC WEIGHTS. 

In his paper on the atomic weight of cadmium,* Huntington gives 
three syntheses and three analyses of silver bromide. The data are as 
follows, with the usual ratio given in the last column : 

1.4852 grm. Ag gave 2.5855 AgBr. 74.084 

1.4080 2.4510 " 74-077 

1.4449 " 2.5150 " 74.060 

4.1450 grm. AgBr gave 2.3817 Ag. 74-35 

1.8172 " 1.0437 " 74-i" 

4.9601 2.84 9 7 74.057 

Mean, 74.071, .0072 

Similar synthetic data are also given by Richards, incidentally to his 
work on copper.f There are two sets of three experiments each, which 
can here be treated as one series, thus : 

:.H235 grm. Ag gave 1.93630 AgBr. 74-73 

2-74335 " 74-044 

3.77170 " 74.076 

" 1.68205 " 74.053 

" 1.6789 " 74.069 

1.6779 " 74-074 




Mean, 74.065, .0035 

Another set of data by Richards appears in his research upon the 
atomic weight of barium ; J in which BaBr 2 was balanced against silver, 
and the AgBr was also weighed. Richards gives from these data the 
percentage of Ag in AgBr, which figures are easily restated in the usual 
form as follows: 

Percentage. Ratio, 

57.460 74.034 

57-455 74.049 

57-447 74 073 

57-445 74-074 

57.448 74-070 

57.442 74-089 

57.451 74.061 

57-455 74-049 

57-443 74.086 

57-445 74-074 

57-445 74-074 



Mean, 74.067, rb .0034 

The same ratio can also be computed indirectly from Cooke's experi- 
ments upon SbBr 3 , Huntington's on CdBr 2 , Thorpe's on TiBr 4 , and 



* Proc. Amer. Acad., 1881. 

fProc. Amer. Acad., 25, pp. 199, 210, 211. 1890. 

I Proc. Amer. Acad., vol. 28. 1893. 



SILVER, POTASSIUM, ETC. 47 

Thorpe and Laurie's on gold. The values so obtained all confirm the 
results already given, varying within their limits, but having probable 
errors so high that their use would not affect the final mean. The latter 
is obtained as follows : 

Marignac 74.077, .0030 

Stas 74.o8i, .0006 

Huntington 74-O7 1 , =b .0072 

Richards, 1st series 74.065, .0035 

" 2d " 74.067,^.0034 



General mean. ... 74.080, .00057 

In this case again, as in so many others, Stas' work alone appears at 
the end, the remaining data having only corroborative value. 

The ratio between silver and potassium bromide was first accurately 
determined by Marignac.* I give, with his weighings, the quantity of 
KBr proportional to 100 parts of Ag : 

2.131 grm. Ag = 2.351 KBr. 110.324 

2.559 " 2.823 " 110.316 

2.447 2.700 " 110.339 

3.025 " 3.336 " 110.283 

3-946 4.353 " 110.314 

11.569 " 12.763 " 110.321 

20.120 " 22.191 " 110.293 



Mean, corrected for weighing in air, 110.343, , .005 



Stas,f working in essentially the same manner, as when he fixed the 
ratio between potassium chloride and silver, obtained the following 

results : 

110.361 
110.360 
110.360 
110.342 
110.346 
110.338 
110.360 
110.336 
110.344 
110.332 
110.343 

110.357 
110.334 
"0.335 

Mean, 110.3463, .0020 

Combining this with Marignac's mean result, 110.343, .005, we get 
a general mean of 110.3459, .0019. 

*Berzelius' Jahresbericht, 24, 72. 

f- Aronstein's translation, pp. 334-347. 



48 THE ATOMIC WEIGHTS. 

The ratios upon which we must depend for the atomic weight of 
iodine are exactly parallel to those used for the determination of bromine. 

To begin with, the percentage of oxygen in potassium iodate has been 
determined by Millon.* In three experiments he found : 

22.46 
22.49 

22.47 



Mean, 22.473, .5 

Millon also estimated the oxygen in silver iodate, getting the follow- 
ing percentages : 

17.05 
17.03 
17.06 



Mean, 17.047, .005 

The analysis of silver iodate has also been performed with extreme 
care by Stas.f From 76 to 157 grammes were used in each experiment, 
the weights being reduced to a vacuum standard. As the salt could not 
be prepared in an absolutely anhydrous condition, the water expelled in 
each analysis was accurately estimated and the necessary corrections ap- 
plied. In two of the experiments the iodate was decomposed by heat, 
and the oxygen given off was fixed upon a weighed quantity of copper 
heated to redness. Thus the actual weights, both of the oxygen and the 
residual iodide, were obtained. In a third experiment the iodate was 
reduced to iodide by a solution of sulphurous acid, and the oxygen was 
estimated only by difference. In the three percentages of oxygen given 
below, the result of this analysis conies last. The figures for oxygen are 
as follows : 

16.976 

16.972 

16.9761 

Mean, 16.9747, d= .0009 

This, combined with Millon's series above cited, gives us a general 
mean of 16.9771, .0009. 

The ratio between silver and potassium iodide seems to have been de- 
termined only by Marignac.J and without remarkable accuracy. In five 
experiments 100 parts of silver were found equivalent to potassium iodide 
as follows : 

*Ann. Chim. Phys. (3), 9, 400. 1843. 
fAronstein's translation, pp. 170-200. 
I Berzelius' I^ehrbuch, 5th ed., 3, 1196. 



SILVER, POTASSIUM, ETC. 49 

1.616 grm. Ag = 2.483X1. Ratio, 153.651 

2.503 " 3.846 " " 153.665 

3.427 5.268 " " 153.720 

2.141 3.290 " " 153-667 

10.821 16.642 " " 153.794 

Mean, 153.6994, d= .0178 

The synthesis of silver iodide has been effected by both Marignac and 
Stas. Marignac, in the paper above cited, gives these weighings. In the 
last column I add the ratio between iodine and 100 parts of silver: 

15.000 grm. Ag gave 31.625 Agl. 117.500 

14-79 " 3 2 .I70 " H7.5I 2 

18.545 " 40.339 " H7.5I9 



Mean, corrected for weighing in air, 117.5335, .0036 

Stas* in his experiments worked after two methods, which gave, how- 
ever, results concordant with each other and with those of Marignac. 

In the first series of experiments Stas converted a known weight of 
silver into nitrate, and then precipitated with pure hydriodicacid. The 
iodide thus thrown down was washed, dried, and weighed without trans- 
fer. By this method 100 parts of silver were found to require of iodine : 

117.529 
117-536 



Mean, 117.5325, .0024 

In the second series a complete synthesis of silver iodide from known 
weights of iodine and metal was performed. The iodine was dissolved 
in a solution of ammonium sulphite, and thus converted into ammonium 
iodide. The silver was transformed into sulphate and the two solutions 
were mixed. When the precipitate of silver iodide was completely de- 
posited the supernatant liquid was titrated for the trifling excess of iodine 
which it always contained. As the two elements were weighed out in the 
ratio of 127 to 108, while the atomic weight of iodine is probably a little 
under 127, this excess is easily explained. From these experiments two 
sets of values were deduced ; one from the weights of silver and iodine 
actually employed, the other from the quantity of iodide of silver col- 
lected. From the first set we have of iodine for 100 parts of silver : 

"7-5390 
117.5380 

117- 53' 8 



117.5420 
117.5300 



Mean, 117.5373, db .0015 



: Aronstein's translation, pp. 136, 152. 



50 THE ATOMIC WEIGHTS. 

From the weight of silver iodide actually collected we get as follows. 
For experiment number three in the above column there is no equivalent 

here: 

117.529 
117.531 
117-539 
117-538 
ii7-53 

Mean, H7-5334, d= .0014 

Now, combining these several sets of results, we have the following 
general mean : 

Marignac H7-5335, .3 6 

Stas, ist series ii7-53 2 5, - OO2 4 

" 2d " "7-5373, .ooi5 

" 3d " II7-5334, =t .0014 

General mean "7-5345, .0009 

One other comparatively unimportant iodine ratio remains for us to 
notice. Silver iodide, heated in a stream of chlorine, becomes converted 
into chloride ; and the ratio between these two salts has been thus deter- 
mined by Berzelius and by Dumas. 

From Berzelius * we have the following data. In the third column I 
give the ratio between Agl and 100 parts of AgCl : 

5.000 grm. Agl gave 3.062 AgCl. 163.292 

12.212 " 7-4755 " 163.360 

Mean, 163.326, .023 

Dumas' f results were as follows: 

3.520 grm. Agl gave 2.149 AgCl. 163. 793 

7.011 " 4.281 " 163.770 



Mean, 163.782, .008 

General mean from the combination of both series, 163.733, .0076. 

For sodium there are but four ratios of any value for present purposes. 

The early work of Berzelius we may disregard entirely, and confine 
ourselves to the consideration of the results obtained by" Penny, Pelouze, 
Dumas, and Stas, together with a single ratio measured incidentally by 
Earn say and Aston. 

The percentage of oxygen in sodium chlorate has been determined 
only by PennyJ, who used the same method which he applied to the 
potassium salt. Four experiments gave the following results : 

* Ann. Chim. Phys. (2), 40, 430. 1829. 
t Ann. Chem. Pharm., 113, 28. 1860. 
J Phil. Transactions, 1839, p. 25. 



SILVER, POTASSIUM, ETC. 51 




Mean, 45.0705, d= .0029. 



The ratio between silver and sodium chloride has been fixed by Pe- 
louze, Dumas, and Stas. Pelouze * dissolved a weighed quantity of silver 
in nitric acid, and then titrated with sodium chloride. Equivalent to 
100 parts of silver he found of chloride : 

54.158 
54.125 
54.139 

Mean, 54.141, .0063 

By Dumas f we have seven experiments, with results as follows. The 
third column gives the ratio between 100 of silver and NaCl : 

2.0535 grm. NaCl = 3-788 grm. Ag. 54-2H 

2.169 4.0095 " 54.097 

4-3554 8.0425 " 54.155 

6.509 12.0140 " 54.178 

6.413 11-8375 " 54.175 

2.1746 4.012 " 54.202 

5- "3 " 9-434 " 54.187 

Mean, 54.172, .0096 

Stas,J applying the method used in establishing the similar ratio for 
potassium chloride, and working with salt from six different sources, 
found of sodium chloride equivalent to 100 parts of silver : 

54.2093 
54.2088 
54.2070 
54-2070 
54.2070 
54.2060 
54.2076 
54.2081 
54-2083 
54.2089 

Mean, 54.2078, .0002 

As in the case of the corresponding ratio for potassium chloride, these 
data needed to be checked by others which took into account the solu- 

*Cotnpt. Rend., 20, 1047. 1845. 

t Ann. Chem. Pharm.. 113. 31. 1860. 

J Aronstein's translation, p. 274. 



52 THE ATOMIC WEIGHTS. 

bility of silver chloride. Such data are given in Stas' paper of 1882,* 
and four results are as follows : 

54.2065 

54.20676 

54.2091 

54-2054 

Mean, 54.20694, db .00045 

Corrected for a trace of silica in the sodium chloride, this mean becomes 
54.2046, it .O0045.t Combining all four series, we have for the NaCl 
equivalent to 100 parts of Ag 

Pelouze 54- HI, .0063 

Dumas 54- 1 7 2 , .0096 

Stas, early series 54.2078, .0002 

Stas, late " 54.2046,^.00045 

General mean 54.2071, .00018 

Here the work of Stas is of such superior excellence that the other de- 
terminations might be completely rejected without appreciably affecting 
our final results. 

In their research upon the atomic weight of boron, Ramsay and Aston J 
converted borax into sodium chloride. In the latter the chlorine was 
afterwards estimated gravimetrically by weighing as silver chloride on a 
Gooch filter. Hence the ratio, AgCl : NaCl : : 100 : x, as follows : 

3.0761 grm. NaCl gave 7.5259 AgCl. Ratio, 40.874 

2.7700 6.7794 " " 40.859 

2.8930 " 7.0804 " " 40-859 

2.7360 " 6.6960 " 40.860 

1.9187 " 46931 " " 40.863 



Mean, 40.867, .0033 

Finally, for the ratios between silver and sodium bromide we have one 
set of measurements by Stas. The bromide was prepared by saturating 
Na. 2 C0 3 with HBr. The NaBr proportional to 100 parts of silver was 

95.4420 

95-4383 
95.4426 

95-4392 



Mean, 95.4405, .0007 

We have now before us the data for computing, with greater or less 
accuracy, the atomic weights of the six elements under discussion. In 

*Mmoires Acad. Roy. de Beige., 43. 1882. 

fSee Van der Plaats, Ann. Chim. Phys. (6), 7, 16. 1886. 

% Chem. News, 66, 92. 1892. 

I Memoires Acad. Roy. Beige., 43. 1882. 



SILVER, POTASSIUM, ETC. 53 

all there are nineteen ratios, involving about two hundred and fifty 
separate experiments. These ratios may now be tabulated and num- 
bered for reference, it being understood that the probable error in each 
case is that of the last term in the proportion. 

(i.) Percentage of O in KC1O 3 . . ... 39.154, .00038 

(2.) " " KBrO 3 28.6755,^.0207 

(3-) " KI O 3 22.473, .0050 

(4.) NaClO 3 45.0705, .0029 

(5.) AgClO 3 25.080, d= .0010 

(6.) " " AgBrO s 20.349, .0014 

(7-) " " AgI0 3 16.9771, .0009 

(8.) Ag : NaCl : : ioo : 54.2071, .00018 

(9.) Ag : NaBr : : 100 : 95.4405, .0007 

(10.) Ag : KC1 : : 100 : 69.1143, .00013 

(li.) Ag : KHr : : 100 : 110.3459, .0019 

(12.) Ag : KI : : 100 : J53- 6 994, .0178 

( ! 3-) Ag : Cl : : loo : 32.8418, .0006 

(14.) Ag : Br : : 100 : 74.080, .00057 

(IS.) Ag : I : : ioo : 117.5345, .0009 

(l6.) AgCl : NaCl : : IOO : 40.867, .0033 

(17.) KC1 : AgCl : : ioo : 192.294, db .0029 

(18.) AgCl : AgBr : : ioo : 131.030, .023 

(19.) AgCl : Agl : : ioo : 163.733, .0076 

Now, from ratios 1 to 7, inclusive, we can at once, by applying the 
known atomic weight of oxygen, deduce the molecular weights of seven 
haloid salts. Let us consider the first calculation somewhat in detail. 

Potassium chlorate yields 39.154 per cent, of oxygen and 60.846 per 
cent, of residual chloride. For each of these quantities the probable 
error is .00038. The atomic weight of oxygen is 15.879, dz .0003, so 
that the value for three atoms becomes 47.637, .0009. We have now 
the following simple proportion : 

39.154 : 60.846 : : 47-637 : *, 

whence the molecular weight of potassium chloride becomes = 74.029. 
The probable error being known for the first, second, and third term 
of this proportion, we can easily find that of the fourth term by the 
formula given in our introduction. It is dz .0073. By this method we 
obtain the following series of values, which may conveniently be num- 
bered consecutively with the foregoing ratios : 

(20) KC1, from (i) = 74.029, .0073 

(21) KBr, " (2) = 118.487, .0923 

(22) KI, " (3) = 164.337, .0382 

(23) NaCl, " (4) = 58.057, .0050 

(24) AgCl, " (5) = 142.303, .0066 

( 2 5) AgBr, " (6) = 186.463, .0137 

(26) Agl, " (7) =. 232.959, .0134 



54 THE ATOMIC WEIGHTS. 

With the help of these molecular weights, we are now able to com- 
pute seven independent values for the atomic weight of silver. 

First, from (10) and (20) Ag 107.1 1 1, db .0106 

Second, " (u) " (21) " = 107.378,^.0837 

Third, " (12) " (22) " = 106.921,^.0278 

Fourth, " ( 8 ) " (23) " = 107. 102, .0092 

Fifth, " (13) " (24) " = 107.122, .0050 

Sixth, " (14) " (25) " =107.113, dr. 0079 

Seventh, " (15) " (26) " = 107.091, dr .0062 

General mean Ag = 107. 108, dr .0031 

It is noticeable that five of these values agree very well. The second 
and third, however, diverge widely from the average, but in opposite 
directions ; they have, moreover, high probable errors, and consequently 
little weight. Of these two, one represents little and the other none of 
Stas' work. Their trifling influence upon our final results becomes 
curiously apparent in the series of silver values given a little further 
along. 

When we consider closely, in all of its bearings, any one of the values 
just given, we shall see that for certain purposes it must be excluded 
from our general mean. For example, the first is derived partly from 
the ratio between silver and potassium chloride. From this ratio, the 
atomic weight of one substance being known, we can deduce that of the 
other. We have already used it in ascertaining the atomic weight of 
silver, and the value thus obtained is included in our general mean. 
But if from it we are to determine the molecular weight of potassium 
chloride, we must use a silver value derived from other sources only, or 
we should be assuming a part of our result in advance. In other words, 
we must now use a general mean for silver from which this ratio with 
reference to silver has been rejected. Hence the following series of silver 
values, which are lettered for reference : 

A. General mean from all eight 107.108, dr .0031 

B. " excluding the first 107.108, dr .0032 

C. " " second 107.107, .0031 

D. " third 107.1 IO, rfc .0031 

E. " " fourth 107. 109, dr .0033 

F. " " fifth 107.099, dr .0039 

G. " sixth 107.106, dr .0034 

H. " seventh .... 107.113, dr .0036 

We are now in a position to determine more closely the molecular 
weights of the haloid salts which we have already been considering. 

For silver chloride, still employing the formula for the probable error 
of the last term of a proportion, we get the following values : 



SILVER, POTASSIUM, ETC. 55 

From (5) AgCl 142.303, .0066 

From (13) and (F) " = 142.276, .0052 

From ( 1 6) " (23) " == 142.063, .0168 

From (17) " (20) " = 142.353,^.0156 

From ( 1 8) " (25) " = 142.306, =b .0271 

From (19) " (26) " = 142.278, =b .0105 



General mean AgCl = 142. 277, .0036 

The third of these values is certainly too low, and although it reduces 
the atomic weight of chlorine by only 0.01, it ought to be rejected. The 
general mean of the other five values is AgCl = 142.287, .0037. Sub- 
tracting from this the atomic weight of silver, 107.108, .0031, we have 
for the atomic weight of chlorine 

1 = 35.179, .0048. 
For silver bromide three ratios are available: 

From (6) AgBr = 186.463, dr .0137 

From (14) and (G) " = 186.450, .0050 

From ( 1 8) " (24) " = 186.459,^.0339 

General mean AgBr= 186.452, .0054 

Hence, applying the atomic weight of silver as before 

Br = 79.344, d= .0062. 

For silver iodide we have 

From (7) ' Agl = 232.950, rh .0134 

From (15) and (H) . " = 233.008, .0079 

From (19) " (24) " =^232.997,^.0153 

General mean Agl = 232.996, rb .0062 

Hence, 

1= 125.888, rb .0069. 

For the molecular weight of sodium chloride three values appear, as 
follows : 

From (4) NaCl = 58.057, .0050 

From (8) and (E) " = 58.061, .0018 

From (16) " AgCl " := 58.148, .0049 

General mean NaCl = 58.069, rh .0016 

Rejecting the third value, which corresponds to the rejected value for 
AgCl and throws out ratio (16) entirely, the mean becomes 

NaCl = 58.060, dz .0017 

From (9) and (A) NaBr = 102.224, .0031 



56 , THE ATOMIC WEIGHTS. 

Deducting from these molecular weights the values already found for 
Cl and Br,two measurements of the atomic weight of sodium are obtained, 
thus: 

From NaCl Na = 22.881, .0051 

FromNaBr.. . " = 22.880, .01 12 



General mean Na = 22.881, 0046 

The rejection of ratio (16) in connection with the atomic weights of 
sodium and chlorine is fully justified by the fact that the data which it 
represents were never intended for use in such computations. They were 
obtained incidentally in connection with work upon boron, and their 
consideration here may have some bearing later upon the discussion of 
the last-named element. 

For potassium, the ratios available give molecular weights for the 
chloride, bromide, and iodide. For the chloride, 

From (i) KC1 = 74.029, db .0073 

From ( 10) and (B) " = 74.027,^.0022 

From (17) " (24) " = 74.003, .0049 

General mean KC1 = 74.025, d= .0019 

For the bromide we have 

From (2) KBr = 118.487, .0923 

From (n ) and (C) " = 118.188, .0073 

General mean -. . . KBr = 118.200, .0073 

And for the iodide 

( 

From (3) KI = 164.337, .0382 

From (12) and (D) " = 164.627, =!= .0052 

General mean KI = 164.622, .0051 

Combining these values with those found for chlorine, bromine, and 
iodine, we have three values for the atomic weight of potassium, as fol- 
lows : 

From KC1 K = 38.846, .0078 

From KBr "= 38.856, .0096 

From KI " =38.734, .0086 



General mean K = 38.817, .0051 

To sum up, the six atomic weights, under discussion may be tabulated 
as follows, both for the standard chosen, and with O = 16 as the base of 
the system : 



SILVER, POTASSIUM, ETC. t 57 

H=i. <9=i6. 

Ag , 107.108, .0031 107.924 

K. 38.817,^.0051 39.112 

Na 22.881, .0046 23.048 

Cl 35.179, .0048 35-447 

Br 79.344,^.0062 79-949 

I 125.888,^.0069 126.847 

It must be remembered that tbese values represent the summing up 
of work done by many investigators. Stas' ratios, taken by themselves, 
give various results, according to the method of combining them. This 
computation has been made by Stas himself, with his older determina- 
tions, and more recently by Ostwald,* Van der Plaats,f and Thomsen, J 
all with the standard of 16. By Van der Plaats two sets of results 
are given : one with Stas' ratios assigned equal weight (A), and the other 
with each ratio given weight inversely proportional to the square of its 
mean error (B). The results of these several computations may well be 
tabulated in comparison with the values obtained in my own general 
discussion, thus : 

Clarke. Stas. Ostwald. V. der P., A. V.derP.,B. Thomsen. 

Ag 107.924 107.930 107.9376 107.9202 107.9244 107.9299 

39-H2 39-*37 39- I 3 61 39- T 4i4 39-HO3, 39- I 57 

23.048 23.043 23.0575 23.0453 23.0443 ' 23.0543 

d 35-447 35-457 35-45 2 9 35-45 16 35-45 6 5 35-4494 

Br 79-949 79 95 2 79-96^8 79-94Q7 79-9548 79.95 10 

I 126.847 126.850 126.8640 126.8445 126.8494 126.8556 

The agreement between the new values and the others is highly satis- 
factory, and gives a strong emphasis to the magnificent accuracy of Stas' 
determinations. No severer test could be applied to them. 

*Lehrbuch der allgemeinen Chemie, i, 41. 1885. 

tCompt. Rend., 116, 1362. 1893. 

t Zeitsch. Physikal. Chem., 13, 726. 1894. 



58 THE ATOMIC WEIGHTS. 



NITROGEN. 

The atomic weight of nitrogen has been determined from the density 
of the gas, and from a considerable variety of purely chemical ratios. 

Upon the density of nitrogen a great many experiments have been 
made. In early times this constant was determined by Biot and Arago, 
Thomson, Dulong and Berzelius, Lavoisier, and others. But all of these 
investigations may be disregarded as of insufficient accuracy ; and, as 
in the case of oxygen, we need consider only the results obtained by 
Dumas and Boussingault, by Regnault, and by recent investigators. 

Taking air as unity, Dumas and Boussingault* found the density of 
nitrogen to be 

.970 
.972 
974 

Mean, .972, .00078 

For hydrogen, as was seen in our discussion of the atomic weight of 
oxygen, the same investigators found a mean of .0693, .00013. Upon 
combining this with the above nitrogen mean, we find for the atomic 
weight of the latter element, N = 14.026, .0295. 

By Regnault f much closer work was done. He found the density of 
nitrogen to be as follows : 

.97148 
.97H8 
97154 
.97155 
.97108 
.97108 



Mean, .97137, d= .000062 

For hydrogen, Regnault's mean value is .069263, .000019. Hence, 
combining as before, N = 14.0244 .0039. 

Both of the preceding values are affected by a correction for the dif- 
ference in volume between the weighing globes when full and when 
empty. This correction, in the case of Regnault's data, has been meas- 
ured by Crafts,J who gives .06949 for the density of H, and .97138 for N. 
Corrected ratio, N = 13.9787. If we assume the same proportional cor- 
rection for the determination by Dumas and Boussingault, that becomes 
N = 13.9771. 

*Compt. Rend., 12, 1005. 1841. 
f Compt. Rend., 20, 975. 1845. 
I Compt. Rend., 106, 1664. 



NITROGEN. 59 

Von Jolly,* working with electrolytic oxygen and with nitrogen pre- 
pared by passing air over hot copper, but not with hydrogen, compared 
the weights of equal volumes of the two gases, with results as follows : 

Oxygen. Nitrogen. 

.442470 1.269609 

.442579 .269389 

.442489 .269307 

.442570 .269449 

442571 .269515 

.442562 .269443 

.442478 . .269478 

Mean, 1.442545, .000013 Mean, 1.269455, . 000024 

The ratio, when O = 16, is N = 14.0802, .0003. Corrected by Ray- 
leigh, the ratio between the weights becomes 14.0805. If = 15.879, 
dz .0003, the final value for N, deducible from Von Jolly's data, is N = 
13.974, .0004. 

The next determination in order of time is Leduc's.f He made nine 
measurements of the density of nitrogen, giving a mean of .97203, with 
extremes of .9719 and .9721; but he neglects to cite the intermediate 
values. Taking the three figures given as representative, and assuming 
a fair distribution of the other values between the indicated limits, the 
probable error of the mean is not far from 0.00002. For hydrogen he 
found .06948, .00006745. The ratio between the two densities gives 
N = 13.9901, .0138. 

Lord Rayleigh,^ preparing nitrogen by passing air over hot copper, 
and weighing in a standard globe, obtained the following weights : 

2.31035 
2.31026 
2.31024 
2.31012 
2.31027 



Mean, 2.31025, 000025 

With corrections for temperature, shrinkage of the globe when ex- 
hausted, etc., this becomes 2.30883, as against 2.37512 for the same volume 
of air. Hence the density of N = .97209, .00001. His former work 
on hydrogen gives .06960, .0000084, for the density of that gas. The 
ratio is N = 13.9678, .0017. 

The foregoing data, however, all apply to nitrogen derived from the 
atmosphere. In a later memoir Rayleigh found that nitrogen from 

* Poggend. Annalen (2), 6, 529-530. 1879. 
fCompt. Rend., 113, 186. 1891. 
j Proc. Roy. Soc., 53, 134. 1894. 
I Chem. News, 69, 231. 1894. 



60 THE ATOMIC WEIGHTS. 

chemical sources, such as oxides of nitrogen, ammonium nitrate, etc., 
was perceptibly lighter ; and not long afterwards the discrepancy was 
explained by the astonishing discovery of argon. The densities given, 
therefore, are all too high, and unavailable for any discussion of atomic 
weight. As, however, the reductions had been completed in nearly all . 
their details before the existence of argon was announced, they may be 
allowed to remain here as part of the record. Summing up, the ratios 
found between hydrogen and atmospheric u nitrogen " are as follows : 

Dumas and Boussingault, corrected 1 3.977 

Regnault, " 13-979 

Von Jolly, " ij-974 

Leduc, " 13.990 

Rayleigh, " 13.968 

Perhaps at some future time, when the density of argon is accurately 
known and its amount in the atmosphere has been precisely determined, 
these figures may be so corrected as to be useful for atomic weight calcu- 
lations. 

In discussing the more purely chemical ratios for establishing the 
atomic weight of nitrogen, we may ignore, for the present, the researches 
of Berzelius and of Anderson. These chemists experimented chiefly 
upon lead nitrate, and their work is consequently now of greater value 
for fixing the atomic weight of lead. Their results will be duly consid- 
ered in the proper connection further on. 

The ratio between ammonium chloride and silver has been determined 
by Pelouze, by Marignac, and by Stas. The method of working is essen- 
tially that adopted in the similar experiments with the chlorides of 
sodium and potassium. 

For the ammonium chloride equivalent to 100 parts of silver, Pelouze* 
found : 

49-556 
49-5<7 

Mean, 49.5365, .013 

Marignac f obtained the following results. The usual ratio for 100 
parts of silver is given also : 



8.063 g rm - 


Ag = 3.992 grm. NH 4 C1. 


49.510 




9.402 


4-656 " 


49-521 




10.339 


" 5.120 " 


49-521 




12.497 


" 6.191 " 


49.540 




"337 


" 5-6i7 " 


49.546 




11.307 


5-595 


49-483 




4.326 


2.143 


49.538 








Mean, 49.523, 


-0055 



*Compt. Rend., 20. 1047. 1845. 

t Berzelius' Lehrbuch, sth ed., vol. 3, 1184, 1185. 



NITROGEN. 61 

But neither of these series can for a moment compare with that of 
Stas. * He used from 12.5 to 80 grammes of silver in each experiment^ 
reduced his weighings to a vacuum standard, and adopted a great variety 
of precautions to insure accuracy. He found for every 100 parts of silver 
the following quantities of NH 4 C1 : 

V 

49.600 

49.599 

49-597 

49.598 

49-597 

49-593 

49-597 

49-5974 

49.602 

49-597 
49598 
49-592 



Mean, 49-5973, .0005 

In this work, as with the similar ratios for potassium and sodium 
chloride, the solubility of silver chloride was not guarded against so fully 
as is needful. Accordingly Stas published a new series of determina- 
tions in 1882,f carefully checked in this particular, with the subjoined 
values for the ratio : 

49.60001 
49-59999 
49-599 
49.600 

49.597 
Mean, 49-S99 2 , .00039 

Combining all four series, we have 

Pelouze 49-5365, =b .013 

Marignac 49-5 2 3> -OQ55 

Stas, early series 49'5973, d= .0005 

Stas, later " 49.5992, .00039 



General mean 49-5983, .00031 

In the paper last cited Stas also gives a similar series of determinations 
for the ratio Ag : NH 4 Br : : 100 : x. The results are as follows, with re- 
duction to vacuum : 

* Aronstein's translation, pp. 56-58. 
fMemoires Acad. Roy. de Beige., 43. 1882. 



62 THE ATOMIC WEIGHTS, 

90.831 

90.831 

90.8297 

90.823 

90.8317 

90.8311 

90.832 



Mean, 90.8299, .0008 

The quantity of silver nitrate which can be formed from a known 
weight of metallic silver has been determined by Penny, by Marignac, 
and by Stas. Penny * dissolved silver in nitric acid in a flask, evapo- 
rated to dryness without transfer, and weighed. One hundred parts of 
silver thus gave of nitrate : 

157.430 
157-437 
157-458 
157.440 

157.43 

157-455 

Mean, 157.4417, .0033 

Marignac'sf results were as follows. In the third column they are 
reduced to the common standard of 100 parts of silver : 

68.987 grm. Ag gave 108.608 grm. AgNO 3 . 1 57. 433 

57.844 " 9 I -47 I57.40I 

66.436 " 104.592 " 157.433 

70.340 110.718 157.404 

200.000 " 3*4.894 " 157.447 

Mean, 157.4236, .0061 

Stas,t employing from 77 to 405 grammes of silver in each experiment, 
made two different series of determinations at two different times. The 
silver was dissolved with all the usual precautions against loss and 
against impurity, and the resulting nitrate was weighed, first after long 
drying without fusion, just below its melting point ; and again, fused. 
Between the fused and the unfused salt there was in every case a slight 
difference in weight, the latter giving a maximum and the former a 
minimum value. 

In Stas' first series there are eight experiments; but the seventh he 
himself rejects as inexact. The values obtained for the nitrate from 100 

* Phil. Trans., 1839. 

fBerzelius' I^ehrbuch, sth ed., 3, pp. 1184, 1185. 

t Aronstein's translation, pp. 305 and 315. 



NITKOGEN. 63 

parts of silver are given below in two columns, representing the two con- 
ditions in which the salt was weighed. The general mean given at the 
end I have deduced from the means of the two columns considered 
separately : 

Unfused. Fused. 

IS7-492 157.474 

157-510 157.481 

157-485 157-477 

157.476 i57-47i 

157.478 157-47 

T57.47I 157.463 

157.488 157-469 



Mean, 157.4857 Mean, 157.472 

General mean, 157.474, .0014 

In the later series there are but two experiments, as follows : 

Unfused. Fused. 

157.4964 I57-488 

157.4940 i57-48o 

Mean, 157.4952 Mean, 157.484 

General mean, 157.486, .0003 

The reverse ratio, namely, the amount of silver obtainable from a 
weighed quantity of nitrate, has been determined electrolytically by 
Hardin.* The data obtained, however, are reducible to the same form 
as in the preceding series, and all are properly combinable together. 
Pure silver was dissolved in pure aqueous nitric acid, and the crystal- 
line salt thus formed was dried, fused, and used for the determinations. 
The silver nitrate, mixed with an excess of pure potassium cyanide solu- 
tion, was electrolyzed in a platinum dish. The results obtained, reduced 
to vacuum weights, were as follows : 

.31202 AgNO 3 gave .19812 Ag. Ratio, 157.490 



.47832 


.30370 " 


157.498 




.56742 


.36030 " 


" 157.485 




.57728 


.36655 " 


" 157.490 




.69409 


.44075 " 


" 157.479 




.86367 


.54843 " 


" 157.479 




.868u 


" -SS^o " 


" 157.466 




.93716 


.59508 


" 157.485 




1.06170 


.67412 " 


" 157.494 


i 


1.19849 


" .76104 " 


J< 157-477 








Mean, 157.484, 


.0020 




* Journ. Amer. Chem. Soc., 


18,995. 1896. 





64 THE ATOMIC WEIGHTS. 

Now, to combine all five sets of results : 

Penny 157-4417, -33 

Marignac 1 57-4236, .0061 

Stas, ist series 157.4740, .0014 

Stas, 2d " 157.4860, =h .0003 

Hardin 157.484, .0020 

General mean 157-479, .0003 

For the direct ratio between silver nitrate and silver chloride there are 
two series of estimations. A weighed quantity of nitrate is easily con- 
verted into chloride, and the weight of the latter ascertained. In two 
experiments Turner* found of chloride from 100 parts of nitrate : 

84-357 
84.389 



Mean, 84.373, i.on 

Penny ,t in five determinations, found the following percentages: 

84-370 
84.388 
84.377 
84.367 
84-370 



Mean, 84.3744, d= .0025 

The general mean from both series is 84.3743, .0025. 

The ratio directly connecting silver nitrate with ammonium chloride 
has been determined only by Stas. J The usual method of working was 
followed, namely, nearly equivalent quantities of the two salts were 
weighed out, the solutions mixed, and the slight excess of one estimated 
by titration. In four experiments 100 parts of silver nitrate were found 
equivalent to chloride of ammonium, as follows: 

3L489 
3L490 
31-487 
31.486 



Mean, 31.488, .0006 

I 

The similar ratio between potassium chloride and silver nitrate- has 

been determined by both Marignac and Stas. 

*Phil. Trans., 1833, 537. 
fPhil. Trans., 1839. 
jAronstein's translation, p. 309. 



NITROGEN. 65 

Marignac* gives the following weights. I add the quantity of KC1 
proportional to 100 parts of AgN0 3 : , 

1.849 grm. KC1 4.218 grm. AgNO 3 . 43.836 

2.473 " 5.640 " 43-848 

3-3I7 7.565 43.847 

2.926 " 6.670 " 43.868 

6.191 " 14.110 " 43.877 

4.351 " 9.918 " 43-870 

Mean, 43.858, .0044 

Stas' f results are given in three series, representing silver nitrate from 
three different sources. In the third series the nitrate was weighed in 
vacuo, while for the other series this correction was applied in the usual 
way. For the KC1 equivalent to 100 parts of AgN0 3 Stas found : 

First Series. 
43-878 
43.875 
43-875 
43-874 

Mean, 43.8755, =h .0005. 

Second Series. 

43-864 
43.869 
43-876 



Mean, 43.8697, .0023 

Third Series. 

43-894 
43-878 
43.885 



Mean, 43.8857, .0031 
i 

Combining all four series we have : 

Marignac 43.858, .0044 

Stas, ist series 43-8755, rfc .o5 

Stas, 2d " 43.8697, .0023 

Stas, 3d " 43-8857, .0031 



General mean 43.8715, =h .0004 

There have also been determined by Penny, by Stas, and by Hibbs a 
series of ratios connecting the alkaline chlorides and chlorates with the 
corresponding nitrates. One of these, relating to the lithium salts, will 
be studied farther on with reference to that metal. 

*Berzelius' L,e'urbuch, sth ed., 3d vol., 1184, 1185. 
t Aronstein's translation, p. 308. 



66 THE ATOMIC WEIGHTS. 

The general method of working upon these ratios is due to Penny. * 
Applied to the ratio between the chloride and nitrate of potassium, it is 
as follows : A weighed quantity of the chloride is introduced into a flask 
which is placed upon its side and connected with a receiver. An excess 
of pure nitric acid is added, and the transformation is gradually brought 
about by the aid of heat. Then, upon evaporating to dryness over a 
sand bath, the nitrate is brought into weighable form. The liquid in 
the receiver is also evaporated, and the trace of solid matter which had 
been mechanically carried over is recovered and also taken into account. 
In another series of experiments the nitrate was taken, and by pure hy- 
drochloric acid converted into chloride, the process being the same. In 
the following columns of figures I have reduced both series to one stand- 
ard, namely, so as to express the number of parts of nitrate correspond- 
ing to 100 of chloride : 

First Series. KCl treated with 

!35- 6 39 
I35-637 
135-640 
135.635 
135-630 
135.640 
135-630 



Mean, 135.636, .0011 

Second Series. KNO^ treated with HCl. 
135.628 

135-635 
135-630 
135-641 
135 630 
135.635 
135-630 

Mean, 135.633, .0011 

Stas' f results are as follows : 

135.643 
135-638 
135.647 

135-649 
135.640 

1 35 -645 
135.655 

Mean, 135.6453, .0014 

*Phil. Trans., 1839. 

t Aronstein's translation, p. 270. 



NITROGEN. 



67 



These figures by Stas represent weighings in the air. Reduced to a 
vacuum standard, this mean becomes 135.6423. 

The determinations made by Hibbs* differ slightly in method from 
those of Penny and Stas. He converted the nitrate into the chloride by 
heating in a stream of gaseous hydrochloric acid. His results were as 
follows, vacuum weights being given 



Weight KNO Z Weight KCl. 
.11090 .08177 

.14871 .10965 

.21067 .15533 

.23360 .17225 

.24284 .17903 



Now, combining, we have : 



Ratio. 

135-624 
135.622 
135.627 
135.620 
135.642 



Mean, 135.627, =h .0026 



Penny, ist series J35-636, .001 1 

Penny, 2d " i35- 6 33> .0011 

Stas I35. 6 423, .0014 

Hibbs 135.627, .0026 



General mean 135.636, .0007 

By the same general process Penny f determined how much potassium 
nitrate could be formed from 100 parts of chlorate. He found as follows : 

82.505 
82.497 
82.498 
82.500 



Mean, 82.500, .0012 



For 100 parts of sodium chlorate he found of nitrate : 

79.875 
79-882 
79.890 

Mean, 79.8823, 4= .0029 



For the ratio between the chloride and nitrate of sodium Penny made 
two sets of estimations, as in the case of potassium salts. The subjoined 
figures give the amount of nitrate equivalent to 100 parts of chloride : 

* Thesis for Doctor's degree, University of Pennsylvania, 1896. Work done under the direction 
of Professor E. F. Smith. 
fPhil. Trans., 1839. 



68 THE ATOMIC WEIGHTS. 

First Series. NaCl treated with 

I45-4T5 
145.408 
145.420 

145.424 
145.410 
145.418 
145.420 

Mean, 145.4164, .0015 

Second Series. NaNO z treated with HCL 

I45-4I9 
I45-39 1 
145.412 

145.415 
145-412 
145.412 

Mean, 145.410, .0026 

Stas* gives the following series : 

145-453 
145.468 

145-465 
145.469 

145-443 

Mean, after reducing to vacuum standard, 145.4526, .0030 

Hibbs't data, obtained by the method employed in the case of the 
potassium compounds, are as follows, vacuum weights being stated : 

Weight NaNOy Weight NaCl. Ratio. 

.01550 .01066 i45-43 

.20976 .14426 I45.4 4 

.26229 .18038 145. 410 

.66645 .458 2 9 145.429 

.93718 .64456 H5-399 

Mean, 145.407, .0026 

Combining, we have as follows : 

Penny, 1st series 145.4164, .0015 

Penny, 2d " 145.410, .0026 

Stas 145.4526, .0030 

Hibbs 145.407, : .0026 

General mean 145.418, .0012 

* Aronstein's translation, p. 278. 

t Thesis, University of Pennsylvania, 1896. 



NITROGEN. 69 

Julius Thomsen, * for the purpose of fixing indirectly the ratio H : O, 
has made a valuable series of determinations of the ratio HC1:NH 3 , 
which may properly be used toward establishing the atomic weight of 
nitrogen. First, pure, dry, gaseous hydrochloric acid is passed into a 
weighed absorption apparatus containing pure distilled water. After 
noting the increase in weight, pure ammonia gas is passed in until a very 
slight excess is present, and the apparatus is weighed again. The excess 
of NH 3 , which is always minute, is measured by titration with standard 
hydrochloric acid. In weighing, the apparatus is tared by one of similar 
form, arid containing about the same amount of water. Three series of 
determinations were made, differing only in the size of the absorption 
apparatus ; so that for present purposes the three may be taken as one. 
Thomsen considers them separately, and so gives greatest weight to the ex- 
periments involving the largest masses of material. I give his weighings, 

TT/tj 

and also, as computed by him, the ratio ^T. 



First series. . 



Second series. 



HCl. 


Nt? 


Ratio. 


5.1624 


2.4120 


2.1403 


39425 


1.8409 


2.1416 


4.6544 


2.1739 


2.1411 


3.9840 


1.8609 


2.1409 


5.3295 


2.4898 


2.1406 


4-2517 


1.9863 


2.1405 


4.8287 


2.2550 


2.1414 


6.4377 


3.0068 


2.1411 


4.1804 


1.9528 


2.1407 


5-3 6 3 


2.35 2 3 


2.1410 


4.6408 


2.1685 


2.1411 


11.8418 


5-5302 


2.14130 


14.3018 


6.6808 


2.14073 


12.1502 


5.6759 


2.14067 


H-5443 


5.3927 


2.14073 


12.3617 


5-7733 


2.14118 


19-3455 


9.0360 


2.14094 


19.4578 


9.0890 


2.14081 



Third series.. 



Mean of all, 2.14093, .000053 
Reduced to vacuo, 2.1394 

From the sums of the weights Thomsen finds the ratio to be 2.14087, 
or 2.13934 in vacuo. From this, using Ostwald's reductions of Stas' data 
for the atomic weights of N and Cl, he finds the atomic weight of H = 
0.99946, when O == 16. 

We have now, apart from the determinations of gaseous density, eleven 
ratios, representing one hundred and sixty-four experiments, from which 

* Zeitsch. Physikal. Chem., 13, 398. 1894. 



70 THE ATOMIC WEIGHTS. 

to calculate the atomic weight of nitrogen. Let us first collect and num- 
ber these ratios : 

(i.) Ag : AgNO 3 : : ioo : 157-479, .o3 

(2.) AgNO 3 : AgCl : : ioo : 84-3743, - OO2 5 

(3.) AgNO 3 : KC1 : : ioo : 43- 8 7i5> .0004 

(4.) AgNO 3 : NH 4 C1 : : ioo : 31.488, .0006 

(5.) Ag : NH 4 C1 : : ioo : 49.5983, dr .00031 

(6.) Ag : NH 4 Br : : ioo : 90.8299, .0008 

(7.) KC1 : KNO 3 : : ioo : 135.636, .0007 

(8.) KC1O 3 : KN0 3 : : ioo : 82.500, .0012 

(9.) NaCl : NaNO 3 : : ioo : 145 418, .001 1 
(10.) NaClO 3 : NaNO 3 : : ioo : 79.8823, .0029 
(n.) NH 3 : HC1 : : i.oo : 2.1394, d= .000053 

From these ratios we are now able to deduce the molecular weight of 
ammonium chloride, ammonium bromide, and three nitrates. For these 
calculations we must use the already ascertained atomic weights of oxy- 
gen, silver, chlorine, bromine, sodium and potassium, and the molecular 
weights of sodium chloride, potassium chloride, and silver chloride. The 
following are the antecedent values to be employed : 

Ag = 107.108, d= .0031 
K = 38.817, =b .0051 
Na 22.881, .0046 
Cl = 35.179, =b .0048 
Br = 79.344, .0062 
O 3 = 47.637, -0009 
AgCl 142.287, .0037 
KC1 = 74.025, .0019 
NaCl = 58.060, .0017 

Now, from ratio number five we get the molecular weight of NH 4 C1 = 
53.124, .0016, and N = 13.945, .0051. 

From ratio number six, NH 4 Br = 97.286, .0029, and N = 13.942, 
.0077. 

From ratio number eleven, NH 3 = 16.911, .0048, and N = 13.911, 
.0048. 

From ratio number four, which involves an expression of the type 
A : B : : C + x : D + x, an independent value is deducible, N = 13.935, 
.0073. 

For the molecular weight of silver nitrate there are three values, 
namely : 

From (i) AgNO 3 == 168.673, .0049 

From (2) " = 168.634, .0066 

From (3) " = 168.731, .0046 

General mean A gNO 3 = 168.690, .0030 

Hence N= 13.945, .0044. 



NITROGEN. 71 

The molecular weight of potassium nitrate is twice calculable, as 
follows : 

From (7) KNO 3 = 100.405, .0026 

From (8) " 100.371, .0059 

General mean. . KNO 3 = 100.401, .0024 

Hence N = 13.947, .0057. 
And for sodium nitrate we have : 

From (9) NaNO 3 = 84.430, .0026 

From (.10) " = 84.433, .0053 

General mean NaNO 3 = 84.431, .0023 

Hence N = 13.913, .0052. 

There are now seven estimates of the atomic weight of nitrogen, to be 
combined by means of the usual formula. 

1. From NH 4 C1 N = 13.945, .0051 

2. " NH 4 Br " = 13.942, =h .0077 

3. " ratio (4) " = 13.935, .0073 

4- " " (n) " = 13.911, .0048 

5. " AgNO 3 "... " = 13.945,^.0044 

6. " KNO 3 " = 13.947, .0057 

7. " NaNO 3 " = 13.913, .0052 

General mean N = 13.935, .0021 

If oxygen is 16, this becomes 14.041. From Stas' data alone, Stas 
finds 14.044 ; Ostwald, 14.0410 ; Van der Plaats, 14.0421 (A), and 14.0519 
(B) ; and Thomsen, 14.0396. The new value, representing all available 
data, falls between these limits of variation. 



72 THE ATOMIC WEIGHTS. 



CARBON. 

Although there is a large mass of material relating to the atomic weight 
of carbon, much of it may be summarily set aside as having no value 
for present purposes. The density of carbon dioxide, which has been 
scrupulously determined by many investigators,* leads to no safe esti- 
mate of the constant under consideration. The numerous analyses of 
hydrocarbons, like the analyses of naphthalene by Mitscherlich, Wosk- 
resensky, Fownes, and Dumas, give results scarcely more satisfactory. 
In short, all the work done upon the atomic weight of carbon before the 
year 1840 may be safely rejected as unsuited to the present requirements 
of exact science. As for methods of estimation we need consider but 
four, as follows : 

First. The analysis of organic salts of silver. 

Second. The determination of the weight of carbon dioxide formed by 
the combustion of a known weight of carbon. 

Third. The method of Stas, by the combustion of carbon monoxide. 

Fourth. From the density of carbon monoxide. 

The first of these methods, which is probably the least accurate, was 
employed by Liebig and Redtenbacher f in 1840. They worked with 
the acetate, tartrate, racemate, and malate of silver, making five ignitions 
of each salt, and determining the percentage of metal. From one to 
nine grammes of material were used in each experiment. 

In the acetate the following percentages of silver were found : 

64.615 
64.624 
64.623 
64.614 
64.610 

Mean, 64.6172, .0018 

After applying corrections for weighing in air, this mean becomes 
64.6065. 

In the tartrate the silver came out as follows : 

59.297 
59-299 
59-287 
59-293 
59-293 



Mean, 59 2938, .0014 
Or, reduced to a vacuum, 59.2806 



* Notably by Lavoisier, Biot and Arago, De Sauss'ure, Dulong and Berzelius, Buff, Von Wrede, 
Regnault, and Marchand. For details, Van Geun's monograph may be consulted, 
f Ann. Chem. Pharm., 38, 137. Mem. Chem. Soc., i, 9. Phil. Mag. (3), 19, 210. 



CARBON. 73 

In the racemate we have : 

59.290 
59.292 
59-287 
59.283 
59.284 



Mean, 59.2872, .0012 
Or, corrected, 59.2769 

And from the malate : 

61.996 
61.972 
62.015 
62.059 
62.011 



Mean, 62.0106, zb .0096 
Or, corrected, 62.0016 

Now, applying to these mean results the atomic weights already found 
for oxygen and silver, we get the following values for carbon : 

From the acetate C = 1 1-959, .0021 

From the tartrate " 11.967, .0019 

From the racemate " = 11.973, =h .0017 

From the malate " = 11.972, .0098 

Now these results, although remarkably concordant, are by no means 
unimpeachable. They involve two possible sources of constant error, 
namely, impurity of material and the volatility of the silver. These 
objections have both been raised by Stas, who found that the silver tar- 
trate, prepared as Liebig and Redtenbacher prepared it, always carried 
traces of the nitrate, and that he, by the ignition of that salt, could not 
get results at all agreeing with theirs. In the case of the acetate a similar 
impurity would lower the percentage of silver, and thus both sources of 
error would reinforce each other and make the atomic weight of carbon 
come out too high. With the three other salts the two sources of error 
act in opposite directions, although the volatility of the silver is probably 
far greater in its influence than the impurity. Even if we had no other 
data relating to the atomic weight of carbon, it would be clear from these 
facts that the results obtained by Liebig and Redtenbacher must be 
decidedly in excess of the true figure. 

Strecker, * however, discussed the data given by Liebig and Redten- 
bacher by the method of least squares, using the Berzeliaii scale, and 
assuming H = 12.51. Thus treated, they gave C = 75.415, and Ag = 
1348.79 ; or, with =16, C = 12.066 and Ag = 107.903. These values 

*Ann. Chem. Pharm., 59, 280. 1846. 



74 THE ATOMIC WEIGHTS. 

of course would change somewhat upon adoption of the modern ratio 
between and H. 

Observations upon silver acetate, like those of Liebig and Redtenbacher, 
were also made by Marignac.* The salt was prepared by dissolving 
silver carbonate in acetic acid, and repeatedly recrystallizing. Two ex- 
periments gave as follows : 

3-3359 g rm acetate gave 2.1561 Ag. 64.633 per cent. 

3.0527 " J -97 2 7 " 64.621 " 

Mean, 64.627, .0040 

Reduced to a vacuum, this becomes 64.609. 

In a second series, conducted with special precautions to avoid me- 
chanical loss by spurting, Marignac found: 

24.717 grm. acetate gave 15.983 Ag. 64.665 per cent. 

21.202 " 13.709 " 64.661 " 

31.734 " 20.521 " 64.666 " 



Mean, 64.664, .0010 
Or, reduced to a vacuum, 64.646 

Other experiments, comparable with the preceding series, have recently 
been published by Hardin, f who sought to redetermine the atomic 
weight of silver. Silver acetate and silver benzoate, carefully purified, 
were subjected to electrolysis in a platinum dish, and the percentage of 
silver so determined. For the acetate, using vacuum weights, he gives 
the following data, the percentage column being added by myself: 

.32470 grm. acetate gave .20987 Ag. 64.635 per cent. 

.40566 " .26223 " 64.643 " 

.52736 " .34086 " 64.635 

.60300 "' .38976 " 64.637 " 

.67235 .43455 64.631 " 

.72452 " .46830 "' 64.636 " 

.78232 " .50563 " 64.632 " 

.79804 " .51590 " 64.646 

.92101 " .59532 " 64.638 ". 

1.02495 " .66250 " 64.637 " 

Mean, 64.637, .0011 
Combining this series with those of the earlier investigators we have : 

Liebig and Redtenbacher 64.6065, .0018 

Marignac, 1st series 64.609, .0040 

Marignac, 2d " 64.646, .0010 

Hardin 64.637, .001 1 



General mean 64.636, .0007 



*Ann. Chem. Pharm., 59, 287. 1846. 

t Journ. Amer. Chem. Soc., 18, 990. 1896. 



CARBOX. 75 

With silver benzoate, C 7 H 5 Ag0 2 , Karelin's results are as follows : 

.40858 grm. benzoate gave .19255 Ag. 47. 127 per cent. 

.46674 " -21999 " 47.133 " 

.48419 " .22815 " 47.120 " 

.62432 .29418 " 47.120 " 

.66496 " .3!34Q " 47-I3I " 

.75853 -35745 " 47.i 2 4 " 

.76918 .3 62 47 " 47.124 " 

.81254 " .38286 " 47.H9 " 

.95673 " .45079 " 47."8 " 

1.00840 " .47526 " 47- I 3 " 



Mean, 47.125, .0012 

A different method of dealing with organic silver salts was adopted 
by Maumene,* in 1846, for the purpose of establishing by reference to 
carbon the atomic weight of silver. We will simply reverse his results 
and apply them to the atomic weight of carbon. He effected the com- 
bustion of the acetate and the oxalate of silver, and, by weighing both 
the residual metal and the carbon dioxide formed, he fixed the ratio 
between these two substances. In the case of the acetate his weighings 
show that for every gramme of metallic silver the weights of CO 2 were 
produced which are shown in the third column : 

8.083 grm. Ag= 6.585 grm. CO 2 . -8147 

11.215 " 9-J35 " -8136 

I4.35 1 " H.6935 " -8148 

9.030 7.358 " .8148 

20.227 " 16.475 " .8145 

Mean, .81448 

The oxalate of silver, ignited by itself, decomposes too violently to 
give good results ; and for this reason it was not used by Liebig and 
Redtenbacher. Maumene, however, found that when the salt was mixed 
with sand the combustion could be tranquilly effected. The oxalate 
employed, however, with the exception of the sample represented in the 
last experiment of the series, contained traces of nitrate, so that these 
results involve slight errors. For each gramme of silver the appended 
weights of C0 2 were obtained : 

14,299 grm. Ag. = 5.835 grm. CO 2 . .4081 



17.754 


7.217 


4059 


".550 


4.703 " 


.4072 


10.771 


4-387 


4073 


8.674 


3-533 


4073 


"4355 


4.658 


4073 






Mean, .40718 



*Ann. Chim. Phys. (3), 18, 41. 1846. 



76 THE ATOMIC WEIGHTS. 

New*, one of these salts being formed by a bivalent and the other by a 
univalent acid, we have to reduce both to a common standard. Doing 
this, we have the following results for the ratio between the atomic 
weight of silver and the molecular weight of CO 2 ; if Ag = 1.00 : 

From the acetate CO 2 = .40724, .000076 

From the oxalate . . " .40718, =b .000185 

General mean CO 2 = .40723, .000071 

Here the slight error due to the impurity of the oxalate becomes of 
such trifling weight that it practically vanishes. 

As has already been said, the volatility of silver renders all the fore- 
going results more or less uncertain. Far better figures are furnished by 
the combustion of carbon directly, as carried out by Dumas and Stas * 
in 1840 and by Erdmann and Marchandf in 1841. In both investiga- 
tions weighed quantities of diamond, of natural graphite, and of artificial 
graphite were burned in oxygen, and the amount of dioxide produced 
was estimated by the usual methods. The graphite employed was puri- 
fied with extreme care by treatment with strong nitric acid and by fusion 
with caustic alkali. I have reduced all the published weighings to a 
common standard, so as to show in the third column the amount of 
oxygen which combines with a unit weight (say one gramme) of carbon. 
Taking Dumas and Stas' results first in order, we have from natural 
graphite : 

i.ooo grm. C gave 3.671 grm. CO 2 . 2.6710 

.998 " 3.660 " 2.6673 

.994 " 3- 6 45 " 2.6670 

i. 216 4.461 " 2.6686 

1.471 " 5-395 " 2.6676 

Mean, 2.6683, =t - oo 5 

With artificial graphite : 

.992 grm. C gave 3.642 grin. CO 2 . 2.6714 

.998 " 3.662 " 2.6682 

1. 660 " 6.085 " 2.6654 

1.465 " 5-365 " 2.6744 



Mean, 2.66985, .0013 

And with diamond : 

.708 grm. C gave 2.598 grm. CO 2 . 2.6695 

.864 3.1675 " 2.6661 

1.219 4.465 " 2.6628 

1.232 " 4.519 " 2.6680 

1.375 " 5.041 " 2.6662 



Mean, 5.6665 .0007 



* Compt. Rend., 11, 991-1008. Ann. Chira. Phys. (3), i, i. 
f Jour, f Prakt. Chem., 23, 159. 



CARBON. 7/ 

Erdmann and Marchand's figures for natural graphite give the follow- 
ing results : 

J-537 6 g rm - g av e 5.6367 grm. CO 2 . 2.6659 

1.6494 " 6.0384 " 2.6609 

I-4505 " 5.31575 " 2.6647 

In one experiment 1.8935 grm. of artificial graphite gave 6.9355 grm. 

CO 2 . Ratio for 0, 2.6628. This, combined with the foregoing series, 
gives a mean of 2.6636, .0007. 

With the diamond they found : 

.8052 grm. gave 2.9467 grm. CO 2 . 2.6596 

1.0858 " 3-9875 " 2.6632 

1.3557 " 4.9659 " 2.6629 

1-6305 " 5-97945 " 2.6673 

.7500 " 2.7490 " 2.6653 



Mean, 2.6637, .0009 

In more recent years the ratio under consideration has been carefully 
redetermined by Roscoe, by Friedel, and by Van der Plaats. Roscoe* 
made use of transparent Cape diamonds, and in a sixth experiment he 
burned carbonado. The combustions were effected in a platinum boat, 
contained in a tube of glazed Berlin porcelain ; and in each case the ash 
was weighed and its weight deducted from that of the diamond. The 
results were as follows, with the ratios stated as in the preceding series : 

1.2820 grm. C gave 4.7006 CO 2 . 2.6666 

1.1254 " 4.1245 " 2.6649 

1.5287 " 5.6050 " 2.6665 

.7112 " 2.6070 " 2.6656 

1.3842 " 5.0765 " 2.6675 

.4091 " J-4978 " 2.6612 



Mean, 2.6654, .0006 

Friedel's work,f also upon Cape diamond, was in all essential par- 
ticulars like Roscoe's. The data, after deduction of ash, were as follows : 

.4705 grm. C gave 1.7208 CO 2 . 2.6628 

.8616 " 3.1577 " 2.6640 

Mean, 2.6634, .0004 

By Van der Plaats J we have six experiments, numbers one to three 
on graphite, numbers four and five on sugar charcoal, and number six 
on charcoal made from purified filter paper. Each variety of carbon 
was submitted to elaborate processes of purification, and all weights were 

*Ann. Chini. Phys. (5), 26, 136. Zeit. Anal. Chem., 22, 306. 1883. Compt. Rend., 94, 1180. 1882. 
fBull. Soc. Chim., 42, 100, 1884. 
% Compt. Rend., 100, 52. 1885. 



78 THE ATOMIC WEIGHTS. 

reduced to vacuum standards. The data, with ash deducted, are sub- 
joined : 

1. 5.1217 g rm - c g ave 18.7780 CO 2 . 2.6664 

2. 9.0532 " 33- I 93i " 2.6664 

3. 13.0285 " 47.7661 " 2.6663 

4. 11.7352 " 43.0210 " 2.6660 

5. 19.1335 " 7o.i33 6 " 2.6655 

6. 4.4017 16.1-352 " 2.6657 

Mean, 2.6660, =fc .0001 

This combines with the previous series thus : 

Dumas and Stas, first set 2.6683, .0005 

Dumas and Stas, second set 2.66985, .0013 

Dumas and Stas, third set 2.6665, .0007 

Erdmann and Marchand, first set 2.6636, .0007 

Erdmann and Marchand, second set 2.6637, .0009 

Roscoe 2.6654, d= .0006 

Friedel 2.6634, .0004 

Van der Plaats 2.6660, .0001 



General mean 2.6659, .0001 

Another very exact method for determining the atomic weight of car- 
bon was employed by Stas* in 1849. Carefully purified carbon mo- 
noxide was passed over a known weight of copper oxide at a red heat, 
and both the residual metal and the carbon dioxide formed were weighed. 
The weighings were reduced to a vacuum standard, and in each experi- 
ment a quantity of copper oxide was taken representing from eight to 
twenty-four grammes of oxygen. The method, as will at once be seen, 
is in all essential features similar to that usually employed for determin- 
ing the composition of water. The figures in the third column, deduced 
from the weights given by Stas, represent the quantity of carbon mo- 
noxide corresponding to one gramme of oxygen : 

9.265 grm. O = 25.483 CO 2 . .75046 

8.327 " 22.900 " .75010 

13.9438 " 38.35 1 " .75040 

11.6124 " 3L935 " .75oo8 

18.763 " 51.6055 " .75039 

19.581 " 53-8465 " -74994 

22.515 " 61.926 " .75043 

24.360 " 67.003 " -7553 



Mean, 1.75029, db .00005 

For the density of carbon monoxide the determinations made by 
Leducf are available. The globe used contained 2.9440 grm. of air. 

*Bull. Acad. Bruxelles, 1849 (*), 31. 
fCompt. Rend., 115, 1072. 1893. 



CARBON. 79 

Filled with CO, it held the following weights, which give the accom- 
panying densities : 

Wt. CO. Density. 

2.8470 -96705 

2.8468 .96698 

2.8469 .96702 

Mean, .96702, .000015 

Combining this density with Leduc's determination of the density of 
hydrogen, 0.6948, .00006745, it gives for the atomic weight of carbon : 

.C =^.11.957, .0270. 

Leduc himself combines the data with the density of oxygen, taken as 
1.10503, and finds = 11.913. In either case, however, the probable 
error of the result is so high that it can carry little weight in the final 
combination. 

For carbon, including all the foregoing series, we now have the sub- 
joined ratios : 

(i.) Per cent. Ag in silver acetate 64.636, .0007 

(2.) " " tartrate.... 59.2806, =b .0014 

(3.) " " racemate.. 59.2769,1^.0012 

(4.) " malate .... 62.0016, ".0096 

(5.) " benzoate... 47.125, HT .0012 

(6.) Ag : CO 2 : : i.oo : 0.40723, .000071 
(7.) C : O 2 : : i.oo : 2.6659, .0001 
(8.) O : CO : : i.oo : 1.75029, .00005 
(9.) Density of CO (air = i), 0.96702, d= .000015 

Now, computing with = 15.879, .0003, and Ag = 107.108, .0031, 
we get nine values for the atomic weight of carbon, as follows : 

From (i) C= 11.921, .0012 

From (2) " 11.967, .0019 

From (3) "= 11.973, .0017- 

From (4) " = 11.972, .0098 

From (5) ..."== 11.917, .0008 

From (6) " = 11.860, .0077 

From (7) " 11.913, .0006 

From (8) " = 11.914, .0010 

From (9) " = 11.957, db .0270 

General mean C = 11.920, .0004 

If = 16, this becomes C = 12.011. 



80 THE ATOMIC WEIGHTS. 



SULPHUR. 

The atomic weight of sulphur has been determined hy means of four 
ratios connecting it with silver, chlorine, oxygen, sodium ancl carbon. 
Other ratios have also been considered, but they are hardly applicable 
here. The earlier results of Berzelius w r ere wholly inaccurate, and his 
later experiments upon the synthesis of lead sulphate will be used in 
discussing the atomic weight of lead. Erdmann and Marchand deter- 
mined the amount of calcium sulphate which could be formed from a 
known weight of pure Iceland spar; and later they made analyses of 
cinnabar, in order to fix the value of sulphur by reference to calcium and 
to mercury. Their results will be applied in this discussion toward ascer- 
taining the atomic weights of the metals just named. 

First in order let us take up the composition of silver sulphide, as 
directly determined by Dumas, Stas, and Cooke. Dumas'* experiments 
were made with sulphur which had been thrice distilled and twice crys- 
tallized from carbon disulphide. A known weight of silver was heated 
in a tube in the vapor of the sulphur, the excess of the latter was distilled 
away in a current of carbon dioxide, and the resulting silver sulphide 
was weighed. 

I subjoin Dumas' weighings, and also the quantity of Ag 2 S proportional 
to 100 parts of Ag, as deduced from them : 

9-9393 g rm - Ag= 1.473 s - Ratio, 114.820 

9.962 1.4755 " " 114.811 

30.637 4.546 " " 114.838 

30.936 4.586 " " 114.824 

3 .720 4.554 " " 114.824 

Mean, 114.8234, rb .0029 

Dumas used from ten to thirty grammes of silver in each experiment. 
Stas, f however, in his woi& employed from sixty to two hundred and 
fifty grammes at a time. Three of Stas' determinations were made by 
Dumas' method, while in the other two the sulphur was replaced by pure 
sulphuretted hydrogen. In all cases the excess of sulphur was expelled 
by carbon dioxide, purified with scrupulous care. Impurities in the 
dioxide may cause serious error. The five results come out as follows 
for 100 parts of silver : 

114.854 

114.853 
114.854 
114.851 
114.849 

Mean, 114.8522, .00x37 

*Ann. Chem. Pharm., 113, 24. 1860. 
t Aronstein's translation, p. 179. 



SULPHUR. 81 

The experiments made by Professor Cooke* with reference to this ratio 
were only incidental to his elaborate researches upon the atomic weight 
of antimony. They are interesting, however, for two reasons : they serve 
to illustrate the volatility of silver, and they represent, not syntheses, 
but reductions of the sulphide by hydrogen. Cooke gives three series of 
results. In the first the silver sulphide was long heated to full redness 
in a current of hydrogen. Highly concordant and at the same time 
plainly erroneous figures were obtained, the error being eventually traced 
to the fact that some of the reduced silver, although not heated to its 
melting point, was actually volatilized and lost. The second series, from 
reductions at low redness, are decidedly better. In the third series the 
sulphide was fully reduced below a visible red heat. Rejecting the first 
series, we have from Cooke's figures in the other two the subjoined quan- 
tities of sulphide corresponding to 100 parts of silver : 

7.5411 grm. Ag 2 S lost .9773 grm. S. Ratio, 114.889 

5.0364 .6524 " " 114.882 

2.5815 -3345 " " 114.886 

2.6130 .3387 " " 114.892 

2.5724 .3334 " " 114.891 

Mean, 114.888, .0012 

I - I 357 S rm - A S2$ lost -1465 S. Ratio, 114.810 

1.2936 .1670 " " 114.823 

Mean, 114.8165, db .0044 

Now, combining all four series, we get the following results : 

Dumas 1 14.8234, .0029 

Stas '.'-.. 114.8522,^.0007 

Cooke's 2d 114.888, .0012 

Cooke's 3d 1 14.8165, d= .0044 



General mean 1 14.8581, d= .0006 

Here again we encounter a curious and instructive compensation of 
errors, and another evidence of the accuracy of Stas. 

The percentage of silver in silver sulphate has been determined by 
Struve and by Stas. Struve t reduced the sulphate by heating in a cur- 
rent of hydrogen, and obtained these results : 

5.1860 grm. Ag ? SO 4 gave 3.5910 grm. Ag. 69.244 per cent. 

6.0543 4.1922 " 69.243 

8.6465 " 5.9858 " 69.228 " 

11.6460 8.0608 " 69.215 " 

9.1090 6.3045 " 69.212 " 

9.0669 " 62778 " 69.239 " 



Mean 



* Proc. Ainer. Acad. of Arts of Sciences, vol. 12. 1877. 
f Ann. Chem. Pharm., 80, 203. 1^51. 



82 THE ATOMIC WEIGHTS. 

Stas,* working by essentially the same method, with from 56 to 83 
grammes of sulphate at a time, found these percentages : 

69.200 
69.197 
69.204 
69.209 
69.207 
69.202 



Mean, 69.203, .0012 

Combining this mean with that from Struve's series, we get a general 
mean of 69.205, 0011. 

The third sulphur ratio with which we have now to deal is one of 
minor importance. When silver chloride is heated in a current of sul- 
phuretted hydrogen the sulphide is formed. This reaction was applied 
by Berzelius f to determining the atomic weight of sulphur. He gives 
the results of four experiments ; but the fourth varies so widely from the 
others that I have rejected it. I have reason to believe that the varia- 
tion is due, not to error in experiment, but to error in printing ; never- 
theless, as I am unable to track out the cause of the mistake, I must 
exclude the figures involving it entirely from our discussion. 

The three available experiments, however, give the following results : 
The last column contains the ratio of silver sulphide to 100 parts of 
chloride. 

6.6075 grm. AgCl gave 5.715 grm. Ag. 2 S. 86.478 

9.2323 " 7-98325 " 86.471 

10.1775 " 8.80075 " 86.472 

Mean, 86.4737, db .0015 

We have also a single determination of this value by Svanberg and 
Struve.J: After converting the chloride into sulphide they dissolved the 
latter in nitric acid. A trifling residue of chloride, which had been 
enclosed in sulphide, and so protected against change, was left undis- 
solved. Hence a slight constant error probably affects this whole ratio. 
The experiment of Svanberg and Struve gave 86.472 per cent, of silver 
sulphide derived from 100 of chloride. If we assign this figure equal 
weight with the results of Berzelius, and combine, we get a general mean 
of 86.4733, .0011. 

The work done by Richards relative to the atomic weight of sulphur 
is of a different order from any of the preceding determinations. Sodium 
carbonate was converted into sodium sulphate, fixing the ratio Na 2 CO s : 
Na a S0 4 : : 100 : x. The data are as follows, with vacuum weights : 

* Aronstein's translation, pp. 214-218. 

f Berzelius' Lehrbuch, sth ed., vol. 3, p. 1187. 

t Journ. Prakt. Chem., 44, 320. 1848. 

I Proc. Amer. Acad., 26, 268. 1891. 



SULPHUR. 83 



Na 2 CO 3 . Na 2 SO. Ratio. 

1.29930 I.74H3 134.005 

3.18620 4.26790 133-950 

1.01750 1.36330 133.985 

2.07680 2.78260 I 33-985 

1.22427 1.63994 I33-95 2 

1.77953 2.38465 134.005 

2.04412 2.73920 134.004 

3.06140 4.10220 I33.997 



Mean, 133.985, .0055 

The available ratios for sulphur are now as follows : 

(l.) Ag 2 : Ag. 2 S : : loo : 114.8581, .0006 
(2.) Per cent. Ag in Ag 2 SO 4 , 69.205, dz .oou 
(3.) 2 AgCl : Ag 2 S : : 100 : 86.4733, -O 011 
(4.) Na 2 C0 3 : Na 2 SO 4 : : 100 : 133.985, =fc -OO55 

From these ratios, four values for the atomic weight of sulphur are 
deducible. Calculating with 

O = 15.879, rt .0003 
Ag = 107.108, .0031 

Cl -== 35.179, .0048 

Na = 22.88l, .0046 
C = II.92O, rb .0004 
AgCl = 142.287, .0037, 

we have : 

From (i) S = 31.828, =b .0016 

From (2) " = 31.806, zb .0048 

From (3) " = 31.864, i .0086 

From (4) " = 31.835,^1.0191 

General mean S = 31.828, .0015 

If = 16, S = 32.070. From Stas' ratios alone, Stas found 32.074; 
Ostwald, 32.0626; Van der Plaats, (A) 32.0576, (B) 32.0590, and Thorn- 
sen, 32.0606. Here again Stas' determinations far outweigh all others. 



84 THE ATOMIC WEIGHTS. 



LITHIUM. 

The earlier determinations of the atomic weight of lithium by Arfved- 
son, Stromeyer, C. G. Gmelin, and Kralovanzky were all erroneous, 
because of the presence of sodium compounds in the material employed. 
The results of Berzelius, Hagen, and Hermann were also incorrect, and 
need no further notice here. The only investigations which we need to 
consider are those of Mallet, Diehl, Troost, Stas, and Dittmar. 

Mallet's experiments* were conducted upon lithium chloride, which 
had been purified as completely as possible. In two trials the chloride 
was precipitated by nitrate of silver, which was collected upon a filter 
and estimated in the ordinary way. The figures in the third column 
represent the LiCl proportional to 100 parts of AgCl : 

7.1885 grm. LiCl gave 24.3086 grm. AgCl. 29.606 

8.5947 " 29.0621 29.574 

In a third experiment the LiCl was titrated with a standard solution 
of silver. 3.9942 grm. LiCl balanced 10.1702 grm. Ag, equivalent to 
13.511 grm. AgCl. Hence 100 AgCl = 29.563 LiCl. Mean of all three 
experiments, 29.581, .0087. 

Diehl.f whose paper begins with a good resume of all the earlier 
determinations, describes experiments made with lithium carbonate. 
This salt, which was spectroscopically pure, was dried at 130 before 
weighing. It was then placed in an apparatus from which the carbon 
dioxide generated by the action of pure sulphuric acid upon it could be 
expelled, and the loss of weight determined. From this loss the follow- 
ing percentages of C0 2 in Li 2 C0 3 were determined : 

59.422 
59.404 
59.440 
59.401 



Mean, 59.417, .006 

Diehl's investigation was quickly followed by a confirmation from 
Troost.J This chemist, in an earlier paper, had sought to fix the atomic 
weight of lithium by an analysis of the sulphate, and had found a value 
not far from 6.5, thus confirming the results of Berzelius and of Hagen, 
who had employed the same method. But Diehl showed that the BaS0 4 
precipitated from Li. 2 S0 4 always retained traces of Li, which were recog- 

* Silliman's Amer. Journal, November, 1856. Chem. Gazette, 15, 7. 

f Ann. Chem. Pharm., 121, 93. 

JZeit. Anal. Chem., i, 402. 

I Annales d. Chim. et d. Phys., 51, 108. 



LITHIUM. 85 

nizable by spectral analysis, and which accounted for the error. In the 
later paper Troost made use of the chloride and the carbonate of lithium, 
both spectroscopically pure. The carbonate was strongly ignited with 
pure quartz powder, thus losing carbon dioxide, which loss was easily 
estimated. The subjoined results were obtained : 

.97ogrm. Li 2 CO 3 lost .577 grm. CO 2 . 59-485 per cent. 

1.782 " 1.059 " 59.427 " 

Mean, 59.456, .020 

The lithium chloride employed by Troost was heated in a stream of 
dry hydrochloric acid gas, of which the excess, after cooling, was ex- 
pelled by a current of dry air. The salt was weighed in the same tube 
in which the foregoing operations had been performed, and the chlorine 
was then estimated as silver chloride. The usual ratio between LiCl 
and 100 parts of AgCl is given in the third column : 

1.309 grm. LiCl gave 4.420 grm. AgCl. 29 615 

2.750 " 9.300 " 29.570 



Mean, 29.5925, .0145 

This, combined with Mallet's mean, 29.581, .0087, gives a general 
mean of 59.584, .0075. 

Next in order is the work of Stas,* which was executed with his usual 
wonderful accuracy. In three titrations, in which all the weights were 
reduced to a vacuum standard, the following quantities of LiCl balanced 
100 parts of pure silver : 

39.356 

-39-357 

39-361 

Mean, 39.358, .001 

In a second series of experiments, intended for determining the atomic 
weight of nitrogen, LiCl was converted into LiN0 3 . The method was 
that employed for a similar purpose with the chlorides of sodium and 
of potassium. One hundred parts of LiCl gave of LiN0 3 : 

162.588 
162.600 
162.598 

Mean, 162.5953, dr .0025 

The determinations of Dittmarf resemble those of Diehl; but the 
lithium carbonate used was dehydrated by fusion in an atmosphere of 
carbon dioxide. The carbonate was treated with sulphuric acid, and 

* Aroiistein's translation, 279-302. 

t Trans. Roy. Soc. Edinburgh, 35, II, 429. 1889. 



86 THE ATOMIC WEIGHTS. 

the C0 2 was collected and weighed in an absorption apparatus, which 
was tared by a similar apparatus after the method of Regnault. The 
following percentages of CO 2 in Li 2 C0 3 were found : 

59.601 
59.645 

59.529 rejected. 

59.655 
59.683 
59.604 

59.517 

59.663 

60.143 rejected. 

59-794 

59-584 



Mean of all, 59.674 

Rejecting the two experiments which Dittmar regards as untrust- 
worthy, the mean of the remaining nine becomes 59.638, .0173. This 
combines with the work of Diehl and Troost, as follows : 

Diehl 59.417, =b .0060 

Troost 59.456, .0200 

Dittmar 59.638, db .0173 



General mean 59.442, =b .0054 

Dittmar's determinations give a much lower value for the atomic 
weight of lithium than any of the others, and therefore seem to be ques- 
tionable. As, however, they carry little weight in the general combina- 
tion, it is not necessary to speculate upon their possible sources of error. 

The ratios for lithium are now as follows': 

(l.) AgCl : LiCl : : 100 : 29.584, .0075 

(2.) Ag : LiCl : : 100 : 39.358, .001. 

(3.) LiCl : LiNO 3 : : 100 : 162.5953, .0025 

(4.) Per cent, of CO 2 in Li 2 CO 3 , 59.442, .0054 

And the data to use in their reduction are 

O -- 15.879, .0003 N 13.935, =t .0015 

Ag 107.108, .0031 C = 11.920, db .0004 

Cl == 35-179, .0048 AgCl= 142.287, .0037 

These factors give two values for the molecular weight of lithium 
chloride, thus : 

From (i) LiCl = 42.0942, .01 10 

From (2) =42.1556, .0016 



General mean LiCl = 42. 1542, .0016 



RUBIDIUM. 87 

For lithium itself there are three values : 

From molecular weight LiCl Li = 6.9752, .0051 

From (3^ " 6.9855, .0129 

From (4) " 6.9628, d= .0077 



General mean Li r= 6.9729, .0040 

If 16, Li =- 7.026. From Stas' ratios, Stas found Li = 7.022 ; Ost- 
wald, 7.0303; Van cler Plaats (A), 7.0273; (B), 7.0235; and Thomsen, 
7.0307. 



RUBIDIUM. 

i 

The atomic weight of rubidium has been determined by Bunsen, Pic- 
card, Godeffroy, and Hey cock from analyses of the chloride and bromide. 

Bunsen,* employing ordinary gravimetric methods, estimated the ratio 
between AgCl and RbCl. His rubidium chloride was purified by frac- 
tional crystallization of the chloroplatinate. He obtained the following 
results, to which, in a third column, I add the ratio between RbCl and 
100 parts of AgCl : 

One grm. RbCl gave 1.1873 grm. AgCl. 84.225 

1.1873 " 84.225 

1.1850 " 84.388 

I. 1880 " 84.175 

Mean, 84.253, db .031 

The work of Piccardf was similar to that of Bunsen. In weighing, 
the crucible containing the silver chloride was balanced by a precisely 
similar crucible, in order to avoid the correction for displacement of air. 
The filter was burned separately from the AgCl, as usual ; but the small 
amount of material adhering to the ash was reckoned as metallic silver. 
The rubidium chloride was purified by Bunsen's method. The results, 
expressed according to the foregoing standard, are as follows : 

I - 1 S&7 S rm - RbCl= 1.372 AgCl -f- .0019 Ag. 84.300 

1.4055 " 1.6632 " .0030 " 84.303 

i. ooi " 1.1850 " .0024 " 84.245 

" 1-7934 " .0018 " 84.313 



Mean, 84.290, d= .0105 
Godeffroy, J starting with material containing both rubidium and 

*Zeit. Anal. Chem., i, 136. Poggend. Annal., 113, 339. 1861. 

f Journ. fur Prakt. Chem., 86, 454. 1862. Zeit. Anal. Chem., i, 518. 

I Ann. Chem. Pharm., 181, 185. 1876. 



88 THE ATOMIC WEIGHTS. 

caesium, separated the two metals by fractional crystallization of their 
alums, and obtained salts of each spectroscopicalty pure. The nitric 
acid employed was tested for chlorine and found to be free from that 
impurity, and the weights used were especially verified. In two of his 
analyses of RbCl the AgCl was handled by the ordinary process of nitra- 
tion. In the other two it was washed by decantation, dried, and weighed 
in a glass dish. The usual ratio is appended in the third column : 



1.4055 grm. RbCl gave 1.6665 g rm - AgCl. 84.338 

1.8096 " 2.1461 84320 

2.2473 " 2.665 " 84.326 

2.273 " 2.6946 " 84.354 

Mean, 84.3345, .0051 

Combining the three series, we get the following result : 

Bunsen ................. 84.253, .031 Rb = 84.7O2 

Piccard ................. 84.290, .0105 " 1=84.754 

Godeffroy ............... 84.3345, dz .0051 " =84.817 



General mean 84.324, =fc .0045 

Heycock* worked by two methods, but unfortunately his results are 
given only in abstract, without details. First, silver solution was added 
in slight deficiency to a solution of rubidium chloride, and the excess 
of the latter was measured by titration. The mean of seven experiments 
gave 

Ag : RbCl : : 107.93 : 120.801 

Hence Rb = 84.702. 

Two similar experiments with the bromide gave 

Ag : RbBr : : 107.93 : 165.437 
Ag : RbBr : : 107.93 : 1 ^>S'34- 2 



Mean, 165.3895, .0320 

There are now three ratios for the metal rubidium, as follows : 

(i.) AgCl : RbCl : : loo : 84.324, .0045 

(2.) Ag : RbCl : : 107.93 : 120.801 

(3.) Ag : RbBr : : 107.93 ' l6 5-3 8 95> -3 2 

To reduce these ratios we have 

Ag = 107.108, zb .0031 
Br = 79.344, .0062 
C1 = 35- T 79, -0048 
AgCl = 142.287, zh .0037 

* British Association Report, 1882, p. 499. 



CAESIUM. 89 

For the molecular weight of RbCl, two values are calculable : 

From (i) RbCl= 119.981, + .0109 

From (2) " 119.881, .0218 

General mean RbCl = 119.961, =b .0097 

To the value from ratio (2) I have arbitrarily assigned a weight rep- 
resented by the probable error as written above. The data for system- 
atic weighting are deficient, and no other course of procedure seemed 
advisable. 

From RbCl Rb = 84.782, .0109 

From RbBr, ratio (3) " 84.786, .0329 



General mean Rb =r 84.783, .0103 

If = 16 Rb 85.429. 



CESIUM. 

The atomic weight of caesium, like that of rubidium, has been deter- 
mined from the analysis of the chloride. The earliest determination, 
by Bunsen,* was incorrect, because of impurity in the material employed. 

In 1863 Johnson and Allen published their results.f Their material 
was extracted from the lepidolite of Hebron, Maine, and the caesium was 
separated from the rubidium as bitartrate. From the pure caesium 
bitartrate caesium chloride was prepared, and in this the chlorine was 
estimated as silver chloride by the usual gravimetric method. Reducing 
their results to the convenient standard adopted in preceding chapters, 
we have, in a third column, the quantities of CsCl equivalent to 100 
parts of AgCl : 

I-837 1 g rm - CsCl gave 1.5634 grm. AgCl. ' 117.507 

2.1295 " i. Si n " n7-5 8 

2.7018 " 2.2992 " 117-511 

1.56165 " 1.3302 " ( "7-399 

Mean, 117.499, .025 

Shortly after the results of Johnson and Allen appeared a new series 
of estimations was published by Bunsen. J His caesium chloride was 
purified by repeated crystallizations of the chloroplatinate, and the ordi- 

*Zeit. Anal. Chem., i, 137. 

f Atner. Journ. Sci. and Arts (2), 35, 94. 

J Poggend. Annalen, 119, i. 1863. 



90 THE ATOMIC WEIGHTS, 

nary gravimetric process was employed. The following results represent, 
respectively, material thrice, four times, and five times purified : 

1.3835 grm. CsCl gave 1.1781 grm. AgCl. Ratio, 117.435 
1.3682 " 1.1644 " " 117.503 

1.2478 " 1.0623 <l " 117.462 



Mean, 117.467, .013 

Godeffroy's work* was, in its details of manipulation, sufficiently 
described under rubidium. In three of the experiments upon caesium 
the silver chloride was washed by decantation, and in one it was col- 
lected upon a filter. The results are subjoined : 

1.5825 grm. CsCl gave 1.351 grm. AgCl. Ratio, 117.135 

1.3487 " 1.1501 " " 117.265 

1.1880 " 1.0141 " " 117.148 

1.2309 " 1.051 " " 117.107 



Mean, 117.164, =b .023 

We may now combine the three series to form a general mean : 

Johnson and Allen 117.499, .025 Cs = 132.007 

Bunsen 117.467,^.013 " =131.961 

Godeffroy 117.164,1^.023 "=131.560 

General mean.. . 117.413, dz .010 

Hence, if AgCl = 142.287, .0037, and Cl = 35.179, .00-48, Cs = 
131.885, .0142. 

If 0=16, Cs 132.890. 

* Ann. Chem. Pharm., 181, 185. 1876. 



COPPER. 91 



COPPER. 

The atomic weight of copper has been chiefly determined by means of 
{he oxide, the sulphate, and the bromide, and by direct comparison of 
the metal with silver. 

.In dealing with the first-named compound all experimenters have 
agreed in reducing it with a current of hydrogen, and weighing the 
metal thus set free. 

The earliest experiments of any value were those of Berzelius,* whose 
results were as follows : 

7.68075 grm. CuO lost 1.55 grm. O. 79.820 per cent. Cu in CuO. 
9.6115 " 1.939 " . 79.826 " " 

Mean, 79.823, .002 

Erdmann and Marchand,f who come next in chronological order, 
corrected their results for weighing in air. Their weighings, thus cor- 
rected, give us the subjoined percentages of metal in CuO : 

63.8962 grm. CuO gave 51.0391 grm. Cu. 79.878 per cent. 

65.1590 " 5 2 - 363 " 79-860 " 

60.2878 48.1540 " 79.874 " 

46.2700 36.9449 " 79.846 " 

Mean, 79.8645, =fc .0038 

Still later we find a few analyses by Millon and Commaille. J These 
chemists not only reduced the oxide by hydrogen, but they also weighed, 
in addition to the metallic copper, the water formed in the experiments. 
In three determinations the results were as follows : 

6.7145 grm. CuO gave 5.3565 grm. Cu and 1.5325 grm. H 2 O. 79-775 per cent. 
3-39*5 " 2.7085 " .7680 " 79.791 " 

2.7880 " 2.2240 " 79.770 " 



Mean, 79.7787, rb .0043 

For the third of these analyses the water estimation was not made, 
but for the other two it yielded results which, in the mean, would make 
the atomic weight of copper 62.680. This figure has so high a probable 
error that we need not consider it further. 

The results obtained by Dumas are wholly unavailable. Indeed, he 
does not even publish them in detail. He merely says that he reduced 
copper oxide, and also effected the synthesis of the subsulphide, but with- 
out getting figures which were wholly concordant. He puts Cu = 63.5. 

*Poggend. Annal., 8, 177. 1826. 
t Journ. fur Prakt. Chem., 31, 380. 1844. 
| Fresenius' Zeitschrift, 2, 475. 1863. 
I Ann. Chim. et Phys. (3), 55, 129. 1859. 



92 THE ATOMIC WEIGHTS. 

In 1873 Hampe* published his careful determinations, which were 
for many years almost unqualifiedly accepted. First, he attempted to 
estimate the atomic weight of copper by the quantity of silver which 
the pure metal could precipitate from its solutions. This attempt failed 
to give satisfactory results, and he fell back upon the old method of 
reducing the oxide. From ten to twenty grammes of material were 
taken in each experiment, and the weights were reduced to a vacuum 
standard : 

20.3260 grm. CuO gave 16.2279 grm. Cu. 79.838 P er cent. 

20.68851 " 16.51669 " 79.835 " 

10.10793 " 8.06926 " 79-831 " 

Mean, 79.8347, rfc .0013 

Hampe also determined the quantity of copper in the anhydrous sul- 
phate, CuS0 4 . From 40 to 45 grammes of the salt were taken at a time, 
the metal was thrown down by electrolysis, and the weights were all 
corrected. I subjoin the results : 

40.40300 grm. CuSO 4 gave 16.04958 grm. Cu. 39.724 per cent. 
44.64280 " 17.73466 " 39-7 2 6 

Mean, 39.725, .0007 

The last series of data gives Cu =62.839, .0035, and is interesting 
for comparison with results obtained by Richards later. 

In all of the foregoing experiments with copper oxide, that compound 
was obtained by ignition of the basic nitrate. But, as was shown in the 
chapter upon oxygen, copper oxide so prepared always carries occluded 
gases, which are not wholly expelled by heat. This point was thoroughly 
worked up by Richards f in his fourth memoir upon the atomic weight 
of copper, and it vitiates all the determinations previously made by this 
method. 

By a series of experiments with copper oxide ignited at varying tem- 
peratures, and with different degrees of heat during the process of reduc- 
tion, Richards obtained values for Cu ranging from 63.20 to 63.62, when 
, O = 16. In two cases selected from this series he measured the amount 
of gaseous impurity, and corrected the results previously obtained. The 
results were as follows, with vacuum standards : 

1.06253 g rm CuO gave. .84831 grm. Cu. 79.802 per cent. 

1.91656 " 1.5298 " 79.820 " 

Mean, 79.811, .0061 

Correcting for the occluded gases in the oxide, the sum of the two 
experiments gives 79.901 per cent, of copper, whence Cu = 63.605. Three 

* Fresenius' Zeitschrift, 13, 352. 
fProc. Amer. Acad., 26, 276. 1891. 



COPPER. 93 

other indirect results, similarly corrected, gave 79.900 per cent. Cu in 
CuO, or Cu = 63.603. If we assign all five experiments equal weight, 
and judge their value by the two detailed above, the mean percentage 
becomes 79.900, dt .0038. This figure need not be combined with the 
data given by previous observers, so far as practical purposes are con- 
cerned ; but as this work is, in part at least, a study of the compensation 
of errors, it may not be wasted time to effect the combination, as follows : 

Berzelius 79.823, .0020 

Erdmann and Marchand 79.8645, .0038 

Millon and Commaille 79-7787, .0043 

Hampe 79-8347, db .0013 

Richards 79-9, .0038 



General mean 79-8355, .0010 

This result is practically identical with that of Hampe, whose work 
receives excessive weight, as does also that of Berzelius. The oxide of 
copper is evidently of doubtful value in the measurement of this atomic 
weight. 

The composition of the sulphate has been studied, not only by Hampe, 
but also by Baubigny* and by Richards.f Baubigny merely ignited 
the anhydrous salt, weighing both it and the residual oxide, as follows : 

4.022 grm. CuSO 4 gave 2.0035 CuO. 49.813 per cent. 

2.596 1.293 " 49.807 " 

Mean, 49.810, .002 

The same ratio, in reverse that is, the synthesis of the sulphate from 
the oxide was investigated by Richards (p. 275), who shows that the 
results obtained are vitiated by the same errors which affect the copper 
oxide experiments previously cited. The weights given are reduced to 
vacuum standards. The percentage of oxide in the sulphate is stated in 
the third column of figures. 

1.0084 grm. CuO gave 2.0235 S rm - CuSO 4 . 49-835 P er cent. 

2.7292 5-4770 " 49.83 " 

1.0144 2.35 49.848 " 

Mean, 49.838, .0036 

The two series combine thus : 

Baubigny 49.810, .0020 

Richards.. , 49.838, .0036 



General mean 49.816, dr .0017 

Here, plainly, the rigorous discussion gives Baubigny 's work weight 
in excess of its merits. 

* Compt. Rend., 97, 906. 1883. 
fProc. Amer. Acad., 26, 240. 1891. 



94 THE ATOMIC WEIGHTS. 

In the memoir by Richards now under consideration, his fourth upon 
copper, the greater part of his attention is devoted to the sulphate, 
Hampe being followed closely in order to ascertain what sources of 
error affected the work of the latter. Crystallized sulphate, CuS0 4 .5H 2 O 
was purified with every precaution and made the basis of operations. 
Three series of experiments were carried out, the water being determined 
by loss of weight upon heating, and the copper being estimated electro- 
lytically. In the first series the following data were found, the weights 
being reduced to a vacuum, as in all of Richards' determinations : 

CuSO. 5 aq. CuSO at 250. Cu. 

i 2.8815 .7337 

2 2.7152 .6911 

3 3-4639 2.2184 .8817 

Hence the subjoined percentages. 

Water at 250. Cu in Ciyst. Salt. Cu in CuSO r 

i 25.462 

2 25.452 

3 35-95* 25.454 39.745 



Mean, 25.456 

In the second series of analyses, which are stated with much detail, 
several Tefinements were introduced, in order to estimate also the sul- 
phuric acid. These will be considered later. The results, given below, 
are numbered consecutively with the former series. 



aq. CuSO^at 260. CuSO^atjdo . Cu. 

4 ...... . ............... 3.06006 1-9597 1.95637 .77886 

5 ........................ 2.81840 1.8048 . ...... .71740 

6 ........................ 7-549 4-8064 4.79826 1-90973 

Hence percentages as follows : 

Water, 260. Water, 360. Cu in Ciyst. Salt. Cu in CuSO, 260. Ditto, 360. 

4 ...... 35-959 36.068 25.452 39-744 39.8n 

5 ...... 35.964 25.454 39-750 ...... 

6 ...... 35-957 36-065 25.446 f 39-733 39-799 

Mean, 35.960 ' 36.067 25.450 39-742 39.805 

Hampe worked with a sulphate dried at 250, but these data show that 
a little water is retained at that temperature, and consequently that his 
results must have been too low. The third of Richards' series resembles 
the second, but extra precautions were taken to avoid conceivable errors. 

CuSO. 5 aq. CitSO at 260. CuSO 4 at 370. Cu. 

7 .................... - 2.88307 ....... ....... .73380 

8 ........................ 3.62913 2.32373 ....... .92344 

9 ........................ 5.8I35 2 ....... 3.71^80 1.47926 



COPPER. 95 

And the percentages are : 

Water at 260. At j/o . Cu in Cryst. Salt. Cu in CuSO t . 

7 2 5.45 2 

8 35-970 25.446 39.740(260) 

9 36.067 25.445 39-799(370) 

25.448 

In this series the determinations of sulphuric acid gave essentially the 
same results for all three samples of sulphate, although one was not 
dehydrated, and the others were heated to 260 and 370 respectively. 
Hence the loss of weight in dehydration at either temperature represents 
water only, and does not involve partial decomposition of the sulphate. 
Between 360 and 400 copper sulphate is at essentially constant weight, 
but further experiments indicated that even at 400 it retained traces of 
water, and possibly as much as .042 per cent. The last trace is not ex- 
pelled until the salt itself begins to decompose. 

Richards also effected two syntheses of the sulphate directly from the 
metal by dissolving the latter in nitric acid, then evaporating to dryness 
with sulphuric acid, and heating to constant weight at 400. 

.67720 grm. Cu gave 1.7021 grm. CuSO 4 . 39-786 per cent. Cu. 

1.00613 " 2.5292 " 39.78i " 

If we include these percentages in a series with the data from analyses 
4, 6, and 9, which gave percentages of 39.811, 39.799, and 39.799 respect- 
ively of copper in sulphate dried at 360 and upwards, the mean becomes 

CuSO 4 : Cu : : 100 : 39.795, .0036 

Since even this result is presumably too low, the other figures from 
sulphate dried at 250 must be rejected. Since Hampe's work on the 
sulphate is affected by the same sources of error, and apparently to a 
still greater extent, it need not be considered farther. As for Richards' 
nine determinations of Cu in CuS0 4 .5H 2 0, we may take them as one 
series giving a mean percentage of 25.451, .0011. This salt seems to 
retain occluded water, for the percentage of copper in it leads to a value 
for the atomic weight which is inconsistent with the best evidence, as 
will be seen later. 

In the second and third series of Richards' experiments upon copper 
sulphate, the sulphuric acid was estimated by a method, which gave 
valuable results. After the copper had been electrolytically precipitated, 
the acid which was set free was nearly neutralized by a weighed amount 
of pure sodium carbonate, and the slight excess remaining was deter- 
mined by titration. Thus the weight of sodium carbonate equivalent to 
the copper was ascertained. The resulting solution of sodium sulphate 
was then evaporated to dryness, and a new ratio, connecting that salt 
with copper, was also determined. The cross ratio Na 2 C0 3 : Na 2 S0 4 has 



96 THE ATOMIC WEIGHTS. 

already been utilized in a previous chapter. The results, ignoring the 
weights of h yd rated copper sulphate, are as follows, with the experiments 
numbered as before : 

Cu. Na 2 CO s . JVa 2 SO i 

4 77886 1.2993 1.7411 

6 1.90973 3.1862 4.2679 

7 7338o 1.22427 1.63994 

8 92344 L54075 

9 1.47926 3.30658 

Hence, 

Cu : Na.yCO^ ' : IOO : x. Cu : Na. 1 SO^ : : IOO : x. 
166.824 223.549 

166.840 223.482 

166.840 223.538 

166.849 223.529 

Mean, 166.838, .0035 Mean, 223.525, .0098 

In one more experiment the sulphuric acid was weighed as barium 
sulphate, the latter being corrected for occluded salts. 3.1902' grin. 
CuSO,.5H 2 gave 2.9761 BaSO, ; hence CuS0 4 .5H 2 : BaS0 4 : : 100 : 
93.289. The sulphate contained 25.448 per cent, of Cu ; hence BaS0 4 : 
Cu : : 93.289: 25.448. Still other ratios can be deduced from Richards 1 
work on the sulphate, but in view of the uncertainties relative to the 
water in the salt they are hardly worth computing. 

In his third paper upon the atomic weight of copper,* Richards studied 
the dibromide, CuBr. 2 . In preparing this -salt he used hydrobromic 
acid made from pure materials, and further purified by ten distillations. 
This was saturated with copper oxide prepared from pure electrolytic 
copper, and the solution obtained was proved to be free from basic salts. 
As the crystallized compound was not easily obtained in a satisfactory 
condition, weighed quantities of the solution were taken for analysis, in 
which, after expulsion of bromine by nitric and sulphuric acids, the 
copper was determined by electrolysis. In other portions of solution 
the bromine was precipitated by silver nitrate, and weighed as silver 
bromide. The first preliminary series of experiments gave the subjoined 
results, with vacuum weights as usual : 

In 3d Grammes of Solution. 

Cu. AgBr. 

.4164 2.4599 

.4.164 2.4605 

.4164 2.4605 

.4165 2.4599 

Hence 2 AgBr : Cu : : 100 : 16.927, .0013. 

* Proc. Amer. Acad., 25, 195. 1890. 



COPPER. 97 

The second, also preliminary series, was made with more dilute solu- 
tions, and came out as follows: 

In 25 Grammes of Solution. 

Cu. AgBr. 

.26190 1.5478 

.26185 1-5477 

1-5479 

Hence 2 AgBr : Cu : : 100 : 16.919, .0012. 

In the third series, two distinct lots of crystallized bromide were dis- 
solved, and the solutions examined in the same way. 

Cu. AgBr. Ratio. 

.2500 i.477i 16.925 

5473 3. 2 348 16.919 



Mean, 16.922, =b .0020 

In the final set of analyses, the materials used were purified even more 
scrupulously than before, and the process was distinctly modified, as 
regards the determination of the bromine. The solution of the bromide 
was added to a solution of pure silver in nitric, acid, not quite sufficient 
for complete precipitation. The slight excess of bromine was then 
determined by titration with a solution containing one gramme of silver 
to the litre. Thus silver proportional to the copper in the bromide was 
determined, and the silver bromide was weighed in a Gooch crucible as 
before. The results are subjoined : 

In 50 Grammes of Solution. 

Cu. Ag. AgBr. 

.54755 I - 8 586 3. 2 35o 

.54750 !- 8 579 3-2340 

1.8583 3-2348 

Hence Cu : Ag, : -100 : 339.392, .0108, and 2 AgBr : Cu : : 100 : 16.927, 
.0012. 

The latter ratio, combined with the results of the three preceding series, 
gives a general mean of : 

2 AgBr : Cu : : 100 : 16.924, .0007 

In his two earlier papers * Richards determined the Qopper-silver ratio 
directly that is. without the weighing of any comp^u^iq;G?fej,ther metal. 
By placing pure copper in an ice-cold solution .o^-sijyer *Srq,te* metallic 
silver is thrown down, and the weights of the tw.D/fnetals- were 

*Proc. Atner. Acad., 22, 346, and 23, 177. 1886 and 1887". *,,"" > 



98 THE ATOMIC WEIGHTS. 

alent proportions. In the first paper the following results were obtained. 
The third column gives the value of x in the ratio Cu : Ag. 2 : : 100 : x. 

Cu Taken. Ag Found. Ratio. 

.53875 I-8292 339.5 2 7 

.56190 1.9076 339-49 1 

1.00220 3.4016 339.414 

1.30135 4.4173 339.440 

99 s 7o 3.39035 339-477 

1.02050 3.4646 ' 339.500 

Mean, 339.475, =h .0114 

In the second paper Richards states that the silver of the fifth experi- 
ment, which had been dried at 150, as were also the others, still retained 
water, to the extent of four-tenths milligramme in two grammes. If we 
assume this correction to be fairly uniform, as the concordance of the 
series indicates, and apply it throughout, the mean value for the ratio 
then becomes 339.408, .0114. This procedure, however, leaves the 
ratio in some uncertainty, and accordingly some new determinations 
were made, in which the silver, collected in a Gooch crucible, was heated 
to incipient redness before final weighing. Copper from two distinct 
sources was taken, and three experiments were carried out upon one 
sample to two with the other. Treating both sets as one series, the 
results were as follows : 

Cu Taken. Ag found. Ratio. 

.7576o 2.5713 339.40 

.95040 3-2256 339-39 

75993 2.5794 339-42 

1.02060 3-4640 339-42 

.90460 3.0701 339-39 



Mean, 339.404, d= .0046 

a value practically identical with the corrected mean of the previous 
determinations, and w 7 ith that found in the later experiments upon 
copper bromide. 

In various electrical investigations the same ratio, the electrochemical 
equivalent of copper, has been repeatedly measured, and the later results 
of Lord Rayleigh and Mrs. Sidgewick,* Gray,f Shaw, % and Vanni may 
properly be included in this discussion. As the data are somewhat dif- 
ferently stated, I have reduced them all to the common standard adopted 
above. Gray gives 'two sets of measurements, one made with large and 
the other w.ith^syiigill; metallic plates : 

' ' T ' r ''',* Phil. 7>an 



r % British A3soc. Report, 1886. Abstract in Phil. Mag. (5), 23, 138. 
T ' r ' r r ^A?fn' der Phys. (Wiedemanu's) (2), 44, 214. 



COPPER. 



99 



Rayleigh and S. 
340.483 
340.832 

340.367 


Gray i. 
341.297 

34L4I3 
340.815 
340.252 

339-905 
341.064 
340.832 
341.297 
341.064 
34L4I3 


Gray 2. 
340.252 

339.674 
340.020 

339.905 
339-674 
339-328 
340.136 
340.136 
340.136 
340.020 
340.020 
340.136 ' 


Shaiu. 
339-68 
340.05 
339.84 
339-71 
340.04 

339-94 
340.35 
339.82 
340.09 
339.84 
339.90 
339.98 
340.H 
340.56 
339-82 


340.56r, 
.0935 


340.935, 
. 1072 


339-953, 
.0521 



Vanni. 
340.483 
340.600 

340.367 
340.252 
340.600 
340.136 

340.406, 
.0520 






The lack of sharp concordance in these data and the consequently 
high probable errors seem to indicate a distinct superiority of the purely 
chemical method of determination over that adopted by the physicist. 
The eight distinct series now combine as follows : 

Richards, first series corrected 339-48, .0114 

Richards, second series ... 339.404, .0046 

Richards, CuBr 2 series . 339.392, =b .0108 

Rayleigh and Sidgewick 340.561, d= .0935 

Gray, with large plates 34-935, ^ . 1072 

Gray, with small plates 339-953, .0521 

Shaw . .. 339.983, =b .0411 

Vanni 340.406, .0520 

General mean 339-41 1, .0039 

If we combine Richards' three series into a general mean separately, 
we get 339.402, .0040. Hence the other determinations, having high 
>robable errors, practically vanish from the result, and it is a matter of 
idifference whether they are retained or rejected. 

We now have the following ratios from which to compute the atomic 
.'eight of copper : 

(i.) Percentage of Cu in CuO 79-8355, .0010 



(2.) 

(3-) 
(4.) 

(5.) Cu 
(6.) Cu 



of Cu in CuSO 4 39-795, =fc -0036 

of Cu in CuSO 4 , 5H 2 O. . 25.451, .0011 
of CuO in CuSO 4 49-8i6, ^-.0017 



Na,CO, 



Na 2 SO 4 : 



100 

IOO 



166.838, .0035 

223.525, =fc .0098 
(7.) BaSO 4 : Cu : : 93- 28 9 : 25-448- 
(8.) 2AgBr : Cu : : IOO : 16.924, .0007 



(9- 



: Ag 2 



.0039 



100 THE ATOMIC WEIGHTS. 

Reducing these ratios with the subjoined data : 

O - = 15.879, .0003 Na _ 22.881, .0046 

Ag 107.108, .0031 Ha = 136.392, =h .0086 
S = 31.828, .0015 AgBr = 186.452, =b .0054 
C = 11.920, d- .0004 

We have nine values for the atomic weight of .copper. Since ratio (7) 
depends upon one experiment only, it is necessary to assign the value 
derived from it arbitrary weight. This will be taken as indicated by a 
probable error double that of the next highest, obtained from ratio (.2). 
The values then are as follows : 

From (i) ......................... Cu = 62.869, d= .0034 

From (2) .......................... " = 63.022, db .0070 

From (3) .......................... <( = 63.070, .0030 

From (4) ......................... " =63.003, .0042 

From (5) .......................... " =63.127, d= .0051 

From (6).. , ....................... " = 63.128, .0050 

From (7) ................ .......... " 63.215, .0140 

From (8) .............. ........... " = 63. 1 10, .0032 

From (9) .......................... " =63. 114, .0020 

General mean ................ Cu 63.070, d= .0012 

If O = 16, Cu = 63.550. If we include Hampe's analyses of copper 
sulphate, which gave Cu = 62.839, .0035, the general mean becomes 
Cu 63.046, .0011. 

The foregoing means, however, are significant only as showing the 
effect and weight of the older data upon the newer determinations of 
Richards. The seventh of the individual values is also interesting, for 
the reason that the experiment upon which it depends was published by 
Richards previous to his investigation of the atomic weight of barium. 
With the old value for Ba, 137, it gives a value for copper in close agree- 
ment with Richards' other determinations. With the new value for 
barium it becomes discordant, although its weight is so low that it pro- 
duces no appreciable effect upon the final mean. 

Rejecting values 1 to 4, inclusive, the remaining five values give a gen- 
eral mean of 

Cu ==63.119, rfc .0015. 

If = 16, this becomes 63600, and in the light of all the evidence 
these figures are to be preferred. If, again, we combine with this mean 
the results of Richards' work on the oxide and sulphate of copper, the 
final value becomes 

, \\ \\ '', ; Cu = 63.108, .0013, 



with = 16 f $8$$$.'% This departs but little from the previous mean 
'.value', 'bu^it'i'H'el'uclee' 'data which render it, in all probability, a trifle too 
low, l^h'p/v^Hie Cu = 63.119 will be regarded as the best. 



GOLD. 101 



GOLD. 

Among the early estimates of the atomic weight of gold the only ones 
worthy of consideration are those of Berzelius and Levol. 

The earliest method adopted by Berzelius* was that of precipitating 
a solution of gold chloride by means of a weighed quantity of metallic 
mercury. The weight of gold thus thrown down gave the ratio between 
the atomic weights of the two metals. In the single experiment which 
Berzelius publishes, 142.9 parts of Hg precipitated 93.55 of Au. Hence 
if Hg = 200, Au = 196.397. 

In a later investigation f Berzelius resorted to the analysis of potassio- 
auric chloride, 2KC1. A uCl 3 . Weighed quantities of this salt were ignited 
in hydrogen ; the resulting gold and potassium chloride were separated 
by means of water, and both were collected and estimated. The loss of 
weight upon ignition was, of course, chlorine. As the salt could not be 
perfectly dried without loss of chlorine, the atomic weight under inves- 
tigation must be determined by the ratio between the KC1 and the Au. 
If we reduce to a common standard, and compare with 100 parts of KC1, 
the equivalent amounts of gold will be those which I give in the last of 
the subjoined columns : 

4.1445 grm. K 2 AuCl 5 gave .8185 grm. KC1 and 2.159 g rm - Au. 263.775 

2.2495 .44425 " i.7 2 " 26 3- 8l 5 

5 1300 " 1.01375 " 2.67225 " 263.600 

3.4130 " .674 " 1.77725 " 263.687 

4.19975 .8295 " 2.188 263.773 

Mean, 263.730, .026 

Still a third series of experiments by Berzelius $ may be included 
here. In order to establish the atomic weight of phosphorus he em- 
ployed that substance to precipitate gold from a solution of gold chloride 
in excess. Between the weight of phosphorus taken and the weight of 
gold obtained it was easy to fix a ratio. Since the atomic weight of 
phosphorus has been better established by other methods, we may 
properly reverse this ratio and apply it to our discussion of gold. 100 
parts of P precipitate the quantities of Au given in the third column : 

.829 grm. P precipitated 8.714 grm. Au. 1051.15 

.754 " 7-93 " 1051.73 



Mean, 1051.44, d= .196 

Hence if P = 31, Au = 195.568. 

* Poggend. Annalen, 8, 177. 
f Lehrbuch, 5 Aufl., 3, 1212. 
J Lehrbuch, 5 Aufl., 3, 1188. 



102 THE ATOMIC WEIGHTS. 

Level's * estimation of the atomic weight under consideration can 
hardly have much value. A weighed quantity of gold was converted 
in a flask into AuCl 3 . This was reduced by a stream of sulphur dioxide,. 
and the resulting sulphuric acid was determined as BaS0 4 . One gramme 
of gold gave 1,782 grin. BaS0 4 . Hence Au = 195.06. 

All these values may be neglected as worthless, except that derived 
from Berzelius' K 2 AuCl 5 series. 

In 1886 Kriissf published the first of the recent determinations of the 
atomic w r eight under consideration, several distinct methods being re- 
corded. First, in a solution of pure auric chloride the gold was pre- 
cipitated by means of aqueous sulphurous acid. In the filtrate from the 
gold the chlorine was thrown down as silver chloride, and thus the ratio 
Au : 3 AgCl was measured. I subjoin Kriiss' weights, together with a 
third column giving the gold equivalent to 1QO parts of silver chloride: 

Au. AgCl. Ratio. 

7.72076 16.84737 45-828 

5.68290 12.40425 45.814 

3.24773 7.08667 45-828 

4.49167 980475 45-8ii 

3-47949 7-59300 45-825 

3.26836 7 13132 45-832 

5.16181 11.26524 45.821 

4.86044 10.60431 45.834 

Mean, 45.824, .0020 

The remainder of Kruss' determinations were made with potassium 
auribromide, KAuBr 4 , and with this salt several ratios were measured. 
The salt was prepared from pure materials, repeatedly recrystallized 
under precautions to exclude access of atmospheric dust, and dried over 
phosphorus pentoxide. First, its percentage of gold was determined, 
sometimes by reduction with sulphurous acid, sometimes by heating in 
a stream of hydrogen. For this ratio, the weights and percentages are 
as follows, the experiments being numbered for further reference, and the 
reducing agent being indicated. 

KAuBr. Au. Per cent. 

i. SO, 10.64821 3-77753 35476 

2 - S0 2 4.71974 1.67330 35-453 

3- H 7-05762 2.50122 35-440 

4. H 4-49558 1-59434 35-465 

5- SO, 8.72302 3-09448 35-475 

6. SO 2 7.66932 2.71860 35-448 

7- SO, 7.15498 2.53695 35.457 

8 - H 12.26334 4-34997 35-471 

9- II 7-10342 2.51919 35-465 

Mean, 35.461, .0028 

- , , 

* Ann. Chim. Phys. (3), 30, 355. 1850. 
"t Untersuchungen uber das Atomgewicht des Goldes. Mi'mchen, 1886. 112 pp., Svo. 



GOLD. 103 

In five of the foregoing experiments the reductions were effected with 
sulphurous acid ; and in these, after filtering off the gold, the bromine 
was thrown down and weighed as silver bromide. This, in comparison 
with the gold, gives the ratio Au : 4AgBr : : 100 : x. 

Au. <j.AgBr> Ratio. 

i 3-77753 H.39542 381.080 

2 1.67330 6.37952 381.254 

5 3- 9448 ".78993 380.999 

6 2.71860 10.35902 381.042 

7 2.53695 9.66117 380.731 

Mean, 381.021, . .057 

Hence Au : AgBr : : 100 : 95.255, .0142. 

In the remaining experiments, Nos. 3, 4, 8, and 9, the KAuBr 4 was 
reduced in a stream of hydrogen, the loss of weight, Br 3 , being noted. 
In the residue the gold was determined, as noted above, and the KBr 
was also collected and weighed. The weights were as follows : 

Au. Loss, Br z . KBr. 

3 2.50122 3-04422 1.51090 

4 1-59434 1-93937 -96243 

8 4-34997 5- 2 93 l6 2.62700 

9 2.51919 3-06534 L52I53 

From these data we obtain two more ratios, viz., Au : Br 3 : : 100 : SB, 
and Au : KBr : : 100 : x, thus : 

Au : Br z . Au : KBr. 

3 121.710 60.405 

4 121.641 60.365 

8 121.683 60.391 

9 121.680 60.398 



Mean, 121.678, .0100 Mean, 60.390, .0059 

From all the ratios, taken together, Krtiss deduces a final value of 
Au = 197.13, if = 16. It is obviously possible to derive still other 
ratios from the results given, but to do so would be to depart unneces- 
sarily from the author's methods as stated by himself. 

Thorpe and Laurie, * whose work appeared shortly after that of Kruss, 
also made use of the salt KAuBr 4 , but, on account of difficulty in drying 
it without change, they did not weigh it directly. After proving the con- 
stancy in it of the ratio Au : KBr, even after repeated crystallizations, 
they adopted the following method : The unweighed salt was heated 
with gradual increase of temperature, up to about 160, for several hours, 
and afterwards more strongly over a small Bunsen flame. This was done 
in a porcelain crucible, tared by another in weighing, which latter was 
treated in precisely the same way. The residue, KBr -f Au, was weighed, 
the KBr dissolved out, and the gold then weighed separately. The 

* Journ. Chein. Soc., 51, 565. 1887. 



104 



THE ATOMIC WEIGHTS. 



weightjof KBr was taken by difference. The ratio Au:KBr: : 100 : x 

appears in a third column. 

An. KBr. Ratio. 

6.19001 3-73440 60.329 

4.76957 2.87715 60.32? 

4.14050 2.49822 60.336 

3.60344 2.17440 60.342 

3.67963 2.21978 60.326 

4-57757 2.76195 60.337 

5-36659 3-23821 60.326 

5.16406 3. 11533 60.327 

Mean, 60.331, .0016 

This mean combines with Krtiss' thus: 

Kriiss 60.390, .0059 

Thorpe and Laurie 60.331, d= .0016 



General mean 60.338, d= .0015 

The potassium bromide of the previous experiments was next titrated 
with a solution of pure silver by Stas' method, the operation being 
performed in red light. Thus we get the following data for the ratio 
Ag : Au : : 100 : :c, using the weights of gold already obtained : 

Ag. Au. Ratio. 

3.38451 6.19001 182.893 

2.60896 4.76957 182.813 

2.28830 4.18266 182.786 

2.26415 4.14050 182.868 

1.97147 3-60344 182.775 

2.01292 3-67963 182.801 

2.50334 4-57757 182.863 

2.93608 5.36659 182.780 

2.82401 5.16406 182.865 



Mean, 182.827, .0101 

Finally, in eight of these experiments, the silver bromide formed 
during titration was collected and weighed, giving values for the ratio 
Au: AgBr: 



100 : x, as follows : 

An. AgBr. 

6.19001 5.89199 

4.76957 4-54261 

4.18266 3.98288 

4.14050 3-94309 

3-60344 3-43 i5 

3.67963 3-50207 

4.57757 4.35736 

5.36659 5-11045 



Ratio. 

95.186 
95.242 

95-224 
95.232 , 

95.i9i 
95-175 
95-189 
95.227 

Mean, 95.208, .0061 
Kriiss found, 95.255, dr .0142 



General mean, 95.222, .0056 



GOLD. 105 

From the second and third of the ratios measured by Thorpe and 
Laurie an independent value for the ratio Ag : Br may be computed. It 
becomes 100 : 74.072, which agrees closely with the determinations made 
by Stas and Marignac. Similarly, the ratios Ag : KBr and AgBr : KBr 
may be calculated, giving additional checks upon the accuracy of the 
manipulation, though not upon the purity of the original material 
studied. 

Thorpe and Laurie suggest objections to the work done by Kriiss, on 
the ground that the salt KAuBr 4 cannot be completely dried without 
loss of bromine. This suggestion led to a controversy between them and 
Kriiss, which in effect was briefly as follows : 

First, Kriiss* urges that the potassium auribromide ordinarily contains 
traces of free gold, not belonging to the salt, produced by the reducing 
action of dust particles taken up from the air. He applies a correction 
for this supposed free gold to the determinations made by Thorpe and 
Laurie, and thus brings their results into harmony with his own. To 
this argument Thorpe and Laurie f reply, somewhat in detail, stating 
that the error indicated was guarded against by them, and that they 
had dissolved quantities of from eight to nineteen grammes of the auri- 
bromide without a trace of free gold becoming visible. A final note in 
defense of his own work was published by Kriiss a little later. J 

In 1889 an elaborate set of determinations of this constant was pub- 
lished by Mallet, whose experiments are classified into seven distinct 
series. First, a neutral solution of auric chloride was prepared, which 
was weighed off in two approximately equal portions. In one of these 
the gold was precipitated by pure sulphurous acid, collected, washed, 
dried, ignited in a Sprengel vacuum, and weighed. To the second por- 
tion a solution containing a known weight of pure silver was added. 
After filtering, with all due precautions, the silver remaining in the fil- 
trate was determined by titration with a weighed solution of pure hydro- 
bromic acid. We have thus a weight of gold, and the weight of silver 
needed to precipitate the three atoms of chlorine combined with it; in 
other words, the ratio Ag 3 : Au : : 100 : x. All weights in this and the 
subsequent series are reduced to vacuum standards, and all weighings 
were made against corresponding tares. 

Au. Ag y Ratio. 

7.6075 12.4875 60.921 

8.4212 13.8280 60.900 

6.9407 ir -3973 60.898 

3.3682 5.5286 60.923 

2.8244 4.6371 60.909 

Mean, 60.910, .0034 

Hence Ag : Au : : 100 : 182.730, .0102. 

*Ber. Deutsch. Chem. Gesell., 20, 2365. 1887. 
fBerichte, 20, 3036, and Journ. Chem. Soc., 51, 866. 1887. 
t Berichte, 21, 126. 1888. 
% Philosophical Transactions, 180, 395. 1889. 



106 THE ATOMIC WEIGHTS. 

The second series of determina.tions was essentially like the first, ex- 
cept that auric bromide was taken instead of the chloride. The ratio 
measured, Ag 3 : Au, is precisely the same as before. Results as follows : 

Au. Ag y Ratio. 

8.2345 13-5149 60.929 

7.6901 12.6251 60.911 

105233 17.2666 60.945 

2.7498 4.5141 60.916 

3.5620 5-8471 60.919 

3.9081 6.4129 60.941 



Mean, 60.927, .0038 

Hence Ag : Au : : 100 : 182.781, .0114. 

In the third series of experiments the salt KAuBr 4 was taken, purified 

by five recrystallizations. The solution of this was weighed out into 

nearly equal parts, the gold being measured as in the two preceding 

series in one portion, and the bromine thrown down by a standard silver 

solution as before. This gives the ratio Ag 4 : Au : : 100 : x. 

Au. Ag. Ratio. 

5.7048 12.4851 45. 6 93 

7.9612 I7.4I93 45- 6 93 

2 -4455 5.35!3 45- 6 99 

4.1632 9-"53 45- 6 73 

Mean, 45.689, .0040 . 

Hence Ag : Au : : 100 : 182.756, .0160. 

The fifth series of determinations, which for present purposes naturally 
precedes the fourth, was electrolytic in character, gold and silver being 
simultaneously precipitated by the same current. The gold was in solu- 
tion as potassium auro-cyanide, and the silver in the form of potassium 
silver cyanide. The equivalent weights of the two metals, thrown down 
in the same time, were as follows, giving directly the ratio Ag : Au : : 100 : x. 
Au. Ag. Ratio. 

5.2721 2.8849 182.748 

6.3088 3.4487 182.933 

4.2770 2.3393 182.832 

3-5 I2 3 1.9223 182.713 

3.6804 2.0132 182.814 

Mean, 182.808, .0256 

This mean may be combined with the preceding means, and also with 
the determination of the same ratio by Thorpe and Laurie, thus : 

Thorpe and Laurie 182.827, .0.101 

Mallet, chloride series 182.730, .0102 

Mallet, bromide series 182.781, .01 14 

Mallet, KAuBr 4 series 182 756, .0160 

Mallet, electrolytic 182.808, .0256 

General mean 182.778, =h .0055 



GOLD. 107 

Iii Mallet's fourth series a radically new method was employed. Tri- 
m ethyl-ammonium aurichloride, N(CH 3 ) 3 HAuCl 4 , was decomposed ly 
heat, and the residual gold was determined. In order to avoid loss by 
spattering, the salt was heated in a crucible under a layer of fine siliceous 
sand of known weight. Several crops of crystals of the salt were studied, 
as a check against impurities, but all gave concordant values. 

Salt. Residual Au. Percent. A u. 

14-9072 7-3754 49-475 

15.5263 7.6831 49-484 

10.4523 5-1712 49-474 

6.5912 3.2603 49.464 

5-5744 2.7579 49-474 



Mean, 49.474, .0021 

In his sixth and seventh series Mallet seeks to establish, by direct 
measurement, the ratio between hydrogen and gold. In their experi- 
mental details his methods are somewhat elaborate, and only the pro- 
cesses, in the most general way, can be indicated here. First, gold was 
precipitated electrolytically from a solution of potassium aurocyanide, 
and its weight was compared with that of the amount of hydrogen simul- 
taneously liberated in a voltameter by the same current in the same 
time. The hydrogen was measured, and its weight was then computed 
from its density. The volumes are given, of course, at and 760 mm. 

Wt. Au. Vol. H, cc. Wt. H. 

4.0472 228.64 . 2 5483 

4.0226 227.03 .0204046 

4.0955 231.55 , .0208103 

These data, with the weight of one litre of hydrogen taken as 0.89872 
gramme, give the subjoined values in the ratio H : Au : : 1 : x. 

196.960 

197-151 
196.805 



Mean, 196.972, =b .0675 

In the-last series of experiments a known quantity of metallic zinc was 
dissolved in dilute sulphuric acid, and the amount of hydrogen evolved 
was measured. Then a solution of pure auric chloride or'bromide was 
treated with a definite weight of the same zinc, and the quantity of gold 
thrown down was determined. The zinc itself was purified by practical 
distillation in a Sprengel vacuum. From these data the ratio H 3 : Au 
was computed by direct comparison of the weight of gold and that of the 
liberated hydrogen. The results were as follows : 



108 



THE ATOMIC WEIGHTS. 



Wt. Au. 

10.3512 
8.2525 
8.1004 

3-2913 

3.4835 
3.6421 



Vol. H, cc. 

1756.10 

1400.38 

1374.87 

558.64 

590-93 



Wt. H. 

.157824 
125857 

.123565 
.050206 
.053109 
055551 



Hence for the ratio H 3 : Au : : 1 : x we have : 

65-587 
65-571 
65.557 
65.556 
65o93 
65.563 



Mean, 65.571, .00436 

And H : Au : : 1 : 196.713, .0131. This, combined with the value 
found in the preceding series, gives a general mean of 196.722, .0129. 
The ratios available for gold are now as follows : 

(l.) 2KC1 : Au : : 100 : 263.730, .026 

( 2 -) 3^gCl : Au : : 100 : 45.824, ; .0020 

(3.) KAuBr 4 : Au : : 100 : 35.461, db .0028 

(4.) Au : AgBr : : 100 : 95.222, .0056 



(5.) Au : Br 3 : 

(6.) Au : KBr 

(7.) Ag : Au : 

(8. 

(9.) H : Au 



: IOO : 121.678, db .OIOO 
: : TOO : 60.338, d= 0015 



100 : 182.778, d= -0055 

loo : 49.474, .0021 
196.722, dr .0129 



For the reduction of these ratios the antecedent data are : 



Ag= 107.108, zb .0031 
Cl == 35.179, d= .0048 
Br = 79-344, .0062 
K = 38.817, d= .0051 
N = J 3.935, .0021 



C = 11.920, dr .0004 
AgCl 142.287, .0037 
AgBr = 186.452, d= .0054 
KC1 = 74.025, .0019 
KBr = 118.200, .0073 



Hence for the atomic weight of gold we have nine values : 

From (i) Au = 195.226, .0193 



From (2) 
From (3) 
From (4) 
From (5) 
From (6) 
From (7) 
From (8) 
From (9) 



195.605, d= .0099 
= I95-7 11 , .0224 
= 195.808, d= .0126 

= 195.624, .0222 

= T 95- 8 96, db .0131 
= 195.770, db .0082 
= 196.238, =h .0224 

= 196.722, .0129 



General mean Au = 195.850, dz .0044 

If = 16, this becomes Au = 197.342. 



GOLD. 109 

Of the foregoing values the first one, which is derived from Berzelius' 
work, should certainly be rejected. So also, apparently, should the eighth 
and ninth values. Excluding these, values 2 to 7, inclusive, give a gen- 
eral mean of Au = 195.743, .0049. With = 16, this becomes Au = 
197.235. Probably these values are more nearly correct than those which 
include all the determinations. 

The ninth value in the list given above represents Mallet's comparisons 
of gold directly with hydrogen, and is peculiarly instructive. In Mal- 
let's paper the other determinations are discussed upon the basis of 
O = 15.96, which brings them more nearly into harmony with the hydro- 
gen series. The great divergence shown in this recalculation is due to 
the new value for oxygen, 15.879, and its effect upon the atomic weights 
of silver, bromine, etc. The former agreement between the several series 
of gold values was therefore only apparent, and we are now able to see 
that concordance among determinations maybe only coincidence, and 
no proof of accuracy. It is probable, furthermore, that direct compari- 
sons of metals with hydrogen cannot give good measurements of atomic 
weights, for several reasons. First, it is not possible to be certain that 
every trace of hydrogen has been collected and measured, and any loss 
tends to raise the apparent atomic weight of the metal studied ; secondly, 
the weight of the hydrogen is computed from its volume, and a slight 
change in the factors used in reduction of the observations may make a 
considerable difference in the final result. These uncertainties exist in 
all determinations of atomic weights hitherto made by the hydrogen 
method. 



110 THE ATOMIC WEIGHTS. 



CALCIUM. 

For determining the atomic weight of calcium we have sets of experi- 
ments by Berzelius, Erdmann and Marchand, and Dumas. Salvetat * 
also has published an estimation, but without the details necessary to 
enable us to make use of his results. I also find a reference f to some 
work of Marignac, which, however, seems to have been of but little im- 
portance. The earlier work of Berzelius was very inexact as regards 
calcium, and it is not until we come down to the year 1824 that we find 
any material of decided value. 

The most important factor in our present discussion is the composi- 
tion of calcium carbonate, as worked out by Dumas and by Erdmann 
and Marchand. 

In 1842 Dumas J made three ignitions of Iceland spar, and determined 
the percentages of carbon dioxide driven off and of lime remaining. The 
impurities of the material were also determined, the correction for them 
applied, and the weighings reduced to a vacuum standard. The per- 
centage of lime came out as follows : 

56.12 
56.04 
56.06 



Mean, 56.073, .016 

About this same time Erdmann and Marchand began their researches 
upon the same subject. Two ignitions of spar, containing .04 per cent, 
of impurity, gave respectively 56.09 and 56.18 per cent, of residue ; but 
these results are not exact enough for us to consider further. Four other 
results obtained with artificial calcium carbonate are more noteworthy. 
The carbonate was precipitated from a solution of pure calcium chloride 
by ammonium carbonate, was washed thoroughly with hot water, and 
dried at a temperature of 180. With this preparation the following 
residues of lime were obtained : 

56.03 

55.98 

56.00 

55-99 
Mean, 56.00, .007 

It was subsequently shown by Berzelius that calcium carbonate pre- 
pared by this method retains traces of water even at 200, and that 



*Compt. Rend., 17, 318. 1843. 

fSee Oudeman's monograph, p. 51. 

JCompt. Rend., 14, 537. 1842. 

g Journ. fur Prakt. Chem., 26, 472. 1842. 



CALCIUM. Ill 

minute quantities of chloride are also held by it. These sources of error 
are, however, in opposite directions, since one would tend to diminish 
and the other to increase the weight of residue. 

In the same paper there are also two direct estimations of carbonic 
acid in pure Iceland spar, which correspond to the following percentages 
of lime : 

56.00 

56.02 

Mean, 56.01, .007 

In a still later paper* the same investigators give another series of 
results based upon the ignition of Iceland spar. The impurities were 
carefully estimated, and the percentages of lime are suitably corrected : 

4.2134 grm. CaCO 3 gave 2.3594 grm. CaO. 55-997 per cent. 

15.1385 " 8.4810 " 56.022 " 

23.5503 " 13.1958 " 56-031 " 

23.6390. I3-245 6 " 5 6 -3 2 

42.0295 23.5533 " 56.044 " 

49.7007 " 27.8536 " 56.042 " 



Mean, 56.028, .0047 

Six years later Erdmann and March and f published one more result 
upon the ignition of calcium carbonate. They found that the compound 
began giving off carbon dioxide below the temperature at which their 
previous samples had been dried, or about 200, and that, on the other 
hand, traces of the dioxide were retained by the lime after ignition. 
These two errors do not compensate each other, since both tend to raise 
the percentage of lime. In the one experiment now under consideration 
these errors were accurately estimated, and the needful corrections were 
applied to the final result. The percentage of residual lime in this case 
came out 55.998. This agrees tolerably well with the figures found in the 
direct estimation of carbonic acid, and, if combined with those two. gives 
a mean for all three of 56.006, .0043. 

Combining all these series, we get the following result : 

Dumas 56.073, .016 

Erdmann and Marchand . . 56.006, rb .007 

Erdmann and Marchand 56.028, dr .0047 

Erdmann and Marchand 56.006, .0043 



General mean 56.0198, .0029 

For reasons given above, this mean is probably vitiated by a slight 
instant error, which makes the figure a trifle too high. 

* Journ. fur Prakt. Cheni., 31, 269. 1844. 
f Journ. fi'ir Prakt. Chem., 50, 237. 1850. 



112 THE ATOMIC WEIGHTS. 

In the earliest of the three papers by Erdmann and Marchand there is 
also given a series of determinations of the ratio between calcium car- 
bonate and sulphate. Pure Iceland spar was carefully converted into 
calcium sulphate, and the gain in weight noted. One hundred parts of 

spar gave of sulphate : 

136.07 
136.06 
136.02 
136.06 

Mean, 136.0525, .0071 

In 1843 the atomic weight of calcium was redetermined by Berzelius, * 
who investigated the ratio between lime and calcium sulphate. The 
calcium. was first precipitated from a pure solution of nitrate by means 
of ammonium carbonate, and the thoroughly washed precipitate was 
dried and strongly ignited in order to obtain lime wholly free from ex- 
traneous matter. This lime was then, with suitable precautions, treated 
with sulphuric acid, and the resulting sulphate was weighed. Correction 
was applied for the trace of solid impurity contained in the acid, but not 
for the weighing in air. The figures in the last column represent the 
percentage of weight gained by the lime upon conversion into sulphate : 

1.80425 grm. CaO gained 2.56735 grm. 142.295 

2.50400 " 3.57050 " 142.592 

3.90000 S-SSHO " 142.343 

3.04250 " 4.32650 " 142.202 

3.45900 " 4- 93 HO " 142.567 



Mean, 142.3998, .0518 

Last of all we have the ratio between calcium chloride and silver, as 
determined by Dumas, t Pure calcium chloride was first ignited in a 
stream of dry hydrochloric acid, and the solution of this salt was after- 
wards titrated with a silver solution in the usual way. The CaCl 2 pro- 
portional to 100 parts of Ag is given in a third column : 

2.738 grm. CaCl 2 = 5.309 grm. Ag. 51-573 

2.436 " 4.731 " 5 '.490 

1.859 3-6i7 " 5^396 

2.771 5.38*5 " 5L424 

2.240 4.3585 " 5 I -394 



Mean, 51.4554, .0230 

We have now four ratios to compute from, as follows : 

(i.) Percentage CaO in CaCO 3 , 56.0198, .0029 

(2.) CaO : SO 3 : : 100 : 142.3998, .0518 

(3.) CaCO 3 : CaSO 4 : : 100 : 136.0525, .0071 

(4-) Ag 2 : CaC] 2 : : 100 : 51.4554, .0230 

* Journ. fur Prakt. Chem., 31, 263. Ann. Chem. Pharm., 46, 241. 
t Ann. Chim. Phys. (3), 55, 129. 1859. Ann. Chem. Pharm., 113, 34. 



STRONTIUM. 113 

The antecedent values are 

O = 15.879, .0003 c= 11.920, .0004 

Ag = 107.108, .0031 S =31.828, -0015 



Hence the subjoined values for the atomic weight of calcium : 

From (i) .......................... Ca = 39.757, dz .0048 

From (2) ... ...................... " = 39.925, .0203 

From (3) ................. ........ " == 39-706, .0204 

From (4) ......................... " = 39.868, HE .0503 



Mean Ca = 39.764, .0045 

If = 16, Ca = 40.067. 



STRONTIUM. 

The ratios which fix the atomic weight of strontium resemble in gen- 
eral terms those relating to barium, only they are fewer in number and 
represent a smaller amount of work. The early experiments of Stro- 
meyer,* who measured the volume of CO 2 evolved from a known weight 
of strontium carbonate, are hardly available for the present discussion. 
So also we may exclude the determination by Salvetat,f who neglected 
to publish sufficient details. 

Taking the ratio between strontium chloride and silver first in order, 
we have series of figures by Pelouze and by Dumas. Pelouze J employed 
the volumetric method to be described under barium, and in two ex- 
periments obtained the subjoined results. In another column I append 
the ratio between SrCl 2 and 100 parts of silver : 

1.480 grm. SrCl 2 = 2.014 grm. Ag. 73-486 

2.210 " 3.008 " 73-47 1 



Mean, 73.4781, db .0050 

Dumas, by the same general method, made sets of experiments with 
three samples of chloride which had previously been fused in a current 
of dry hydrochloric acid. His results, expressed in the usual way, are 
as follows : 

* Schweigg. Journ., 19, 228. 1816. 

f Compt. Rend., 17, 318 1843. 

I Compt. Rend., 20, 1047. 1845. 

I Ann. Chim. Phys. (3), 55, 29. 1859. Ann Cheat. Pharm., 113, 34. 



114 THE ATOMIC WEIGHTS. 

Series A. 

3.137 grm. SrCl 2 = 4.280 grm. Ag. Ratio, 73.2944 

1.982 " 2.705 " " 73-27I7 

3.041 4.142 " 73.4186 

3.099 " 4.219 " 73-4534 



Mean , 73-3595 
Series B. 

3.356 grm. SrCl 2 = 4-574 grm. Ag. Ratio, 73-3713 

6.3645 8.667 " 73.4327 

7.131 9.712 " 73.4246 

Mean, 73.4095 
Series C. 



7.213 grm. SrC 


I 2 9.811 grm. Ag. 


Ratio, 73-5J95 


2.206 " 


3.006 " 


" 73.3866 


4.268 


5.816 " 


" 73.5529 


4.018 " 


5-477 " 


" 73.3613 



Mean, 73.455 1 
Mean of all as one series, 73.4079, .0170 

Combining these data we have : 

Pelouze 73.478i, rb .0050 

Marignac 73.4079, .0170 



General mean 73.4725, zb .0048 

The foregoing figures apply to anhydrous strontium chloride. The 
ratio between silver and the crystallized salt, SrCl,.6H,O, has also been 
determined in two series of experiments by Marignac.* Five grammes 
of salt were used in each estimation, and, in the second series, the per- 
centage of water was first determined. The quantities of the salt corre- 
sponding to 100 parts of silver are given in the last column : 

Series A. 

5 grm. SrCl 2 .6H 2 O =4.0515 grm. Ag. 123.411 

4.0495 " 123.472 

4.0505 " 123.442 



Mean, 123.442 
Series B. 

5 grm. SrCl. 2 . 6 H 2 O 4.0490 grm. Ag. 123.487 

4.0500 " 123.457 

4.049 " 123.487 



Mean, 123.477 
Mean of all as one series, 123.460, .0082 



* Journ. fur Prakt. Chem., 74, 216. 1858. 



STRONTIUM. 



115 



In the same paper Marignac gives two sets of determinations of the 
percentage of water in crystallized strontium chloride. The first set, cor- 
responding to u B " above, is as follows : 

40.55 6 
40.568 
40.566 

Mean, 40.563 

In the second set ten grammes of salt w.ere taken at a time, and the 
following percentages were found : 

40.58 

40.59 
40.58 



Mean, 40.583 
Mean of all as one series, 40.573, .0033 

The chloride used in the series of estimations last given was subse- 
quently employed for ascertaining the ratio between it and the sulphate. 
Converted directly into sulphate, 100 parts of chloride yield the quanti- 
ties given in the third column : 



5.942 grm. SrCl 2 gave 6.887 grm. SrSO 4 . 
5-941 " 6.8855 " 

5.942 " 6.884 



II5-932 
i '5-949 
H5.927 

Mean, 115.936, .004 



Richards.* in his study of strontium bromide, followed pretty much 
the lines laid down in his work on barium. The properties of the 
bromide itself were carefully investigated, and its purity established 
beyond reasonable doubt, and then the two usual ratios were deter- 
mined. First, the ratio Ag 2 : SrBr 2 : : 100 : x, by titration with standard 
solutions of silver. For this ratio there are three series of measurements, 
by varied processes, concerning which full details are given. The data 
obtained, with weights reduced to a vacuum, are as follows : 



First Series. 



Wt. Ag. 

1.30755 
2.10351 

2.23357 
5-3684 



Wt. 

1.49962 
2.41225 

2.56153 
6.15663 



Ratio. 
114.689 
114.677 
114.683 
114.683 



Mean, 114.683 
* Proc. Amer. Acad. of Sciences, 1894, p. 369. 



116 



THE ATOMIC WEIGHTS. 



Second Series. 



Wt. Ag. 
1.30762 
2.10322 
4-57502 
5.3680 



.S434 
3-3957 
3.9607 

4.5750 



Wt. 
i. 49962 
2.41225 
5.24727 
6.15663 



Third Series. 

2.9172 
3.8946 
4.5426 
5-2473 



Ratio. 

114.683 

114.693 

114.694 

114.691 

Mean, 114.690 



114.697 
1 14.692 
114.692 
114.695 



Mean, 114.694 
Mean of all as one series, 114.689, db .0012 



For the ratio, measured gravimetrically, 2AgBr : SrBr 2 : : 100 : x, two 



series of determinations are given : 

First Series. 



Wt. AgBr. 

2.4415 
2.8561 

6.9337 



2.27625 
3.66140 
3-88776 
9.34497 



Wt. SrBr., 
i. 6086 
1.8817 
4.5681 



Second Series. 

1.49962 
2.41225 

2.56153 
6.15663 



Ratio. 
65.886 
65.884 
65.883 

Mean, 65.884 



65.881 
65.883 
65.887 
65.882 



Mean, 65.883 
Mean of all as one series, 65.884, .0006 

For the atomic weight of strontium we now have the subjoined ratios 



(i.) Ag 2 : SrCl 2 : : 100 : 73.47 2 5, . 

(2.) Ag 2 : SrCl 2 .6H 2 O : : 100 : 123.460, dr .0082 

(3.) Per cent. H 2 O in SrCl 2 .6H 2 O, 40.573, =b .0033 

(4.) SrCl 2 : SrSO 4 : : 100 : 115.936, .0040 

(5.) Ag 2 : SrBr 2 : : 100 : 114.689, H= .0012 

(6.) 2 AgBr : SrBr 2 : : 100 : 65.884, .0006 



The antecedent values are 

O. = 15.879, .0003 
Ag 107.108, .0031 
Ci = 35.179, .0048 



Br = 79-344, .0062 
S : 31.828, db .0015 

AgBr 186.452, .0054 



STRONTIUM. 117 

For the molecular weight of SrCl 2 three estimates are available : 

From (i) SrCI 2 157.390, =}= .0112 

From (2) " = 157.197, .0192 

From (3).... " = 157-123, .'57 

General mean SrCl 2 = 157.281, .0083 

For SrBr 2 there are two values : 

From (5) SrBr 2 = 245.682, .0076 

From (6) " = 245.684, rb .0075 



General mean SrBr 2 = 245.683, .0053 

Finally, with these intermediate data we obtain three independent 
measures of the atomic weight of strontium, as follows : 

From molecular weight SrCl 2 Sr = 86.923, .0127 

From molecular weight SrBr 2 " = 86.995, =t - OI 35 

From ratio (4) " = 86.434, .081 1 



General mean Sr = 86.948, .0092 

If = 16, Sr = 87.610. Rejection of the third value, which is worth- 
less, raises these means by 0.01 only. The second value, 86.995, which 
represents Richards' work, is undoubtedly the best of the three. 



118 THE ATOMIC WEIGHTS. 



BARIUM. 

For the atomic weight of barium we have a series of eight ratios, estab- 
lished by the labors of Berzelius, Turner, Struve, Marignac, Dumas, and 
Richards. Andrews* and Salvetat,f in their papers upon this subject, 
gave no details nor weighings, and therefore their work may be properly 
disregarded. First in order, we may consider the ratio between silver 
and barium chloride, as determined by Pelouze, Marignac, Dumas, and 
Richards. 

Pelouze, J in 1845, made the three subjoined estimations of this ratio, 
using his well known volumetric method. A quantity of pure silver was 
dissolved in nitric acid, and the amount of barium chloride needed to 
precipitate it was carefully ascertained. In the last column I give the 
quantity of barium chloride proportional to 100 parts of silver: 

3.860 grin. BaCl 2 ppt. 4.002 grm. Ag. 96.452 

5.790 " 6.003 " 9 6 -452 

2.895 " 3-Qoi " 96.468 



Mean, 96.4573, .0036 

Essentially the same method was adopted by Marignac in 1848. His 
experiments were made upon four samples of barium chloride, as fol- 
lows. A, commercial barium chloride, purified by recrystallization from 
water. B, the same salt, calcined, redissolved in water, the solution 
saturated with carbonic acid, filtered, and allowed to crystallize. C, the 
preceding salt, washed with alcohol, and again recrystallized, D, the 
same, again washed with alcohol. For 100 parts of silver the following 
quantities of chloride were required, as given in the third column : 

Ag. BaCL. Ratio. 





( 3-4445 


3-3190 


96.356 


) 


A. 


\ 3.748o 


3.6110 


96.345 


\ Mean, 96.354 




(6.3446 


6.1140 


96.362 


) 




| 4.3660 


4.1780 


96.356 


| 


B. 


{ 4-8390 


4.6625 . 


96.352 


1 Mean, 96.354 




j 6.9200 


6.6680 


96.358 


~j 


C. 


{ 5.6230 


5-4185 


96.363 


f- Mean, 96.360 




( 5-8435 


5.6300 


96.346 


1 




1 8.5750 


8.2650 


96.384 


1 


. 


) 4.8225 


4.6470 


96.361 


[ 




[6.8460 


6.5980 


96.377 


J 








Mean, 96.360 


, .0024 



* Chemical Gazette, October, 1852. 

fCompt. Rend., 17, 318. 

I Compt. Rend., 20, 1047. Journ. fur Prakt. Chern., 35, 73. 

g Arch, d. Sci. Phys. etNat., 8, 271. 



BARIUM. 



119 



Dumas* employed barium chloride prepared from pure barium 
nitrate, and took the extra precaution of fusing the salt at a red heat in 
a current of dry hydrochloric acid gas. Three series of experiments 
upon three samples of chloride gave the following results : 




L7585 
3.8420 
2.1585 
4.0162 
1.6625 
2.4987 
3.4468 
4.0822 
4.2062 
4.4564 
8.6975 
2.2957 
4.I372 
4.2662 

4.4764 
5.6397 



Ratio. 

9 6 -303 1 

9 6 .339 [ 

96.340 | 
96.358 j 
96.265^ 

96-304 

96.306 

96.290 

96.289 

96.271 

96.307 

96.3 l6> | 

96.371 

96.303 \ 

96.3 2 9 
96-372J 



Mean, 96.333 



>. Mean, 96.290 



Mean, 96.338 



Mean, 96.316, dr .0055 



The work done by Richards f was of a much more elaborate kind, for 
it involved some collateral investigations as to the effect of heat upon 
barium chloride, etc. Every precaution was taken to secure the spectro- 
scopic purity of the material, which was prepared from several sources, 
and similar care was taken with regard to the silver. For details upon 
these points the original paper must be consulted. As for the titrations, 
three methods were adopted, and a special study was made with refer- 
ence to the accurate determination of the end point ; in which particular 
the investigations of Pelouze, Marignac, and Dumas were at fault. In the 
first series of determinations, silver was added in excess, and the latter 
was measured with a standard solution of hydrochloric acid. The end 
point was ascertained by titrating backward and forward with silver 
solution and acid, and was taken as the mean between the two apparent 
end points thus observed. The results of this series, with weights reduced 
to vacuum standards, were as follows : 



AS- 


Bad,. 


Ratio. 




6.1872 


5.9717 


96.517 




5.6580 


5-4597 


96.495 




3-5988 


3.4728 


96.499 




9.4010 


9.0726 


96.507 




.7199 


.6950 


96.541 








Mean, 96.512, d= 


0055 


*Ann. Chem. 


Pharm., 113, 22. 1860. Ann. Chim. 


Phys. (3), 55, 129. 





120 THE ATOMIC WEIGHTS. 

In the second series of experiments a small excess of silver was added 
as before, and the precipitate of silver chloride was removed by filtra- 
tion. The filtrate and wash waters were concentrated to small bulk 
whereupon a trace of silver chloride was obtained and taken into account. 
The excess of silver remaining was then thrown down as silver bromide, 
and from the weight of the latter the silver was calculated, and sub- 
tracted from the original amount. 

Ag. BaCl T Ratio. 

6.59993 6.36974 96.512 

5-552 2 9 5-3 6oi 96.539 

4.06380 3.92244 96.522 



Mean, 96.524, .0054 

The third series involved mixing solutions of barium chloride and 
silver in as nearly as possible equivalent amounts, and then determining 
the actual quantities of silver and chlorine left unprecipitated. The 
filtrate and wash waters were divided into two portions, one-half being 
evaporated with hydrobromic acid and the other with silver nitrate. 
The small amounts of silver bromide and chloride thus obtained were 
determined by reduction and the use of Volhard's method : 

Ag. BaCl v Ratio. 

4-4355 4.2815 96.528 

2.7440 2.6488 96.531 

6.1865 5-97 12 96.520 

3 4023 3.2841 96.526 



Mean, 96.526, .0035 

Two final experiments were carried out by Stas' method, somewhat as 
in the first series, with variations and greater refinement in the observa- 
tion of the end point. The results were as follows : 

Ag. Bad*. Ratio. 

6.7342 6.50022 96.525 

10.6023 IO - 2 3365 96.523 



Mean, 96.524, .0007 

A careful study of Richards' paper will show that, although the last 
two experiments are probably the best, they are not entitled to such pre- 
ponderance of weight as the " probable error" here computed would 
give them. I therefore treat Richards' work as I have already done that 
of Marignac and Dumas, regarding all of his series as one, which gives for 
the value of the ratio 96.520, .0025. This combines with the previous 
series thus : 



BARIUM. 121 

Pelouze 96.457, rfc .0036 

Marignac 96.360, .0024 

Dumas 96.316, db .0055 

Richards 96.520, .0025 



General mean .................... 96.434, .0015 

The ratio between silver and crystallized barium chloride has also 
been fixed by Marignac.* The usual method was employed, and two 
series of experiments were made, in the second of which the water of crys- 
tallization was determined previous to the estimation. Five grammes of 
chloride were taken in each determination. The following quantities of 
BaCl 7 .2H 2 O correspond to 100 parts of silver : 

113.109") 
A. J 113.135 V Mean, 113.114 



- 

B. J 113.122 V- Mean, 113.106 
(113.060) 

Mean, 113.110, .0079 

The direct ratio between the chlorides of silver and barium has been 
measured by Berzelius. Turner, and Richards. Berzelius t found of 
barium chloride proportional to 100 parts of silver chloride 

72.432 
72.422 



Mean, 72.427 

Turner J made five experiments, with the following results : 

72.754 
72.406 
72.622 
72.664 
72.653 



Mean, 72.680, .0154 

Of these, Turner regards the fourth and fifth as the best ; but for 
present purposes it is not desirable to so discriminate. 

Richards' determinations fall into three series, and all are character- 
ized by their taking into account chloride of silver recovered from the 
wash waters. In the first series the barium chloride was ignited at low 
redness in air or nitrogen ; in the second series it was fused in a stream 
of pure hydrochloric acid ; and in the third series it was not ignited at 
all. In the last series it was weighed in the crystallized state, and the 

* Tourn. fur Prakt. Chem., 74, 212. 1858. 

t Poggend. Annalen, 8, 177. 

t Phil. Trans., 1829, 291. 

\ Proc. Amer. Acad., 29, 55, 1893. 



122 THE ATOMIC WEIGHTS. 

amount of anhydrous chloride was computed from the data so obtained. 
The data, corrected to vacuum standards, are as follows : 

AgCl. Bad*. Ratio. 

( 8.7673 6.3697 72.653 } 

I 5-1979 3.7765 72.654 

A. 1 4.9342 3.5846 72.648 ^ Mean, 72.649 

| 2.0765 1.5085 72.646 | 

U-427I 3.2163 72.650 J 

2.09750 1.52384 72-650 ^ 

B. ^7.37610 5.36010 72.669 V- Mean, 72.6563 

5.39906 3-92244 72.650 ) 

8.2189 5.97123 72.6524 1 

4.5199 3.28410 72.6587} P an ' 72 -' 



Mean, 72.653, .0014 

If we assign Berzelius' work equal weight with that of Turner, the 
three series representing the ratio 2AgCl : BaCl 2 combine as follows 

Berzelius 72.427, =b .01 54 

Turner 72.680, .0154 

Richards 72.653, .0014 



General mean 72.650, i .0014 

Incidentally to some of his other work, Marignac* determined the 
percentage of water in crystallized barium chloride. Two sets of three 
experiments each were made, the first upon five grammes and the socond 
upon ten grammes of salt. The following are the percentages obtained : 

f 14.79*0 

A. J 14.796 y Mean, 14.795 
(14.800) 

c 14.80 S 

. B. 1 14.81 C Mean, 14.803 
(14-80 ) 

Mean, 14.799, .0018 

The ratio between barium nitrate and barium sulphate has been de- 
termined only by Turner, f According to his experiments 100 parts of 
sulphate correspond to the following quantities of nitrate : 

112.060 
111.990 
112.035 



Mean, 112.028, .014 

For the similar ratio between barium chloride and barium sulphate, 
there are available determinations by Turner, Berzelius, Struve, Marignac, 
and Richards. 



* Journ. fur Prakt. Chem., 74, 312. 1858. 
fPhil. Trans., 1833. 538. 



BARIUM. 123 

Turner * found that 100 parts of chloride ignited with sulphuric acid 
gave 112.19 parts of sulphate. By the common method of precipitation 
and nitration a lower figure was obtained, because of the slight solubility 
of the sulphate. This point bears directly upon many other atomic 
weight determinations. 

Berzelius,f treating barium chloride with sulphuric acid, obtained 
the following results in BaS0 4 for 100 parts of BaCl 2 : 

112.17 
112.18 



Mean, 112.175 

Struve, I in two experiments, found : 

112.0912 
112.0964 

Mean, 1 12.0938 

Marignac's three results are as follows : 

8.520 grm. BaCI 2 gave 9.543 BaSO 4 . Ratio, 112.007 

8.519 9.544 " " 112.032 

8.520 " 9-542 " " ui-995 



Mean, 112.011, .0071 

Richards, in his work on this ratio, regards the results as of slight 
value, because of the occlusion of the chloride by the sulphate. This 
source of error he was never able to avoid entirely. Another error in 
the opposite direction is found in the retention of sulphuric acid b} r the 
precipitated sulphate. Eight experiments were made in two series, one 
set by adding sulphuric acid to a strong solution of barium chloride in a 
platinum crucible, the other by precipitation in the usual way. Rich- 
ards gives in his published paper only the end results and the mean of 
his determinations ; the details cited below I owe to his personal kind- 
ness. The weights are reduced to vacuum standards : 

Bad.,. BaSO* Ratio. 

1.78934 2.0056 112.086 

2.07670 2.3274 112.072 

1.58311 i.774i 112.064 

3.27563 3- 6 7i2 112.076 

3.02489 3-393 112.080 

3.87091 4.3385 112.080 

(3.02489 3-9726 112.076 

nd - (3,87091 3.4880 112.085 

Mean, 112.077, .0017 

* Phil. Trans., 1829, 291. 

t Poggend. Annalen, 8, 177. 

1 Ann. Cheni. Pharm., 80, 204. 1851. 

g Journ. fi'ir Prakt. Chem., 74, 212. 1858. 



First. 



124 THE ATOMIC WEIGHTS. 

This mean is subject to a small correction due to loss of chlorine on 
drying the chloride, which reduces it to 112.073. Omitting Turner's 
single determination as unimportant, and assigning to the work of Ber- 
zelius and of Struve equal weight with that of Marignac, the measure- 
ments of this ratio combine thus : 

Berzelius 112.175, =t .0071 

Struve ii 2.094, =t .7 r 

Marignac... 112.011,^.0071 

Richards 1 12.073, .0017 



General mean 112.075, .0016 

In an earlier paper than the one previously cited, Richards* studied 
with great care the ratios connecting barium bromide with silver and 
silver bromide. The barium bromide was prepared by several distinct 
processes, its behavior upon dehydration and even upon fusion'was 
studied, and its specific gravity was determined. The ratio with silver 
was measured by titration, a solution of hydrobromic acid being used 
for titrating back. The data are subjoined, with the BaBr 2 equivalent 
to 100 parts of silver stated : 

BaBr T Ag. Ratio. 

2.28760 1.66074 137.746 

3.47120 2.52019 I37-73 6 

2.19940 1.59687 I37.73 2 

2 -3597i i.7'3 2 3 '37-735 

2.94207 2.13584 137-748 

1.61191 1.17020 137.747 

2.10633 i.5 2 92i 137.740 

2.19682 2.11740 137.755 

237290 1.72276 137.738 

1.84822 L34I75 137.747 

5.66647 4.11360 I37.75 

3.52670 2.56010 37.756 

4-3 l6 90 3- I 343 I37-73 1 

3-36635 2.44385 137.748 

3.46347 2.51415 137-759 



Mean, 137.745, .0015 

The silver bromide in most of these determinations, and in some others, 
was collected and weighed in a Gooch crucible with all necessary pre- 
cautions. Vacuum standards were used throughout for both ratios. I 
give in a third column the BaBr 2 equivalent to 100 parts of AgBr : 

Proc. Amer. Acad., 28. 1893. 



BARIUM. 125 

AgBr. Ratio. 

2.28760 2.89026 79-149 

3-47120 4.3*635 79.136 

3.81086 4.81688 79.133 

2.35971 2.98230 79-124 

2.94207 3-71809 79-129 

2.10633 2.66191 79.128 

2.91682 3.68615 79.129 

2.37290 2.99868 79.131 

1.84822 2.33530 79.143 

1.90460 2.40733 79.116 

5.66647 7.16120 79.127 

3.52670 4.45670 79-133 

2.87743 3-63644 79-127 

3.46347 4-37669 79.135 

Mean, 79.132, .0015 
The ratios for barium now sum up as follows: 

(I.) Ag 2 : BaC) 2 : : 100 : 96.434, .0015 

(2.) Ag 2 : BaCl 2 .2H 2 O : : 100 : 113.110, .0079 

(3.) 2AgCl : BaG 2 : : 100 : 72.650, =fc .0014 

(4.) Per cent, of H 2 O in BaCl 2 .2H 2 O, 14.799, =b .0018 

(5.) BaSO 4 : BaN 2 O 6 : : 100 : 112.028, .014 

(6.) BaCl 2 : BaSO 4 : : 100 : 112.075, =h .0016 

(7.) Ag 2 : BaBr 2 : : 100 : 137-745, .0015 

(8.) 2AgBr : BaBr 2 : : 100 : 79.132, .0015 

The reduction of these ratios depends upon the subjoined antecedent 
values : 

Ag= 107.108, .0031 N = 13.935, =b .0021 

Cl = 35.179,^.0048 S == 31.828, .0015 

Br = 79.344, .0062 AgCl = 142.287, dz .0037 

O = 15.879, .0003 AgBr = 186.452, .0054 

With these factors four estimates are obtainable for the molecular 
weight of barium chloride : 

From (i) BaCl 2 = 206.577, .0068 

From (2) " = 206.542, .0183 

From (3) " 206.745, .0067 

From (4) " = 205.866, .0257 

General mean BaCl 2 = 206.629, .0045 

For barium bromide we have : 

From (7) BaBr 2 295.070, .0091 

From (8) " =295.086,^.0102 



General mean BaBr 2 = 295.078, .0068 



126 THE ATOMIC WEIGHTS. 

And for barium itself, four values are finally available, thus : 

From molecular weight BaCl 2 Ba = 136.271, .0106 

From molecular weight BaBr. 2 " = 136.390, .0141 

From ratio (5) " 135.600, rb .2711 

From ratio (6) " = 136.563, .0946 



General mean Ba = 136.315, d= .0085 

Or, if = 16, Ba = 137.354. 

In the foregoing computation all the data, good or bad, are included. 
Some of them, as shown -by the weights, practically vanish ; but others, 
as in the chloride series, carry an undue influence. A more trustworthy 
result can be deduced from Richards' experiments alone, which reduce 
as follows : 

From Ag 2 : BaCl 2 BaCl 2 = 206.761, .0080 

From 2AgCl : BaCl 2 " = 206.754, .0067 



General mean BaCl 2 = 206.755, 

From the bromide, as given above, Ba = 136.390, dz .0141. From the 
value just found for the chloride, Ba 136.397, .0109. Combining 
the two values 

Ba = 136.392, .0086. 

Or, if = 16, Ba = 137.434. This determination will be adopted in 
subsequent calculations as the most probable. 



LEAD. 127 



LEAD. 

For the atomic weight of lead we have to consider experiments made 
upon the oxide, chloride, nitrate, and sulphate. The researches of Ber- 
zelius upon the carbonate and various organic salts need not now be 
considered, nor is it worth while to take into account any work of his 
done before the year 1818. The results obtained by Dobereiner* and 
by Longchamp f are also without special present value. 

For the exact composition of lead oxide we have to depend upon the 
researches of Berzelius. His experiments were made at different times 
through quite a number of years ; but were finally summed up in the 
last edition of his famous *' Lehrbuch." J In general terms his method 
of experiment was very simple. Perfectly pure lead oxide was heated 
in a current of hydrogen, and the reduced metal weighed. From his 
weighings I have calculated the percentages of lead thus found and 
given them in a third column : 

Earlier Results. 

8.045 g rm - PbO S ave 74675 grm. Pb. 92.8217 per cent. 

14.183 " 13.165 " 92.8224 " 

10.8645 " 10.084 " 92.8160 " 

13.1465 " 12.2045 " 92.8346 " 

21.9425 " 20.3695 " 92.8313 " 

11.159 " IO -359 " 92.8309 " 

Latest. 

6.6155 6.141 " 92.8275 " 

14.487 " 13.448 " 92.8280 " 

14.626 <( 13-5775 " 92.8313 " 



Mean, 92.8271, .0013 

For the synthesis of lead sulphate we have data by Berzelius, Turner, 
and Stas. Berzelius, whose experiments were intended rather to fix 
the atomic weight of sulphur, dissolved in each estimation ten grammes 
of pure lead in nitric acid, then treated the resulting nitrate with sul- 
phuric acid, brought the sulphate thus formed to dryness, and weighed. 
One hundred parts of metal yield of PbS0 4 : 

146.380 
146.400 
146.440 
146.458 

Mean, 146.419, .012 

* Schweig. Journ., 17, 241. 1816. 
f Ann. Chim. Phys., 34, 105. 1827. 
t Bd. 3, s. 1218. 
I I^ehrbuch, sth ed., 3, 1187. 



128 THE ATOMIC WEIGHTS, 

Turner,* in three similar experiments, found as follows : 

146.430 
146.398 
146.375 



Mean, 146.401, .on 

In these results of Tamer's, absolute weights are implied. 
The results of Stas' syntheses,t effected after the same general method, 
but with variations in details, are as follows. Corrections for weighing 
in air were applied : 

146.443 

146.427 

146.419 

146.432 

146.421 

146.423 

Mean, 146.4275, .0024 

Combining, we get the subjoined result: 

Berzelius 146.419, .012 

Turner 146.401, .01 1 

Stas 146.4275, .0024 



General mean 146.4262, .0023 

Turner, in the same paper, also gives a series of syntheses of lead sul- 
phate, in which he starts from the oxide instead of from the metal. One 
hundred parts of PbO, upon conversion into PbS0 4 , gained weight as 
follows : 

35-84 

35-71 

35.84 

35-75 

35-79 

35.78 

35.92 

Mean, 35.804, .018 

These figures are not wholly reliable. Numbers one, two, and three 
represent lead oxide contaminated with traces of nitrate. The oxide of 
four, five, and six contained traces of minium. Number seven was free 
from these sources of error, and, therefore, deserves more consideration. 
The series as a whole undoubtedly gives too low a figure, and this error 
would tend to slightly raise the atomic weight of lead. 

*Phil. Trans., 1833, 527-538. 
t Aronstein's translation, 333. 



LEAD. 129 

Still a third series by Turner establishes the ratio between the nitrate 
and the sulphate, a known weight of the former being in each experi- 
ment converted into the latter. One hundred parts of sulphate represent 

of nitrate: 

109.312 
109.310 
109.300 



Mean, 109.307, .002 

In all these experiments by Turner the necessary corrections were 
made for weighing in air. 

In 1846 Marignac* published two sets of determinations of only 
moderate value. First, chlorine was conducted over weighed lead, and 
the amount of chloride so formed was determined. The lead chloride 
was fused before weighing. The ratio to 100 Pb is given in the last 
column : 

20.506 grm. Pl> gave 27.517 PbCl 2 . 134.190 

16.281 " 21.858 " 134.225 

25.454 34.H9 " '34.159 

Mean, 134.19^ .013 

Secondly, lead chloride was precipitated by silver nitrate and the ratio 
between PbCl, and 2AgCl determined. The third column gives the AgCl 
formed by 100 parts of PbCl 2 : 

12.534 grm. PbCl 2 gave 12.911 AgCl. 103.01 

14.052 14.506 " JO3.23 

25.533 " 26.399 " 103.39 

Mean, 103.21, .0745 

For the ratio between lead chloride and silver we have a series of re- 
sults by Marignac and one experiment by Dumas. There are also un- 
available data by Turner and by Berzelius. 

Marignac,t applying the method used in his researches upon barium 
and strontium, and working with lead chloride which had been dried at 
200, obtained these results. The third column gives the ratio between 
PbCl 2 , and 100 parts of Ag: 

4.9975 grm. PbCl 2 = 3.8810 grm. Ag. 128.768 

4.9980 " 3.8835 " 128.698 

5.0000 3.8835 " 128.750 

5.0000 " 3.8860 " 128.667 

Mean, 128.721, .016 

Dumas, J in his investigations, found that lead chloride retains traces 

*Aun. Chern. Pharrn., 59, 289; and 290. 1846. 
t Journ. fiir Prakt. Chem., 74, 218. 1858. 
I Ann. Chem. Pharm., 113, 35. 1860. 



130 THE ATOMIC WEIGHTS. 

of water even at 250, and is sometimes also contaminated with oxychlo- 
ride. In one estimation 8.700 grammes PbCl 2 saturated 6.750 of Ag. 
The chloride contained .009 of impurity ; hence, correcting, Ag : PbCI 2 : : 
100 : 128.750. If we assign this figure equal weight with those of Marig- 
nac, we get as the mean of all 128.7266, .013. The sources of error in- 
dicated by Dumas, if they are really involved in this mean, would tend 
slightly to raise the atomic weight of lead. 

The synthesis of lead nitrate, as carried out by Stas,* gives excellent 
results. Two series of experiments were made, with from 103 to 2pO 
grammes of lead in each determination. The metal was dissolved in 
nitric acid, the solution evaporated to dryness with extreme care, and 
the nitrate weighed. All weighings were reduced to the vacuum standard. 
In series A the lead nitrate was dried in an air current at a temperature 
of about 155. In series B the drying was effected in vacuo, 100 of lead 
yield of nitrate : 

A. 

159-973 
159.975 

159.982 

159-975 
159.968 

J59-973 
Mean, 159.9743, =fc .0012 



159.970 
159.964 
159-959 
I59-965 

Mean, 159.9645, .0015 
Mean from both series, 159.9704, 2 .0010 

There is still another set of experiments upon lead nitrate, originally 
intended to fix the atomic weight of nitrogen, which may properly be 
included here. It was carried out by Anderson f in Svanberg's labora- 
tory, and has also appeared under Svanberg's name. Lead nitrate was 
carefully ignited, and the residual oxide weighed, with the following 
results : 

5.19485 grm. PbN 2 O 6 gave 3.5017 grm. PbO. 67.4071 per cent. 

9.7244 6.5546 " 67.4037 " 

9.2181 6.2134 " 67.4044 " 

9.6530 6.5057 " 67.3957 

Mean, 67.4027, i .0016 

* Aronsteiii's translation, 316. 

t Ann. Chim. Phys. (3), 9, 254. 1843. 



LEAD. 131 

We have now nine ratios from which to compute : 

(i.) Per cent, of Pb in PbO, 92.8271, .0013 
(2.) Per cent of PbO in PbN 2 O 6 , 67.4027, .0016 
(3.) Pb : PbSO 4 : : 100 : 146.4262, .0023 
(4.) PbO : PbSO 4 : : 100 : 135.804, .0180 
(5.) PbSO 4 : PbN 2 O 6 : : 100 : 109.307, .0020 
(6.) Pb : PbN 2 O 6 : : iqo : 159.9704, .0010 
(7.) Pb : PbC) 2 : : 100 : 134.191, .013 
(8.) PbCl 2 : 2AgCl : : 100 : 103.21, .0745 
(9.) Ag 2 : PbCl 2 : : 100 : 128.7266, db .0130 

To reduce these ratios we must use the following data : 

O =. 15.879, .0003 s = 31.828, .0015 

Ag= 107.108, =b .0031 N 13.935,^.0021 

Cl == 35.179, db .0048 AgCl= 142.287, .0037 

For the molecular weight of lead oxide we now get three estimates : 

From (i) PbO = 221.375, d= .0403 

From (2) " 221.796, .0132 

From (4) " = 221.944, d= .1116 



General mean PbO = 221.757, =b .0125 

For lead chloride we have 

From (8) PbCl 2 = 275.723, .1989 

From (9) " = 275.753,^.0290 

General mean PbO 2 = 275.752, dr .0287 

Including these results, six values are calculable for the atomic weight 
of lead : 

From molecular weight of PbO Pb = 205.878, dr .0126 

From molecular weight of PbCl 2 " = 205.394, .0302 

From (3) " = 205.367, dr .0051 

From (5) " = 203.352, .0479 

From (6) " = 205.341, db .0068 

From (7) " = 205.779, .0831 



General mean Pb = 205.395, .0038 

If = 16, Pb = 206.960. If we reject the first, fourth, and sixth of 
these values, which are untrustworthy, the remaining second, third, and 
fifth give a general mean of Pb = 205.358, .0040. If O = 16, this 
becomes Pb = 206.923. From Stas' ratios alone Stas calculates Pb = 
206.918 to 206.934 ; Ostwald finds 206.911 ; Van der Plaats (A), 206.9089, 
(B), 206.9308, and Thomson 206.9042. The value adopted here repre- 
sents mainly the work of Stas, and with H = 1 is 

Pb = 205.358, .0040. 



132 THE ATOMIC WEIGHTS. 

GLUCINUM. 

Our knowledge of the atomic weight of glucinum is chiefly derived 
from experiments made upon the sulphate. Leaving out of account the 
single determination by Berzelius, * we have to consider the data fur- 
nished by Awdejew, Weeren, Klatzo, Debray, Nilson and Pettersson, and 
Kriiss and Moraht. 

Awdejew, f whose determination was the earliest of any value, analyzed 
the sulphate. The sulphuric acid was thrown down as barium sulphate ; 
and in the nitrate, from which the excess of barium had been first re- 
moved, the glucina was precipitated by ammonia. The figures which 
Awdejew publishes represent the ratio between S0 3 and G10, but not 
absolute weights. As, however, his calculations were made with S0 3 = 
501.165, and Ba probably 855.29, we may add a third column showing 
how much BaS0 4 is proportional to 100 parts of G10 : 

SO S . GIO. Ratio. 



4457 !4o 921.242 

4531 1420 9 2 7.304 

7816 2480 9 I 5-93 

12880 4065 920 814 



Mean, 921.316, LS77 

The same method was followed by Weeren and by Klatzo, except that 
Weeren used ammonium sulphide instead of ammonia for the precipita- 
tion of the glucina. Weeren J gives the following weights of GIO and 
BaS0 4 . The ratio is given in a third column, just as with the figures by 
Awdejew : 

GIO. BaSO. Ratio. 

.3163 2.9332 927.031 

.2872 2.6377 918 419 

.2954 2.7342 9 2 5-592 

.5284 4.8823 902.946 



Mean, 918.497, =b 3.624 

Klatzo's figures are as follows, with the third column added by the 

writer : 

GIO. BaSO. Ratio. 

.2339 2.1520 920.052 

.1910 J-7556 919.162 

.2673 2.4872 930-49 

3585 3-3"5 9 2 3.7io 

.2800 2.5842 922.989 

Mean, 923.281, 1.346 

* Poggend. Annal., 8, i. 

t Poggend. Aiinal., 56, 106. 1842. 

t Poggend. Aiinal., 92, 124. 1854. 

g Zeitschr. Anal. Chem., 8, 523. 1869. 



GLUCINUM. 133 

Combining these series into a general mean, we get the subjoined result : 

Awdejew 921.316, L577 

Weeren 9 l8 -497, 3.624 

Klatzo 923.281, -_h 1.346 



General mean 922.164, dr 0.985 

Hence G10 = 25.130, .0269. 

Debray* analyzed a double oxalate of glucinum and ammonium, 
G1(NH 4 ) 2 C 4 8 . In this the glucina was estimated by calcination, after 
first converting the salt into nitrate. The following percentages were 
found : 

ii.5 

II. 2 

ii. 6 



Mean, 11.433, d= .081 

The carbon was estimated by an organic combustion. I give the 
weights, and put in a third column the percentages of CO 2 thus obtained : 

Salt. CO* Per cent. CO V 

.600 .477 79 500 

.603 .478 79.270 

.600 .477 79-5 



Mean, 79.423, .052 

Calculating the ratio between C0 2 and G10, we have for the molecular 
weight of the latter, G1O = 25.151, .1783. 

In 1880 the careful determinations of Nilson and Pettersson appeared.f 
These chemists first attempted to work with the sublimed chloride of 
glucinum, but abandoned the method upon finding the compound to 
be contaminated with traces of lime derived from a glass tube. They 
finally resorted to the crystallized sulphate as the most available salt 
for their purposes. This compound, upon strong ignition, yields pure 
glucina. The data are as follows : 

GISO^H.,O. GIO. Percent. GIO. 

3-8014 .5387 

2.6092 -3697 

> 4. 307 2 .6099 

3.0091 .4266 

Mean, 14.169, .0023 

Kriiss and MorahtJ in their work follow the general method adopted 

*Ann. Chim. Phys. ($\ 44, 37- l8 55- 

f Berichte d. Deutsch. Chem. Gesell., 13, 1451. 1880. 

J Ann. d. Chem., 262, 38. 1891. 







- -_-_._ v 



---: 
:-:.-: 

' ; 






--- ; : 

- - ' ;- 

-55 



-':- 



- --- 



- ' 




- : - - 
- 



C \\jyx 

. 




: 

- 

: 



= -: 5 = ~ : : 



e 



I: 0= 1- >- - - ">': 

Tl 



:: ... - 



: . -- :-:,-:. . 







-" 



:, :-; 

.,. .,. 



136 THE ATOMIC WEIGHTS. 

In a later note* Scheerer shows that the barium sulphate of these ex- 
periments carries down with it magnesium salts in such quantity as to 
make the atomic weight of magnesium 0.039 too low. 

The work of Bahr, Jacquelain, Macdonnell, and Marignac, and in part 
that of Svanberg and Nordenfeldt, also relates to the composition of 
magnesium sulphate. 

Jacquelain's experiments were as follows : f Dry magnesium sulphate 
was prepared by mixing the ordinary hydrous salt to a paste with sul- 
phuric acid, and calcining the mass in a platinum crucible over a spirit 
lamp to constant weight and complete neutrality of reaction. This dry 
sulphate was weighed and intensely ignited three successive times. The 
weight of the residual MgO having been determined, it was moistened 
with sulphuric acid and recalcined over a spirit lamp, thus reproducing 
the original weight of MgS0 4 . Jacquelain's weighings for these two 
experiments show that 100 parts of MgO correspond to the quantities 
of MgS0 4 given in the last column : 

1.466 grm. MgSO 4 gave .492 grm. MgO. 297.968 

.492 " MgO " 1.466 " MgSO 4 . 297.968 

Jacquelain also made one estimation of sulphuric acid in the foregoing 
sulphate as BaS0 4 . His result (1.464 grm. MgS0 4 = 2.838 grm. BaSOJ, 
reduced to the standard adopted in dealing with Scheerer's experiments, 
gives for 100 parts of MgS0 4 , 193.852 BaS0 4 . If this figure be given equal 
weight with a single experiment in Scheerer's series, and combined with 
the latter, the mean will be 193.700, .0331. This again is subject to 
the correction pointed out by Scheerer for magnesium salts retained by 
the barium sulphate, but such a correction determined by Scheerer for 
a single experiment is only a rough approximation, and hardly worth 
applying. 

The determinations published by Macdonnell J are of slight impor- 
tance, and all depend upon magnesium sulphate. First, the crystallized 
salt, MgS0 4 .7H 2 0, was dried in vacuo over sulphuric acid and then de- 
hydrated at a low red heat. The following percentages of water were 
found : 

5^7 

51.14 

51.26 
51.28 
5 r - 2 9 

Mean, 51.21, .020 

*Poggend. Annalen, 70, 407. 

f Ann. Chim. Phys. (3), 32, 202. 

J Proc. Royal Irish Acad., 5, 303. British Association Report, 1852, part 2, p. 36. 






MAGNESIUM. 137 



Secondly, anhydrous magnesium sulphate was precipitated with ba- 
rium chloride. From the weight of the barium sulphate, with S0 3 = 
80 and Ba = 137, Macdonnell computes the percentages of S0 3 given 
below. I calculate them back to the observed ratio in uniformity with 
Scheerer's work : 






Per cent. SO,. Ratio, MgSO : 

66.67 194.177 

66.73 '94-35 1 

66.64 194.089 

66.65 194.118 
66.69 194-239 



In another experiment 60.05 grains MgS0 4 gave 116.65 grains BaS0 4 , 
a ratio of 100 : 194.254. Including this with the preceding figures, they 
give a mean of 194.205, .027. This, combined with the work of 
Scheerer and Jacquelain, 193.700, .033, gives a general mean of 

MgSO 4 : BaSO 4 : : 100 : 194.003, .021. 

In one final experiment Macdonnell found that 41.44 grains of pure 
magnesia gave 124.40 grains of MgSO 4 , or 300.193 per cent. 

Bahr's * work resembles in part that of Jacquelain. This chemist 
converted pure magnesium oxide into sulphate, and from the increase 
in weight determined the composition of the latter salt. From his weigh- 
ings 100 parts of MgO equal the amounts of MgS0 4 given in the third 
column : 

1.6938 grm. MgO gave 5.0157 grm. MgSO 4 . 296.122 

2.0459 " 6.0648 " 296.437 

1.0784 " 3.I9 2 5 " 296.040 



Mean, 296.200, d= .0815 

About four years previous to the investigations of Bahr the paper of 
Svanberg and Nordenfeldtf appeared. These chemists started with the 
oxalate of magnesium, which was dried at a temperature of from 100 
to 105 until it no longer lost weight. The salt then contained two 
molecules of water, and upon strong ignition it left a residue of MgO. 
The percentage of MgO in the oxalate comes out as follows : 



7.2634 grm. 


oxalate gave 1.9872 grm. oxide. 


27.359 per cent. 




6-3795 


1.7464 


27-375 " 




6.3653 


1.7418 


27-364 " 




6.2216 


1.7027 


27.368 " 






Mean, 


27.3665, zb .OO2 


3 



* Journ. fur Prakt. Chem., 56, 310. 1852. 
f Journ. fi'ir Prakt. Chem., 45, 473. 1848. 



138 THE ATOMIC WEIGHTS. 

In three of these experiments the MgO was treated with H 2 S0 4 , and 
converted, as by Jacquelain and by Bahr in their later researches, into 
MgS0 4 . One hundred parts of MgO gave of MgSO 4 as follows : 

1.9872 grin. MgO gave 5.8995 grm. MgSO 4 . 296.875 

1.7464 " 5- x 783 " 296.513 

1.7418 " 5.1666 " 296.624 



Mean, 296. 67 r, .072 

In 1850 the elaborate investigations of Marchand and Scheerer * ap- 
peared. These chemists undertook to determine the composition of 
some natural magnesites, and, by applying corrections for impurities, to 
deduce from their results the sought-for atomic weight. The magnesite 
chosen for the investigation was, first, a yellow, transparent variety from 
Snarum ; second, a white opaque mineral from the same locality ; and,, 
third, a very pure quality from Frankenstein. In each case the im- 
purities were carefully determined ; but only a part of the details need 
be cited here. Silica was of course easily corrected for by simple sub- 
traction from the sum of all of the constituents; but iron and calcium,, 
when found, having been present in the mineral as carbonates, required 
the assignment to them of a portion of the carbonic acid. In the atomic 
weight determinations the mineral was first dried at 300. The loss in 
weight upon ignition was then carbon dioxide. It was found, however, 
that even here a correction was necessary. Magnesite, upon drying at 
300, loses a trace of C0 2 , and still retains a little water ; on the other 
hand, a minute quantity of C0 2 remains even after ignition. The C0 2 
expelled at 300 amounted in one experiment to .054 per cent. ; that 
retained after calcination to .055 per cent. Both errors tend in the same 
direction, and increase the apparent percentage of MgO in the magnesite. 
On the yellow mineral from Snarum the crude results are as follows, 
giving percentages of MgO, FeO, and CO 2 after eliminating silica : 

CO.,. MgO. FeO. 

51.8958 47-3278 .7764 

51.8798 47-3393 -7809 

51.8734 47.3154 -8112 

5'-*8 7 5 47.3372 .7753 

Mean, 47.3299, .0037 

After applying corrections for loss and retention of C0 2 , as previously 
indicated, the mean results of the foregoing series become 

CO.,. MoO. FeO. 

51.9931 47.2743 -7860 

The ratio between the MgO and the C0 2 , after correcting for the iron, 
will be considered further on. 

* Journ. fi'ir Prakt. Chem., 50, 385. 



MAGNESIUM. 139 

Of the white magnesite from Snarum but a single analysis was made, 
which for present purposes may be ignored. Concerning the Franken- 
stein mineral three series of analyses were executed. In the first series 
the following results were obtained : 

8.996 grm. CO 2 = 8.2245 grm. MgO. 47.760 per cent. MgO. 

7-960 " 7.2775 " 47.76i 

9-3 2 65 8.529 47.767 

7-553 " 6.9095 " 47-775 



Mean, 47.766, .0022 

This mean, corrected for loss of C0 2 in drying, becomes 47.681. I give 
series second with corrections applied : 

6.8195 S rm - MgCO 3 gave 3.2500 grm. MgO. 47.658 per cent. 

11.3061 " - 5-3849 " 47.628 " 

9-7375 " 4-635 (( 47-599 " 

12.3887 5.9033 47.650 

32.4148 15.453 47-674 " 

38.8912 18.5366 " 47.663 " 

26.5223 12.6445 " 47.675 " 

Mean, 47.650, d= .0069 

The third series was made upon very pure material, so that the cor- 
rections, although applied, were less influential. The results were as 
follows : 

4.2913 grm. MgCO 3 gave 2.0436 grm. MgO. 47.622 per cent. 

27.8286 " 13-2539 " 47.627 " 

14.6192 " 6.9692 " 47.672 " 

18.3085 '< 8.7237 " 47-648 " 

Mean, 47.642, =fc .0077 

In a supplementary paper* by Scheerer, it was shown that an impor- 
tant correction to the foregoing data had Been overlooked. Scheerer, re- 
examining the magnesites in question, discovered in them traces of lime, 
which had escaped notice in the original analyses. With this correction 
the two magnesites in question exhibit the following mean composition : 

Snarum. Frankenstein. 

C0 2 52.131 52.338 

MgO 46.663 47-437 

CaO 430 . 225 

FeO. 776 



100.000 100.000 



Correcting for lime and iron, by assigning each its share of C0 2 , the 
Snarum magnesite gives as the true percentage of magnesia in pure 



* Ann. d. Chem. und Pharm., no, 240. 



140 THE ATOMIC WEIGHTS. 

magnesium carbonate, the figure 47.624. To this, without serious mis- 
take, we may assign the weight indicated by the probable error, .0037, 
the quantity previously deduced from the percentages of MgO given in 
the unconnected analyses. 

From the Frankenstein mineral, similarly corrected, the final mean 
percentage of MgO in MgC0 3 becomes 47.628. This, however, represents 
three series of analyses, whose combined probable errors may be prop- 
erly assigned to it. The combination is as follows : 

dr .OO22 
dz .0069 

2 .0077 

Result, .0020, probable error of the general mean. 

We may now combine the results obtained from both magnesites: 

Snarum mineral Per cent. MgO, 47.624, .0037 

Frankenstein mineral " 47.628, d= .0020 

General mean Per cent. MgO, 47.627, .0018 

The next investigation upon the atomic weight of magnesium which 
we have to consider is that of Dumas. * Pure magnesium chloride was 
placed in a boat of platinum, and ignited in a stream of dry hydrochloric 
acid gas. The excess of the latter having been expelled by a current of 
dry carbon dioxide, the platinum boat, still warm, was placed in a closed 
vessel and weighed therein. After weighing, the chloride was dissolved 
and titrated in the usual manner with a solution containing a known 
quantity of pure silver. The weighings which Dumas reports give, as 
proportional to 100 parts of silver, the quantities of MgCL 2 stated in the 
third column : 

2.203 8 rm - MgCl 2 = 4.964 grm. Ag. 44.380 

2.5215 " 5.678 " 44.408 

2.363 5-325 " 44-376 

3.994 " 9.012 " 44.319 

2.578 5.834 " 44.189 

2.872 " 6.502 " 44.i7t 

2.080 4Jio " 44.161 

2.214 " 5- 2 " 44.262 

2.086 " 4.722 " 44.176 

1.688 <( 3823 " 44.154 

1.342 " 3.031 " 44.276 

Mean, 44.261, dz .020 

This determination gives a very high value to the atomic weight of 
magnesium, which is unquestionably wrong. The error, probably, is 
due to the presence of oxychloride in the magnesium chloride taken, an 

*Ann. Chem. Pharm., 113, 33. 1860. 



MAGNESIUM. 



141 



impurity tending to raise the apparent atomic weight of the metal. 
Richards 1 and Parker's revision of this ratio is more satisfactory. 

Marignac, * in 1883, resorted to the old method of determination, de- 
pending upon the direct ratio between MgO and S0 3 . This ratio he 
measured both synthetically and analytically. First, magnesia from 
various sources was converted into sulphate. The MgS0 4 from 100 parts 
of MgO is given in the third column : 

MgO. MgSO. Ratio. 

4.6620 298.17 

4.2025 298.32 

4.7480 298.30 

4.3855 298.23 

4.4060 298.15 

4-8530 298.33 

4.0740 298.37 

5.8390 298.29 

5.0600 298.26 

5.5715 298.26 

Mean, 298.27, .0149 

The magnesia for experiments 1 to 5 was prepared by calcination of 
the nitrate, that of 6 to 8 from the sulphate, and the remaining two from 
the carbonate. But Richards and Rogers t have shown that magnesia 
derived from the nitrate always contains occluded gaseous impurity, so 
that the experiments depending upon its use are somewhat questionable. 
The results tend to give an atomic weight for magnesium which is pos- 
sibly too high. Whether the other samples of magnesia are subject to 
similar objections I cannot say. 

Marignac's second series was obtained by the calcination of the sul- 
phate, with results as follows : 



J 


.5635 


2 . .... 


.4087 


3 


.5917 


4 


47O5 


c 


4778 


6 


6267 


7 


7657 


8 


.ocyt: 


Q 


606^ 


10. . 


.8680 



MgSOv 


MgO. 


Ratio. 


3-7705 i 


.2642 


298.25 


4.7396 i 


.5884 


298.39 


3-3830 


.1345 


298.19 


4.7154 


.5806 


298.33 


4.5662 


.5302 


298.43 


4.5640 


.5300 


298.30 


3-2733 


.0979 


298.14 


4.8856 


.6378 


298.30 


5.0092 


.6792 


298.31 


5.3396 


.7898 


298.33 


5.1775 


.7352 


298.38 


5.0126 


.6807 


298.24 


5-0398 


.6894 


298.32 






Mean, 298 30, .0150 



* Arch. Sci. Phys. et Nat. (3), 10, 206. 
f Am. Chem. Journ., 15, 567. 1893. 



142 THE ATOMIC WEIGHTS. 

These data may now be combined with the work of previous investi- 
gators, giving Macdonnell's one result and Jacquelain's two, each equal 
weight with a single experiment in Bahr's series: 

Macdonnell 300.193, .1413 

Jacquelain 297.968, -b .0999 

Bahr 296.200, .0815 

Svanberg and Nordenfeldt 296.671, d= .0720 

Marignac, synthetic 298.27, H~ .0149 

Marignac, calcination 298.30, dz .0150 

General mean 298. 210, .0103 

Burton and Vorce,* who published their work on magnesium in 1890, 
started out with the metal itself, which had been purified by distillation 
in a Sprengel vacuum. This metal was dissolved in pure nitric acid, 
and the resulting nitrate was converted into oxide by calcination at a 
white heat. The oxide was carefully tested for oxides of nitrogen, which 
were proved to be absent, but occluded gases, the impurity pointed out 
by Richards and Rogers, were not suspected. This impurity must have 
been present, and it would tend to lower the apparent atomic weight of 
magnesium as calculated from the data obtained. The results were as 
follows, together with the percentage of Mg in MgO : 

Mg Taken. MgO Formed. Per cent. Mg. 

.33009 .54766 60.273 

.34512 .57 2 5 2 60.281 

.26058 .43221 60.290 

.28600 .47432 60.297 

.30917 .5^273 60.299 

.27636 .45 8 53 60.271 

.36457 .60475 60.284 

.32411 .53746 60.304 

.32108 .53263 60.282 

.28323 .46988 60.262 



Mean, 60.2845, =h .0027 

The latest determinations of all are those of Richards and Parker,f 
who studied magnesium chloride with all the precautions suggested by 
the most recent researches. The salt itself was not only free from oxy- 
chloride, but also spectroscopically pure as regards alkaline contamina- 
tions, and all weighings were reduced to a vacuum standard. The first 
series of experiments gives the ratio between silver chloride and mag- 
nesium chloride, and I have reduced the data to the form 2AgCl : MgCl 2 : : 
100 : x. The weighings and values for x are subjoined : 

* Am. Chem. Journ., 12, 219. 1890. 
fZeitsch. Anorg. Chem., 13, 81. 1896. 



MAGNESIUM. 



143 



MgCl*. 

L 33550 
I.5I60I 



1.40664 
1.25487 



AgCl. Ratio. 

4.01952 33-225 

4.5 6 3 6 9 33-219 

3.98528 33.226 

4.23297 33-231 

3.77670 33 227 

Mean, 33.226, .0013 



The remaining series of experiments, three in number, relate to the ratio 
2Ag : MgCl 2 , which was earlier investigated by Dumas. For the elaborate 
details of manipulation the original memoir must be consulted. I can 
give little more than the weights found, and their reduction to the usual 
form of ratio, Ag 2 : MgCl 2 : : 100 : x : 



MgCl v 

2.78284 
2.29360 
2-36579 



Second Series. 

Ag. ' 
6.30284 
5.19560 
5.35989 



Ratio. 
44.152 
44.145 
44.13 

Mean, 44.142, .0043 



This series gives slightly higher results than the others, and the 
authors, for reasons which they assign, discard it : 



Third Series. 



MgCl*. 

1.99276 

1.78870 
2.12832 

2.51483 
2.40672 
1.95005 



4-05256 
4.82174 
5.69714 
545294 
4.41747 



Ratio. 

44.^31 
44.138 
44. 140 

44.I4I 



44- H4 



Mean, 44.138, =b .0013 



The fourth series, because of the experience gained in the conduct of 
the preceding determinations, is best of all, and the authors adopt its 
results in preference to the others : 

Fourth Series. 

Ag. Ratio. 

4.60855 44-136 

4.32841 44.138 

4.75635 44.137 

4.12447 44.137 

4o5 I 5 I 44-138 

2.51876 44.138 

Mean, 44.137, db .0003 



2.03402 
1.91048 

2.09932 
1.82041 
1.92065 
1.11172 



144 THE ATOMIC WEIGHTS. 

These series combine with that of Dumas as follows : 

Dumas 44.261, zb .0200 

Richards and Parker, second series 44.142, zb .0043 

Richards and Parker, third series 44.138, zb .0013 

Richards and Parker, fourth series 44. 137, db .0x303 



General mean 44. 138, .0003 

Here the first two values practically vanish, and the third and fourth 
series of Richards and Parker appear alone. 

To sum up, we now have the subjoined ratios, bearing upon the atomic 
weight of magnesium : 

(i.) MgSO 4 : BaSO 4 : : IOO : 194.003, .021 

(2.) MgO : MgSO 4 : : 100 : 298.210, .0103 

(3.) Per cent, of water in MgSO 4 , 7H 3 O, 51.21, .020 

(4.) Per cent, of MgO in oxalate, 27.3665, .0023 

(5.) Per cent, of MgO in carbonate, 47.627, .0018 

(6.) Per cent, of Mg in MgO, 60.2845, .0027 

(7.) 2Ag : Mgd 2 : : IOO : 44.138, .0003 

(8.) 2AgCl : MgCl 2 : : 100 : 33.226, .0013 

To reduce these ratios we have 

O = 15.879, zb .0003 C . 11.920, zb .0004 

Ag=: 107.108, .0031 Ba = 136.392, zb .0086 

Cl = 3S> 1 79, -48 AgCl = 142.287, .0037 
S = 31.828, zb .0015 

For the molecular weight of MgSO 4 , two values are now calculable : 

From (i) MgSO 4 = 119.450, zb .0137 

From (3) " = 119.239,^.0675 

General mean MgSO 4 == 119.443, .0135 

Hence Mg = 24.099, .0136. 
For MgO, three values are found : 

From (2) MgO = 40.091, zb .0023 

From (4) " 40.404, dr .0037 

From (5) " =: 39 721, rb .0021 

General mean MgO = 39.974, =b .0014 

Hence Mg = 24.095, .0014. 
For MgCl 2 there are two values : 

From (7) MgCl 2 = 94-551, db - OO 32 

From (8) " =94.553,^.0044 



General mean MgCl 2 = 94.552, .0026 

Hence Mg 24.194, .0099. 



MAGNESIUM. 



145 



With the aid of these intermediate values, four estimates of the atomic 
weight of magnesium are available, as follows : 

From molecular weight of MgSO 4 . ... Mg 24.099, .0136 

From molecular weight of MgO " = 24.095, + .0014 

From molecular weight of MgCl 2 " = 24. 194, .0099 

From ratio (6) " 24. 103, db .0020 



General mean Mg = 24. TOO, .001 1 

If = 16, this becomes Mg = 24.283. 

On purely chemical grounds the third of the foregoing values, that 
derived from magnesium chloride, seems to be the best. I should un- 
hesitatingly adopt it, rejecting the others, were it not for the fact that it 
rests upon one compound of magnesium alone, and therefore is not ab- 
solutely conclusive. It agrees admirably, however, with the sulphate 
determinations of Marignac, and it is highly probable that it may be 
fully confirmed later by evidence from other sources. 

Marignac's data, taken alone, give Mg = 24.197. The fourth series of 
Richards and Parker, by itself, gives Mg = 24.180. The approximate 
mean of these, 24.19, may be preferred by many chemists to the general 
mean derived from all the observations. 



10 



146 THE ATOMIC WEIGHTS. 



ZINC. 

The several determinations of the atomic weight of zinc are by no 
means closely concordant. The results obtained by Gay-Lussac* and 
Berzelius f were undoubtedly too low, and may be disregarded here. 
We need consider only the work done by later investigators. 

In 1842 Jacquelain published the results of his investigations upon 
this important constant. J In two experiments a weighed quantity of 
zinc was converted into nitrate, and that by ignition in & platinum cruci- 
ble was reduced to oxide. In two other experiments sulphuric acid 
took the place of nitric. As the zinc contained small quantities of lead 
and iron, these were estimated, and the necessary corrections applied. 
From the weights of metal and oxide given by Jacquelain the percent- 
ages have been calculated : 

Nitric Series. 

9.917 grm. Zn gave 12.3138 grm. ZnO. 80.536 per cent. Zn. 

9.809 " 12.1800 " 80.534 " 



Sulphuric Series. 

2 -398 grm. Zn gave 2.978 grm. ZnO. 80.524 

3.197 " 3.968 " 80.570 



Mean of all four, 80.541, .007 

Hence Zn = 65.723. 

The method adopted by Axel Erdmann is essentially the same as 
that of Jacquelain, but varies from the latter in certain important details. 
First, pure zinc oxide was prepared, ignited in a covered crucible with 
sugar, and then, to complete the reduction, ignited in a porcelain tube 
in a current of hydrogen. The pure zinc thus obtained was converted 
into oxide by means of treatment with nitric acid and subsequent igni- 
tion in a porcelain crucible. Erdmann's figures give us the following 
percentages of metal in the oxide : 

80.247 
80.257 
80.263 
80.274 



Mean, 80.260, .0037 

Hence Zn = 64.562. 



* Memoire d'Arceuil, 2, 174. 

tGilb. Annal., 37, 460. 

I Compt. Rend., 14, 636. 

$ Poggend. Annal., 62, 611. Berz. lyehrb., 3, 1219. 



ZINC. 147 

Upon comparing Erdmann's results with those of Jacquelain two 
points are worth noticing : First, Erdmann worked with purer material 
than Jacquelain, although the latter applied corrections for the impuri- 
ties which he knew were present ; secondly, Erdmann calcined his zinc 
nitrate in a porcelain crucible, while Jacquelain used platinum. In the 
latter case it has been shown that portions of zinc may become reduced 
and alloy themselves with the platinum of the crucible ; hence a lower 
weight of oxide from a given quantity of zinc, a higher percentage of 
metal, and an increased atomic weight. This source of constant error 
has undoubtedly affected Jacquelain's experiments, and vitiated his 
results. In Erdmann's work no such errors seem to be present. 

Favre * employed two methods of investigation. First, zinc was dis- 
solved in sulphuric acid, the hydrogen evolved was burned, and the 
weight of water thus formed was determined. To his weighings I ap- 
pend the ratio between metallic zinc and 100 parts of water : 

25.389 grm. Zn gave 6.928 grm. H 2 O. 366.469 

30.369 " 8.297 " 366024 

31.776 " 8.671 " 366.463 

Mean, 366.319, .088 

Hence Zn = 65.494. 

The second method adopted by Favre was to burn pure zinc oxalate, 
and to weigh the oxide and carbonic acid thus produced. From the 
ratio between these two sets of weights the atomic weight of zinc is easily 
deducible. From Favre 's weighings, if C0 2 = 100, ZnO will be as given 
in the third column below : 

7.796 grm. ZnO = 8.365 grm. CO 2 . 93. 198 

7-342 " 7.883 " 93-137 

5.2065 " 5.588 " 93-173 

Mean, 93.169, .012 

Hence Zn = 65,521. 

Both of these determinations are open to objections. In the water 
series it was essential that the hydrogen should first be thoroughly dried 
before combustion, and then that every trace of water formed should be 
collected. A trivial loss of hydrogen or of water would tend to increase 
the apparent atomic weight of zinc. 

In the combustion of the zinc oxalate equally great difficulties are 
encountered. Here a variety of errors are possible, such as are due, for 
example, to impurity of material, to imperfect drying of the carbon 
dioxide, and to incomplete collection of the latter. Indeed a fourth 
combustion is omitted from the series as given, having been rejected by 
Favre himself. In this case the oxide formed was contaminated by traces 
of sulphide. 

'Ann. Chim. Phys. (3), 10, 163. 1844. 



148 THE ATOMIC WEIGHTS. 

Baubigny,* in 1883, resorted to the well-known sulphate method. 
Zinc sulphate, elaborately purified, was dried at 440 to constant weight, 
and then calcined at a temperature equal to the fusing point of gold. 
These data were obtained: 

ZnSO 4 . ZnO. Per cent. ZnO. 

6.699 3.377 5 -4io 

8.776 4.4245 50-416 



Mean, 50.413, .0020 

Hence Zn = 64.909. 

In Marignac's determinations of the atomic weight of zinc, published 
also in 1883,f there is a peculiar complication. After testing and criti- 
cising some other methods, he finally decided to study the double salt 
K 2 ZnCl 4 , which, however, is difficult to obtai n in absolutely definite con- 
dition. Although the compound was purified by repeated crystalliza- 
tions, it was found to deliquesce readily, and thereby to undergo partial 
dissociation, losing chloride of zinc, and leaving the porous layer on the 
crystalline surfaces richer in potassium. In order to evade this diffi- 
culty, Marignac placed a large quantity of the salt in a funnel, and col- 
lected the liquid product of deliquescence as it ran down. In this 
product he determined chlorine by volumetric titration with a standard 
solution of silver, and also estimated zinc by precipitation with sodium 
carbonate, and weighing as oxide. From the data thus obtained equa- 
tions were formed, giving for each a nalysis an atomic weight of zinc 
which is independent of the proportion between ZnCl 2 and KC1 in the 
substance analyzed. The data unfortunately are too bulky for repro- 
duction here and the calculations are complex ; but the results found for 
zinc, when Ag = 107.93, Cl 35.457, and K = 39.137, are as follows : 

1. One titration Zn 65.22 

2. Two titrations 65.37 

3. Two titrations ... 65.31 

4. Two titrations 65.28 

5. One titration 65. 26 

Each of these values represents a distinct sample of the deliquesced 
material, and the number of chlorine determinations is indicated. 

A second set of determinations was made by the same analytical 
method directly upon the recrystallized and carefully dried K 2 ZnCl 4 . 
The values for Zn are as follows : 

6. Two titrations N . Zn = 65.28 

7. Two titrations 65.39 

8. One titration 65.32 

* Ccmpt. Rend., 97, 906. 1883. 
tArch. Sci. Phys. et Nat. (3), 10, 194. 



ZINC. 149 

In order to adapt these data to the uniform scheme of calculation em- 
ployed in this work, taking into account their probable error and the 
probable errors of the antecedent values for K, Cl, and Ag, it seems to 
be best to calculate them back with the atomic weights used by Marignac 
into the form of the ratio A 4 : K 2 Z nd 4 : : 100 : x. Doing this, and tak- 
ing each value as many times as there are titrations represented in it 
that is, giving the results of a double determination twice the weight of a 
single one we have the following series of data for the ratio in question : 

From 1 ................................... 66.090 

From 2.. 



66.124 

f 66. no 
From 3 .................................... { 

l66.no 

f 66.104 
P rom 4 .................................... < 

166.104 

From 5 .................................... 66.099 

f 66.104 
P rom 6 .................................... 4 

(. 66.104 

f 66.129 
From 7 ................................... \ 

166.129 

From 8 ................................... 66.113 



Mean, 66.111, d= .0023 

Hence, from Marignac's work, Ag 4 : K 2 ZnCl 4 : : 100 : 66.111, .0023, a 
ratio which can be discussed along with others at the close of this chapter. 

During the years between 1883 and 1889, a number of determinations 
were made of the direct ratio between zinc and hydrogen that is, 
weighed quantities of zinc were dissolved in acid, the hydrogen evolved 
was measured, and from its volume, with Regnault's data, the weight of 
H was computed. First in order are Van der Plaats' determi nations j* 
whose results, as given by himself, are subjoined. The weights are 
reduced to a vacuum. Sulphuric acid was the solvent. 

Zn, grms. H, litres. Zn = 

6.6725 1.1424 65.21 

9.1271 i.5 6 43 65.14 

13.8758 2.3767 65.18 

Mean, 65.177, .0137 

With the new value for the weight of hydrogen, .089872 gramme per 
litre, this becomes Zn = 64.980, db .0137. 

Reynolds and Ramsay made 29 determinations of this ratio.f rejecting, 
however, all but 5. The weighings were reduced to vacuum, and in each 
experiment the volume of hydrogen was fixed by the mean of seven or 
eight readings. The values for Zn are as follows : 

* Compt. Rend., 100, 52. 1885. 
f Journ. Chem. Soc., 51, 854. 1887. 



150 THE ATOMIC WEIGHTS. 

65.5060 
65.4766 

65.445 
65.5522 
65.4141 



Mean, 65.4787, rh .0161 

These values were computed with Regnault's data for the weight of H. 
Corrected by the new value the mean becomes Zn = 65.280, .0161. 

A few determinations by Mallet were made incidentally to his work on 
the atomic weight of gold, and appear in the same paper.* According 
to these experiments, one gramme of zinc gives 

341.8500. H., and Zn = 65.158 
341.91 " " 65.146 

341-93 " 65.143 

342.04 " " 65.122 



Mean, 65.142, .0039 

In this case the Crafts-Regnault weight of H was taken, one litre 
.08979 gramme. Corrected, the mean gives Zn = 65.082, .0039. 

Two other series of determinations of questionable value remain to 
be noticed before leaving the consideration of the direct H : Zn ratio. 
They represent really the practice work of students, and are interesting 
as an illustration of the closeness with which such work can be done. 
The first series was made in the laboratory of the Johns Hopkins Uni- 
versity, under the direction of Morse and Keiser,f and contains 51 deter- 
minations, as follows : 



64.68 


65.74 


65.40 


65.26 


64.72 


64.80 


65.32 


65.26 


65.20 


65.20 


64.74 


64.40 


65.60 


64.72 


65.00 


64.60 


65.10 


64.40 


65.00 


64.76 


65-24 


65.68 


64.90 


64.60 


65.38 


64.92 


64.80 


65.06 


64.64 


65.H 


64.84 


65.24 


64.84 


64.88 


64.72 


64.82 


65.00 


65.20 


64.80 


65.08 


65.12 


64.40 


65.06 


66.40 


64.60 


64.74 


64.60 


64.80 


65.12 


65.60 


64.74 




Mean of all, Zn = 64.997, .0328 





*Amer. Chern. Journ., 12, 205. 1890. 
f Amer. Chem. Journ., 6, 347. 1884. 



ZINC. 151 

Corrected for the difference between Regnault's value for H and the 
new value, this becomes Zn = 64.800, .0328. 

The second student series was published by Torrey,* who gives 15 
determinations, as follows : 



65.36 64.96 

65.30 64.70 

64.92 65.00 

64.72 64.78 

65.04 64.44 

64.80 65.24 

65.20 64.92 
64.90 
Mean, 64.952, dr .0436 

Corrected as in the other series, this gives Zn 64.755, .0436. 
The five corrected means for the ratio H : Zn may now be combined, 
thus : 

Van der Plaats 64.980, .0137 

Reynolds and Ramsay 65.280, .0161 

Mallet 65.082, .0039 

Morse and Keiser 64.800, .0328 

Torrey 64.755, .0436 



General mean 65.079, .0036 

Morse and Burton, f in their determinations of the atomic weight of 
zinc, returned essentially to the old method adopted by Erdmann and 
by Jacquelain. Their zinc was obtained spectroscopically pure by dis- 
tillation in a vacuum, and was oxidized by nitric acid which left abso- 
lutely no residue upon evaporation. The conversion to oxide was 
effected in a porcelain crucible, which was enclosed in a larger one, and 
the ignition of the nitrate was carried out in a muffle. In weighing, the 
crucible was tared by one of nearly equal weight. Results as follows : 

Wf. Zn. Wt. ZnO. Percent. Zn in ZnO. 





.11616 


1.38972 


80.320 




.03423 


1.28782 


80.308 




.11628 


1.38987 


80.315 




.05760 


1.31681 


80.316 




.04801 


1.30492 


80.313 




.02957 


1.28193 


80.318 




.09181 


1.35944 


80.315 




[.16413 


1-44955 


80.305 




.07814 


1.34248 


80.305 




.12754 


1.40400 


80.306 




.91112 


1.13446 


80.310 



* Amer. Chem. Journ., 10, 74, 1888. 
t Anier. Chem. Journ., 10, 311. 1888. 




152 THE ATOMIC WEIGHTS. 

i.iooii 1.36981 

1.17038 1^45726 

1.03148 1.28436 

L05505 I.3I365 

Mean, 80.3115, 00084. 

Combining this mean with the means found by the earlier investigators, 
we have 

Jacquelain 80.541, .0070 

Erdmann 80.260, .0037 

Morse and Burton 80.3115, d= .00084 

General mean 80.317, .0008 

Morse and Burton verified by experiment the stability of oxide of zinc 
at the temperatures of ignition, and found that it did not dissociate. 
They also proved the absence of oxides of nitrogen from the zinc oxide. 
The investigations of Richards and Rogers,* however, have shown that 
zinc oxide prepared by ignition of the nitrate always carries gaseous 
occlusions, so that the atomic weight of zinc computed from the data of 
Morse and Burton is probably too low. But for that objection, their work 
would leave little to be desired on the score of accuracy. 

The determinations made by Gladstone and Hibbard f represent still 
another process for measuring the atomic weight of zinc. Zinc was dis- 
solved in a voltameter, and the same current was used to precipitate 
metallic silver or copper in equivalent amount. The weight of zinc dis- 
solved, compared with the weight of the other metal thrown down, gives 
the atomic weight sought for. Two voltameters were used in the experi- 
ments, giving duplicate estimates for zinc with reference to each weigh- 
ing of silver or copper. The silver series is as follows, with the ratio 
Ag 2 : Zn : : 100 : x in the third column : 



Zn. 


4r- 


Ratio. 


.7767 


2.5589 


30.353 


.7758 


2.5589 


30.318 


.5927 


1.9551 


30.316 


.5924 


1.9551 


30.300 


.2277 


7517 


30.291 


.2281 


.7517 


30.345 


7452 


2.4588 


30.307 


7475 


2.4588 


30.401 


. .8770 


2.9000 


30.241 


.8784 


2.9000 


30.290 


9341 


3.0809 


30-3!9 


.9347 


3.0809 


30.339 






Mean, 30.318, =b .0077 



* Proc. Amer. Acad., 1893, 200. 

t Journ. Chem. Soc., 55, 443. 1889. 



ZINC. 



153 



To the copper series I add the ratio Cu : Zn : : 100 : x. 



Zn. 

.7767 
.7758 
.5927 
.5924 
.2277 
.2281 
.8770 
.8784 
9341 
9347 



Cu. 

.7526 
.7526 
5737 
5737 
.2209 
.2209 
.8510 
.8510 
.9038 
.9038 



Ratio. 

103-13 
103.08 

I03-3 1 
103.26 
103.08 
103.26 
103.05 
103.22 
103.36 
103.42 

Mean, 103.22, =fc .0261 



Richards and Rogers,* in their investigation of the atomic weight of 
zinc, studied the anhydrous bromide. This was prepared by solution 
of zinc oxide in hydrobromic acid, evaporation to dryness, and subse- 
quent distillation in an atmosphere of carbon dioxide. In some experi- 
ments, however, the bromide was heated in an atmosphere of nitrogen, 
mingled with gaseous hydrobromic acid. All water can thus be removed, 
without formation of oxy bromides. 

The zinc bromide so obtained was dissolved in water, and precipitated 
with a solution containing a known amount of silver in the form of 
nitrate. The silver bromide was weighed on a Gooch crucible, and the 
ratio 2AgBr: ZnBr 2 thus found. An excess of silver was always used, 
and in one series of experiments it was estimated by precipitation with 
hydrobromic acid. Deducting the excess thus found from the original 
quantity of silver, the amount of the latter proportional to the zinc 
bromide was found; hence the ratio Ag 2 : ZnBr 2 . The results, with 
vacuum weights, are as follows : 

Series A. 

ZnBr. 2 . AgBr. Ratio. 

1.69616 2.82805 59.976 

1.98198 3.3 45o 59-978 

1.70920 2 84949 59-984 

2.35079 3-9'94i 59.978 

2.66078 4-4375 l 59.9 6 i 

Mean, 59.975, .0034 







Series B. 






ZnBr^. 


Ag. 


AgBr. 


Ag Ratio. 


AgBr Ratio. 


2.33882 


2. 24063 


3.90067 


104.382 


59-959 


1.97142 


1.88837 


3.28742 


104.398 


59.969 


2.14985 


2.05971 


3-58539 


104.376 


59.96i 


2.00966 


1.92476 


3-35074 


104 411 


59-977 








Mean, 104.392, 


Mean, 59.967, 








.0054 


=b .0027 



*Zeitsch. Aiiorg. Chem., 10, i. 1895. 



154 THE ATOMIC WEIGHTS. 

At the end of the same paper, Richards alone gives two more series of 
determinations made upon zinc bromide prepared by the action of pure 
bromine upon pure electrolytic zinc. The bromide so obtained was 
further refined by sublimation or distillation, and dried by heating in a 
stream of carbon dioxide and gaseous hydrobromic acid. Thus was 
ensured the absence of basic salts and of water. The weights and results 
found in the two series were as follows : 

Series C. 

ZnBr v . Ag. Ratio. 

6.23833 5-9766 104.379 

5 26449 5-0436 104.380 

9.36283 8.9702 104.377 

Mean, 104.379, .0007 

Series D. 

ZnBr. 2 . AgBr. Ratio. 

2.65847 4.4335 8 59.962 

2.30939 3-85149 59.96i 

5.26449 8.77992 59-961 



Mean, 59.961, .0004 

In some details of manipulation these series differ from those given 
by Richards and Rogers jointly, but their minutiaB are not essential to 
the present discussion. 

Combining these several series, we have 

For Ag^ : ZnBr^ : : 100 : x. 

Series E 104.392, .0054 

Series C 104.379, .0007 

General mean 104.380, .0007 

For 2 AgBr : ZnBr^ : : zoo : x. 

Series A 59-975, .0034 

Series B 59.967, =b .0027 

Series D.. 59. 961, d= .0004 

General mean 59.962, .0004 

From the Ag ratio ZnBr 2 = 223.599, .0066 

From the AgBr ratio " 223.601, .0066 



General mean ZnBr 2 223.600, .0047 

And Zn = 64.912, d= .0133 



ZINC. 155 

For computing the atomic weight of zinc we now have these ratios: 

(i.) Per cent. Zn in ZnO, 80.317, .0008 

(2.) Per cent. ZnO in ZnSO 4 , 50.413, rb .0020 

(3.) H 2 O : Zn : : 100 : 366.319, .088 

(4.) 2CO 2 : Zn : : 100 : 93.169, rb -OI2 

(5.) H : Zn : : I : 65.079, .0036 

(6.) Ag 4 : K 2 ZnCl 4 : : 100 : 66. in, .0023 

(7.) Ag 2 : Zn : : 100 : 30.318, .0077 

(8.) Cu : Zn : : 100 : 103.22, =b .0261 

(9.) Ag 2 : ZnBr 2 : : 100 : 104.38, rb .0007 

(10.) 2AgBr : ZnBr 2 : : 100 : 59.962, rb .0004 

The antecedent atomic weights, with H = 1, are 

O 15.879, rb .0003 C = 11.920, rb .0004 

Cl = 35.179, .0048 S = 31.828, rb .0015 

Br = 79.344, rb .0062 Cu 63.119, rb .0015 

Ag = 107.108, rb .0031 AgBr = 186.452, rb .0054 
K = 38.817, rb .0051 

With these data, combining ratios 9 and 10 into one (see preceding 
paragraphs), we have nine independent values for the atomic weight of 
zinc, as follows : 

From (i) Zn = 64.795, d= .0030 

From (2) " = 64.909, rb .0073 

From (3) " = 65.494, rb .0019 

From (4) " =65.521, rb .0115 

From (5) " = 65.079, rb .0036 

From (6) " = 64.891, rb .0253 

From (7) " = 64.947, rb .0166 

From (8) " =65.151, .0166 

From (9) and (10) " = 64.912, rb .0133 



General mean of all Zn = 65.152, .0014 

With O = 16 Zn = 65.650 

Of these values, Nos. 3 and 4, representing Favre's work, are unques- 
tionably far wrong. Rejecting them, the general mean of the remaining 
seven values becomes 

Zn = 64.912, .OO2I. 

If = 16, this gives Zn = 65.407. These figures are identical, except 
as regards the lower probable error, with the result deduced from Rich- 
ards and Rogers' determinations alone, and they may be taken as 
satisfactory. 



156 THE ATOMIC WEIGHTS. 



CADMIUM. 

The earliest determination- of the atomic weight of this metal was by 
Stromeyer, who found that 100 parts of cadmium united with 14.352 of 
oxygen.* With our value for the atomic weight of oxygen, these figures 
make Cd = 110.64. This result has now only a historical interest. 

The more modern estimates of the atomic weight of cadmium begin 
with the work of v. Hauer.f He heated pure anhydrous cadmium sul- 
phate in a stream of dry hydrogen sulphide, and weighed the cadmium 
sulphide thus obtained. His results were as follows, with the percent- 
age of CdS in CdS0 4 therefrom deduced : 

7.7650 grm. CdSO 4 gave 5.3741 grm. CdS. 69.209 per cent. 

6.6086 " 4.5746 " 69.222 " 

7-3821 " $.1117 " 69.245 " 

6.8377 " 4.7336 " 69.228 

8.1956 " 5.6736 " 69.227 " 

7.6039 " 5.2634 " 69.220 " 

7.1415 4-943 1 69.217 " 

5.8245 4.0335 69.251 " 

6.8462 4.74I5 69.257 " 

Mean, 69.231, .0042 

LenssenJ worked upon pure cadmium oxalate, handling, however, 
only small quantities of material. This salt, upon ignition, leaves the 
following percentages of oxide : 

.5128 grm. oxalate gave .3281 grm. CdO. 63.982 per cent. 

.6552 " .4193 " 63.996 " 

.4017 .2573 64.053 " 

Mean, 64.010, d= .014 

Dumas 1 1 dissolved pure cadmium in hydrochloric acid, evaporated 
the solution to dryness, and fused the residue in hydrochloric acid gas. 
The cadmium chloride thus obtained was dissolved in water and titrated 
with a solution of silver after the usual manner. From Dumas' weigh- 
ings I calculate the ratio between CdCl 2 and 100 parts of silver : 

2-369 grm. CdCl 2 = 2.791 grm. Ag. 84.880 

4.540 " 5.348 " 84.892 

6.177 " 7-260 " 85.083 

2.404 " 2.841 " 84.618 

3.5325 " 4.166 " 84.794 

4.042 " 4.767 84.791 

Mean, 84.843, .026 

* See Berz. Lehrbuch. sth Aufl., 3, 1219. 
t Journ. fiir Prakt. Chem., 72, 350. 1857. 
t Journ. fi'ir Prakt. Chem., 79, 281. 1860. 
|| Ann. Chem. Pharm., 113, 27. 1860. 



CADMIUM. 157 

Next in order comes Huntington's* work, carried out in the laboratory 
of J. P. Cooke. Bromide of cadmium was prepared by dissolving the 
carbonate in hydrobromic acid, and the product, dried at 200, was puri- 
fied by sublimation in a porcelain tube. Upon the compound thus ob- 
tained two series of experiments were made. 

In one series the bromide was dissolved in water, and a quantity of 
silver not quite sufficient for complete precipitation of the bromine was 
then added in nitric acid solution. After the precipitate had settled, 
the supernatant liquid was titrated with a standard solution of silver 
containing one gramme to the litre. The precipitate was washed by de- 
cantation, collected by reverse filtration, and weighed. To the weigh- 
ings I append the ratio between CdBr 2 and 100 parts of silver bromide : 

1.5592 grm. CdBr 2 gave 2.1529 grm. AgBr. Ratio, 72.423 

* 3.745 6 5- I 7 2 4 " " 7 2 .4i5 
2.4267 3.3511 " " 72.415 

* 3.6645 5.0590 " 72.435 

* 3.7679 5.2016 " " 72.437 
2.7938 3- 8 5 8 3 " " 7 2 .4io 

* i. 9225 2.6552 " " 72.405 
3-4473 " 4-7593 " " 72.433 



Mean, 72.4216, .0028 

The second series was like the first, except that the weight of silver 
needed to effect precipitation was noted, instead of the weight of silver 
bromide formed. In the experiments marked with an asterisk, both the 
amount of silver required and the amount of silver bromide thrown down 
were determined in one set of weighings. The third column gives the 
CdBr 2 proportional to 100 parts of silver: 

* 3. 7456 grm. CdBr. 2 =: 2.9715 grm. Ag. 126.051 
5.0270 " 3.9874 " 126.072 

* 3.6645 " 2.9073 " 126.045 

* 3.7679 " 2.9888 " 126.067 

* 1. 9225 " 1.5248 " 126.082 
2.9101 " 2.3079 " 126.093 
3.6510 " 2.8951 " 126.110 
3.9782 " 3.1551 " 126.088 

Mean, 126.076, .0052 

According to Huntington's own calculations, these experiments fix the 
ratio between silver, bromine, and cadmium as Ag : Br : Cd : : 108 : 80 
112.31. 

In 1890, Partridge f published determinations of the atomic weight 
of cadmium, made by three methods, the weighings being reduced to 

* Proc. Araer. Acad., 1881. 

t Amer. Journ. Sci. (3), 40, 377. 1890. 



158 



THE ATOMIC WEIGHTS. 



vacuum standards throughout. First, Leiissen's method was followed, 
viz., the ignition of the oxalate, with the subjoined results: 



CdC.,0,. 
.09898 
.21548 
.10711 
.17948 
.16066 

17995 
34227 

.43154 
53510 
.41311 



CdO. 
.70299 
.77746 
.70807 
75440 
.74327 
75471 
.85864 

.91573 
.98197 
.80397 



Percent. CdO. 
63.966 
63.962 
63.957 
63.959 
63.959 
63.964 
63.968 
63-970 
63.968 
63-971 



Mean, 63.964, .0010 



Second!} 7 , v. Hauer's experiments were repeated, cadmium sulphate 
being reduced to sulphide by heating in a stream of H 2 S. The following 
data were obtained : 



1.60514 

1.55831 
1.67190 
1.66976 
1.40821 
1.56290 
1.63278 
1.58270 

1.53873 
1.70462 



as. 


Percent. CdS. 


.11076 


69.204 


.07834 


69.197 


.15669 


69.185 


.15554 


69.200 


.9745 


69.202 


.08156 


69.205 


.12985 


69.194 


.09524 


69.198 


.06481 


69.201 


.17962 


69.201 



Mean, 69.199, =h .0012 
v. Hauer found, 69.231, .0042 



General mean, 69.202, .0012 

In the third set of determinations cadmium oxalate was transformed 
to sulphide by heating in H 2 S, giving the ratio CdC 2 4 : CdS : : 100 : x. 



1.57092 

1.73654 
2.19276 

1.24337 
1.18743 
1.54038 

1-38905 
2.03562 
2.03781 
1.91840 



CdS. 
1.13065 
1.24979 
1.57825 

.89492 

.85463 
1.10858 

99974 
1.46517 
1.46658 
1.38075 



Per cent CdS. 
71.972 
71.973 
71-974 
7L974 
71-975 
71.968 
71.976 
71.979 
71.970 
71.971 



Mean, 71.973, =b .0007 



CADMIUM. 159 

This work of Partridge was presently discussed by Clarke,* with ref- 
erence to the concordance of the data, and it was shown that the three 
ratios determined could be discussed algebraically, giving values for the 
atomic weights of Cd, S, and C, when = 16. These values are 

Cd= 111.7850 
C = 11.9958 
S = 32.0002, 

and are independent of all antecedent values except that assumed for 
the standard, oxygen. 

Morse and Jones, f starting out from cadmium purified by fractional 
distillation in vacuo, adopted two methods for their determinations. 
First, they effected the synthesis of the oxide from known weights of 
metal by dissolving the latter in nitric acid, evaporating to dryness, and 
subsequent ignition of the product. The oxide thus obtained was found 
to be completely free from oxides of nitrogen. The weighings,-which are 
given below, were made in tared crucibles. The third column gives the 
percentage of Cd in CdO. 

Cd Taken, CdO Found. Per cent. Cd. 

.77891 2.03288 87.507 

.82492 2.08544 87.508 

.74688 1.99626 87.507 

.57000 1.79418 87.505 

.481 2.26820 87.506 

.27297 2.59751 87.504 

.75695 2.00775 87.508 

.70028 1.94305 87.505 

.92237 2.19679 87.508 

.92081 2.19502 87.508 

Mean, 87.5066, rb .00032 

The second method employed by Morse and Jones was that of Lenssen 
with cadmium oxalate. This salt they find to be somewhat hygroscopic, 
a property against which the operator must be on his guard. The data 
found are as follows : 

CdC 2 O t . CdO. Percent. CdO.' 

53937 .98526 64.004 

.77483 1.13582 63996 

.70211 1.08949 64.008 

.70238 1.08967 64.004 

.74447 1.11651 64.003 

Mean, 64.003, .0042 

Lorimer and Smith, like Morse and Jones, determined the atomic 
weight of cadmium by means of the oxide, but by analysis instead of 

*Am. Chem. Jourii., 13, 34. 1891. 
t Am. Chem. Journ., 14, 261. 1892. 



160 THE ATOMIC WEIGHTS. 

synthesis. Weighed quantities of oxide were dissolved in potassium 

cyanide solution, from which metallic cadmium was thrown down elec- 

trolytically. The weights are reduced to vacuum standards. 

CdO Taken. Cd Found. Per cent. Cd. 

.34767 .30418 87.491 

.41538 -36352 87.515 

1.04698 .91618 87.507 

1.04066 .9 1 5 87.493 

1.26447 1.10649 87.506 

.78493 .68675 87.492 

.86707 .75884 87.518 

.67175 -58785 87.510 

1.44362 1.26329 87.508 

Mean, 87.5044, .0023 

Mr. Bucher's dissertation* upon the atomic weight of cadmium does 
not claim to give any final measurements, but rather to discuss the vari- 
ous methods by which that constant has been determined. Neverthe- 
less, it gives many data which seem to have positive value, and which 
are certainly fit for discussion along with those which have preceded 
this paragraph. Bucher begins with cadmium purified by distillation 
nine times in vacuo, and from this his various compounds were prepared. 
His first series of determinations was made by reducing cadmium oxalate 
to oxide, the oxalate having been dried fifty hours at 150. The reduc- 
tion was effected by heating in jacketed porcelain crucibles, with various 
precautions, and the results obtained, reduced to vacuum standards, are 
as follows : 

Oxalate. Oxide. Percent. Oxide. 

.97674 1.26414 63.951 

.94912 1.24682 63.968. 

.96786 1.25886 63.971 

.87099 1.19675 . 63.958 

3755 -87994 63.972 

.33313 .85308 63.991 

94450 1.24452 64.002 

2.01846 1.29210 64.014 

Mean, 63.978, d= .0052 

Combining this with the means found by previous experimenters, we 
have for the percentage of oxide in oxalate 

Lenssen 64.010, .0140 

Partridge 63.962, . .0010 

Morse and Jones. 64.003, .0042 

Bucher 63.978, .0052 

General mean 63.966, .0010 

* "An examination of some methods employed in determining the atomic weight of cadmium." 
Johns Hopkins University doctoral dissertation. By John B. Bucher. Baltimore, 1895. 



CADMIUM. 



161 



Bucher's next series of determinations was by Partridge's method 
the conversion of cadmium oxalate into cadmium sulphide by heating 
in a stream of sulphuretted hydrogen. The sulphide was finally cooled 
in a current of dry nitrogen. The vacuum weights and ratios are sub- 
joined : 

Oxalate. Sulphide. Percentage. 

2.56319 1.84716 72.065 

2.18364 I-5734I 72.055 

2.11643 1.52462 72.037 

3.13105 2.25582 72.047 

Mean, 72.051, =b .0127 
Partridge found, 71.973, .0007 

General mean, 71.974, .0007 

Here Bucher's mean practically vanishes. 

The third method employed by Bucher was that of weighing cadmium 
chloride, dissolving in water, precipitating with silver nitrate, and weigh- 
ing the silver chloride found. The cadmium chloride was prepared, 
partly by solution of cadmium in hydrochloric acid, evaporation to 
dryness, and sublimation in vacuo; and partly by the direct union of 
the metal with chlorine. The silver chloride was weighed in a Gooch 
crucible, with platinum sponge in place of the asbestos. To the vacuum 
weights I append the ratio 2AgCl : CdCl 2 : : 100 : x. 



3.09183 
2.26100 

1-35729 

2.05582 

1.89774 

3-53 6 7 

2.70292 

4.24276 

3.40200 

4.60659 

2.40832 

2.19144 

2.84628 

2.56748 

2.31003 

.25008 

.96015 

.29787 

.94227 

.10976 

.63080 



AgCl. 

4.83856 

3.53854 
2.12431 
3.21727 
2.97041 

5.48473 
4.23087 
6.63598 

5-3 2 3 r 4 
7.20386 



3.42724 

4-45477 
4.01651 
3.61370 
1.95652 
3- 6 54i 
3-59391 
3.03811 

1.73547 
2.55016 



Ratio. 
63.900 
63.896 

63-893 
63.899 
63.886 
63.880 
63.886 
63.936 
63.910 
63.946 
63.930 
63.942 

63-893 
63923 
63.924 
63-893 
63.944 
63.938 

63.9'5 
63.946 

63-949 



Mean, 63.916, .0032 

Bucher gives a rather full discussion of the presumable errors in this 
method, which, however, he regards as somewhat compensatory. 
11 



The 



162 THE ATOMIC WEIGHTS. 

series is followed by a similar one with cadmium bromide, the latter 

having been sublimed in vacuo. Results as follows : 

CdBr 2 . AgBr. Ratio. 

4.39941 6.07204 7 2 .454 

3.18030 4-38831 7 2 .472 

3.60336 4.97I5 72.480 

4.04240 5-58062 72.453 

3.60505 4.97519 72.461 

Mean, 72.464, .0035 
Huntington found, 72.4216, .0028 



General mean, 72.438, .0022 

In order to fix a minimum value for the atomic weight of cadmium, 
Bucher effected the synthesis of the sulphate from the metal. 1.15781 
grammes of cadmium gave 2.14776 of sulphate. 

Hence Cd =.- 111.511. , 

The sulphate produced was dried at 400, and afterwards examined 
for free sulphuric acid, giving a correction which was applied to the 
weighings. The corrected weight is given above. Any impurity in the 
sulphate would tend to lower the apparent atomic weight of cadmium, 
and therefore the result is believed by the author to be a minimum. 

Finally, Bucher examined the oxide method followed by Morse and 
Jones. The syntheses of oxide were effected in double crucibles, first 
with both crucibles porcelain, and afterwards with the small inner cruci- 
ble of platinum. Two experiments were made by the first method, three 
by the last. Weights and percentages (Cd in CdO) as follows : 

Cd. CdO. Percentage. 

{1.26142 1.44144 87.511 

.99785 1.14035 87.504 

Mean, 87.508 

^1.11321 1.27247 87.484 

4 1.02412 1.17054 87.491 

(2.80966 3.21152 87.487 



Mean, 87.487 
Mean of alias one series, 87.495, .0035 

The two means given above, representing work done with porcelain 
and with platinum crucibles, correspond to a difference of about 0.2 in 
the atomic weight of cadmium. Experiments were made with pure 
oxide of cadmium by converting it into nitrate and then back to oxide, 
exactly as in the foregoing syntheses. In each case the oxide obtained 
at the end of the operation represented an increase in weight, but the 
increase was greater in platinum than in porcelain. Hence the weigh- 
ings of cadmium oxide in the foregoing determinations probably are 
subject to constant errors, and cannot be trusted to fix the atomic weight 



CADMIUM. 



163 



of cadmium. Their mean, taken in one series, has really no significance ; 
but as the computations in this work involve a study of compensation 
of errors, the data may be combined with their predecessors, as follows : 

Morse and Jones 87.5066, .00032 

Lorimer and Smith 87.5044, rh .0023 

Bucher 87.495, .0035 

General mean 87.5064, db .0003 

This is equivalent to the absolute rejection of Buchers data, and is 
therefore not wholly fair to them. His work throws doubt upon the 
validity of the ratio, as determined, altogether. 

The latest determinations relative to the atomic weight of cadmium 
are those of Hardin.,* who effected the electrolysis of the chloride and 
bromide, and also made a direct comparison between cadmium and 
silver. The aqueous solutions of the salts, mixed with potassium 
cyanide, were electrolyzed in platinum dishes. The cadmium which 
served as the starting point for the investigation was purified by distil- 
lation in hydrogen. All weights are reduced to a vacuum. The data 
for the chloride series are as follows, with a column added for the per- 
centage of Cd in CdCl a : 



Weight CdCl v 

.43 HO 

.49165 

.71752 

.72188 

.77264 

.81224 

.90022 
1.02072 
1.26322 
L52344 



Weight Cd. 

.26422 
.30112 
43942 
.44208 



.49742 

.55135 
.62505 

.77365 
933*4 



Percentage Cd. 
61.247 
61.247 
61.241 
61.241 
61.245 
61.240 
61.246 
61.236 
61.244 
61.252 

Mean, 61.244, .0010. 



The results for the bromide, similarly stated, are these: 



Weight CdBr^. 


Weight Cd. 


Percentage Cd. 


.57745 


.23790 


41.198 


.76412 


.31484 


41.203 


.91835 


.37842 


41.207 




.01460 


.41808 


41.206 




I 574 


.474H 


41.203 




2475 1 


51392 


41.196 




2595 1 


.51905 


41.210 




51805 


.62556 


41.208 




63543 


.67378 


4i.i99 


2.15342 


.88722 


4 1 . 200 






Mean, 41.203, 0010. 



' Journ. Amer. Gheni. Soc., 18, 1016. 1896. 



164 THE ATOMIC WEIGHTS. 

The direct comparison of cadmium and silver was effected by the 
simultaneous electrolysis, in the same current, of double cyanide solu- 
tions. Silver was thrown down in one platinum dish, and cadmium in 
another. The process was not altogether satisfactory, and gave diver- 
gent results, those which are cited below having been selected by Har- 
din from the mass of data obtained. I have added in a third column 
the cadmium proportional to 100 parts of silver : 

Weight Cd. Weight Ag. Ratio. 

.12624 -24335 5L 8 76 

.11032 .21262 51.886 

.12720 .24515 51.887 

.12616 -2433 1 51-852 

.22058 .42520 51-877 



Mean, 51.876, d= .0041 

For cadmium we now have the following ratios : 

(I.) Per cent, of Cd in CdO, 87.5064, .0003 
(2.) Per cent, of CdO in CdC 2 O 4 , 63.966, .0010 
(3.) Per cent, of CdS from CdC 2 O 4 , 71.974, .0007 
(4.) Per cent, of CdS from CdSO 4 , 69.202, dz .0012 
(5.) Ag 2 : CdCl 2 : : 100 : 84.843, .0260 
(6.) 2AgCl : CdCl 2 : : 100 : 63.916, .0032 
(7.) Ag 2 : CdBr 2 : : 100 : 126.076, .0052 
(8.) 2AgBr : CdBr 2 : : 100 : 72.438, .0022 
(9.) Per cent, of Cd in CdG 2 , 61.244, .0010 

(10.) Per cent of Cd in CdBr 2 , 41.203, =b .0010 

(il.) 2Ag : Cd : : 100 : 51.876, .0041 

Bucher's single experiment upon the synthesis of the sulphate, although 
important and interesting, cannot carry weight enough to warrant its 
consideration in connection with the other ratios, and is therefore not 
included. 

The antecedent values, for use in computation are 

O = I 5-879, .0003 S = 31.828, =b .0015 

Ag = 107.108, d= .0031 C = 11.920, dr .0004 

Cl == 35.179, .0048 AgCl = 142.287, ,0037 

Br = 79.344, .0062 AgBr = 186.452, .0054 

For the molecular weight of cadmium chloride, two values are now 
deducible : 

From (5) CdCl 2 = 181.739, .0560 

From (6) " 181.888, + .0103 

General mean CdCl 2 = 181.883, .0138 

Hence Cd = 111.525, .0138. 



CADMIUM. 165 

For cadmium bromide we have 

From (7) CdBr 2 = 270.073, =b .0136 

From (8) " = 270.124,^.0113 



General mean CdBr 2 = 270.105, .0087 

Hence Cd = 111.417, .0151. 

For cadmium there are nine independent values, as follows : 

From (3) Cd = 1 10.793, d= .0081 

From (4) " = i 10.890, .0069 

From (2) " = 1 1 1.004, db - OO 47 

From (11) " = 111.127, -0095 

From (9) " = 1 1 1. 183, .0155 

From (10) " = 111.202, .0093 

From (i). " = 111.227, -0034 

From molecular weight CdBr 2 " = 111.417, =b .0151 

From molecular weight CdCl 2 ....... ".= 111.525, .0138 

General mean Cd = iii.ioo, dz .0022 

If 0=16, Cd= 111.947. 

This result is obviously uncertain. The data are far from being con- 
clusive, however, and I am therefore inclined to trust the mean rather 
than any one of the values taken separately. It is quite possible that 
the highest of all the figures may be nearest the truth, as Bucher's ex- 
periments seem to indicate ; but until new evidence is obtained it would 
hardly be wise to make any selection. The mean obtained agrees well 
with the data of Morse and Jones, Lorimer and Smith, and Hardin. 



166 THE ATOMIC WEIGHTS. 



MERCURY. 

In dealing with the atomic weight of mercury we may reject the early 
determinations by Sefstrom* and a large part of the work done by Tur- 
ner, f The latter chemist, in addition to the data which will be cited 
below, gives figures to represent the percentage composition of both the 
chlorides of mercury ; but these results are neither reliable nor in proper 
shape to be used. 

First in order we may consider the percentage composition of mercuric 
oxide, as established by Turner and by Erdmann and Marchand. In 
both investigations the oxide was decomposed by heat, and the mercury 
was accurately weighed. Gold leaf served to collect the last traces of 
mercurial vapor. 

Turner gives four estimations. Two represent oxide obtained by the 
ignition of the nitrate, and two are from commercial oxide. In the first 
two the oxide still contained traces of nitrate, but hardly in weighable 
proportions. A comparison of the figures from this source with the others 
is sufficiently conclusive on this point. The third column represents the 
percentage of mercury in HgO : 

144 805 grains Hg = 11.54 grains O. 92.619 per cent. 

125.980 " 10.08 " 92.592 " 

I73-5 61 " 13.82 " 92.625 " 

114.294 " 9.101 " 92.620 " 



Mean, 92.614, db .0050 

In the experiments of Erdmann and Marchand J every precaution was 
taken to ensure accuracy. Their weighings, reduced to a vacuum stand- 
ard, give the subjoined percentages : 

82.0079 grm. HgO gave 75.9347 grm. Hg. 92.594 per cent. 

51.0320 47.2538 " 92.597 " 

84.4996 " 78.2501 " 92.604 " 

44-6283 " 41-3285 " 92.606 " 

118.4066 " 109.6408 " 92.597 " 



Mean, 92.5996, .0015 

Hardin's determination of the same ratio, being different in character, 
will be considered later. 

With a view to establishing the atomic weight of sulphur, Erdmann 
and Marchand also made a series of analyses of pure mercuric sulphide. 
These data are now best available for discussion under mercury. The 

*Sefstrom. Berz. L,ehrb., 5th ed., 3, 1215. Work done in 1812. 

fPhil. Trans., 1833, 531-535. 

J Journ. fur Prakt. Chem., 31, 395. 1844. 



MERCURY. 167 

v 

sulphide was mixed with pure copper and ignited, mercury distilling 
over and copper sulphide remaining behind. Gold leaf was used to 
retain traces of mercurial vapor, and the weighings were reduced to 
vacuum : 

34.3568 grm. HgS gave 29.6207 grm. Hg. 86.215 P er cent - H g. 

24.8278 " 21.40295 " 86.206 " 

37.2177 " 32.08416 " 86.207 " 

80.7641 " 69.6372 " 86.223 " 

Mean, 86.2127, .0027 

For the percentage of mercury in mercuric chloride we have data by 
Turner, Millon, Svanberg, and Hardin. Turner,* in addition to some 
precipitations of mercuric chloride by silver nitrate, gives two experi- 
ments in which the compound was decomposed by pure stannous 
chloride, and the mercury thus set free was collected and weighed. The 
results were as follows : 

44.782 grains Hg = 15.90 grains CI. 73-798 per cent. 

73.09 " 25.97 " 73.784 " 

Mean, 73.791, .005 

Millon f purified mercuric chloride by solution in ether and sublima- 
tion, and then subjected it to distillation with lime. The mercury was 
collected as in Erdmann and Marchand's experiments. Percentages of 
metal as follows : 

73-87 
73-8i 
73-83 
73-87 



Mean, 73.845, .010 

Svanberg, J following the general method of Erdmann and Marchand, 
made three distillations of mercuric chloride with lime, and got the 
following results : 

12.048 grm. HgC) 2 gave 8.889 grm. Hg. 73.780 per cent. 

12.529 " 9-24S 6 " 73-794 " 

12.6491 " 9-3363 " 73-8io " 

Mean, 73.795, .006 

The most recent determinations of the atomic weight of mercury are 
due to Hardin, whose methods were entirely electrolytic. First, pure 
mercuric oxide was dissolved in dilute, aqueous potassium cyanide, and 

*Phil. Trans., 1833, 53 I -535- 
fAnn. Chirn. Phys. (3), 18, 345. 1846. 
I Journ. fur Prakt. Chem., 45, 472. 1848. 
I Journ. Amer. Chem. Soc., 18, 1003. '1896. 



168 THE ATOMIC WEIGHTS. 

electrolyzed in a platinum dish. Six determinations are published, out 
of a larger number, but without reduction of the weights to a vacuum. 
The data, with a percentage column added, are as follows : 

Weight HgO. Weight Hg. Per cent. Hg. 

.26223 .24281 92.594 

.23830 .22065 9 2 .593 

.23200 .21482 92.595 

.14148 .13100 92.593 

.29799 .27592 92.594 

.19631 .18177 92.593 

Mean, 92.594, d= 0003. 

Various sources of error were detected in these experiments, and the 
series is therefore rejected by Hardin. It combines with previous series 
as follows : 

Turner % 92.614, rfc .0050 

Erdmann and Marchand 92.5996, .0015 

Hardin 92. 594, .0003 



General mean 9 2 -595, rb .0003 

Hardin also studied mercuric chloride, bromide, and cyanide, and the 
direct ratio between mercury and silver, with reduction of weights to a 
vacuum. Electrolysis was conducted in a platinum dish, as usual. 
With the chloride and bromide, the solutions were mixed with dilute 
potassium cyanide. The data for the chloride are as follows, the per- 
centage column being added by myself: 

Weight HgCL v Weight Hg. Per cent. Hg. 

45932 -33912 

54735 -40415 

.56002 .41348 

.63586 .46941 

.64365 .47521 

.73281 .54101 

.86467 .63840 

1.06776 .78825 

1.07945 .79685 . 

1.51402 1.11780 73-830 

Mean, 73.829, .0012 




Combining this with the earlier determinations, we hav 



Turner 73-791, db .0050 

Millon 73.845, .0100 

Svanberg 73-795, .0060 

Hardin 73.829, .001 2 

General mean 73.826, d= .001 1 



MERCURY. 



169 



For the bromide Hardin's data are 



Weight HgBr v 
.70002 



57*42 

.77285 

.80930 

.85342 

1.11076 

i 17270 

1.26186 

1.40142 



And for the cyanide 

Weight HgC 2 N 2 . 

.55776 

.63290 

.70652 

.80241 

.65706 

.81678 
1.07628 
1.22615 
1.66225 
2.11170 



Weight Hg. 
.38892 
.3135 
.3i75 
.42932 
.44955 
.47416 
.61708 
.65145 
.70107 
.77870 



Weight Hg. 

.44252 
.50215 

.56053 
.63663 
.52130 
.64805 
.85392 
.97282 

1.31880 

1.67541 



Per cent. Hg. 

55-558 
55-555 
55-563 
55-550 
55.548 
55-56o 
55-555 
55-55 1 
55-559 
55-565 



Mean, 55.556, .0012 



Per cent. Hg. 

79-337 
79-341 
79-337 
79-340 
79-338 
79-342 
79-340 
79-339 
79-338 
79-339 

Mean, 79.339, .0004 



In the last series cited no potassium cyanide was used, but the solution 
of mercuric cyanide, with the addition of one drop of sulphuric acid, 
was electrolyzed directly. 

The direct ratio between silver and mercury was determined by throw- 
ing down the two metals, simultaneously, in the same electric current. 
Both metals were taken in double cyanide solution. With Hardin's 
equivalent weights I give a third column, showing the quantity of mer- 
cury corresponding to 100 parts of silver. Many experiments were re- 
jected, and only the following seven are published by the author : 



Weight Hg. 

.06126 
.06190 
.07814 
.10361 
.15201 
.26806 
.82808 



Weight Ag. 
.06610 
.06680 
.08432 
.11181 
. 1 6402 
.28940 
.89388 



Ratio. 
92.678 
92.665 
92.671 
92.666 
92.678 
92.626 
92.639 



Mean, 92.660, .0051 



170 THE ATOMIC WEIGHTS. 

We now have six ratios involving the atomic weight of mercury, as 
follows : 

(i.) Per cent, of Hg in HgO, 92.595, .0003 

(2.) Per cent, of Hg in HgS, 86.2127, =b .0027 

(3.) Per cent, of Hg in HgCl a> 73.826, .0011 

(4.) Per cent, of Hg in HgBr 2 , 55.556, .0012 

(5.) Per cent, of Hg in HgC 2 N 2 , 79.339, .0004 

(6.) 2Ag : Hg : : 100 : 92.660, .0051 

The calculations involve the following values : 

O = 15.879, -.0003 Br=r 79.344, .0062 

Ag= 107.108, .0031 S =31.828, .0015 

Cl = 35.179, .0048 C = 11.920, .0004 

N = 13.935, .0021 

Hence the values for mercury are 

From (I) Hg = 198.557, .0084 

From (2) " = 199.027, H= .0406 

From (3) " = 198.482, .0285 

From (4) " = 198.364,^.0170 

From (5) 198.568, .0170 

From (6) " = 198.493, .0124 

General mean Hg = 198.532, db .0059 

If 0= 16, Hg = 200.045. 

But according to Hardin the value derived from the analyses of mer- 
curic oxide is untrustworthy. Rejecting this, and also the abnormally 
high -result from the sulphide series, the general mean of the four re- 
maining values is 

Hg = 198.491, .0083, 

or, with = 16, Hg = 200.004. These figures seem to be the best for 
the atomic weight of mercury. 



BORON. 171 



BORON. 

In the former edition of this work the data relative to boron were few 
and unimportant. There was a little work on record by Berzelius and 
by Laurent, and this was eked out by a discussion of Deville's analyses 
of boron chloride and bromide. As the latter were not intended for 
atomic weight determinations they will be omitted from the present re- 
calculation, which includes the later researches of Hoskyns-Abrahall, 
Ramsay and Aston, and Rimbach. 

Berzelius* based his determination upon three concordant estima- 
tions of the percentage of water in borax. Laurent f made use of two 
similar estimations, and all five may be properly put in one series, thus : 

47-10] 

47.10 j- Berzelius. 
47-ioj 

47- '5 I Laurent. 

47-20* 

Mean, 47.13, .013 

In 1892 the posthumous notes of the late Hoskyns-Abrahall were 
edited and published by Ewan and Hartog. J This chemist especially 
studied the ratio between boron bromide and silver, and also redeter- 
mined the percentage of water in crystallized borax. The latter work, 
which was purely preliminary, although carried out with great care, gave 
the following results, reduced to vacuum standards : 



Na^BtPv Per cent. 

7.00667 3.69587 47.2069 

12.95936 6.82560 47.3308 

4.65812 2.45248 47.35 4 

4.47208 3-9395 6 47. 2 7 6 3 

4.94504 2.60759 47.2686 

Mean, 47.2866, db .0171 

Two sets of determinations were made with the bromide, which was 
prepared from boron and bromine directly, freed from excess of the 
latter by standing over mercury, and finally collected, after distillation, 
in small, weighed, glass bulbs. It was titrated with a solution of silver 
after all the usual precautions. The first series of experiments was as 
follows, with BBr 3 proportional to 100 parts of silver stated as the ratio : 

*Poggend. Annalen, 8, i. 1826. 

t Journ. fur Prakt. Chem., 47, 415. 1849. 

I Journ. Chem. Soc., 61, 650. August, 1892. 






-v 



v, .- - 



' 






v, :v 

- :.-S,v 

- :x- ; 
-. . :;-^ 



\". 







-- --- = 




-- --.- = 



. . 










: : 



. . : 

-- 
- 

-' 
- ' : 



: : 

----- 



:: ;- 



L>- 



174 THE ATOMIC WEIGHTS. 

Na^B^O,. AgCl. Ratio. 

5.3118 7.5 2 59 70.580 

4.7806 6.7794 70.517 

4.9907 7.0801 70.489 

4.7231 6.6960 70.53 6 

3.3138 4-693 1 70.610 

Mean, 70.546, .0146 

Rimbach * based his determination of the atomic weight of boron upon 
the fact that boric acid is neutral to methyl orange, and that therefore 
it is possible to titrate a solution of borax directly with hydrochloric 
acid. His borax was prepared from carefully purified boric acid and 
sodium carbonate, and his hydrochloric acid was standardized by a series 
of precipitations and weighings as silver chloride. It contained 1.84983 
per cent, of actual HC1. The borax, dissolved in water, was titrated by 
means of a weight-burette. I give the weights found in the first and 
second columns of the following table, and in the third column, calcu- 
lated by myself, the HC1 proportional to 100 parts of crystallized borax. 
Rimbach himself computes the percentage of Na 2 O and thence the atomic 
weight of boron, but the ratio Na 2 B 4 7 .10H 2 : 2HC1 is the ratio actually 
determined. 

Na^B^O-f.wH^O. HCl Solution. Ratio. 

10.00214 103.1951 19.0853 

15.32772 158-1503 19.0864 

15.08870 155-7271 19.0917 

10.12930 104.5448 19.0922 

5.25732 54-2571 19.0908 

15.04324 155-2307 19.0883 

15-04761 I55-2959 19.0908 

10.43409 107.6602 19.0868 

5.04713 52.0897 i9-9 I 5 

Mean, 19.0893, d= .0006 , 

Obviously, this error should be increased by the probable errors in- 
volved in standardizing the acid, but they are too small to be worth 
considering. 

The following ratios are now available for boron : 

(1) Percentage of water in Na 2 B 4 O 7 .ioH 2 O, 47.1756, =h .0066 

(2) 3Ag : BBr 3 : : 100 : 77.425, .0017 

(3) Na 2 B 4 O 7 : 2NaCl : : 100 : 57-933, .0074 

(4) 2AgCl : Na 2 B 4 O 7 : : 100 : 70.546, + .0146 

(5) Na 2 B 4 O 7 .ioH 2 O : 2HC1 : : 100 : 19.0893, .0006 

* Berichte Deutsch. Chein. Gesell., 26, 164. 1893. 



BORON. 175 

For reduction we have the antecedent atomic and molecular weights 

O = 15-879, -0003 Na = 22.881, .0046 

Ag= 107.108, .0031 NaCl=; 58.060, .0017 

Cl = 35.179,^.0048 AgCl= 142.287, rb .0037 
Br = 79-344, =b .0062 

For the molecular weight of Na 2 B 4 7 we now have 

From (i) . . . .' Na 2 B 4 O 7 = 200. 198, .0377 

From (3) " = 200.439, .0263 

From (4) " = 200.756, .0419 

From (5) " = 200.260, .0518 

General mean Na 2 B 4 O t = 200.421, .0180 

Hence B = 10.876, .0051. 

From ratio (2), B = 10.753, .0207. The two values combined give 

B =1 10.863, .0050. 

Or, if = 16, B == 10.946. 

If we consider ratios (1), (3), (4), and (5) separately, they give the fol- 
lowing values for B : 

From (i) B = 10.821 

From (3) " = 10.881 

From (4) " = 10.960 

From (5) " = 10.836 

Of these, the second and third involve the data from which, in a 
previous section of this work, the ratio NaCl : AgCl was computed. In 
using that ratio for measuring the molecular weights of its component 
molecules, discordance was noted, which again appears here. The chief 
uncertainty in it seems to be connected with ratio (4), which is therefore 
entitled to comparatively little credence, although its rejection is not 
necessary at this point. In ratio (2), Abrahall's determination, the high 
probable error of B is due to the also high probable error of 3Br, and it 
is quite likely that the result is undervalued. The general mean, B = 
10.863, .0050, however, can hardly be much out of the way. It is cer- 
tainly more probable than any one of the individual values. 



176 THE ATOMIC WEIGHTS. 



ALUMINUM. 

The atomic weight of aluminum has been determined by Berzelius, 
Mather, Tissier, Dumas, Isnard, Terrell, Mallet, and Baubigny. The 
early calculations of Davy and of Thomson we may properly disregard. 

Berzelius' * determination rests upon a single experiment. He ignited 
10 grammes of dry aluminum sulphate, A1 2 (S0 4 ) 3 , and obtained 2.9934 
grammes of A1 2 3 as residue. 

Hence Al = 27.103. 

In 1835 1 Mather published a single analysis of aluminum chloride, 
from which he sought to fix the atomic weight of the metal. 0.646 grm. 
of A1CL, gave him 2.056 of AgCl and 0.2975 of A1 2 3 . These figures give 
worthless values for Al, and are included here only for the sake of com- 
pleteness. From the ratio between AgCl and A1C1 3 , Al = 28.584. 

Tissier's J determination, also resting on a single experiment, appeared 
in 1858. Metallic aluminum, containing .135 per cent, of sodium, was 
dissolved in hydrochloric acid. The solution was evaporated with nitric 
acid to expel all chlorine, and the residue was strongly ignited until only 
alumina remained. 1.935 grm. of Al gave 3.645 grm. of A1. 2 3 . If we 
correct for the trace of sodium in the aluminum, we have Al = 26.930. 

Essentially the same method of determination was adopted by Isnard, 
who, although not next in chronological order, may fittingly be men- 
tioned here. He found that 9 grm. of aluminum gave 17 grm. of A1. 2 3 . 
Hence Al = 26.8 

In 1858 Dumas, 1 1 in connection with his celebrated revision of the 
atomic weights, made seven experiments with aluminum chloride. The 
material was prepared in quantity, sublimed over iron filings, and finally 
resublimed from metallic aluminum. Each sample used was collected 
in a small glass tube, after sublimation from aluminum in a stream of 
dry hydrogen, and hermetically enclosed. Having been weighed in the 
tube, it was dissolved in water, and the quantity of silver necessary for 
precipitating the chlorine was determined. Reducing to a common 
standard, his weighings give the quantities of A1C1 3 stated in the third 
column, as proportional to 100 parts of silver : 



1.8786 grm. Alt 


.1 3 =4.543 grm. Ag. 


41.352 


3.021 " 


7.292 


41.459 Bad. 


2.399 


5.802 


41.348 


1.922 " 


4.6525 " 


41.311 


1.697 


4.1015 


4L375 


4-3165 


10.448 " 


4L3H 


6.728 


16.265 


41.365 



*Poggend. Annal., 8, 177. 

tSilliman's Amer. Journ., 27, 241. 

J Cotnpt. Rend., 46, 1105. 

I Compt. Rend., 66, 508. 1868. 

|| Ann. China. Phys. (3), 55, 151. Ann. Cheni. Pharm., 113, 26. 



ALUMINUM. 177 

In the second experiment the A1C1 3 contained traces of iron. Reject- 
ing this experiment, the remaining six give a mean of 41.344, .007. 
These data give a value for Al approximating to 27.5, and were for 
many years regarded as satisfactory. It now seems probable that the 
chloride contained traces of an oxy-compound, which would tend to 
raise the atomic weight. 

In 1879 Terreil * published a new determination of the atomic weight 
under consideration, based upon a direct comparison of the metal with 
hydrogen. Metallic aluminum, contained in a tube of hard glass, was 
heated strongly in a current of dry hydrochloric acid. Hydrogen was 
set free, and was collected over a strong solution of caustic potash. 
0.410 grm. of aluminum thus were found equivalent to 508.2 cc., or 
.045671 grm. of hydrogen. Hence Al = 26.932. 

About a year after Terrell's determination appeared, the lower value 
for aluminum was thoroughly confirmed by J. W. Mallet.f After giving 
a full resume of the work done by others, exclusive of Isnard, the author 
describes his own experiments, which may be summarized as follows : 

Four methods of determination were employed, each one simple and 
direct, and at the same time independent of the others. First, pure 
ammonia alum was calcined, and the residue of aluminum oxide was 
estimated. Second, aluminum bromide was titrated with a standard 
solution of silver. Third, metallic aluminum was attacked by caustic 
soda, and the hydrogen evolved was measured. Fourth, hydrogen was 
set free by aluminum, and weighed as water. Every weight was care- 
fully verified, the verification being based upon the direct comparison, 
by J. E. Hilgard, of a kilogramme weight with the standard kilogramme 
at Washington. The specific gravity of each piece was determined, and 
also of all materials and vessels used in the weighings. During each 
weighing both barometer and thermometer were observed, so that every 
result represents a real weight in vacuo. 

The ammonium alum used in the first series of experiments was 
specially prepared, and was absolutely free from ascertainable impuri- 
ties. The salt was found, however, to lose traces of water at ordinary 
temperatures a circumstance which tended towards a slight elevation 
of the apparent atomic weight of aluminum as calculated from the 
weighings. Two sets of experiments were made with the alum ; one 
upon a sample air-dried for two hours at 21-25, the other upon mate- 
rial dried for twenty-four hours at 19-26. These sets, marked A and 
B respectively, differ slightly, B being the less trustworthy of the two, 
judged from a chemical standpoint. Mathematically it is the better of 
the two. Calcination was effected with a great variety of precautions, 
concerning which the original memoir must be consulted. To Mallet's 
weighings I append the percentages of A1 2 3 deduced from them : 

* Bulletin de la Soc. Chimique, 31, 153. 
f Phil. Trans., 1880, p. 1003. 
12 



178 THE ATOMIC WEIGHTS. 

Series A. 

8.2144 grm. of the alum gave .9258 grm. A1 2 O 3 . 11.270 per cent. 

14.0378 " 1.5825 " 11.273 " 

5.6201 " '.6337 " 11.275 " 

11.2227 " 1.2657 " 11.278 " 

10.8435 " 1. 2216 " 11.266 " 

Mean, 11.2724, .0014 
Series B. 

12.1023 grm. of the alum gave 1.3660 grm. A1 2 O 3 . 11.287 per cent. 

10.4544 " 1.1796 " 11.283 

6.7962 " .7670 " 11.286 " 

8.5601 " .9654 " 11.278 

4.8992 .5528 " 11.283 " 

Mean, n.,2834, .0011 

Combined, these series give a general mean of 11.2793, . 0008. Hence 
Al === 26.952. 

The aluminum bromide used in the second series of experiments was 
prepared by the direct action of bromine upon the metal. The product 
was repeatedly distilled, the earlier portions of each distillate being re- 
jected, until a constant boiling point of 263. 3 at 747 mm. pressure was 
noted. The last distillation was effected in an atmosphere of pure nitro- 
gen, in order to avoid the possible formation of oxide or oxy-bromide of 
aluminum ; and the distillate was collected in three portions, which 
proved to be sensibly identical. The individual samples of bromide 
were collected in thin glass tubes, which were hermetically sealed after 
nearly filling. For the titration pure silver was prepared, and after 
fusion upon charcoal it was heated in a Sprengel vacuum in order to 
eliminate occluded gases. This silver was dissolved in specially purified 
nitric acid, the latter but very slightly in excess. The aluminum bro- 
mide, weighed in the sealed tube, was dissolved in water, precautions be- 
ing taken to avoid any loss by splashing or fuming which might result 
from the violence of the action. To the solution thus obtained the silver 
solution was added, the silver being something less than a decigramme 
in deficiency. The remaining amount of silver needed to complete the 
precipitation of the bromine was added from a burette, in the form of a 
standard solution containing one milligramme of metal to each cubic 
centimetre. The final results were as follows, the figures in the third 
column representing the quantities of bromide proportional to 100 parts 
of silver. Series A is from the first portion of the last distillate of AlBr 3 ; 
series B from the second portion, and series C from the third portion : 

Series A. 

6.0024 grm. AlBr 3 = 7.2793 grm. Ag. 82.458 
8.6492 10.4897 " 82.454 

3.1808' " 3.8573 " 82.462 



ALUMINUM. 



179 



6.9617 grm. AlBr a 
11.2041 " 
3.7621 
5.2842 
9.7338 



Series B. 

8.4429 grm 

13.5897 

4.5624 

6.4085 
11.8047 



Ag. 



82.456 
82.445 
82.459 
82.456 
82.457 



9-35I5 S rm - 

4.4426 

5.2750 



Series C. 

AlBr 3 i= 1 1. 3424 grm. Ag. 

5.3877 
" 6.3975 



82.447 
82.458 
82.454 

Mean, 82.455, .001 



Hence Al = 26.916. 

The experiments to determine the amount of hydrogen evolved by the 
action of caustic soda upon metallic aluminum were conducted with pure 
metal, specially prepared, and with caustic soda made from sodium. 
The soda solution was so strong as to scarcely lose a perceptible amount 
of water by the passage through it of a dry gas at ordinary temperature. 
As the details of the experiments are somewhat complex, the original 
memoir must be consulted for them. The following results were obtained, 
the weight of the hydrogen being calculated from the volume, reckoned 
at .089872 gramme per litre. 



Wt. AL 

3697 
3769 
.3620 

7579 
73*4 

7541 



Vol. H. 
458.8 
467.9 
449-1 
941-5 
907.9 

936.4 



Wt. H. 

.041234 
.042051 
.040362 
.084614 
.081595 
.084156 



At. Wt. 

26.898 
26.889 
26.907 
26.872 
26.891 
26.882 



Mean, 26.890, .0034 



'he closing series of experiments was made with larger quantities of 
aluminum than were used in the foregoing set. The hydrogen, evolved 
by the action of the caustic alkali, was dried by passing it through two 
drying tubes containing pumice stone and sulphuric acid, and two others 
containing asbestos and phosphorus pentoxide. Thence it passed 
through a combustion tube containing copper oxide heated to redness. 
A stream of dry nitrogen was employed to sweep the last traces of hy- 
drogen into the combustion tube, and dry air was afterwards passed 
through the entire apparatus to reoxidize the surface of reduced copper, 
and to prevent the retention of occluded hydrogen. The water formed 
by the oxidation of the hydrogen was collected in three drying tubes. 



180 THE ATOMIC WEIGHTS. 

The results obtained were as follows. The third column gives the amount 
of water formed from 10 grammes of aluminum. 

2.1704 grm. Al gave 2.1661 grm. H 2 O. 9.9802 

2.9355 " 2.9292 9-9785 

5.2632 " 5- 2 5 62 " 9-9 86 7 

Mean, 9.9818, .0017 

Hence Al = 26.867. 

From the last two series of experiments an independent value for the 
atomic weight of oxygen may be calculated. It becomes O = 15.895. 
The closeness of this figure to some of the best determinations affords a 
good indication of the accuracy of Mallet's work. 

In connection with Mallet's work it is worth noting that Torrey * pub- 
lished a series of measurements of the H : Al ratio, representing determi- 
nations made under his direction by elementary students. These meas- 
urements are thirteen in number, and calculated with Regnault's old 
value for the weight of hydrogen, range from 26.661 to 27.360, or in mean, 
27.049, .323. Corrected by the latest value for the weight of H, this 
mean becomes 26.967. The result, of course, has only confirmatory 
significance. 

By Baubignyf we have only two determinations, based upon the 
calcination of anhydrous aluminum sulphate, A1 2 (SOJ 3 . 

3.6745 grm. salt gave 1.0965 A1 2 O 3 . 29.841 per cent. 

2.539 " -7572 " 29.823 " 

Mean, 29.832, .0061 

Hence Al = 26.858. 

It is clear that the single determinations of Berzelius, Mather, Tissier, 
Isnard, and Terrell may now be safely left out of account, for the reason 
that none of them could affect appreciably the final value for Al. The 
ratios to consider are as follows : 

(I.) 3Ag : A1C1 3 : : TOO : 41. 344, .0070 

(2.) Percentage of A1 2 O 3 in ammonium alum, 11.2793, rb .0008 

(3-) 3^g : A113r 3 : : 100 : 82.455, .0010 

(4.) H : Al : : I : 26.890, .0034 

(5-) A1 2 : 3 H 2 O : : 10 : 9.9818, .0017 

(6.) Percentage of A1 2 O 3 in A1 2 (SO 4 ) 3 , 29.832, .0061 

The antecedent values are 

O = 15.879,43.0003 Br= 79-344, .0062 

Ag= 107.108, .0031 N= 13.935, d=.oo2i 

Cl = 35.179, .0048 S == 31.828, .0015 

* Am. Chem. Journ., 10, 74. 1888. 
f Compt. Rend., 97, 1369. 1883. 



GALLIUM. 181 

Hence for aluminum we have 

From (i) Al = 27.31 1, .0270 

From (2) " = 26.952, db .0037 

From (3) " = 26.916, .0201 

From (4) " = 26.890, rh .0034 

From (5) " = 26.867, .0046 

From (6) " = 26.858, .0113 

General mean Al = 26.906, .0021 

With = 16, Al = 27.111. The rejection of Dumas' data only lowers 
the result to 26.903. 



GALLIUM. 

Gallium has been so recently discovered, and obtained in such small 
quantities, that its atomic weight has not as yet been determined with 
much precision. The following data were fixed by the discoverer, 
Lecoq de Boisbaudran : * 

3.1044 grammes gallium ammonium alum, upon ignition, left .5885 
grm. Ga. 2 O 3 . 

Hence Ga = 69.595. If = 16, Ga = 70.125. 

.4481 grammes gallium, converted into nitrate and ignited, gave 
.6024 grm. Ga 2 O 3 . 

Hence Ga = 69.171. If O = 16, Ga = 69.698. 

These values, assigned equal weight, give these means : 

With H = i, Ga = 69.383. With O = 16, Ga = 69.912 

* Journ. Chem. Soc., 1878, p. 646. 



182 THE ATOMIC WEIGHTS. 



INDIUM. 

Reich and Richter, the discoverers of indium, were also the first to 
determine its atomic weight.* They dissolved weighed quantities of the 
metal in nitric acid, precipitated the solution with ammonia, ignited the 
precipitate, and ascertained its weight. Two experiments were made, as 
follows : 

5 T 35 S rm - indium gave .6243 grm. In 2 O 3 . 
.699 .8515 

Hence, in mean, In = 110.61, if = 16 ; a value known now to he 
too low. 

An un weighed quantity of fresh, moist indium sulphide was also dis- 
solved in nitric acid, yielding, on precipitation, 

.2105 grm. In 2 O 3 and .542 grm. BaSO 4 . 

Hence, with BaS0 4 = 233.505, In = 112.03 ; also too low. 

Soon after the publication of Reich and Richter's paper the subject 
was taken up by Winkler .f He dissolved indium in nitric acid, evap- 
orated to dryness, ignited the residue, and weighed the oxide thus 
obtained. 

5574 S rm - I* 1 gave .6817 S rm - In 2 O 3 . 
.6661 " .8144 " 
.5011 " .6126 " 

Hence, in mean, if = 16, In = 107.76 ; a result even lower than the 
values already cited. 

In a later paper by Winkler J better results were obtained. Two 
methods were employed. First, metallic indium was placed in a solu- 
tion of pure, neutral, sodio-auric chloride, and the amount of gold pre- 
cipitated was weighed. I give the weighings and, in a third column r 
the amount of indium proportional to 100 parts of gold : 

In. Au. Ratio. 

.4471 grm. .8205 grm. 57-782 

.8445 1.4596 " 57.858 

Mean, 57.820, .026 

Hence, if Au = 195.743, .0049, In = 113.179, .0517. 
Winkler also repeated his earlier process, converting indium into 
oxide by solution in nitric acid and ignition of the residue. An ad- 

* Journ. fur Prakt. Chem., 92, 484. 
t Journ. fur Prakt. Chem., 94, 8. 
% Journ. fur Prakt. Chem., 102, 282. 



INDIUM. 183 

ditional experiment, the third as given below, was made after the method 
of Reich and Richter. The third column gives the percentage of In in 

In 2 3 : 

1.124 g rm - J n gave 1.3616 grm. In 2 O 3 . Per cent., 82.550 

1.015 " 1.2291 " " 82.581 

.6376 " .7725 82.537 

These figures were confirmed by a single experiment of Bunsen's,* 
published simultaneously with the specific heat determinations which 
showed that the oxide of indium was In 2 3 , and not InO, as had been 
previously supposed : 

1.0592 grm. In gave 1.2825 grm. In 2 O 3 . Per cent. In, 82.589 

For convenience we may add this figure in with Winkler's series, which 
gives us a mean percentage of In in In 2 s of 82.564, .0082. Hence, if 
= 15.879, .0003, In = 112.787, .0542. 

Combining both values, we have 

From gold series In = 113.179, =b .0517 

From oxide series '. (( = 112.787, .0542 



General mean In = 1 12.992, .0374 

If = 16, In = 113.853. 

* Poggend. Annal., 141, 28. 



184 



THE ATOMIC WEIGHTS. 



THALLIUM. 

The atomic weight of this interesting metal has been fixed by the re- 
searches of Lamy, Werther, Hebberling, Crookes, and Lepierre. 

Lamy and Hebberling investigated the chloride and sulphate ; Wer- 
ther studied the iodide; Crookes' experiments involved the synthesis of 
the nitrate. Lepierre's work is still more recent, and is based upon 
several compounds. 

Lamy * gives the results of one analysis of thallium sulphate and three 
of thallium chloride. 3.423 grammes T1 2 S0 4 gave 1.578 grm. BaS0 4 ; 
whence 100 parts of the latter are equivalent to 216.920 of the former. 
In the thallium chloride the chlorine was estimated as silver chloride. 
The following results were obtained. In the third column I give the 
amount of T1C1 proportional to 100 parts of AgCl : 

3.912 grm. T1C1 gave 2.346 grm. AgCl. 166.752 

3.000 " 1.8015 u 166.528 

3.912 " 2.336 " 167.466 

Mean, 166.915, .1905 

Hebberling's f work resembles that of Lamy. Reducing his weighings 
to the standards adopted above, we have from his sulphate series, as 
equivalent to 100 parts of BaS0 4 , the amounts of T1,S0 4 given in the 
third column : 

1.4195 grm. T1 2 SO 4 gave .6534 grm. BaSO 4 . 217.248 

1.1924 " .5507 " 216.524 

.8560 " .3957 " 216.325 



Mean, 216.699 

Including Lamy's single result as of equal weight, we get a mean of 
216.754, .1387. 

From the chloride series we have these results, with the ratio stated 
as usual : 

.2984 grm. T1C1 gave .1791 grm. AgCl. 166.611 

.5452 " .3 2 78 " 166.321 

Mean, 166,465, =b .097 

Lamy's mean was 166.915, .1905. Both means combined give a 
general mean of 166.555, .0865. 

Werther'sJ determinations of iodine in thallium iodide were made by 
two methods. In. the first series Til was decomposed by zinc and potas- 
sium hydroxide, and in the filtrate the iodine was estimated as Agl. 

*Zeit. Anal. Chem., 2, 211. 1863. 
f Ann. Chem. Pharm., 134, n. 1865. 
% Journ. fur Prakt. Chem., 92, 128. 1864. 



THALLIUM. 185 

One hundred parts of Agl correspond to the amounts of Til given in 
the last column : 

.720 grm. Til gave .51 grm. Agl. 141.176 

2.072 " 1.472 " 140.761 

.960 " .679 " 141-384 

3 8 5 -273 " 141.026 

1.068 " .759 " 140.711 



Mean, 141.012, .085 

In the second series the thallium iodide was decomposed by ammonia 
in presence of silver nitrate, and the resulting Agl was weighed. Ex- 
pressed according to the foregoing standard, the results are as follows : 

1.375 grm. Til gave .978 grm. Agl. Ratio, 140.593 

1.540 1.095 " " 140.639 

1.380 " .981 " " 140.673 

Mean, 140.635, db .016 

General mean of both series, 140.648, .016. 

In 1873 Crookes,* the discoverer of thallium, published his final deter- 
mination of its atomic weight. His method was to effect the synthesis of 
thallium nitrate from weighed quantities of absolutely pure thallium. 
No precaution necessary to ensure purity of materials was neglected ; the- 
balances were constructed especially for the research ; the weights were 
accurately tested and all their errors ascertained ; weighings were made 
partly in air and partly in vacuo, but all were reduced to absolute stand- 
ards ; and unusually large quantities of thallium were employed in each 
experiment. In short, no effort was spared to attain as nearly as possi- 
ble absolute precision of results. The details of the investigation are too 
voluminous, however, to be cited here ; the reader who wishes to become 
familiar with them must consult the original memoir. Suffice it to say 
that the research is a model which other chemists will do well to copy. 

The results of ten experiments by Professor Crookes may be stated as 
follows. In a final column I give the quantity of nitrate producible 
from 100 parts of thallium. The weights given are in grains : 



Thallium. 


TINO^ + Glass. 


Glass Vessel. 


Ratio. 


497.972995 


1121.851852 


472.557319 


130.3875 


293.193507 


i i 11.387014 


729.082713 


130.393 


288 562777 


971.214142 


594.949719 


130.3926 


324.963740 


1142.569408 


718.849078 


1 30. 3900 


183.790232 


1005.779897 


766.133831 


130.3912 


190.842532 


997.334615 


748.491271 


130.3920 


195.544324 


1022.176679 


767.203451 


I30-39I5 


201.816345 


1013.480135 


750.332401 


130.3897 


295.683523 


H53.947672 


768.403621 


130.3908 


299.203036 


1159.870052 


769.734201 


130.3917 






Mean, 


130.3910, .00034 



* Phil. Trans., 1873, p. 277. 



186 THE ATOMIC WEIGHTS. 

Lepierre's* determinations were published in 1893, and represented 
several distinct methods. First, thallous sulphate was subjected to elec- 
trolysis in presence of an excess of ammonium oxalate, the reduced 
metal being dried and weighed in an atmosphere of hydrogen. The cor- 
rected weights, etc., are as follows: 

J - 8 935 grm. T1 2 SO 4 gave 1.5327 Tl. 80.945 per cent. 

2.7243 " 2.2055 " 80.957 

2.8112 " 2.2759 " 80.958 " 



Mean, 80.953, =t .0030 

Secondly, weighed quantities of crystallized thallic oxide were con- 
verted into thallous sulphate by means of sulphurous acid, and the solu- 
tion was then subjected to electrolysis, as in the preceding series. 

3.2216 grm. T1 2 O 8 gave 2.8829 Tl. 89.487 per cent. 

2.5417 " 2.2742 " 89.475 

Mean, 89.481, =h .0040 

In the third set of experiments a definite amount of thallous sulphate 
or nitrate was fused in a polished silver crucible with ten times its weight 
of absolutely pure caustic potash. Thallic oxide was thus formed, which, 
with various precautions, was washed with water and alcohol, and finally 
weighed in the original crucible. One experiment with the nitrate gave 

2.7591 grm. T1NO 3 yields 2.3649 T1 2 O 3 . 85.713 per cent. 

Two experiments were made with the sulphate, as follows : 

3.1012 grm. T1 2 SO 4 gave 2.8056 T1 2 O 3 . 90.468 per cent. 

2.3478 " 2.1239 " 90-463 " 

Mean, 90.465, .0020 

Finally, crystallized thallic oxide was reduced by heat in a stream of 
hydrogen, and the water so formed was collected and weighed. 

2.7873 grm. T1 2 O 3 gave .3301 H 2 O. 11.843 P er cent - 

3.9871 " .4716 " 11.828 " 

4.0213 " .4761 " 11-839 " 



Mean, 11.837, d= .0029 

Iii a supplementary notef Lepierre states that his weights were all 
reduced to vacuum standards. 

Some work by Wells and Penfield, J incidentally involving a deter- 
mination of atomic weight, but primarily intended for another purpose, 
may also be taken into account. Their question was as to the constancy 
of thallium itself. The nitrate was repeatedly crystallized, and the last 
crystallization, with the mother liquor representing the opposite end of 

* Bull. Soc. Chim. (3), 9, 166. 
fBull. Soc. Chim. (3), n, 423. 1894. 
J Amer. Journ. Sci. (3), 47, 466. 1894. 



THALLIUM. 187 

the series, were both converted into chloride. In the latter the chlorine 
was estimated as silver chloride, which was w r eighed on a Gooch filter, 
with the results given below, which are sensibly identical. The T1C1 
equivalent to 100 parts of AgCl is stated in the last column. 

TICl. AgCl. Ratio. 

Crystals 3-9*46 2.3393 167.341 

Mother liquor 3-34'5 1.9968 167. 343 

Mean, 167.342 

The general mean of Lamy's and Hebberling's determinations of this 
ratio gave 166.555, : .0865. If we arbitrarily assign Wells and Pen- 
field's mean equal weight with that, we get a new general mean of 
166.948, .0610. 

The ratios to be considered are now as follows : 

(I.) BaSO 4 : T1 2 SO 4 : : 100 : 216.754, .1387 
(2.) AgCl : TICl : : 100 : 166.948, .0610 
(3.) Agl : Til : : 100 : 140.648, .016 
(4.) Tl : T1NO 3 : : 100 : 130.391, + .00034 
(5.) T1 2 S0 4 : T1 2 : : 100 : 80.953, .0030 
(6.) T1 2 O 3 : T1 2 : : IOO : 89.481, .0040 
( 7 .) 2T1N0 3 : T1 2 3 : : 100:85.713 
(8.) T1 2 SO 4 : T1 2 O 3 : : 100 : 90.465, .0020 
(9.) T1 2 O 3 : 3H 2 O : : IOO : 11.837, .0029 

And the antecedent data are these : 

= 15.879, db .0003 N = 13.935, db .0021 
Ag= 107.108, =b .0031 S = 31.828, it .0015 
Cl = 35.179, =fc .0048 AgCl = 142.287, i .0037 

1 = 125.888, .0069 Agl = 232.996, db .0062 

Ratio number seven rests upon a single experiment, and the atomic 
weight of thallium derived from it must therefore be arbitrarily weighted. 
It has been assumed, therefore, that its probable error is the same as that 
from number eight. Taking this much for granted, we have nine values 
for thallium, as given below : 

From (i) Tl = 203.478, .1610 

Fro'm (2) " = 202.366, db .0872 

From (3) " = 201.816, .0389 

From (4) ' ' = 202. 595, .0117 

From (5) " = 202.614, .0330 

From (6) " = 202 620, .0775 

From (7) " = 202.679, d= .0483 

From (8) " = 202.496, .0483 

From (9) '* = 202.746, d= .0576 

General mean Tl = 202.555, .0098 

If = 16, Tl = 204.098. 






188 THE ATOMIC WEIGHTS. 

If we reject the first three values, retaining only those due to the ex- 
periments of Crookes and Lepierre, we have 

Tl = 202.605, .0103 

If O = 16, this becomes 204.149. This mean exceeds Crookes' deter- 
mination only by 0.01, and may be regarded as fairly satisfactory. 
Crookes' ratio evidently outweighs all the others. 



SILICON. 

Although Berzelius * attempted to ascertain the atomic weight of 
silicon, first by converting pure Si into Si0 2 , and later from the analysis 
of BaSiF 6 , his results were not satisfactory. We need consider only the 
work of Pelouze, Schiel, Dumas, and Thorpe and Young. 

Pelouze,f experimenting upon silicon tetrachloride, employed his 
usual method of titration with a solution containing a known weight of 
silver. One hundred parts of Ag gave the following equivalencies of 
SiCl 4 : 

39-4325 
39.4570 



Mean, 39.4447, .0083 

Essentially the same method was adopted by Dumas. J Pure SiCl 4 
was weighed in a sealed glass bulb, then decomposed by water, and 
titrated. The results for 100 Ag are given in the third column : 

2.899 grm. SiCl 4 = 7.3558 grm. Ag. 39.41 1 

1.242 " 3.154 " 39-379 

3.221 8.1875 " 39.340 

Mean, 39.377, db .014 

Dumas' and Pelouze's series combine as follows : 

Pelouze 39.4447, dr .0083 

Dumas 39.377, .014 

General mean 39.4265, =fc .0071 

Schiel, also studying the chloride of silicon, decomposed it by am- 
monia. After wanning and long standing it was filtered, and in the 

* Lehrbuch, 5 Aufl., 3, 1200. 
f Compt. Rend., 20, 1047. 1845. 
I Ann. Cheni. Pharm., 113, 31. 1860. 
Ann. Chem. Pharm., 120,94. 



SILICON. 189 

filtrate the chlorine was estimated as AgCl. One hundred parts of AgCl 
correspond to the quantities of SiCl 4 given in the last column : 

.6738 grm. SiCl 4 gave 2.277 g rm - AgCl. 29.592 

1.3092 " 4.418 " 29.633 



Mean, 29.6125, .0138 

Thorpe and Young,* working with silicon bromide, seem to have ob- 
tained fairly good results. The bromide was perfectly clear and color- 
less, and boiled constantly at 153. It was weighed, decomposed with 
water, and evaporated to dryness,the crucible containing it being finally 
ignited. The crucible was tared by one precisely similar, in which an 
equal volume of water was also evaporated. Results as follows, with 
weights at vacuum standards : 

9.63007 grm. SiBr 4 gave 1.67070 SiO 2 . 17.349 per cent. 

12.36099 " 2.14318 " 17.338 

12.98336 2.25244 " 17-349 " 

9.02269 " L5 6 542 " I7-350 " 

15.38426 " 2.66518 " 17.324 " 

9.74550 1.69020 " 17-343 

6.19159 " 1.07536 " 17.368 " 

9.51204 " 1.65065 " 17.353 " 

10.69317 1.85555 " '7-353 " 

Mean, 17.347, .0027 

The ratios now available are 

(i.) 4Ag : SiCl 4 : : 100 : 39.4265, .0071 
(2.) 4AgCl : SiCl 4 : : 100 : 29.6125, =b .0138 
(3.) SiBr 4 : SiO 2 : : loo : 17.347, .0027 

Reducing these ratios with 

O = I 5-879, db .0003 Br = 79.344, .0062 
Ag= 107.108, .0031 AgCl = 142.287, .0037, 
Cl =. 35.179, =h .0048 

we have the following values for the atomic weight of silicon : 

From (i) Si = 28.200, .0363 

From (2) " = 27.823, .0810 

From (3) .... " = 28.187, =b .0122 



General mean Si 28.181, .0114 

If = 16, Si = 28.395. 

*Journ. Chem. Soc., 51,576. 1887. 



190 THE ATOMIC WEIGHTS. 



TITANIUM. 

The earliest determinations of the atomic weight of titanium are due 
to Heinrich Rose.* In his first investigation he studied the conversion 
of titanium sulphide into titanic acid, and obtained erroneous results ; 
later, in 1829, he published his analyses of the chloride, f This compound 
was purified by repeated rectifications over mercury and over potassium, 
and was weighed in bulbs of thin glass. These were broken under water 
in tightly stoppered flasks ; the titanic acid was precipitated by ammo- 
nia, and the chlorine was estimated as silver chloride. The following 
results were obtained. In a fourth column I give the Ti0 2 in percentages 
referred to TiCl 4 as 100, and in a fifth column the quantity of TiCl 4 pro- 
portional to 100 parts of AgCl : 

TiCl. TiO T AgCl. Percent. TiO. 2 . AgCl Ratio. 

.885 grm. .379 grm. 2.661 grm. 42.825 33- 2 S8 

2.6365 " 1. 120 " 7.954 " 42.481 33-147 

I.7I57 " -73 2 " 5- I 72 " 42.665 33.173 

3.0455 " 1.322 " 9.198 " 43.423 33-100 

2.4403 " 1.056 ' 7.372 " 43-273 33.102 

Mean, 42.933, .121 33.156, .019 

If we directly compare the AgCl with the Ti0 2 we shall find 100 parts 
of the former proportional to the following quantities of the latter : 

14.243 
14.081 
14-153 
H.373 
14.324 



Mean, 14.235, .036 

Shortly after the appearance of Rose's paper, MosanderJ published 
some figures giving the percentage of oxygen in titanium dioxide, from 
which a value for the atomic weight of titanium was deduced. Although 
no details are furnished as to experimental methods, and no actual weigh- 
ings are given, I cite his percentages for whatever they may be worth : 

40.814 

40.825 

40.610 

40. 1 80 

40.107 

40.050 

40.780 

40.660 

39-830 

Mean, 40.428 

* Gilbert's Annalen, 1823, 67 and 129. 

t Poggend. Annalen, 15, 145. Berz. I,ehrbuch, 3, 1210. 

j Berz. Jahresbericht, 10, 108. 1831. 



TITANIUM. 191 

These figures, with O = 15.879, give values for Ti ranging from 46.03 
to 47.98; or, in mean, Ti = 46.80. They are not, however, sufficiently 
explicit to deserve any farther consideration. 

In 1847 Isidor Pierre made public a series of important determina- 
tions.* Titanium chloride, free from silicon and from iron, was pre- 
pared by the action of chlorine upon a mixture of carbon with pure, 
artificial titanic acid. This chloride was weighed in sealed tubes, these 
were broken under water, and the resulting hydrochloric acid was titrated 
with a standard solution of silver after the method of Pelouze. I subjoin 
Pierre's weighings, and add, in a third column, the ratio of TiCl 4 to 100 
parts of silver : 

TiClt. Afr. Ratio. 

.8215 grm. 1.84523 gran. 44-5 2 

.7740 " i.739 9 " 44-506 

7775 " I.746I3 " 44.527 

.7160 " 1.61219 " 44412 

.8085 " 1.82344 " 44-339 

.6325 " 1.42230 " 44.470 

8155 " 1-83705 " 44-39.2 

.8165 1.83899 " 44.399 

.8065 " 1.81965 " 44.322 



Mean, 44.432, .0173 

It will be seen that the first three of these results agree well with each 
other and are much higher than the remaining six. The last four ex- 
periments were made purposely with tubes which had been previously 
opened, in order to determine the cause of the discrepancy. According 
to Pierre, the opening of a tube of titanium chloride admits a trace of 
atmospheric moisture. This causes a deposit of titanic acid near the 
mouth of the tube, and liberates hydrochloric acid. The latter gas being 
heavy, a part of it falls back into the tube, so that the remaining chloride 
is richer in chlorine and poorer in titanium than it should be. Hence, 
upon titration, too low figures for the atomic weight of titanium are 
obtained. Pierre accordingly rejects all but the first three of the above 
estimations. 

The memoir of Pierre upon the atomic weight of titanium was soon 
followed by a paper from Demoly, f who obtained much higher results. 
He also started out from titanic chloride, which was prepared 'from rutile. 
The latter substance was found to contain 1.8 per cent, of silica ; whence 
Demoly inferred that the TiCl 4 investigated by Rose and by Pierre might 
have been contaminated with SiCl 4 , an impurity which would lower the 
value deduced for the atomic weight under consideration. Accordingly, 
in order to eliminate all such possible impurities, this process was resorted 

*Ann. Chim. Phys. (3), 20, 257. 

t Ann. Chem. Pharm., 72, 214. 1849. 



192 THE ATOMIC WEIGHTS. 

to : the chloride, after rectification over mercury and potassium, was 
acted upon by dry ammonia, whereupon the compound TiCl 4 .4NH 3 was 
deposited as a white powder. This was ignited in dry ammonia gas, and 
the residue, by means of chlorine, was reconverted into titanic chloride, 
which was again repeatedly rectified over mercury, potassium, and po- 
tassium amalgam. The product boiled steadily at 135. This chloride, 
after weighing in a glass bulb, was decomposed by water, the titanic acid 
was precipitated by ammonia, and the chlorine was estimated in the 
filtrate as silver chloride. Three analyses were performed, yielding the 
following results. I give the actual weighings : 

1.470 grm. TiCl 4 gave 4.241 grm. AgCl and .565 grm. TiO 2 
2.330 " 6.752 .801 " 

2.880 " 8.330 " 1.088 " 

The ".801 " in the last column is certainly a misprint for .901. Assum- 
ing this correction, the results may be given in three ratios, thus : 



Per cent. TiOifrom TiClv TiCl: looAgCl. TiO 2 : woAgCL 

38.435 34-662 13-322 

38669 34. 508 13.344 

37.778 34-574 13.061 



Mean, 38.294, .180 34-58i, .030 13.242, zfc .061 

These three ratios give three widely divergent values for the atomic 
weight of titanium, ranging from about 36 to more than 56, the latter 
figure being derived from the ratio between AgCl and TiCl 4 . This value, 
56, is assumed by Demoly to be the best, the others being practically 
ignored. 

Upon comparing Demoly's figures with those obtained by Rose, certain 
points of similarity are plainly to be noted. Both sets of results were 
reached by essentially the same method, and in both the discordance 
between the percentages of titanic acid and of silver chloride is glaring. 
This discordance can rationally be accounted for by assuming that the 
titanic chloride was in neither case absolutely what it purported to be ; 
that, in brief, it must have contained impurities, such for example as 
hydrochloric acid, as shown in the experiments of Pierre, or possibly 
traces of oxy chlorides. Considerations of this kind also throw doubt 
upon the results attained by Pierre, for he neglected the direct estimation 
of the titanic acid altogether, thus leaving us without means for correctly 
judging as to the character of his material. 

In 1883* Thorpe published a series of experiments upon titanium 
tetrachloride, determining three distinct ratios and getting sharply con- 
cordant results. The first ratio, which was essentially like Pierre's, by 

* Berichte Deutsch. Chem. Gesell., 16, 3014. 1883. 



TITANIUM. 193 

decomposition with water and titration with silver, was in detail as 
follows : 



7VC/4. 


Ag. 


7VC7 4 : iooAg. 


2-43275 


5.52797 


44.008 


5-42332 


12.32260 


44.015 


3.59601 


8.17461 


44.000 


3.31222 


7.52721 


44.003 


4.20093 


9.54679 


44.004 


5.68888 


12.92686 


44.008 


5.65346 


12.85490 


43-979 


4.08247 


9.28305 


43.978 



Mean, 43.999, =b .0032 
Pierre found, 44.432, d= .0073 

General mean, 44.017, db .0031 

The second ratio, which involved the weights of TiCl 4 taken in the last 
five determinations of the preceding series, included the weighing of the 
silver chloride formed. The TiCl 4 proportional to 100 parts of AgCl is 
given in a third column : 

7Ya 4 . AgCl. Ratio. 

3.31222 10.00235 33- "4 

4.20093 12.68762 33.111 

5.68888 17.17842 33.117 

5.65346 17.06703 33- I2 5 

4.08247 12.32442 33- I2 5 

Mean, 33.118, .0019 
Rose found, 33.156, =b .019 
Demoly found, 34.581, .030 



General mean, 33.123, .0019. 

In the third series the chloride was decomposed by water, and after 
evaporation to dry ness the resulting Ti0 2 was strongly ignited. 

TtC/ t . TiO v Percent. TiO.,. 

6.23398 2.62825 42.160 

8.96938 3./8335 42.181 

10.19853 4.30128 42.176 

6.56894 2.77011 42.170 

8.99981 3-79575 42.176 

8.32885 3-5"58 42.162 



Mean, 42.171, .0022 
Rose found, 42.933, dr .121 
Demoly found, 38.294, .180 



General mean, 42.171, .0022 

In short, the work of Rose, Pierre, and Demoly practically vanishes. 
Furthermore, as will be seen later, the three ratios now give closely 
13 



194 THE ATOMIC WEIGHTS. 

agreeing values for the atomic weight of titanium. The cross ratio, 
4AgCl : Ti0 2 is not directly given by either of Thorpe's series ; but the 
data furnished by Rose and Demoly combine into a general mean of 
4AgCl : Ti0 2 : : 100 : 13.980, .0303. 

Some two years later Thorpe published his work more in detail,* and 
added a set of determinations, like those made upon the chloride, in 
which titanium tetrabromide was studied. Three ratios were measured, 
as was the case with the chloride. In the first, the bromide was decom- 
posed by water and titrated with a silver solution. 

TiBr. Ag. TiBr : rooAg. 

2.854735 3-349 2 7 85.235 

3.120848 3.66*22 85.241 

4-73"i 8 5-5597 85.230 

6.969075 8.17645 85.234 

6.678099 7.83493 85.234 

Mean, 85.235, + .0027 

In the four last experiments of the preceding series, the silver bromide 
formed was weighed. The third column gives the TiBr 4 proportional to 
100 parts of AgBr. 

TiBr^. AgBr, Ratio. 

3.120848 6.375391 48.951 

4.731118 9-663901 48.957 

6.969075 14.227716 48.982 

6.678099 I3-639956 48.959 

Mean, 48.962, .0049 

For the third ratio the bromide was decomposed by water ; and after 
evaporation with ammonia the residual titanic oxide was ignited and 



TiO.,. Percent. TiO 2 . 
6.969730 1.518722 21.790 

8.836783 1.923609 21.768 

9.096309 . I-9795J3 21.762 

Mean, 21.773, .0062 

Ignoring Mosander's work as unavailable, we have the following ratios 
to consider : 

(I.) 4Ag : TiCl 4 : : 100 : 44.017, i .0031 
(2.) 4AgCl : TiCl 4 : : 100 : 33- I2 3, .0019 
(3.) 4AgCl : TiO 2 : : 100 : 13.980, =h .0303 
(4.) TiCl 4 : TiO 2 :: 100 : 42.171, .0022 
(5.) 4 Ag : TiBr, : : 100 : 85.235, .0027 
(6.) 4AgBr : TiBr 4 : : 100 : 48.962, .0049 
(7.) TiBr 4 : TiO 2 : : 100 : 21.773, .0062 

* Journ. Chem. Soc., Feb., 1885, p. 108, and March, p. 129. 






GERMANIUM. 195 

These are to be computed with 

O = -- 15.879, + .0003 Br 79.344, zb .0062 

Ag = 107. 108, .0031 AgCl = 142.287, .0037 

cl = 35- z 79, =b - 48 AgBr = 186.454, =b -54 

For the molecular weight of titanium chloride they give two values : 

From (i) ...................... TiCl 4 == 188.583, .0144 

From (2) ...................... " = 188.519, rb .0119 

General mean ............. TiCl 4 = 188.545, .0092 

For TiBr we have 






From (5) ...................... TiBr 4 = 365.i74, .0157 

From (6) ...................... " = 365.163,^.0380 

General mean ............ TiBr 4 = 365. 172, =b .0145 

And for the atomic weight of titanium five values are calculable, as 
follows : 

From molecular weight of TiCl 4 ...... Ti = 47.829, rb .0213 

From molecular weight of TiBr 4 . ..... " =47.796, rb .0260 

From (3) .......................... " = 47.809. .1725 

From (4) ---- , ..................... " =47.698, .0268 

From (7) ....... .................. " = 47-738, .0787 

General mean ..... . ........... Ti = 47.786, d= .0138 

If = 16, this becomes Ti = 48.150. 



GERMANIUM. 

The data relative to the atomic weight of germanium are rather scanty, 
and are due entirely to the discoverer of the element, Winkler.* The 
pure tetrachloride was decomposed by sodium carbonate, mixed with a 
known excess of standard silver solution, and then titrated back with 
ammonium sulphocyanate. The data given are as follows : 



Cl Found. Percent. Cl. 
.1067 .076112 66.177 

.1258 .083212 66.146 

.2223 .147136 66.188 

.2904 .192190 66.182 



Mean, 66.173 

Hence, with Cl = 35.179, Ge = 71.933. If O = 16, Ge = 72.481. 

* Journ. fiir Prakt. Chem. (2), 34, 177. 1886. 



196 THE ATOMIC WEIGHTS. 



ZIRCONIUM. 

The atomic weight of zirconium has been determined by Berzelius, 
Hermann, Marignac, Weibull, and Bailey. Berzelius* ignited the 
neutral sulphate, and thus ascertained the ratio in it between the Zr0 2 
and the SO 3 . Putting S0 3 at 100, he gives the following proportional 
quantities of Zr0 2 : 

75-84 

75-92 

75.80 

75-74- 

75-97 

75.85 

Mean, 75.853, .023 

This gives 43.134, .0142 as the percentage of zirconia in the sulphate. 

Hermann's t estimate of the atomic weight of zirconium was based 
upon analyses of the chloride, concerning which he gives no details nor 
weighings. From sublimed zirconium chloride he finds Zr = 831.8, 
when = 100; and from two lots of the basic chloride 2ZrOCl 2 ,9H 2 0, 
Zr = 835.65 and 851.40 respectively. The mean of all three is 839.62 ; 
whence, with modern formulae and O = 15.879, Zr becomes = 88.882. 

Marignac's results J were obtained by analyzing the double fluoride of 
zirconium and potassium. His weights are as follows : 

i.ooo grm. gave .431 grm. ZrO 2 and .613 grm. K 2 SO 4 . 

2.000 " .864 " 1.232 " 

.654 " .282 " .399 

5.000 " 2.169 3-78 " 

These figures give us three ratios. A, the Zr0 2 from 100 parts of salt; 
B, the K 2 SO 4 from 100 parts of salt ; and C, the ZrO 2 proportional to 100 
parts of K 2 SO, : 

A. B. C. 

43.100 61.300 70-3 10 

43.200 61.600 70.130 

43.119 61.000 70.677 

43.380 61.560 70.468 

Mean, 43.200, d= .043 Mean, 61.365, =h .094 Mean, 70.396, 079. 

Weibull, following Berzelius, ignited the sulphate, and also made a 

*Poggend. Annal , 4, 126. 1825. 

t Journ. fi'ir Prakt. Chem., 31, 77. Berz. Jahresb., 25, 147. 

jAnn. Chim. Phys. (3), 60, 270. 1860. 

I Lund. Arsskrift, v. 18. i88i-'82. 



ZIRCONIUM, 197 

similar set of experiments with the selenate of zirconium, obtaining re- 
sults as follows : 

Sulphate. Zr(SO^ v 

1.5499 grm. salt gave .6684 ZrO 2 . 43.126 per cent. 

1-5445 " -6665 " 43- r 53 " 

2.1683 " .9360 " 43.168 " 

1.0840 " .4670 " 43.081 " 

.7913 " .3422 " 43-321 " 

.6251 .2695 " 43. 113 " 

.4704 .2027 " 43. 9i " 

Mean, 43.150, =fc .0207 

Selenate. Zr(SeO^. 

i. 02 1 2 grm. salt gave .3323 ZrO 2 . 32.540 per cent. 

.8418 " .2744 " 32.597 " 

.6035 .1964 " 32.544 " 

.8793 .2870 " 32.640 " 

.3089 " .1003 " 3 2 .470 " 



Mean, 32.558, .0192 

Bailey * also ignited the sulphate, after careful investigation of his 
material, and of the conditions needful to ensure success. He found that 
the salt was perfectly stable at 400, while every trace of free sulphuric 
acid was expelled at 350. The chief difficulty in the process arises from 
the fact that the zirconia produced by the ignition is very light, and 
easily carried off mechanically, so that the percentage found is likely to 
be too low. This difficulty was avoided by the use of a double crucible, 
the outer one retaining particles of zirconia which otherwise might be 
lost. The results, corrected for buoyancy of the air, are as follows : 

2.02357 salt gave .87785 ZrO a . 43-38i per cent. 

2.6185 " I.I3S4 " 43-36o " 

2.27709 " .98713 " 43-35 " 

2.21645 " -96152 " 43-385 " 

L75358 " .76107 " 43-402 " 

1.64065 " .7120 " 43.397 " 

2.33255 " 1.01143 " 43.36i " 

1.81105 " .78485 " 43-337 " 



Mean, 43.372, .0056 

This, combined with previous determinations, gives 

Berzelius 43. 134, .0142 

Weibull 43. 150, .0207 

Bailey 43-37 2 , .0056 

General mean 43-3 I 7, .0051 

* Proc. Roy. Soc., 46, 74. Chem. News, 60, 32. 



198 THE ATOMIC WEIGHTS. 

For computing the atomic weight of zirconium we now have the sub- 
joined ratios : 

(i.) Percentage ZrO 2 in Zr(SO 4 ) 2 , 43.317, .0051 

(2.) Percentage ZrO 2 in Zr(SeO 4 ) 2 , 32.558, .0192 

(3.) Percentage ZrO 2 from K 2 ZrF 6 , 43.200, .043 

(4.) Percentage K 2 SO 4 from K 2 ZrF 6 , 61.365, .094 

(5.) K 2 S0 4 : Zr0 2 : : 100 : 70.396, .079 

Tlie antecedent atomic weights are 

O = 15.879, .0003 K = 38.817, dt .0051 

S =31.828, .0015 F = 18.912, .0029 

Se = 78.419, .0042 

With these data we first get three values for the molecular weight of 
zirconia : 

From (i) ZrO 2 121.454, .0182 

From (2) " = 121.708, .0798 

From (5) " = 121.770, .1370 



General mean ZrO 2 121.471, .0176 

Finally, there are three independent estimates for the atomic weight 
of zirconium : 

From molecular weight ZrO 2 Zr = 89.713, d= .0177 

From ratio (3) " = 89.437, .2390 

From ratio (4) " 90.778, .4326 

General mean Zr = 89.716, .0175 

If = 16, Zr 90.400. 

Here the first value alone carries appreciable weight. 



TIN. 199 



TIN. 

The atomic weight of tin has been determined by means of the oxide, 
the chloride, the bromide, the sulphide, and the stannichlorides of potas- 
sium and ammonium. 

The composition of stannic oxide has been fixed in two \vays : by 
synthesis from the metal and by reduction in hydrogen. For the first 
method we may consider the work of Berzelius, Mulder and Vlaanderen, 
Dumas, Van der Plaats, and Bongartz and Classen. 

Berzelius * oxidized 100 parts of tin by nitric acid, and found that 
127.2 parts of Sn0 2 were formed. 

The work done by Mulder and Vlaanderen f was done in connection 
with a long investigation into the composition of Banca tin, which was 
found to be almost absolutely pure. For the atomic weight determina- 
tions, however, really pure tin was taken prepared from pure tin oxide. 
This metal was oxidized by nitric acid, with the following results. 100 
parts of tin gave of SnO 2 : 

127.56 Mulder. 
127.56 Vlaanderen. 
1 27.43 Vlaanderen. 

Mean, 127.517, .029 

Dumas J oxidized pure tin by nitric acid in a flask of glass. The re- 
sulting Sn0 2 was strongly ignited, first in the flask and afterwards in 
platinum. His weighings, reduced to the. foregoing standard, give for 
dioxide from 100 parts of tin the amounts stated in the third column : 

12.443 grm. Sn gave 15.820 grm. SnO 2 . 127.14 

15.976 " 20.301 " 127.07 



Mean, 127.105, =b .024 

In an investigation later than that previously cited, Vlaanderen 
found that when tin was oxidized in glass or porcelain vessels, and the 
resulting oxide ignited in them, traces of nitric acid were retained. 
When, on the other hand, the oxide was strongly heated in platinum, 
the latter was perceptibly attacked, so much so as to render the results 
uncertain. He therefore, in order to fix the atomic weight of tin, reduced 
the oxide by heating it in a porcelain boat in a stream of hydrogen. Two 
experiments gave Sn = 118.08, and Sn = 118.24. These, when =s 16, 
become, if reduced to the above common standard, 



*Poggend. Annal., 8, 177. 

t Journ. fur Prakt. Chem., 49, 35. 1849. 

t Ann. Chem. Pharm., 113, 26. 

3 Jahresbericht, 1858, 183. 



200 THE ATOMIC WEIGHTS. 

127.100 
127.064 

^ Mean, 127. 082, =b .012 

Van der Plaats * prepared pure stannic oxide from East Indian tin 
(Banca), and upon the material obtained made two series of experiments J 
one by reduction and one by oxidation. The results, with vacuum 
weights, are as follows, the ratio between Sn and Sn0 2 appearing in the 

third column : 

Oxidation Series. 

9.6756 grm. tin gave 12.2967 SnO 2 . 127.091 

12.7356 16.1885 " 127.114 

23.4211 " 29.7667 " 127.093 

Reduction Series. 

5-5 OI 5 g rm - Sn 2 S ave 4.3280 tin. 127. 1 14 

4.9760 3-9 T 45 " 127.117 

3.8225 " 3.0278 " 127.086 

2.9935 " 2.3553 " 127.096 



Mean of both series as one, 127.102, .0033 

The reductions were effected in a porcelain crucible. 

Bongartz and Classen f purified tin by electrolysis, and oxidized the 
electrolytic metal by means of nitric acid. The oxide found was dried 
over a water-bath, then heated over a weak flame, and finally ignited for 
several hours in a gas-muffle. Some reduction experiments gave values 
which were too low. The oxidation series was as follows, with the usual 
ratio added by me in a third column : 

Sn. SnO^ Ratio. 

2.5673 3- 2 57o 126.865 

3.8414 4-8729 126.852 

7.3321 9. 2 994 126.831 

5.43 6 7 6.8962 126.845 

7.3321 9- 2 994 126.831 

9.8306 12.4785 126.935 

11.2424 14.2665 126.896 

5.5719 7.0685 126.860 

9.8252 12.4713 126.932 

4-3959 5-5795 126.925 

6.3400 8.0440 126.877 

Mean, 126.877, .0080 

- We now have six series of experiments showing the amount of SnO a 
formed from 100 parts of tin. To Berzelius' single determination may be 
assigned the weight of one experiment in Mulder and Vlaanderen's 
series : 

* Corapt. Rend., 100, 52. 1885. 

fBerichte Deutsch. Chem. Gesell., 21, 2900. 1888. 



TIN. 



201 



Berzelius 127.20x3, .041 

Mulder and Vlaanderen 127.517, dr .029 

Dumas 127. 105, .024 

Vlaanderen 127.082, d= .012. 

Van der Plaats 127. 102, .0033 

Bongartz and Classen 126.877, .0080 



General mean , 127.076, dr .0026 

Dumas, in the paper previously quoted, also gives the results of some 
experiments with stannic chloride, SnCl 4 . This was titrated with a solu- 
tion containing a known weight of silver. From the weighings given, 
100 parts of silver correspond to the quantities of SnCl 4 named in the 
third column : 

1.839 grm. SnC! 4 3.054 grm. Ag. 60.216 

2.665 4.427 " 60.199 

Mean, 60.207, =t '6 

Tin tetrabromide and the stannichlorides of potassium and ammonium 
were all studied by Bongartz and Classen ; who, in each compound, 
carefully purified, determined the tin electrolytically. The data given 
are as follows, the percentage columns being added by myself: 



Taken. 
8.5781 

9-5850 

9.9889 
10.4914 
16.8620 
16.6752 
11.1086 
10.6356 
11.0871 
19.5167 



Tin Tetrabromide. 
Sn Found. 
2.3270 
2.6000 
2.7115 
2.8445 

4.5735 
4.5236 



2.8840 
3.0060 
5-2935 



Percent. Sn. 

27.127 
27.126 

27.145 
27.113 
27.123 
27.119 
27.116 

27.113 
27.123 
27.128 



Mean, 27.123, dr .0020 



2.5718 
2.2464 

9-3353 

12.1525 
12.4223 
15.0870 
10.4465 
18.9377 
18.4743 
17.6432 



Potassium Stannichloride. 

Sn Found. Per cent. Sn. 

.7472 29.054 

.6524 29.042 

2.7100 29.030 
3-5285 ^ 29.035 

3.6070 29.036 

4.3812 29.040 

3.0330 29.034 

5.5029 29.058 

5.3630 29.029 

5.1244 29.045 



Mean, 29.040, .0021 



202 THE ATOMIC WEIGHTS. 

Ammonium Stannichloride. 

Am^SnQl^ Sn Found. Per cent. Sn. 

1-6448 .5328 3 2 .393 

1.8984 .6141 32.347 

2.0445 .6620 32.381 

2.0654 .6690 32.391 

2.0058 .6496 32.386 

2.4389 .7895 32.371 

4.0970 L3254 32. 35 1 

3.4202 1.1078 32.390 

3.6588 1.1836 32.349 

1.5784 .5108 32-362 

7.3248 2.3710 32.37 

13.1460 4.2528 32.351 

11.9483 3-8650 32.348 

18.4747 5.9788 32-362 

18.6635 6.0415 32.371 

17.8894 5.7923 32.378 



Mean, 32.369, .0088 

One other method of determination for the atomic weight of tin was 
employed by Bongartz and Classen. Electrolytic tin was converted into 
sulphide, and the sulphur so taken up was oxidized by means of hydrogen 
peroxide, by Classen's method, and weighed as barium sulphate. The 
results, as given by the authors, are subjoined : 

Sn Taken. Per cent, of S Gained. 

2.6285 53.91 

7495 53.87 

1.4785 53-94 

2.5690 53.94 

2.1765 53.85 

1.3245 53-88 

9897 53.83 

2.7160 53-86 



Mean, 53.885, =h .0098 

This percentage of sulphur, however, was computed from weighings 
of barium sulphate. What values were assigned to the atomic weights 
of barium and sulphur is not stated, but as Meyer and Seubert's figures 
are used for other elements throughout this paper, we may assume that 
they apply here also. . Putting O = 15.96, S = 31.98, and Ba = 136.86, 
the 53.885 per cent, of sulphur becomes 392.056, .0713 of BaS0 4 , the 
compound actually weighed. This gives us the ratio 

Sn : 2BaSO 4 : : loo : 392.056, d= .0713 

as the real result of the experiments, from which, with the later values 
for Ba, S, and 0, the atomic weight of tin may be calculated. 



TIN. 203 

We now have, for tin, the following available ratios : 

(l.) Sn : SnO 2 : : loo : 127.076, dr .0026 

(2.) 4Ag : SnG 4 : : 100 : 60.207, -0060 

(3.) Percentage of tin in SnBr 4> 27.123, .0020 

(4.) Percentage of tin in K 2 SnCl 6 , 29.040, .0021. 

(5.) Percentage of tin in Am 2 SnCI 6 , 32.369, .0088 

(6.) Sn : 2BaSO 4 : : 100 : 392.056, .0713 

The antecedent values are 

O = 15.879, .0003 K= 38.817, d= .0051 

Ag = 107.108, rb .0031 N = 13.935, .0021 

Cl = 35.179, .0048 S = 31.828, .0015 

Br = 79.344, dr .0062 Ba = 136.392, .0086 

With these, six independent values for Sn are computable, as follows : 

From (i). Sn 117.292, .0115 

From (2) " = 117.230, =h -0331 

From (3) " = 1 18.120, .0131 

From (4) " = 118.152, d=. 0155 

From (5) " = 118.190, .0382 

From (6) " = 118.216, .0220 

General mean Sn = 1 17.805, .0069 

If = 16, Sn = 118.701. 

If we reject the first two of these values, which include all of the older 
work, and take only the last four, which represent the concordant results 
of Bongartz and Classen, the general mean becomes 

Sn 1 1 8. 150, =b .0089 

Or, with O = 16, Sn = 119.050. This mean I regard as having higher 
probability than the other. 

A single determination of the atomic weight of tin, made by Schmidt,* 
ought not to be overlooked, although it was only incidental to his research 
upon tin sulphide. In one experiment, 0.5243 grm. Sn gave 0.6659 Sn0 2 . 
Hence, with = 16, Sn = 118.49. This lies about midway between the 
two sets of values already computed. 

* Berichte, 27, 2743. 1894. 



204 THE ATOMIC WEIGHTS. 



THORIUM. 

The atomic weight of thorium has been determined from analyses of 
the sulphate, oxalate, formate, and acetate, with widely varying results. 
The earliest figures are due to Berzelius,* who worked with the sulphate, 
and with the double sulphate of potassium and thorium. The thoria 
was precipitated by ammonia, and the sulphuric acid was estimated as 
BaS0 4 . The sulphate gave the following ratios in two experiments. The 
third column represents the weight of ThO 2 proportional to 100 parts of 
BaSO, : 

6 754 g rm - ThO 2 1.159 grm. BaSO 4 . Ratio, 58.274 
1.0515 " 1.832 " 57.396 

The double potassium sulphate gave .265 grm. Th0 2 , .156 grin. S0 3 , 
and .3435 K 2 S0 4 . The S0 3 , with the Berzelian atomic weights, repre- 
sents .4537 grm. BaS0 4 . Hence 100 BaSO 4 is equivalent to 58.408 Th0 2 . 
This figure, combined with the two previous values for the same ratio, 
gives a mean of 58.026, .214. 

From the ratio between the K 2 S0 4 and the Th0 2 in the double sul- 
phate, Th0 2 = 266.895. 

In 1861 new determinations were published by Chydenius.t whose 
memoir is accessible to me only in an abstract J which gives results with- 
out details. Thoria is regarded as a monoxide, ThO, and the old equiv- 
alents (O = 8) are used. The following values are assigned for the 
molecular weight of ThO, as found from analyses of several salts : 

From Sulphate. From K. Th. Sulphate. 
66.33 67. 2 

67.13 

67.75 
68.03 



Mean, 67.252, d= .201 

From Acetate. From Formate. From Oxalate. 

67.31 68.06 65.87-^ Two results 

66.59 67.89 65.95 j by Berlin. 

67.27 68.94 65.75 

67.06 65.13 

68.40 Mean, 68.297, rb .219 6654 

65.85 

Mean, 67.326, .201 

Mean, 65.85, .123 

* Poggend. Annal., 16, 398. 1829. Lehrbuch, 3, 1224. 

t Keraisk undersokning af Thorjord och Thorsalter. Helsingfors, 1861. An academic disser- 
tation. 
I Poggeud. Annal., 119, 55. 1863. 



THORIUM. 



205 



We may fairly assume that these figures were calculated with = 8, 
C = 6, and S = 16. Correcting by the values for these elements which 
have been found in previous chapters, Th0 2 becomes as follows : 

From sulphate ThO 2 = 267.170, rfc .7950 

From acetate " = 267.488, .7950 

From formate " = 271.239, .8698 

From oxalate " = 261.478, d= .4884 



General mean ............. ThO 2 = 265.103, -3394 

The single result from the double potassium sulphate is included with 
the column from the ordinary sulphate, and the influence of the atomic 
weight of potassium is ignored. 

Chydenius was soon followed by Marc Delafontaine, whose researches 
appeared in 1863.* This chemist especially studied thorium sulphate ; 
partly in its most hydrous form, partly as thrown down by boiling. In 
Th(S0 4 ) 2 .9H 2 0, the following percentages of Th0 2 were found : 

45.08 
44.90 
45.06 

45- 21 
45.06 

Mean, 45.062, dz .0332 

The lower hydrate, 2Th(SO 4 ) 2 .9H 2 0, was more thoroughly investi- 
gated. The thoria was estimated in two ways : First (A), by precipita- 
tion as oxalate and subsequent ignition ; second (B), by direct calcination. 
These percentages of Th0 2 were found : 

52.83! 



52.72 

52.I3J 

52.47 

52.49 

52.53 

52-13 

52.13 

52.43 

52.60 

52.40 

52.96 

52.82 



Mean, 52.511, .047 

In three experiments with this lower hydrate the sulphuric acid was 
also estimated, being thrown down as barium sulphate after removal of 
the thoria : 



*Arch. Sci. Phys. et Nat. (2), 18, 343. 



206 THE ATOMIC WEIGHTS. 

1.2425 grm. gave .400 SO 3 . (1.1656 grm. BaSO 4 .) 

1.138 " .366 " (1.0665 " ) 

.734 .2306 ( .6720 ) 

The figures in parentheses are reproduced by myself from Delafon- 
taine's results, he having calculated his analyses with O = 100, S = 200, 
and Ba = 857. These data may be reduced to a common standard, so 
as to represent the quantity of 2Th(S0 4 ) 2 .9H 2 0, equivalent to 100 parts 
of BaS0 4 . We then have the following results : 

106.597 
106.704 
109.226 



Mean, 107.509, .585 



Delafontaine was soon followed by Hermann,* who published a single 
analysis of the lower hydrated sulphate, as follows : 

Th0 2 52.87 

S0 3 32.11 

H 2 15.02 



IOO.OO 

Hence, from the ratio between S0 3 and Th0 2 , Th0 2 = 262.286. Prob- 
ably the S0 3 percentage was loss upon calcination. 

Both Hermann's results and those of Delafontaine are affected by one 
serious doubt, namely, as to the true composition of the lower hydrated 
sulphate. The latest and best evidence seems to establish the fact that 
it contains four molecules of water instead of four and a half,f a fact 
which tends to lower the resulting atomic weight of thorium consid- 
erably. In the final discussion of these data, therefore, the formula 
Th(S0 4 ) 2 .4H 2 will be adopted. As for Hermann's single analysis, his 
percentage of Th0 2 , 52.87, may be included in one series with Delafon- 
taine's, giving a mean of 52.535, .0473. 

The next determinations to consider are those of Cleve,J whose results, 
obtained from both the sulphate and the oxalate of thorium, agree ad- 
mirably. The anhydrous sulphate, calcined, gave the subjoined per- 
centages of thoria : 

62.442 

62.477 

62.430 

62.470 

62.357 
62.366 

Mean, 62.423, .014 

* Journ. fur Prakt. Chetn., 93, 114. 

t See Hillebrand, Bull. 90, U. S. Geol. Survey, p. 29. 

I K. Sveuska Vet. Akad. Handling., Bd. 2, No. 6, 1874. 



THORIUM. 207 

The oxalate was subjected to a combustion analysis, whereby both 
thoria and carbonic acid could be estimated. From the direct percentages 
of these constituents no accurate value can be deduced, there having 
undoubtedly been moisture in the material studied. From the ratio 
between C0 2 and Th0 2 , however, good results are attainable. This ratio 
I put in a fourth column, making the thoria proportional to 100 parts of 
carbon dioxide : 

Oxalate. ThO^. CO.,. Ratio. 

I -7 I 35 S rm - 1.0189 grm. .6736 grm. 151.262' 

1.3800 " .8210 " .5433 " 151.114 

1.1850 " .7030 " -4650 " 151.183 

1.0755 " .6398 " .4240 " 150.896 



Mean, 151.114, .053 

Iii 1882, Nilson's determinations appeared.* This chemist studied 
both the anhydrous sulphate, and the salt with nine molecules of water, 
using the usual calcination method, but guarding especially against the 
hygroscopic character of the dry Th (SOJ 2 and the calcined Th0 2 . The 
hydrated sulphate gave results as follows : 



Percent. ThO.,. 



2.0549 .9267 45.097 

2.1323 .9615 45-092 

3.0017 1.3532 45-081 

2.7137 1.2235 45-086 

2.6280 1.1849 45.088 

1.9479 .8785 45.. 099 

Mean, 45.091, .0019 
Delafontaine found, 45.062, it .0332 



General mean, 45.090, .0019 

The anhydrous sulphate gave data as follows : 

Th(SO^. ThO v Percent. 

1.4467 -9013 62.300 

1.6970 1.0572 62.298 

2.0896 1.3017 62.294 

1.5710 .9787 62.298 



Mean, 62.297, =b .0009 

The last four determinations appear again in a paper published five 
years later by Kriiss and Nilson,f who, however, give four more made 



*Ber. Deutsch. Chem. Gesell., 15, 2519. 1882. 
f Ber. Deutsch. Chem. Gesell., 20, 1665. 1887. 



208 THE 'ATOMIC WEIGHTS. 

upon material obtained from a different source. The new data are sub- 
joined : 

Th(SOJ v ThO 2 . Percent. ThO.,. 

1.1630 .7245 62.296 

.8607 .5362 62.298- 

1.5417 .9605 62.301 

1.5217 .9479 62.292 

Mean, 62.297, .0013 

Nilson's series, 62.297, .0009 

Cleve found, 62.423, zb .0140 



General mean, 62.298, .0007 

From Chydenius' work we have four values for the molecular weight 
of thoria, which, combined as usual, give a general mean of Th0 2 = 
265.103, db .3394. We also have the following ratios : 

(I.) 2BaSO 4 : ThO 2 : : ZOO : 58.026, dz .214 

(2.) 2BaSO 4 : Th(SO 4 ) 2 .4H 2 O : : 100 : 107.509, .585 

(3.) 4CO 2 : ThO 2 :: 100 : 151.114, .053 

(4.) Percentage of ThO 2 in Th(SO 4 ) 2 .9H 2 O, 45.090, =b .0019 

(5.) Percentage of ThO 2 in Th(SO 4 ) 2 .4H 2 O, 52.535, .0473 

(6.) Percentage of ThO 2 in Th(SO 4 ) 2 .62.298, =h .0007 

Reducing with the following data, seven values for the atomic weight 
of thoria are calculable : 

O = 15.879, .0003 C = 11.920, .0004 

S = 31.828, .0015 Ba = 136.392, .0086 

The values for Th0 2 are 

Chydenius' determinations ThO 2 265.103, -3394 

From(i) =268.937, -9919 

From (2) " rr= 268.021, 2.7115 

From (3) " =264. 1 20, dr .0927 

From (4) " =262.641, .0149 

From (5) " = 255.061, .3426 

From (6) " =262.613, .0081 

General mean ThO 2 = 262.626, .0071 

Hence Th = 230.868, .0071. 
If = 16, Th = 232.626. 



PHOSPHORUS. 209 



PHOSPHORUS. 

The material from which we are to calculate the atomic weight of 
phosphorus is by no means abundant. Berzelius, in his Lehrbuch,* 
adduces only his own experiments upon the precipitation of gold by 
phosphorus, and ignores all the earlier work relating to the composition 
of the phosphates. These experiments have been considered with refer- 
ence to gold. 

Pelouze,t in a single titration of phosphorus trichloride with a stand- 
ard solution of silver, obtained a wholly erroneous result ; and Jacque- 
lain, J in his similar experiments, did even worse. Schrdtter's criticism 
upon Jacquelain sufficiently disposes of the latter. 

Only the determinations made by Schrotter, Dumas, and Van der 
Plaats remain to be considered. 

Schrotter || burned pure amorphous phosphorus in dry oxygen, and 
weighed the pentoxide thus formed. One gramme of P yielded P 2 3 in 

the following proportions : 

2.28909 
2.28783 
2.29300 
2.28831 
2.29040 
2.28788 
2.28848 
2.28856 
2.28959 
2.28872 

Mean, 2.289186, =h .60033 

Dumas ^| prepared pure phosphorus trichloride by the action of dry 
chlorine upon red phosphorus. The portion used in his experiments 
boiled between 76 and 78. This was titrated with a standard solution 
of silver in the usual manner. Dumas publishes weights, from which I 
calculate the figures given in the third column, representing the quantity 
of trichloride proportional to 100 parts of silver : 

1.787 grm. PC1 3 = 4.208 grm. Ag. 42.4667 

1.466 " 3.454 " 42.4435 

2.056 " 4.844 " 42.4443 

2.925 " 6.890 " 42.4528 

3.220 7.582 " 42.4690 

Mean, 42.4553, d= .0036 

*5th ed., 1188. 
fCompt. Rend., 20, 1047. 
J Compt. Rend., 33, 693. 
% Journ. fur Prakt. Cheni., 57, 315. 
|| Journ. fur Prakt. Chera., 53, 435. 1851. 
11 Ann. Chem. Pharm., 113, 29. 1860. 
14 



210 THE ATOMIC WEIGHTS. 

By Van der Plaats* three methods of determination were adopted, 
and all weights were reduced to vacuum standards. First, silver was 
precipitated from a solution of the sulphate by means of phosphorus. 
The latter had been twice distilled in a current of nitrogen. The silver, 
before weighing, was heated to redness. The phosphorus equivalent to 
100 parts of silver is given in the third column. 

.9096 grm. P gave 15.8865 Ag. 5-7 2 56 

.5832 " 10.1622 " 5.7389 

Mean, 5.7322, .0045 

The second method consisted in the analysis of silver phosphate ; but 
the process is not given. Van der Plaats states that it is difficult to be 
sure of the purity of this salt. 

6.6300 grm. Ag 3 PO 4 gave 5.1250 Ag. 77.3 P er cent. 

12.7170 " 9.8335 " 77.326 " 



Mean, 77.313, .0088 

In the third set of determinations, yellow phosphorus was oxidized by 
oxygen at reduced pressure, and the resulting P 2 5 was weighed. 

10.8230 grm. P gave 24.7925 P 2 O 5 . Ratio, 2 29072 

7.7624 I7-79 J 5 " " 2.29201 

As these figures fall within the range of Schrotter's, they maybe aver- 
aged in with his series, the entire set of twelve determinations giving 
a mean of 2.28955, .00032. 

From the following ratios an equal number of values for P may now 
be computed : 

(i.) 2P : P 2 O 3 : : l.o : 2.28955, .00032 
(2.) 3Ag : PC1 3 : : 100 : 42-4553, -0036 
(30 5 A S : p : : I0 : 5-7322, .0045 
(4.) Ag 3 PO 4 : 3Ag : : 100 : 77.313, .0088 

Starting with = 15.879, .0003, Ag = 107.108, .0031, and Cl = 
35.179, .0048, we have 

From (i) P = 30.784, =fc .0077 

From (2) " = 30.882, .0189 

From (3) " 30.698, =b .0241 

From (4) " = 30.774, .0382 



General mean P = 30.789, .0067 

If = 16, P = 31.024. 

The highest of these figures is that from ratio number two, represent- 
ing the work of Dumas. This is possibly due to the presence of oxy- 
chloride, in traces, in the trichloride taken. Such an impurity, if present, 
would tend to raise the apparent atomic weight of phosphorus. 

*Compt. Rend., 100, 52. 1885. 



VANADIUM. 211 



VANADIUM. 

Roscoe's determination of the atomic weight of vanadium was the first 
to have any scientific value. The results obtained by Berzelius * and by 
Czudnowicz f were unquestionably too high, the error being probably 
due to the presence of phosphoric acid in the vanadic acid employed. 
This particular impurity, as Roscoe has shown, prevents the complete 
reduction of V 2 O 5 to V 2 O 3 by means of hydrogen. All vanadium ores 
contain small quantities of phosphorus, which can only be detected with 
ammonium molybdate a reaction unknown in Berzelius' time. Fur- 
thermore, the complete purification of vanadic acid from all traces of 
phosphoric acid is a matter of great difficulty, and probably never was 
accomplished until Roscoe undertook his researches. 

In his determination of the atomic weight, Roscoe J studied two com- 
pounds of vanadium, namely, the pentoxide, V 2 O 5 , and the oxychloride, 
VOC1 3 . The pentoxide, absolutely pure, was reduced to V 2 O 3 by heating 
in hydrogen, with the following results : 

7-7397 g rm - V 2 O 5 gave 6.3827 grm. V 2 O 3 . 17-533 P er cent, of loss. 

6.5819 5-4296 " i7-57 

5-1895 4-2819 " 17.489 

5.0450 4.1614 " 17.515 

5. 4296 grm. V 2 O 3 , reoxidized, gave 6. 5814 grm. V 2 O 5 . 17.501 per cent, difference. 

Mean, 17.509, =b .005 

Hence V = 50.993, .0219. 

Upon the oxychloride, VOC1 3 , two series of experiments were made 
one volumetric, the other gravimetric. In the volumetric series the com- 
pound was titrated with solutions containing known weights of silver, 
which had been purified according to the methods recommended by 
Stas. Roscoe publishes his weighings, and gives percentages deduced 
from them ; his figures, reduced to a common standard, make the quan- 
tities of VOCL given in the third column proportional to 100 parts of 
silver. He was assisted by two analysts : 







Analyst A. 




2.4322 grm. 


VOC1 3 


= 4.5525 grm. Ag. 


53.425 


4.6840 


" 


8.7505 


53.528 


4.2188 


1 1 


7.8807 " 


53-533 


3-949 


" 


7-3799 


53-5'Q 


9243 


< < 


1.7267 


53-530 


1-4330 


" 


2.6769 


53.532 



* Poggend. Annal., 22, 14. 1831. 

t Poggend. Annal., 120, 17. 1863. 

t Journ. Chem. Soc., 6, pp. 330 and 344. 1868. 



212 THE ATOMIC WEIGHTS. 

Analyst B. 

2.853ogrm. VOCI 3 = 5.2853 grm. Ag. 53-98o 

2.1252 " 3-9535 " 53-755 

1.4248 " 2.6642 " 53-479 



Mean, 53.586, =b .039 

The gravimetric series, of course, fixes the ratio between VOC1 3 and 
AgCl. If we put the latter at 100 parts, the proportion of VOC1 3 is as 
given in the third column : 

Analyst A. 

1.8521 grm. VOC1 3 gave 4.5932 grm. AgCl. 40.323 

.7013 " 1.7303 " 40.53 1 

.7486 1.8467 " 40.537 

1.4408 3-57I9 " 40.337 

9453 2.3399 " 40.399 

1.6183 " 4.0282 " 40.174 

Analyst B. 

2.1936 grm. VOC1 3 gave 5.4039 grm. AgCl. 40.391 

2.5054 " 6.2118 " 40.333 



Mean, 40.378, b .028 

These two series give us two values for the molecular weight of VOC1 3 : 

From volumetric series . . VOC1 3 = 172.185, rb .1254 

From gravimetric series " = 172.358, .1196 



General mean VOC1 3 172.277, zfc .0866 

Hence V = 50.881, .0877. 

Combining the two values for V, we have : 

From VOC1 3 V = 50.881, .0877 

From V 2 O 5 " = 50.993, .0219 



General mean V = 50.986, .0212 

If = 16, V = 51.376. These values are calculated with = 15.879, 
.0003; Cl = 35.179, .0048; Ag = 107.108, .0031, and AgCl = 

142.287, .0037. 



ARSENIC. 213 



ARSENIC. 

For the determination of the atomic weight of arsenic three compounds 
have been studied the chloride, the trioxide, and sodium pyroarsenate. 
The bromide may also be considered, since it was analyzed by Wallace 
in order to establish the atomic weight of bromine. His series, in the 
light of more recent knowledge, may properly be inverted, and applied 
to the determination of arsenic. 

In 1826 Berzelius * heated arsenic trioxide with sulphur in such a way 
that only S0 2 could escape. 2.203 grammes of As 2 3 , thus treated, gave 
a loss of 1.069 of S0 2 . Hence As = 74.460. 

In 1845 Pelouzef applied his method of titration with known quan- 
tities of pure silver to the analysis of the trichloride of arsenic, AsCl 3 . 
Using the old Berzelian atomic weights, and putting Ag = 1349.01 and 
Cl = 443.2, he found in three experiments for As the values 937.9, 937.1, 
and 937.4. Hence 100 parts of silver balance the following quantities 

of AsCl s : 

56.029 

56.009 
56.016 

Mean, 56.018, .004 

Later, the same method was employed by Dumas, J whose weighings, 
reduced to the foregoing standard, give the following results : 

4.298 grm. AsCl 3 = 7.673 grm. Ag. Ratio, 56.015 

5.535 " 9.880 " " 56.022 

7.660 " 13.686 " " 55-97 

4-680 " 8.358 " " 55-993 

Mean, 56.000, -_h .008 

The two series of Pelouze and Dumas, combined, give a general mean 
-of 56.014, .0035, as the amount of AsCl 3 equivalent to 100 parts of 
silver. Hence As = 74.450, .019, a value closely agreeing with that 
deduced from the single experiment of Berzelius. 

The same process of titration with silver was applied by Wallace to 
the analysis of arsenic tribromide, AsBr 3 . This compound was repeatedly 
distilled to ensure purity, and was well crystallized. His weighings 
.show that the quantities of bromide given in the third column are pro- 
portional to 100 parts of silver : 

8.3246 grm. AsBr 3 = 8.58 grm. Ag. 97.023 

4.4368 " 4-573 " 97.022 

5.098 " 5.257 " 96.970 

Mean, 97.005, .012 

* Poggend. Annalen, 8, i. 
fCompt. Rend., 20, 1047. 
I Ann. Chim. Phys. (3), 55, 174. 1859. 
I Phil. Mag. (4), 18, 270. 



214 THE ATOMIC WEIGHTS. 

Hence As = 73.668, .0436. Why this value should be so much 
lower than that from the chloride is unexplained. 

The volumetric work done by Kessler.* for the purpose of establishing 
the atomic weights of chromium and of arsenic, is described in the 
chromium chapter. In that investigation the amount of potassium 
dichromate required to oxidize 100 parts of As. 2 O 3 to As 2 5 was determined 
and compared with the quantity of potassium chlorate necessary to pro- 
duce the same effect. From the molecular weight of KC10 3 , that of 
K 2 Cr 2 O 7 was then calculable. 

From the same figures, the molecular weights of KC10 3 and of K 2 Cr 2 
being both known, that of As 2 3 may be easily determined. The quan- 
tities of the other compounds proportional to 100 parts of As 2 3 are as- 

follows : 

A- 2 2 <9 7 . KCIO* 

98.95 4i.i5 6 

98.94 41.116 

99.17 41.200 

98.98 41-255 

99.08 41.201 

99.15 41.086 

41.199 

Mean, 99.045, .028 41.224 

41.161 

4M93 
41.149 
41.126 



Mean, 41.172, db .009 

Another series with the dichromate gave the following figures : 

99.08 
99.06 
99.10 
98.97 
98.97 



Mean, 99.036, .019 
Previous series, 99.045, =b .028 



General mean, 99.039, =h .016 

Other defective series are given to illustrate the partial oxidation of 
the As 2 3 by the action of the air. From Kessler's data we get two 
values for the molecular weight of As 2 O 3 , thus : 

From KC1O 3 series As 2 O 3 = 196.951, .0445 

From K 2 Cr 2 O 7 series " = 196.726, db .0562 

General mean As 2 O 3 = 196.851, =b .0349 

And As = 74.607, .0175. 

* Poggend Annal., 95, 204. 1855. Also 113, 134. 1861. 



ARSENIC. 215 

The determinations made by Hibbs* are based upon an altogether 
different process from any of the preceding measurements. Sodium 
pyroarsenate was heated in gaseous hydrochloric acid, yielding sodium 
chloride. The latter was perfectly white, completely soluble in water, 
unfused, and absolutely free from arsenic. The vacuum weights are 
subjoined, with a column giving the percentage of chloride obtained 
from the pyroarsenate. 

Na^As^O^. NaCl. Percentage. 

.02177 - OI 439 66. 100 

.04713 .03"5 ' 66.094 

.05795 .03830 66.091 

.40801 .26981 66.128 

.50466 -33345 66.092 

.77538 .51249 66.095 

.82897 .54791 66.095 

1.19124 .78731 66.092 

1.67545 1.10732 66.091 

3.22637 2.13267 66. 101 

Mean, 66.098, .0030 

Hence As = 74.340, .0235. 

In the calculation of the foregoing values for arsenic, the subjoined 
atomic weights have been assumed : 

O ---- 15.879, .0003 K = 38.817, .0051 

Ag 107.108, db .0031 Na = 22.881, .0046 

Cl =. 35.179, zb .0048 S = 31.828, ib. ooi 5 

Br = 79.344, -0062 Cr = 51.742, .0034 

To the single determination by Berzelius we may arbitrarily assign a 
weight equal to that of the result from Wallace's bromide series. The 
general combination is then as follows : 

From Berzelius' experiment As = 74.460, .0436 

" = 74.45> . OI 9 

" = 73.668, .0436 

From As 2 O 3 (Kessler) " = 74.607, .0175 

From Na 4 As 2 O 7 " = 74.340, db .0235 

General mean As 74.440, .0106 

If O = 16, As = 75.007. 

* Doctoral thesis, University of Pennsylvania, 1896. Work done under the direction of Professor 
E. F. Smith. In the fifth experiment the weight of NaCl is printed .33045. This is evidently a 
misprint, which I have corrected by comparison with the other data. The rejection of this ex- 
periment would not affect the final result appreciably. 



216 THE ATOMIC WEIGHTS. 



ANTIMONY. 

After some earlier, unsatisfactory determinations, Berzelius,* in 1826, 
published his final estimation of the atomic weight of antimony. He 
oxidized the metal by means of nitric acid, and found that 100 parts of 
antimony gave 124.8 of Sb 2 O 4 . Hence, if O 16, Sb = 129.03. The 
value 129 remained in general acceptance until 1855, when Kessler, f by 
special volumetric methods, showed that it was certainly much too high. 
Kessler's results will be considered more fully further along, in connec- 
tion with a later paper; for present purposes a brief statement of his 
earlierj conclusions will suffice. Antimony and various compounds of 
antimony were oxidized partly by potassium dichromate and partly by 
potassium chlorate, and from the amounts of oxidizing agent required 
the atomic weight in question was deduced : 

By oxidation of Sb 2 O 3 from 100 parts of Sb Sb = 123.84 

By oxidation of Sb with K 2 Cr 2 O 7 " 123.61 

By oxidation of Sb with KC1O 3 + K 2 Cr 2 O 7 " = 123.72 

By oxidation of Sb 2 O 3 with KC1O 3 + K 2 Cr 2 O 7 . . . " = 123.80 

By oxidation of Sb 2 S s with K 2 Cr 2 O 7 " = 123.58 

By oxidation of tartar emetic " = 1 19.80 

The figures given are those calculated by Kessler himself. A recalcu- 
lation with our newer atomic weights for O, K, Cl, Cr, S, and C would 
yield lower values. It will be seen that five of the estimates agree closely, 
while one diverges widely from the others. It will be shown hereafter 
that the concordant values are all vitiated by constant errors, and that 
the exceptional figure is after all the best. 

Shortly after the appearance of Kessler's first paper, Schneider J pub- 
lished some results obtained by the reduction of antimony sulphide in 
hydrogen. The material chosen was a very pure stibnite from Arnsberg, 
of which the gangue was only quartz. This was corrected for, and cor- 
rections were also applied for traces of undecom posed sulphide carried 
off mechanically by the gas stream, and for traces of sulphur retained 
by the reduced antimony. The latter sulphur was estimated as barium 
sulphate. From 3.2 to 10.6 grammes of material were taken in each ex- 
periment. The final corrected percentages of S in Sb 2 S 3 were as follows : 

28.559 
28.557 
28.501 

28.554 
28.532 

*Poggend. Aimalen, 8, i. 

tPoggend. Annalen, 95, 215. 

I Poggend. Annalen, 98, 293. 1856. Preliminary note in Bd. 97. 



ANTIMONY. 217 

28.485 
28.492 
28.481 



Mean, 28.520, db .008 

Hence, if S = 32, Sb = 120.3. 

Immediately after the appearance of Schneider's memoir, Rose* pub- 
lished the result of a single analysis of antimony trichloride, previously 
made under his supervision b} 7 Weber. This analysis, if Cl = 35.5, makes 
Sb = 120.7, a value of no great weight, but in a measure confirmatory of 
that obtained by Schneider. 

The next research upon the atomic weight of antimony was that of 
Dexter,f published in 1857. This chemist, having tried to determine 
the amount of gold precipitable by a known weight of antimony, and 
having obtained discordant results, finally resorted to the original method 
of Berzelius. Antimony, purified with extreme care, was oxidized by 
nitric acid, and the gain in weight was determined. From 1.5 to 3.3 
grammes of metal were used in each experiment. The reduction of the 
weights to a vacuum standard was neglected as being superfluous. From 
the data obtained, we get the following percentages of Sb in Sb. 2 4 : 

79.268 
73.272 

79-255 
79.266 

79-253 
79.271 
79.264 
79.260 
79.286 

79-274 
79.232 

79-395 
79-379 



Mean, 79.283, .009 

Hence, if = 16, Sb = 122.46. 

The determinations of Dumas J were published in 1859. This chemist 
sought to fix the ratio between silver and antimonious chloride, and ob- 
tained results for the atomic weight of antimony quite near to those of 
Dexter. The SbCl 3 was prepared by the action of dry chlorine upon 
pure antimony; it was distilled several times over antimony powder, 
and it seemed to be perfectly pure. Known weights of this preparation 
were added to solutions of tartaric acid in water, and the silver chloride 
was precipitated without previous removal of the antimony. Here, as 

* Poggend. Annalen, 98, 455. 1856. 
t Poggend. Annalen, 100, 363. 1857. 
I Ann. Chim. Phys. (3), 55, 175. 



218 THE ATOMIC WEIGHTS. 

Cooke has since shown, is a possible source of error, for under such 
circumstances the crystalline argento-antimoiiious tartrate may also be 
thrown down and contaminate the chloride of silver. But be that as it 
may, Dumas' weighings, reduced to a common standard, give as propor- 
tional to 100 parts of silver, the quantities of SbCl 3 which are stated in 
the third of the subjoined columns : 

i.876grm. SbCl 3 = 2.66o grm. Ag. 70.526 

4.336 " 6.148 " 70.527 

5.065 " 7.175 " 70.592 

3-475 4-93 " 70.487 

3.767 5.350 70.411 

5.910 " 8.393 " 70.416 

4.828 " 6.836 " 70.626 

Mean, 70.512, .021 

Hence, if Ag = 108, and Cl = 35,5, Sb = 122. 

In 1861 Kessler's second paper * relative to the atomic weight of an- 
timony appeared. Kessler's methods were somewhat complicated, and 
for full details the original memoirs must be consulted. A standard 
solution of potassium dichromate was prepared, containing 6.1466 
grammes to the litre. With this, solutions containing known quantities 
of antimony or of antimony compounds were titrated, the end reaction 
being adjusted with a standard solution of ferrous chloride. In some 
cases the titration was preceded by the addition of a definite weight of 
potassium chlorate, insufficient for complete oxidation ; the dichromate 
then served to finish the reaction. The object in view was to determine 
the amount of oxidizing agent, and therefore of oxygen, necessary for 
the conversion of known quantities of antimonious into antimonic com- 
pounds. 

In the later paper Kessler refers to his earlier work, and shows that 
the values then found for antimony were all too high, except in the case 
of the series made with tartar emetic. That series he merely states, and 
subsequently ignores, evidently believing it to be unworthy of further 
consideration. For the remaining series he points out the sources of 
error. These need not be rediscussed here, as the discussion would have 
no value for present purposes ; suffice it to say that in the series repre- 
senting the oxidation of Sb 2 s with dichromate and chlorate, the ma- 
terial used was found to be impure. Upon estimating the impurity and 
correcting for it, the earlier value of Sb = 123.80 becomes Sb = 122.36, 
according to Kessler's calculations. 

In the paper now under consideration four series of results are given. 
The first represents experiments made upon a pure antimony trioxide 
which had been sublimed, and which consisted of shining colorless 
needles. This was dissolved, together with some potassium chlorate, in 

*Poggend. Annalen, 113, 145. 1861. 



ANTIMONY. 219 

hydrochloric acid, and titrated with dichromate solution. Six experi- 
ments were made, but Kessler rejects the first and second as untrust- 
worthy. The data for the others are as follows : 

S 2 <9 3 . KCIO*. K.jCr.jO^ sol. in cc. 

1,7888 grm. .4527 grm. 19.200. 

1.6523 " .45 6 " 3-9 " 

3.2998 " .8806 " 16.5 " 

1.3438 " .3492 " 10.2 " 

From these figures Kessler deduces Sb = 122.16. 

These data, reduced to a common standard, give the following quanti- 
ties of oxygen needed to oxidize 100 parts of Sb 2 3 to Sb 2 O 5 . Each cubic 
centimetre of the K 2 Cr 2 7 solution corresponds to one milligramme of : 

10.985 
10.939 
10.951 
10.936 



Mean, 10.953, - OO 75 

In the second series of experiments pure antimony was dissolved in 
hydrochloric acid with the aid of an unweighed quantity of potassium 
chlorate. The solution, containing both antimonious and antimonic 
compounds, was then reduced entirely to the antimonious condition by 
means of stannous chloride. The excess of the latter was corrected with 
a strong hydrochloric acid solution of mercuric chloride, then, after 
diluting and filtering, a weighed quantity of potassium chlorate was 
added, and the titration with dichromate was performed as usual. Cal- 
culated as above, the percentages of oxygen given in the last column 
correspond to 100 parts of antimony: 

Sb. KClO y A" 2 O a <9 7 sol. cc. Per cent. O. 

1.636 grm. 0.5000 grm. 18.3 13.088 

3.0825 " 0.9500 " 30.2 i3-5 

4.5652 " 1.4106 " 45.5 13.098 



Mean, 13.079, .0096 

This series gave Kessler Sb = 122.34. 

The third and fourth series of experiments were made with pure 
antimony trichloride, SbCl 3 , prepared by the action of mercuric chloride 
upon metallic antimony. This preparation, in the third series, was dis- 
solved in hydrochloric acid, and titrated. In one experiment solid 
K 2 O 2 7 in weighed amount was added before titration; in the other two 
estimations KC10 3 was taken as usual. The third column gives the 
percentages of oxygen corresponding to 100 parts of SbCl 3 . 



220 THE ATOMIC WEIGHTS. 

Per cent. O. 

1.8576 grm. SbCl 3 needed .5967 grm. K 2 Cr 2 O 7 and 33.4 cc. sol. 7.0338 
1.9118 " .3019 " KC1O 3 " 16.2 " 7.0321 

4.1235 " .6801 " KC1O 3 " 23.2 " 7.0222 

Mean, 7.0294, .0024 

The fourth set of experiments was gravimetric. The solution of Sb01 3 
mixed with tartaric acid, was first precipitated by hydrogen sulphide, 
in order to remove the antimony. The excess of H 2 S was corrected by 
copper sulphate, and then the chlorine was estimated as silver chloride 
in the ordinary manner. 100 parts of AgCl correspond to the amounts 
of SbCl 3 given in the third column. 

1.8662 grm. SbCl 3 gave 3.483 grm. AgCl. 53-58o 

1.6832 3.141 " 53.588 

27437 5-IH5 " 53-677 

2.6798 5.0025 " 53.569 

5.047 9.411 53.629 

3.8975 " 7.2585 " 53.696 



Mean, 53.623, =b .015 

The volumetric series with'SbC! 3 gave Kessler values for Sb ranging 
from 121.16 to 121.47. The gravimetric series, on the other hand, yielded 
results from Sb = 124.12 to 124.67. This discrepancy Kessler rightly 
attributes to the presence of oxygen in the chloride; and, ingeniously 
correcting for this error, he deduces from both sets combined the value of 
Sb = 122.37. 

The several mean results for antimony agree so fairly w r ith each other, 
and with the estimates obtained by Dexter and Dumas, that we cannot 
wonder that Kessler felt satisfied of their general correctness, and of the 
inaccuracy of the figures published by Schneider. Still, the old series 
of data obtained by the titration of tartar emetic with dichromate con- 
tained no evident errors, and was not accounted for. This series,* if 
we reduce all of Kessler's figures to a single common standard, gives a 
ratio between K 2 Cr 2 7 and C 4 H 4 KSb0 7 .H 2 0. 100 parts of the former 
will oxidize of the latter : 

336.64 

338.01 

336.83 

337-93 

338.59 

335 ; 79 

Mean, 337.30, .29 

From this, if K,Cr 2 7 = 292.271, Sb = 118.024. 

The newer atomic weights found in other chapters of this work will 

*Poggend. Annalen, 95, 217. 



ANTIMONY. 221 

be applied to the discussion of all these series further along. It may, 
however, be properly noted at this point that the probable errors assigned 
to the percentages of oxygen in three of Kessler's series are too low. 
These percentages are calculated from the quantities of KC10 3 involved 
in the several reactions, and their probable errors should be increased 
with reference to the probable error of the molecular weight of that salt. 
The necessary calculations would be more laborious than the importance 
of the figures would warrant, and accordingly, in computing the final 
general mean for antimony, Kessler's figures will receive somewhat higher 
weight than they are legitimately entited to. 

Naturally, the concordant results of Dexter, Kessler, and Dumas led 
to the general acceptance of the value of 122 for antimony as against the 
lower figure, 120, of Schneider. Still, in 1871, linger * published the re- 
sults of a single analysis of Schlippe's salt, Na 3 SbS 4 .9H 2 0. This analysis 
gave Sb = 119.76. if S = 32 and Na = 23, but no great weight could be 
attached to the determination. It served, nevertheless, to show that the 
controversy over the atomic weight of antimony was not finally settled. 

More than ten years after the appearance of Kessler's second paper the 
subject of the atomic weight of antimony was again taken up, this time 
by Professor Cooke. His results appeared in the autumn of 1877 1 and 
were conclusive in favor of the lower value, approximately 120. For full 
details the original memoir must be consulted ; only a few of the leading 
points can be cited here. 

Schneider analyzed a sulphide of antimony which was already formed. 
Cooke, reversing the method, effected the synthesis of this compound. 
Known weights of pure antimony were dissolved in hydrochloric acid 
containing a little nitric acid. In this solution weighed balls of antimony 
were boiled until the liquid became colorless ; subsequently the weight 
of metal lost by the balls was ascertained. To the solution, which now 
contained only antimonious compounds, tartaric acid was added,* and 
then, with a supersaturated aqueous sulphhydric acid, antimony trisul- 
phide was precipitated. The precipitate was collected by an ingenious 
process of reverse filtration, converted into the black modification by 
drying at 210, and weighed. After weighing, the Sb. 2 S 3 was dissolved 
in hydrochloric acid, leaving a carbonaceous residue unacted upon. 
This was carefully estimated and corrected for. About two grammes of 
antimony were taken in each experiment and thirteen syntheses were 
performed. In two of these, however, the antimony trisulphide was 
weighed only in the red modification, and the results were uncorrected 
by conversion into the black variety and estimation of the carbonaceous 
residue. In fact, every such conversion and correction was preceded by 
a weighing of the red modification of the Sb,S 3 . The mean result of these 
weighings, if S 32, gave Sb = 119.994. The mean result of the cor- 

* Archiv. der Pharmacie, 197, 194. Quoted by Cooke. 
f Proc. Amer. Acad., 5, 13. 



222 THE ATOMIC WEIGHTS. 

reeled syntheses gave Sb = 120.295. In these eleven experiments the 
following percentages of S in Sb a S 3 were established : 

28.57 
28.60 
28.57 
28.43 
28.42 

28.53 
28.50 
28.49 
28.58 
28.50 
28.51 



Mean, 28.5182, =b .0120 

These results, confirmatory of the work of Schneider, were presented 
to the American Academy in 1876. Still, before publication, Cooke 
thought it best to repeat the work of Dumas, in order to detect the cause 
of the old discrepancy between the values Sb = 120 and Sb = 122. Ac- 
cordingly, various samples of antimony trichloride were taken, and puri- 
fied by repeated distillations. The final distillate was further subjected 
to several recrystallizations from the fused state ; or, in one case, from a 
saturated solution in a bisulphide of carbon. The portions analyzed 
were dissolved in concentrated aqueous tartaric acid, and precipitated 
by silver nitrate, many precautions being observed. The silver chloride 
was collected by reverse filtration, and dried at temperatures from 110 
to 120. In one experiment the antimony was first removed by H 2 S. 
Seventeen experiments were made, giving, if Ag = 108 and Cl = 35.5. a 
mean value of Sb = 121.94. If we reduce to a common standard, Cooke's 
analyses give, as proportional to 100 parts of AgCl, the quantities of SbCl s 
stated in the third column : 

i.5974grm. SbCl 3 gave 3.0124 grm. AgCl. 53.028 

1.2533 " 2.3620 " 53.061 

.8876 1.6754 52.978 

.8336 i 5 6 74 53-^4 

.5326 " i. 0021 " 53-H8 

.7270 " i.3 6 9 T " 53- T i 

1.2679 " 2.3883 " 53.088 

1.9422 3.6646 52.999 

1-7702 " 3-3384 " 53.025 

2.5030 4-7184 53.048 

2.1450 " 4.0410 " 53.081 

1.7697 " 3.3281 " 53.175 

2-3435 4.4157 53.072 

1.3686 " 2.5813 " 53-O2O 

1.8638 " 3-5'46 " 53.03 

2.0300 " 3.8282 " 53.028 

2.4450 " 4.6086 53.053 

Mean, 53 066, zfc .0096 



ANTIMONY. 



223 



This mean may be combined with that of Kessler's series, as follows : 

Kessler ............. ' ................ . ... 53.623, d= .015 

Cooke ............ ---- ............ ____ 53.o66, .0096 



General mean ................... 53.2311, .008 

The results thus obtained with SbCl 3 confirmed Dumas' determination 
of the atomic weight of antimony as remarkably as the syntheses of Sb 2 S 3 
had sustained the work of Schneider. Evidently, in one or the other 
series a constant error must be hidden, and much time was spent by 
Cooke in searching for it. It was eventually found that the chloride of 
antimony invariably contained traces of oxychloride, an impurity which 
tended to increase the apparent atomic weight of the metal under con- 
sideration. It was also found, in the course of the investigation, that 
hydrochloric acid solutions of antimonious compounds oxidize in the air 
during boiling as rapidly as ferrous compounds, a fact which explains 
the high values for antimony found by Kessler. 

In order to render "assurance doubly sure." Professor Cooke also 
undertook the analysis of the bromide and the iodide of antimony. The 
bromide, SbBr s , was prepared by adding the finely powdered metal to a 
solution of bromine in carbon disulphide. It was purified by repeated 
distillation over pulverized antimony, and by several recrystallizations 
from bisulphide of carbon. The bromine determinations resemble those 
of chlorine, and gave, if Ag = 108 and Br = 80, a mean value for anti- 
mony of Sb = 120. Reduced to a common standard, the fifteen analyses 
give the subjoined quantities of SbBr 3 proportional to 100 parts of silver 
bromide : 



1.8621 grm. SbBr 3 gave 2.9216 grm. AgBr. 



.9856 
1.8650 
1.5330 
1.3689 
1.2124 

.9417 
2.5404 
1.5269 
1.8604 
1.7298 
3-2838 
2.3589 
L3323 
2.6974 



1.5422 
2.9268 
2.4030 

2.1445 
1.8991 
1.4749 
3-9755 
2.3905 
2.9180 
2.7083 
5.1398 
3.6959 
2.0863 
4.2285 



63-736 
63.909 
63.721 
63.795 
63-833 
63841 
63.848 
63.901 
63-874 
63-756 
63.870 
63.890 
63.825 
63-859 
63-791 

Mean, 63.830, .008 



The iodide of antimony was prepared like the bromide, and analyzed 
in the same way. At first, discordant results were obtained, due to the 
presence of oxyiodide in the iodide studied. The impurity, however, 



224 



THE ATOMIC WEIGHTS. 



was removed by subliming the iodide in an atmosphere of dry carboi 
dioxide. With this purer material, seven estimations of iodine wei 
made, giving, if Ag = 108 and I = 127, a value for antimony of Sb = 120. 
Reduced to a uniform standard, Cooke's weighings give the following 
quantities of SbI 3 proportional to 100 parts of silver iodide : 

1.1877 grm. SbI 3 gave 1.6727 grm. Agl. 71.005 



.4610 

3.2527 
1. 8068 
1.5970 
2.3201 
3496 



.6497 



2.5389 
2.2456 



.4927 



70.956 
71.150 
71.165 
71.117 
71.071 
70.956 

Mean, 71.060, .023 



Although Cooke's work was practically conclusive, as between the rival 
values for antimony, his results were severely criticised by Kessler,* who 
evidently had read Cooke's paper in a very careless way. On the other- 
hand, Schneider published in Poggendorff 's Annalen a friendly review 
of the new determinations, which so well vindicated his own accuracy. 
In reply to Kessler, Cooke undertook still another series of experiments 
with antimony bromide,f and obtained absolute confirmation of his 
previous results. To a solution of antimony bromide was added a solu- 
tion containing a known weight of silver not quite sufficient to precipi- 
tate all the bromine. The excess of the latter was estimated by titration 
with a normal silver solution. Five analyses gave values for antimony 
ranging from 119.98 to 120.02, when Ag = 108 and Br = 80. Reduced 
to a common standard, the weights obtained gave the amounts of SbBr 
stated in the third column as proportional to 100 parts of silver : 

2.5032 grm. SbBr 3 = 2.2528 grm. Ag. 
2.0567 " 1.8509 
2.6512 " 2.3860 " 
3-353 " 2.9749 



2.7495 



2-4745 



111.115 
111.119 
111.115 
111.106 
111.113 

Mean, 1 11.114, .0014 



Schneider^ also, in order to more fully answer Kessler's objections, 
repeated his work upon the Arnsberg stibmte. This he reduced in hydro- 
gen as before, correcting scrupulously for impurities. The following 
percentages of sulphur were found : 

28.546 

28.534 
28.542 

Mean, 28 541, db .0024 

*Berichte d. Deutsch. Chem. Gesell., 12, 1044. 1879. 

f Amer. Journ. Sci. and Arts, May, 1880. Berichte, 13, 951. 

JJourn. fur Prakt. Chem. (2), 22, 131. 



ANTIMONY 



225 



These figures confirm his old results, and may be fairly combined with 
them and with the percentages found by Cooke, as follows : 

Schneider, early series 28.520, .008 

Schneider, late series 28.541, .0024 

Cooke 28.5182, .0120 



General mean 28.5385, =b .0023 



In 1881 Pfeifer * determined electrolytically the direct ratios between 
silver and antimony, and copper and antimony. With copper the fol- 
lowing data were obtained : 



G/ 



1.412 grm, 

1.902 

3.367 



Sb = 1.1008 Cu. 
1.4832 " 
2.6249 " 



Sb} : : IOO 
128.270 
128.236 
128.272 



If Cu = 63.6, Sb = 122.36. 
With silver he found 



5.925 grm. Sb= 15.774 Ag. 



6.429 
10.116 

4 865 
4.390 
9.587 
4.525 



17.109 
26.972 
13.014 
11.697 
25.611 
12.097 



Mean, 128.259, .0077 



Ag^ : Sb : \ 100 : ,r. 
37.562 
37-577 
37.506 
37.383 
37-531 
37.433 
37.406 

Mean, 37.485, d= .0198 



If Ag = 108, Sb == 121.45. 

The latter ratio was also determined by Popper, f several years after- 
wards. The two metals were precipitated simultaneously by the same 
current ; and in some experiments two portions of antimony were thrown 
down against one of silver. These are indicated in the subjoined table 
by suitable bracketing, and the ratio is given in the third column : 



Sb. 


Ag. 


Ratio. 


1.4856) 
1.4788 / 


3-9655 


37.463 
37.292 


2.OI2O | 
2.OO74 ) 
3.88821 

3.8903 


5-3649 
10.3740 


37.503 
37.417 
37.48o 

37.50 


4.1885 


11.1847 


37-455 
37-447 



* Ann. Chem. Pharm., 209, 161. 
t Ann. Chem., 233, 153. 



15 



226 THE ATOMIC WEIGHTS. 



gfig 37.507 

4.2752 j 37.545 

5.6860 1 37.460 

5.6901 / 37.487 

4.4117 11.8014 37.383 

4.9999 13.3965 37.322 

5.2409 14.0679 37.250 

Mean, 37.434, .0149 
Pfeifer found, 37.485, .0198 



General mean, 37.452, .0119 

If Ag = 108, Popper's figures give in mean Sb = 121.3. 

I am inclined to attach slight importance to these electrolytic data, 
for the reasons that it would be very difficult to ensure the absolute 
purity and freedom from occlusions of the antimony as weighed, or to 
guarantee that no secondary reactions had modified the ratios. 

The work done by Bongartz * in 1883 was quite different from any of 
the determinations which had preceded it. Carefully purified 'antimony 
was weighed as such, and then dissolved in a concentrated solution of 
potassium sulphide. From this, after strong dilution, antimony trisul- 
phide was thrown down by means of dilute sulphuric acid. After 
thorough washing, this sulphide was oxidized by hydrogen peroxide, by 
Classen's method, and the sulphur in it was weighed as barium sulphate. 
The ratio measured, therefore, was 2Sb : 3BaS0 4 , and the data were as 
follows. The BaS0 4 equivalent to 100 parts of Sb is the ratio stated : 

Sb Taken. BaSO Found. Ratio. 

1.4921 4.3325 290.362 

.6132 1.7807 290.394 

.5388 1.5655 290.553 

T.2II8 3.5205 290.518 

.9570 2.7800 290.491 

.6487 1.8855 290.349 

.7280 2. 1 100 289.835 

9535 2.7655 290.036 

I.O275 2.9800 290.024 

.9635 2.7980 290.399 

.9255 2.6865 290.275 

.7635 2.2175 290.438 



Mean, 290.306, .0436 

We have now before us the following ratios, good and bad, from which 
to calculate the atomic weight of antimony. The single results obtained 
by Weber and by Unger, being unimportant, are not included : 

* Ber. Deutsch. Chem. Gesell., 16, 1942. 1883. 



ANTIMONY. 227 

(i.) Percentage of S in Sb 2 S 3 , 28.5385, .0023 

(2.) Percentage of Sb in Sb 2 O 4 , 79.283, .009 

(3.) O needed to oxidize 100 parts SbCJ 3 , 7.0294, .0024 

(4.) O needed to oxidize 100 parts Sb 2 O 3 , 10.953, -O75 

(5.) O needed to oxidize 100 parts Sb, 13.079, Hh .0096 

(6.) K 2 Cr 2 O 7 : tartar emetic : : 100 : 337.30, .29 

(7-) A Ss ' SbCl 3 : : 100 : 70.512, .021 

(8.) 3AgCl : SbG 3 : : 100 : 53.2311, .008 

(9-) A 3 ' SbBr 3 : : loo : 111.114, .0014 

(10.) 3AgBr : SbBr 3 : : loo : 63.830, .008 

(11.) 3AgI : SbI 3 : : 100 : 71.060, .023 

(12.) Cu 3 : Sb 2 : : 100 : 128.259, .0077 

( T 3-) A 3 = Sb : : 100 : 37.452, .0119 

(14.) Sb 2 : 3BaSO 4 : : 100 : 290.306, rb .0436 

In the reduction of these ratios a considerable number of antecedent 
atomic weights are required, thus : 

= 15.879, + .0003 C = 11.920, .0004 
Ag = 107.108, .0031 Cu = 63.119, .0015 
cl =:: 35-179, .0048 Ba = 136.392, .0086 
Br == 79-344, .0062 Cr = 51.742, .0034 

1 = 125.888,^.0069 AgCl = 142.287, .0037 
K = = 38.817, .0051 AgBr=r 186.452, .0054 
S ;= 31.828,^.0015 Agl =232.996,^3.0062 

Three of the ratios give the molecular weight of antimony trichloride, 
and two give corresponding values for the bromide. These values may 
be combined, as follows : First, for the chloride 

From (3) SbCl 3 = 225.894, .0771 

From (7) , " = 226.572, .0678 

From (8) " = 227.223, dr .0347 



General mean SbCl 3 = 226.924, .0286 

Hence Sb = 121.387, dr .0321. 
For the bromide we have 

From (9) r. SbBr 3 357.036, .0113 

From ( 10) " = 357.037, .0250 



General mean SbBr 3 = 357.036, .0103 

Hence Sb = 119.005, .0212. 

All the data yield eleven values for antimony, which are arranged 
below in the order of their magnitude : 



228 THE ATOMIC WEIGHTS. 

1. From tartar emetic, ratio (6) Sb = 118.024, .2827 

2. From SbBr 3 " = 119.005, d= .0212 

3. From SbI 3 , ratio (i i ) "= 119.037, .1626 

4. From Sb 2 S 3 , ratio (i) " = 119.548, .0069 

5. From ratio (14) " = 119.737, .0188 

6. From ratio (13) " = 120.342, .0384 

7. From ratio (4) " = 121.155, .1000 

8. From SbCl 3 " =. 121.387, .0321 

9. From ratio (5) " 121.408, .0891 

10. From ratio (12) " = 121.434, .0078 

11. From Sb 2 O 4 , ratio (2) u = 121.542, .0546 



General mean Sb = 120.299, zb .0047 

If = 16, this becomes Sb = 121.218. 

Among these figures the discordance is so great that the mathematical 
combination has no real value. We must base our judgment in this case 
mainly upon chemical evidence, and this, as shown in the investigations 
of Cooke and of Schneider, favors a lower rather than a higher value for 
the atomic weight of antimony. Dumas' work was affected by constant 
errors which are now known, and Dexter's data are also presumably in 
the wrong. A general mean of values 2, 3, 4, and 5 gives Sb = 119.521, 
.0062, or, if = 16, Sb = 120.432. Even now the range of uncertainty 
is greater than it should be, but none of the four values combined can 
be accepted exclusively or rejected without more evidence. This result, 
therefore, should be adopted until new determinations, of a more con- 
clusive nature, have been made. 



BISMUTH. 229 



BISMUTH. 

Early in the century the combining weight of bismuth was approxi- 
mately fixed through the experiments of Lagerhjelm.* Effecting the 
direct union of bismuth and sulphur, he found that ten parts of the metal 
yield the following quantities of trisulphide : 

12.2520 
12.2065 
12.2230 
12.2465 



Mean, 12.2320 

Hence Bi = 215 in round numbers, a value now known to be much too 
high. Lagerhjelm also oxidized bismuth with nitric acid, and, after igni- 
tion, weighed the trioxide thus formed. Ten parts of metal gave the 
following quantities of Bi 2 3 : 

11.1382 
11.1275 

Mean, 11.13285 

Hence, if = 16, Bi = 211.85, a figure still too high. 

In 1851 the subject of the atomic weight of bismuth was taken up by 
Schneider,f who, like Lagerhjelm, studied the oxidation of the metal 
with nitric acid. The work was executed with a variety of experimental 
refinements, by means of which every error due to possible loss of mate- 
rial was carefully avoided. For full details the original paper must be 
consulted ; there is only room in these pages for the actual results, as 
follows. The figures represent the percentages of Bi in Bi 2 O 3 : 

89.652 
89.682 
89.644 
89.634 
89.656 
89.666 
89-655 
89-653 



Mean, 89.6552, .0034 

Hence, if = 16, Bi = 208.05. 

Next in order are the results obtained by Dumas. J Bismuth tri- 

* Annals of Philosophy, 4, 358. 1814. Adopted by Berzelius. 
t Poggend. Annalen, 82, 303. 1851. 
I Ann. Chitn. Phys. (3), 55, 176. 1859. 



230 THE ATOMIC WEIGHTS. 

chloride was prepared by the action of dry chlorine upon bismuth, and 
repeatedly rectified by distillation over bismuth powder. The product 
was weighed in a closed tube, dissolved in water, and precipitated with 
sodium carbonate. In the filtrate, after strongly acidulating with nitric 
acid, the chlorine was precipitated by a known amount of silver. The 
figures in the third column show the quantities of BiCl 3 proportional to 
100 parts of silver : 

98.90x3 

9 8 -373 
98.005 
97.829 

97.99 6 
97.806 

97.643 
97.712 
97.762 






3.506 grm. BiC 


H 3 = 3.545 g rm 


. Ag. 


1.149 " 


1.168 


i < 


1.5965 


1.629 


" 


2.1767 


2.225 


( ( 


3.081 


3-H4 


" 


2.4158 


2.470 


it 


1.7107 


I-75 2 


n 


3.523 


3-6055 


i < 


5.241 


5.36i 


" 



- Mean, 98.003, .090 

Hence, with Ag = 108 and Cl = 35.5, Bi = 211.03. 

The first three of the foregoing experiments were made with slightly 
discolored material. The remaining six percentages give a mean of 
97.791, whence, on the same basis as before, Bi = 110.79. Evidently 
these results are now of slight value, for it is probable that the chloride of 
bismuth, like the corresponding antimony compound, contained traces 
of oxy chloride. This assumption fully accounts for the discordance be- 
tween Dumas' determination and the determinations of Schneider and 
of still more recent investigators. 

In 1883 Marignac * took up the subject, attacking the problem by two 
methods. His point of departure was commercial subnitrate of bismuth, 
which was purified by re-solution and reprecipitation, and from which 
he prepared the oxide. First, bismuth trioxide was reduced by heating 
in hydrogen, beginning with a moderate temperature and closing the 
operation at redness. The results were as follows, with the percentage 
of Bi in Bi 2 3 added : 

2.6460 grm. Bi. 2 O 3 lo^t 0.2730 grm. O. 89.683 per cent. 

6.7057 " .6910 " 89.696 " 

3.6649 " .3782 " 89.681 " 

5.8024 " .5981 " 89.692 " 

5.1205 " .5295 " 89.658 " 

5.5640 .5742 " 89.680 " 

Mean, 89.682, i: .0036 

Hence, if = 16, Bi = 208.60. 

*Arch. Sci. Phys. et Nat. (3), 10, 10. 



BISMUTH. 231 

Marignac's second method of determination was by conversion of the 
oxide into the sulphate. The oxide was dissolved in nitric acid, and 
then sulphuric acid was added in slight excess from a graduated tube. 
The mass was evaporated to dryness with great care, and finally heated 
over a direct flame until fumes of S0 3 no longer appeared. The third 
column gives the sulphate formed from 100 parts of oxide : 

2.6503 Bi 2 O 3 gave 4.0218 Bi 2 (SO 4 ) 3 . Ratio, 151.749 

2.8025 4.2535 " " 151.775 

2.710 4.112 " " I5L734 

2.813 " 4- 26 7 " " 151.688 

2.8750 4.3 62 5 " ". I5I-739 

2.7942 " 4-2383 " " 151.682 



Mean, 151.728, .0099 

Hence, with O = 16 and S = 32.06, Bi = 208.16. 

This result needs to be studied in the light of Bailey's observation,* 
that bismuth sulphate has a very narrow range of stability. It loses the 
last traces of free sulphuric acid at 405, and begins to decompose at 418, 
so that the foregoing ratio is evidently uncertain. The concordance of 
the data, however, is favorable to it. 

The next determination of this atomic weight was by L6we,f who 
oxidized the metal with nitric acid, and reduced the nitrate to oxide by 
ignition. Special care was taken to prepare bismuth free from arsenic, 
and the oxide was fused before weighing. In the paper just quoted 
Bailey calls attention to the volatility of bismuth oxide, which doubt- 
less accounts for the low results found in this investigation. The data 
are as follows : 

Bi Taken. Bi^O^ Found. Per cent. Bi. 

11.309 12.616 89.640 

12.2776 !3'694 89.656 



Mean, 89.648, .0040 

Hence, if = 16, Bi = 207.84. 

In Classen's J work upon the atomic weight of bismuth, the metal 
itself was first carefully investigated. Commercial samples, even those 
which purported to be pure, were found to be contaminated with lead 
and other impurities, and these were not entirely removable by many 
successive precipitations as subnitrate. Finally, pure bismuth was ob- 
tained by an electrolytic process, and this was converted into oxide by 
means of nitric acid and subsequent ignition to incipient fusion. Results 
as follows, with the percentage of Bi in Bi 2 O 3 added : 

* Journ. Chem. Soc., 51, 676. 
tZeit. Anal. Chem., 22, 498. 
\ Ber. Deutsch. Chem. Gesell., 23, 938. 1890. 



232 THE ATOMIC WEIGHTS. 

Bi Taken. Bi^O z Found. Per cent. Bi. 

25.0667 27.9442 89.703 

21.0691 23.4875 89.7035 

27.2596 30.3922 89.693 

36.5195 40.713^ 89.700 

27.9214 3H295 89.6944 

32.1188 35-8103 89.692 

30.1000 33.5587 89.694 

26.4825 59.5257 89.693 

19.8008 22.0758 89.695 



Mean, 89.696, .0009 

Hence, if == 16, Bi = 208.92, or, reduced to vacuum standards, 208.90. 

Classen's paper was followed by a long controversy between Schneider 
and Classen,* in which the former upheld the essential accuracy of the 
work done by Marignac and himself. Schneider had started out with 
commercial bismuth, and Classen found that the commercial bismuth 
which he met with was impure. Schneider, by various analyses, showed 
that other samples of bismuth were so nearly pure that the common 
modes of purification were adequate ; but Classen replied that the original 
sample used by Schneider in his atomic weight investigation had not 
been reexamined. Accordingly, Schneider published a new series of 
determinations f made by the old method, but with metal which had 
been scrupulously purified. Results as follows : 

Bi. Bi^. Percent. Bi. 

5.0092 5.5868 89.661 

3.6770 4.1016 89.648 

7.2493 8.0854 89.659 

9.2479 10.3142 89.662 

6.0945 6.7979 89.653 

12.1588 13.5610 89.660 



Mean, 89.657, .0015 

Hence with O = 16, Bi = 208.05, a confirmation of the earlier deter- 
minations. 

Although the results so far are not final, a combination of the data 
relative to bismuth oxide is not without interest. 

1. Lagerhjelm .......................... 89.865, db .0650 

2. Schneider, 185 1 ................. ..... 89.655, =b .0034 

3. Marignac ............................ 89.682, .0036 

4. Lowe ............................... 89.648, .0040 

5. Classen ........................... 89. 696, .0009 

6. Schneider, 1894 ...................... 89.657, .0015 



General mean 89.681, rb .0007 



* Journ. fiir Prakt. Chem. (2), 42, 553 ; 43, 133 ; and 44, 23 and 411. 
t Journ. fiir Prakt. Chem. (2), 50, 461. 1894. 



BISMUTH. 233 

Omitting the first and fifth means, the other data give a general mean 
percentage of 89.659, .0012. 

The ratios now before us are as follows : 

(I.) Percentage of Hi in Bi 2 O 3 , 89.681, .0007 
(2.) Bi 2 O 3 : Bi 2 (SO 4 ) 3 : : 100 : 151.728, .0099 
13.) 3Ag : BiCl 3 : : 100 : 98.003, .090 

For computation we have 

O = 15.879, =b .0003 Ag = 107. 108, zh .0031 

8=31.828,^.0015 Cl = 35.179, .0048 

Hence, reducing the ratios 

From (i) Bi = 207.003, .0150 

From (2) .... " = 206.613, -444 

From (3) " = 209.370, .2847 

General mean Bi = 206.971, =b .0142 

If O = 16, Bi = 208.548. 

Classen's data alone give Bi = 207.389, or, with = 16, 208.969. 
Omitting this set of determinations and rejecting Dumas', the remaining 
data give 

From Bi 2 O 3 Bi 206.512, .0244 

From Bi 2 (SO 4 ) 3 " = 206.613, .0444 



General mean Bi = 206.536, .0214 

If = 16, this becomes Bi = 208.11. Between this figure and Classen's, 
future investigation must decide. The confirmation afforded by the 
sulphate series is in favor of the lower value. 



234 THE ATOMIC WEIGHTS. 



COLUMBIUM.* 

The atomic weight of this metal has been determined by Rose, Her- 
mann, Blomstrand, and Marignac. Rosef analyzed a compound which 
he supposed to be chloride, but which, according to Rammelsberg, J must 
have been nearly pure oxychloride. If it was chloride, then the widely 
varying results give approximately Cb = 122 ; if it was oxychloride, the 
value becomes nearly 94. If it was chloride, it was doubtless contami- 
nated with tantalum compounds. 

Hermann's results seem to have no present value, and Blomstrand's || 
are far from concordant. The latter chemist studied columbium penta- 
chloride and sodium columbate. In the first case he weighed the colum- 
bium as columbium pentoxide, and the chlorine as silver chloride, the 
oxide being determined by several distinct processes. In some cases it 
was thrown down by water, in others by sulphuric acid, and in still 
others by sodium carbonate or ammonia jointly with sulphuric acid. The 
weights given are as follows : 



Cb.,0,. AgCl. 

591 -294 ..... 

.8085 .401 2.085 

633 .317 ..... 

.195 .0974 .500 

.507 .2505 1.302 

.9415 -472 2.454 

.563 .2796 ..... 

.9385 .4675 2.465 

.4788 .2378 

.408 .204 1.067 

9065 .45 1 5 

Hence the subjoined percentages, and the ratios 5AgCl : CbCl 5 : : 100 : x, 
and 5 AgCl : Cb 2 O 5 : : 100 : x. 



Percent. C6 2 <9 5 . 


AgCl : CbCl,. 


AgCl : Ct>,0,. 


40 788 






T"-7 / 

49.598 


38-777 


19.233 


50.079 







49-949 


39.000 


19-435 


49.408 


38.940 


19.240 


50.135 


38.366 


19-234 



*This name has priority over the more generally accepted " niobium," and therefore deserves 
preference. 

fPoggend. Annal., 104, 439. 1858. 
JPoggend. Annal., 136,353. r86g. 
I Journ. fiir Prakt. Chem., 68, 73. 1856. 
| Acta Univ. Lund. 1864. 



COLUMBIUM. 235 

49.662 ...... ...... 

49.813 38-073 18.966 

49.666 ...... ...... 

50.000 3 8 -238 19.119 

49.807 



Mean, 49.806, zh .045 Mean, 38.566, .108 Mean, 19.205, .043 

From these means the atomic weight of columbium may be computed, 
thus: 

From 2CbCl 5 : Cb 2 O 5 ........................ Cb 95.397 

From CbCl 5 : 5AgCl ........................ ";== 98.477 

From 5 AgCl : Cb 2 O 5 ........................ = 96.933, 

when == 15,879, Ag = 107.108, and Cl = 35.179. 

The series upon sodium columbate, which salt was decomposed with 
sulphuric acid, both Cb 2 5 and Na 2 S0 4 being weighed, is too discordant 
for discussion. The exact nature of the salt studied is not clear, and the 
data given, when transformed into the ratio Na 2 SO 4 : Cb 2 6 : : 100 : a;, give 
values for x ranging from 151.65 to 161.20. Further consideration of this 
series would therefore be useless. It seems highly probable that Blom- 
strand's materials were not entirely free from tantalum, however, since 
the atomic weight of columbium derived from his analyses of the chloride 
are evidently too high. 

Marignac* made about twenty analyses of the potassium nuoxy colum- 
bate, CbOF 3 .2KF.H 2 O. 100 parts of this salt give the following percent- 
ages : 

Cb 2 O 5 ............ Extremes 44.15 to 44.60 Mean, 44.36 

K 2 SO,... ......... 57.60-58.05 

H 2 ............. " 5.75 " 5.98 

F ................ " 30.62 " 32.22 

From the mean percentage of Cb 2 O 5 , Cb = 92.852. If = 16, this 
becomes 93.56. 

From the mean between the extremes given for K 2 S0 4 , Cb = 93.192. 
If = 16, this becomes 93.90. 

As Beville ami Troost'sf results for the vapor density of the chloride 
and oxychloride agree fairly well with Cb = 94, we may adopt this value 
as approximately correct. The mean of the two values computed from 
Marignac's data is 93.022 when H = 1, and 93.73 when == 16. 

* Arch. Sci. Phys. Nat. (2), 23. 1865. 
f Compt. Rend., 56, 891. 1863. 



236 THE ATOMIC WEIGHTS. 



TANTALUM. 

The results obtained for the atomic weight of this metal by Berzelius,* 
Rose,f and Hermann J may be fairly left out of account as valueless. 
These chemists could not have worked with pure preparations, and their 
data are sufficiently summed up in Becker's " Digest." 

Blomstrand's determinations, as in the case of columbium, were 
made upon the pentachloride. His weights are as follows : 



Ta. 2 Or,. AgCl. 

.9808 .598 ...... 

1.4262 .867 2.906 

2.5282 1.5375 5.0105 

1.0604 . 6 455 2.156 

2.581 i.577 ...... 

8767 -534 

Hence the subjoined percentages of Ta 2 5 from TaCl 5 , and the ratios 
SAgCl : TaCl 5 : : 100 : x, and 5AgCl : Ta 2 5 : : 100 : x. 

Percent. Ta,O 5 . AgCl : TaCl y AgCl : Ta,O- . 

60.971 ...... f ...... 

60.791 49. 78 29.835 

60.814 50.458 30685 

60.873 49.297 29.940 

60.960 ...... ...... 

60.924 ...... 



Mean, 60.889, .0208 49-6ir, =b .289 30.153, dr .180 

From these ratios we get for the atomic weight of tantalum : 

From per cent. Ta 2 O 5 Ta = 172.342 

From 5AgCl : TaCl 5 ; " = 177.055 

From 5 AgCl : Ta 2 O 5 " =174.821 

These results are too low. Probably Blomstrand's material still con- 
tained some columbium. 

In 1866 Marignac's determinations appeared. || He made four analyses 
of a pure potassium fluotantalate, and four more experiments upon the 
ammonium salt. The potassium compound, K 2 TaF 7 , was treated with 
sulphuric acid, and the mixture was then evaporated to dryness. The 
potassium sulphate was next dissolved out by water, while the residue 

* Poggend. Annalen, 4, 14. 1825. 

f Poggend. Annalen, 99, 80. 1856. 

1 Journ. fur Prakt. Chem., 70, 193. 1857. 

g Acta Univ. I^und, 1864 

|| Arch. Sci. Phys. Nat. (2), 26, 89. 1866. 



TANTALUM. 



237 



was ignited and weighed as Ta 2 5 . 100 parts of the salt gave the follow- 
ing quantities of Ta 2 O 5 and K 2 S0 4 : 






56.50 
56.75 
56.55 
56.56 

Mean, 56.59, .037 



44-37 
44-35 
44.22 
44.24 



Mean, 44.295, .026 



From these figures, 100 parts of K 2 S0 4 correspond to the subjoined 
quantities of Ta 2 5 : 

127.338 
127.960 
128.178 
127.848 

Mean, 127.831, .120 

The ammonium salt, (NH 4 ) 2 TaF 7 , ignited with sulphuric acid, gave 
these percentages of Ta 2 O 5 . The figures are corrected for a trace of K 2 SO 4 
which was always present : 

63.08 

63.24 

63.27 

63.42 

Mean, 63.25, .047 

Hence we have four values for Ta : 

From potassium salt, per cent. Ta 2 O 5 Ta = 182.336 

From potassium salt, per cent. K 2 SO 4 " 180.496 

From potassium salt, K 2 SO 4 : Ta 2 O 5 " 181.422 

From ammonium salt, per cent. Ta 2 O 5 " = 181.559 

Average Ta = 181.453 



'Or, if = 16, Ta = 182.836. 
These values are computed with O 
N = 13.935, and F = 18.912. 



15.879, K = 38.817, S = 31.828, 



238 THE ATOMIC WEIGHTS. 



CHROMIUM. 

Concerning the atomic weight of chromium there has been much dis- 
cussion, and many experimenters have sought to establish the true 
value. The earliest work upon it having any importance was that of 
Berzelius,* in 1818 and 1826, which led to results much in excess of the 
correct figure. His method consisted in precipitating a known weight 
of lead nitrate with an alkaline chromate and weighing the lead chro- 
mate thus produced. The error in his determination arose from the fact 
that lead chromate, except when thrown down from very dilute solu- 
tions, carries with it minute quantities of alkaline salts, and so has its 
apparent weight notably increased. When dilute solutions are used, a 
trace of the precipitate remains dissolved, and the weight obtained is too 
low. In neither case is the method trustworthy. 

In 1844 Berzelius' results were first seriously called in question. The 
figure for chromium deduced from his experiments was somewhat over 
56 ; but Peligot f now showed, by his analyses of chromous acetate and 
of the chlorides of chromium, that the true number was near 52.5. 
Unfortunately, Peligot's work, although good, was published with in- 
sufficient details to be useful here. For chromous acetate he gives the 
percentages of carbon and hydrogen, but not the actual weights of salt, 
carbon dioxide, and -water from which they were calculated. His figures 
vary considerably, moreover enough to show that their mean would 
carry but little weight when combined with the more explicit data fur- 
nished by other chemists. 

Jacquelain's work we may omit entirely. He gives an atomic weight 
for chromium which is notoriously too low (50.1), and prints none of the 
numerical details upon which his result rests. The researches which 
particularly command our attention are those of Berlin, Moberg, Lefort, 
Wildenstein, Kessler, Siewert, Baubigny, Rawson, and Meineke. 

Among the papers upon the atomic weight under consideration that 
by Berlin is one of the most important. His starting point was normal 
silver chromate; but in one experiment the dichromate Ag. 2 Cr,0 7 was 
used. These salts, which are easily obtained in a perfectly pure condi- 
tion, were reduced in a large flask by means of hydrochloric acid and 
alcohol. The chloride of silver thus formed was washed by decantation, 
dried, fused, and weighed without transfer. The united washings were 
supersaturated with ammonia, evaporated to dry ness, and the residue 
treated with hot water. The resulting chromic oxide was then collected 
upon a filter, dried, ignited, and weighed. The results were as follows : 

*Schweigg. Journ., 22, 53, and Poggend. Annal., 8, 22. 

fCompt. Rend., 19, 609, and 734; 20, 1187 ; 21, 74. 

I Compt. Rend., 24, 679. 1847. 

f Journ. fur Prakt. Chem., 37, 509, and 38, 149. 1846. 



CHROMIUM. 239 

4.6680 grm. Ag 2 CrO 4 gave 4.027 grm. AgCl and 1.0754 grm. Cr 2 O 3 . 
3.4568 " 2.983 " .7960 

2.5060 " 2.1605 " .5770 " 

2.1530 " 1.8555 " -4945 

4-3335 g rm - Ag 2 Cr 2 O 7 gave 2.8692 i.53 " 

From these weighings three values are calculable for the atomic weight 
of chromium. The three ratios upon which these values depend we will 
consider separately, taking first that between the chromic oxide and the 
original silver salt. In the four analyses of the normal chromate the 
percentages of Cr 2 3 deducible from Berlin's weighings are as follows : 




Mean, 23.014, =fc .on 

And from the single experiment with Ag 2 Cr 2 7 the percentage of Cr 2 O, 
was 35.306. 

For the ratio between Ag 2 Cr0 4 and AgCl, putting the latter at 100, we 
have for the former : 

115-917 
115.883 
115.992 
116.033 



Mean, 115.956, rb .023 

In the single experiment with dichromate 100 AgCl is formed from 
151.035 Ag. 2 Cr 2 O 7 . 

Finally, for the ratio between AgCl and Cr 2 3 , the five experiments of 
Berlin give, for 100 parts of the former, the following quantities of the 
latter : 

26.705 

26.685 

26.707 

26.650 

26.662 

Mean, 26.682, .0076 

These results will be discussed, in connection with the work of other 
investigators, at the end of this chapter. 

In 1848 the researches of Moberg* appeared. His method simply 
consisted in the ignition of anhydrous chromic sulphate and of am- 
monium chrome alum, and the determination of the amount of chromic 

* Journ. fi'ir Prakt. Cheni., 43, 114. 



240 THE ATOMIC WEIGHTS. 

oxide thus left as residue. In the sulphate, Cr 2 (S0 4 ) 3 , the subjoined per- 
centages of Cr 2 3 were found. The braces indicate two different sam- 
ples of material, to which, however, we are justified in ascribing equal 
value : 

.542 grm. sulphate gave .212 grm. Cr 2 O 3 . 39.114 per cent. ~\ 

1.337 " .523 " 39.117 " 

.5287 .207 " 39. 153 " 3 

1.033 .406 " 39o03 " ) 

.868 " .341 " 39-286 " 



Mean, 39.1946, .0280 

From the alum, NH 4 .Cr(S0 4 ) 2 .12H 2 0, we have these percentages of 
O 2 O 3 . The first series represents a salt long dried under a bell jar at a 
temperature of 18. The crystals taken were clear and transparent, but 
may possibly have lost traces of water,* which would tend to increase 
the atomic weight found for chromium. In the second series the salt was 
carefully dried between folds of filter paper, and results were obtained 
quite near those of Berlin. Both of these series are discussed together, 
neither having remarkable value: 

1.3185 grm. alum gave .213 grm. Cr 2 O 3 . 1 ^> 1 55 P er cent. 

.7987 " .129 " 1 6. 151 " 

1.0185 " .1645 " 16.151 " 

1.0206 .1650 " 16.167 " 

.8765 .1420 " 16.201 " 

.7680 " .1242 " 16.172 " 

1.6720 " .2707 " 16.190 " 

.5410 .0875 <( 16.174 

1.2010 " .1940 " T 6.i53 " 

i. ooio " .1620 " 16.184 " 

.7715 " .1235 " 16.007 

1.374 " .2200 " 16.012 " 



Mean, 16.143, .0125 

The determinations made by Lefortf are even less valuable than those 
by Moberg. This chemist started out from pure barium chromate, which, 
to thoroughly free it from moisture, had been dried for several hours at 
250. The chromate was dissolved in pure nitric acid, the barium thrown 
down by sulphuric acid, and the precipitate collected upon a filter, dried, 
ignited, and weighed in the usual manner. The natural objection to the 
process is that traces of chromium may be carried down with the sul- 
phate, thus increasing its weight. In fact, Lefort's results are somewhat 
too high. Calculated from his weighings, 100 parts of BaS0 4 correspond 
to the amounts of BaCr0 4 given in the third column : 



* This objection is suggested by Berlin in a note upon I v efort's paper. Journ. fur Prakt. Chem. 
71, 191. 
t Journ. fur Prakt. Chem., 51, 261. 1850. 



CHROMIUM. 241 

1.2615 g rm - BaCrO 4 gave 1.1555 g rm - BaSO 4 . 109.174 

1.5895 " L458o " 109.019 

2.3255 " 2.1340 108.974 

3.0390 2.7855 " 109.101 

2.3480 2.1590 " 108.754 

1.4230 1.3060 u 108.708 

I.I975 1.1005 108.814 

3.4580 " 3-1690 " 109.119 

2.0130 1.8430 " 109.224 

3.5570 " 3-2710 " 108.744 

1.6470 " 1.5060 " 109.363 

1.8240 1-6725 " 109.058 

1.6950 " 1.5560 " 108.933 

2.5960 " 2.3870 " 108.756 



Mean, 108.9815, .0369 

Wildenstein,* in 1853, also made barium chromate the basis of his 
researches. A known weight of pure barium chloride was precipitated 
by a neutral alkaline chromate, and the precipitate allowed to settle until 
the supernatant liquid was perfectly clear. The barium chromate was 
then collected on a filter, washed with hot water, dried, gently ignited, 
and weighed. Here again arises the objection that the precipitate may 
have retained traces of alkaline salts, and again we find deduced an 
atomic weight which is too high. One hundred parts BaCr0 4 correspond 



to BaCl 2 as follows : 



81.87 81.57 

81.80 81.75 
81.61 81.66 
81.78 81.83 
81.52 81.66 

81.84 81.80 

81.85 81.66 
81.70 81.85 
81.68 81.57 

81.54 81.83 
81.66 81.71 

81.55 81.63 

81.81 81.56 

81.86 81.58 
81.54 81.67 
81.68 81 84 



Mean, 81.702, .014 

Next in order we have to consider two papers by Kessler, who em- 
ployed a peculiar volumetric method entirely his own. In brief, he com- 
pared the oxidizing power of potassium dichromate with that of the 
chlorate, and from his observations deduced the ratio between the mo- 
lecular weights of the two salts. 



t Journ. fiir Prakt. Chem., 59, 27. 

16 



242 THE ATOMIC WEIGHTS. 

Iii his earlier paper* the mode of procedure was about as follows: 
The two salts, weighed out in quantities having approximate chemical 
equivalency, were placed in two small flasks, and to each was added 
100 cc. of a ferrous chloride solution and 30 cc. hydrochloric acid. The 
ferrous chloride was added in trifling excess, and, when action ceased, 
the amount unoxidized was determined by titration with a standard solu- 
tion of dichrpmate. As in each case the quantity of ferrous chloride was 
the same, it became easy to deduce from the data thus obtained the ratio 
in question. I have reduced all of his somewhat complicated figures to 
a simple common standard, and give below the amount of chromate 
equivalent to 100 of chlorate : 

120.118 

120.371 

120.138 

120.096 

120.241 

120.181 



Mean, 120.191, .028 

In his later paper f Kessler substituted arsenic trioxide for the iron 
solution. In one series of experiments the quantity of dichromate needed 
to oxidize 100 parts of the arsenic trioxide was determined, and in an- 
other the latter substance was similarly compared with 'the chlorate. 
The subjoined columns give the quantity of each salt proportional to 100 
of As 2 3 : 




Mean, 99.045, .028 



Mean, 41.172, .009 

Reducing the later series to the standard of the earlier, the two com- 
bine as follows : 

'(l) 2KC1O 3 : K 2 Cr 2 O 7 : : 100 : 120.191, .028 
(2) 2KC1O 3 : K 2 Cr 2 O 7 : : 100 : 120.282, .043 

General mean ...... 120.216, .0235 

*Poggend. Annalen, 95, 208 1855. 
fPoggend. Annalen, 113, 137. 1861. 



CHROMIUM. 243 

Siewert's determinations, which do not seem to have attracted general 
attention, were published in 1861.* He, reviewing Berlin's work, found 
that upon reducing silver chromate with hydrochloric acid and alcohol, 
the chromic chloride solution always retained traces of silver chloride 
dissolved in it. These could be precipitated by dilution with water ; 
but, in Berlin's process, they naturally came down with the chromium 
hydroxide, making the weight of the latter too high ; hence too large a 
value for the atomic weight of chromium. In order to find a more cor- 
rect value Siewert resorted to the analysis of sublimed, violet, chromic 
chloride. This salt he fused with sodium carbonate and a little nitre, 
treated the fused mass with water, and precipitated from the resulting 
solution the chlorine by silver nitrate in presence of nitric acid. The 
weight of the silver chloride thus obtained, estimated after the usual 
manner, gave means for calculating the atomic weight of chromium. 
His figures, reduced to a common standard, give, as proportional to 100 
parts of chloride of silver, the quantities of chromic chloride stated in 
the third of the subjoined columns : 

.2367 grm. CrCl s gave .6396 grm. AgCl. 37-Oo; 

.2946 " .7994 3 6 .853 

.2593 -7039 36-838 

.4935 I -3395 36.842 

.5850 " 1.5884 " 36-830 

.6511 " 1.76681 " 36.852 

.5503 " L4939I " 36.836 

Mean, 36.865, .0158 

The first of these figures varies so widely from the others that we are 
justified in rejecting it, in which case the mean becomes 86.842, .0031. 

Siewert also made two analyses of silver dichromate by the following 
process. The salt, dried at 120, was dissolved in nitric acid. The silver 
was then thrown down by hydrochloric acid, and, in the filtrate, chro- 
mium hydroxide was precipitated by ammonia. Reduced to a uniform 
standard, we find from his results, corresponding to 100 parts of AgCl, 
Ag 2 O 2 7 as in the last column : 

.7866 grm. Ag 2 Cr 2 O 7 gave .52202 AgCl and .2764 Cr 2 O 3 . 150.684 

1.089 " .72249 " .3840 " 150.729 

Berlin's single determination of this ratio gave 151.035. Taking all 
three values together as one series, they give a mean of 150.816, .074. 

Siewert's percentages of Cr. 2 3 obtained from Ag 2 O 2 O r are as follows, 
calculated from the above weighings : 

35-'39 
35.262 

Mean, 35.2005, .0415 
* Zeit. Gesammt. Wissenschaften, 17, 530. 



244 THE ATOMIC WEIGHTS. 

Combining, as before, with Berlin's single result, giving the latter equal 
weight with one of these, we have a general mean of 35.236, .0335. 

For the ratio between silver chloride and chromic oxide, Siewert's two 
analyses of the dichromate come out as follows. For 100 parts of AgCl 
we have of Cr 2 8 : 



Mean, 53.049, .068 

This figure, reduced to the standard of Berlin's work on the mono- 
chromate, becomes 26.525, .034. Berlin's mean was 26.682, .0076. 
The two means, combined, give a general mean of 26.676, .074. 

By Baubigny * we have only three experiments upon the calcination 
of anhydrous chromic sulphate, as follows : 

1.989 grm. Cr 2 (SO 4 ) 8 gave .7715 grm. Cr. 2 O 3 . 38.788 per cent. 

3.958 " 1.535 " 38.782 " 

2.6052 1.0115 " 38.826 " 

Mean, 38:799, .0092 

Moberg found for the same ratio the percentage 39.195, .028. The 
general mean of both series, Moberg's and Baubigny's, is 38.838, .0087. 

In Rawson's work f ammonium dichromate was the substance studied. 
Weighed quantities of this salt were dissolved in water, and then reduced 
by hydrochloric acid and alcohol. After evaporation to dryness the mass 
was treated with water and ammonia, reevaporated, dried five hours at 
140, and finally ignited in a muffle. The residual chromic oxide was 
bright green, and was tested to verify its purity. The corrected weights 
are as follows : 

Am^Cr^O-. Cr. 2 O s . Percent. Cr. 2 O 3 . 

1.01275 -61134 60.365 

1.08181 .65266 60.330 

1.29430 -78090 60.334 

1.13966 .68799 60.368 

98778 .59595 60.332 

1.14319 .68987 60.346 






Mean, 60.346, .0046 

Latest in time and most elaborate of all, we come to the determinations 
of the atomic weight of chromium made by Meineke,J who studied the 
chromate and ammonio-chromate of silver, and also the dichromates of 
potassium and ammonium. For the latter salt he measured the same 
ratio that Rawson determined, but by a different method. He precipi- 



*Compt. Rend., 98, 146. 

tjourn. Chem. Soc., 55, 213. 

t Ann. d. Chem., 261, 339. 1891. 





CHROMIUM. 



245 



tated its solution with mercurous nitrate, and ignited the precipitate, 
with the subjoined results. Vacuum weights are given ; 

Am. 2 Cr. 2 O r Cr 2 O s . Percent. Cr 2 O s . 

2.0416 1.2316 60.325 

2.1618 1.3040 60.320 

2.0823 1.2562 60.328 

2.1913 1.3221* 60.335 

2.0970 1.2656 60.353 



Mean, 60.332, .0037 
Rawson found, 60.346, .0046 



General mean, 60.337, =b .0029 

The chromate of silver, Ag. 2 Cr0 4 , and the ammonio-chromate, 
Ag,Cr0 4 .4NH 3 , both prepared with all necessary precautions to insure 
purity, were first treated essentially as in Berlin's experiments, except 
that the traces of silver chloride held in solution by the chromic chloride 
were thrown out by sulphuretted hydrogen, estimated, and their amount 
added to the main portion. Thus the chief error in Berlin's work was 
avoided. I subjoin the data obtained, with vacuum standards, as usual. 
All of Meineke's results are so corrected : 



Ag.CrO,. 

2.7826 
3.2627 
3.6362 
4.6781 
3-2325 
3-9I37 



AgCL 

2.4047 
2.8199 
3.1416 
4.0414 
2.7930 
3-3805 



.6384 

.7480 

8338 

1.0726 

-74H 
.8976 



Hence we have the following ratios, as in the case of Berlin's data : 

Percent. Cr. 2 O s . looAgCl : Ag^CrO^. looAgCl : 

22.943 "5-7I5 26.548 

22.926 "5.703 26.526 

22.931 115.744 26.602 

22.928 115.754 26.601 

22.924 "5.736 26.531 

22.935 "5-773 26.552 



Mean, 22.931, .0019 
Berlin, 23.014, =t .0110 



Mean, 115.737, .0072 Mean, 26.560, .0093 
Berlin, 115.956, db .0230 



General mean, 22.934, =h .0018 General mean, 115.760, .0069 

With the ammonio-chromate Meineke found as follows : 
' AgCL Cr,O,. 



4.1518 
4.2601 
5.9348 



2.9724 
3.0592 
4.2654 



794 

.8125 

1.1317 



* Calculated back from Meineke's value for Cr, to replace an evident misprint in the original. 



246 THE ATOMIC WEIGHTS. 

And the ratios become 

Percent. Cr.,O. A . looAgCl : Salt. woAgCl : Cr.,O 3 . 
19.037 139-679 26.591 

19.072 139.255 26.559 

19.059 i39- I 38 26.532 

Mean, 19.059, HZ .0074 Mean, 139.357, .1 109 Mean, 26.561, =h .01 15 

The first of these three analyses is rejected by Meineke as suspicious, 
but for the present I shall allow it to remain. The data in the third 
column may now be combined with the corresponding figures from the 
normal chromate, as found by Meineke and his predecessors. 

Berlin 26.682, .0076 

Siewert, from Ag 2 Cr 2 O 7 26.525, .0340 

Meineke, from Ag 2 CrO 4 26.560, .0093 

Meineke, from Ag 2 CrO 4> 4NH 3 26.561, dr .0115 






General mean ..................... 26.620, rb .0052 

: Cr 2 O 3 : : 100 : 26.620, .0052 



Obviously, this mean is vitiated by the known error in Berlin's work, 
the ultimate effect of which is yet to be considered. 

In all four of the salts studied by Meineke he determined volumetric- 
ally the oxygen in excess of the normal oxides by measuring the amount 
of iodine liberated in acid solutions. With the silver salts the process 
was essentially as follows : A weighed quantity of the chromate was dis- 
solved in weak ammonia, and the solution was precipitated with potas- 
sium iodide. After the silver iodide had been filtered off, five or six 
grammes of potassium iodide were added to the filtrate, which was then 
acidulated with phosphoric acid and a little sulphuric. The liberated 
iodine was then titrated with sodium thiosulphate solution, which had 
been standardized by means of pure iodine, prepared by Stas' method, 
From the iodine thus measured the excessive oxygen was computed, and 
from that datum the atomic weight of chromium was found. For pres- 
ent purposes, however, the data may be used more directly, as giving the 
ratios I 3 : Ag 2 Cr0 4 and I, : Ag 2 Cr0 4 .4NH 3 . Thus treated, the weights are 
as follows, reduced to a vacuum. Reckoning the salt as 100, the third 
column gives the percentage of iodine liberated : 

Ag.fr O. I Set Free. Percentage. 

.43838 .50251 114.628 

.90258 1.03432 H4-595 

.89858 1.02980 114.603 

.89868 1.03072 T 14.693 

Mean, 114.630, .015 



CHROMIUM. 247 

The next series, obviously, gives the ratio I 3 : Ag 2 CrO 4 .4NH 3 . 

/ Set Free. Percentage * 



.54356 .51784 95-267 

.54856 .5 20 46 94.877 

.54926 .52322 95.258 

.54906 .52376 95.392 

.54466 .5*910 95.307 

.54536 .51891 95- 15 

Mean, 95.208, =b .0497 

In dealing with the two dichromates Meineke used the acid potassium 
iodate in place of potassium iodide, the chromate and the iodate reacting 
in the molecular ratio of 2:1. The thiosulphate was standardized by 
means of the acid iodate, so that we have direct ratios between the latter 
and the two chromates. The data are as follows, with the amount of 
iodate proportional to one hundred parts of the dichromate in the third 
column : 

Percentage. 



.25090 


.16609 


66.198 


.25095 


.16613 


66.200 


.25078 


.16601 


66.197 


.24979 


.16541 


66.220 


.24987 


.16540 


66.192 


.24966 


16543 


66.262 


.25015 


16559 


66.196 


.25012 


.16559 


66.204 


.24977 


.16546 


66.245 


.25034 


.16572 


66.198 


.25025 


.16567 


66.202 


.25015 


.16568 


66.234 






Mean, 66.212, .0044 


Am. 2 Cr. l0r 


KHI^O, 


Percentage. 


.21457 


.16584 


77.290 


.21465 


.16588 


77.279 


.21464 


.16584 


77-264 


.21416 


.'6543 


77.246 


.21447 


.16564 


77.232 


.21427 


16559 


77.281 


.22196 


.17152 


77.272 


.22194 


17151 


77.278 


.22180 


'7139 


77-272 






Mean, 77.268, .0041 



* These figures are not wholly in accord with the percentages of oxygen computed by Meineke. 
I suspect that there is a misprint among his data as published, probably in the second experi- 
ment, but I cannot trace it with certainty. 



248 THE ATOMIC WEIGHTS. 

The following ratios are now available for computing the atomic weight 
of chromium : 

(i.) Percentage Cr 2 O 3 from Ag 2 CrO 4 , 22.934, .0018 
(2.) Percentage Cr 2 O 3 from Ag 2 Cr 2 O 7 , 35.236, =b .0335 
(3.) 2AgCl : Ag 2 CrO 4 : : loo : 115.760, rb .0069 
(4.) 2AgCl : Ag 2 Cr 2 O 7 : : 100 : 150.816, .074 
(5.) 4AgCl : Cr 2 O 3 : : loo : 26.620, rb .0052 
(6.) Percentage Cr 2 O 3 in Cr 2 (SO 4 ) 3 , 38.838, =b .0087 
(7.) Percentage Cr 2 O 3 in AmCr(SO 4 ) 2 . 12H 2 O, 16.143, .0125 
(8.) BaSO 4 : BaCrO 4 : : 100 : 108.9815, .0369 
/ (9.) BaCrO 4 : BaCl 2 : : 100 : 81.702, .014 
(10.) 3AgCl : CrCl 3 : : 100 : 36.842, .0031 
(II.) 2KC1O 3 : K 2 Cr 2 O 7 : : 100 : 120.216, rb .0235 
(12.) Percentage Cr 2 O 3 in Ag 2 CrO 4 .4NH 3 , 19.059, .0074 
(13 ) 2AgCl : Ag 2 CrO 4 .4NH 3 : : 100 : 139.357, d= .1109 
(14.) Percentage Cr 2 O 3 in Am 2 Cr 2 O 7 , 60.337, .0029 
(15.) Ag 2 CrO 4 : 3! : : 100 : 114.630, .015 
(16.) Ag 2 CrO 4 .4NH 3 : 3! : : 100 : 95.208, -O497 
(17.) 2K 2 Cr 2 O 7 : KHI 2 O 6 : : 100 : 66.212, =b .0044 
(18.) 2Am 2 Cr 2 O 7 : KHI 2 O 6 : : 100 : 77.268, .0041 

The antecedent values to use in the reduction are 

= 15 879, .0003 S = 31.828, rb .0015 
Ag = 107. 108, zb .0031 N = 13.935, rb .0021 
Cl = 35.179, rb .0048 Ba 136.392, rb .0086 

1 = 125.888, rb .0069 AgCl = 142.287, .0037 
K = 38.817, .0051 

For the molecular weight of Cr a O s , seven values are now calculable, as 
follows : 

From (i) ................ ...... Cr 2 O 3 151.120, .0130 

From (2) ...................... " = 151.105, rb .1636 

From (5) ...................... " = 151.507, .0299 

From (6) .................. ---- " = 151.384,^.0341 

Prom (7) ..................... " =.- 153.756, .1205 

From (12) ..................... " 151.478, .0606 

From (14) ..................... " = 151.190, .0110 

General mean ............ Cr 2 O 3 = 151.229, .0039 

For silver chromate there are two values 

From (3) .................... Ag 2 CrO 4 = 329.423, .0195 

From (15) ................... " =r 329.464, it .0467 

General mean .......... Ag 2 CrO 4 = 329.430, rb .0180 

And for the ammonio-chromate we have 



From (13) ............. Ag 2 CrO 4 .4NH 3 = 396-574, - 

From (16) ............. " = 396.673, rb .2082 



General mean Ag. 2 CrO 4 .4NH 3 = 396.647, .1738 



CHROMIUM. 249 

From (4) Ag 2 Cr 2 O 7 = 429-177, .2109 

From (10) CrCl 3 = 157.266, dr .01 13 

From (18) Am 2 Cr 2 O 7 250.341, dr .0164 

For the molecular weights of K 2 Cr 2 7 and BaCr0 4 there are two esti- 
mates each, as given below : 

From (u) K 2 Cr 2 O 7 = 292.433, =b .0189 

From (17) " = 292.143, =b .0224 



General mean K 2 Cr 2 O 7 = 292.311, dr .0144 

From (8) BaCrO 4 = 252.549, ,dr .0966 

From (9) " = 253.054, .0377 

General mean BaCrO 4 252.985, .0351 

Finally, from these molecular weights, eight independent values are 
obtained for the atomic weight of chromium : 

From Cr 2 O 3 Cr = 5 1 . 796, dr .0039 

From Ag 2 CrO 4 " === 51.698, dr .0191 

From Ag 2 CrO 4 , 4NH 3 " =51.175, .1741 

From Ag 2 Cr 2 O 7 " = 51.904, dr .1055 

From Am 2 Cr 2 O 7 " 51.659, .0085 

From K 2 Cr 2 O 7 "= 51.762, .0102 

From CrCl 3 " =51.729, dr .0183 

From BaCrO 4 " = 53.077, .0362 

General mean Cr = 51.778, dr -0032 

If = 16, Cr = 52.172. 

Rejecting the last of the eight values, that from barium chromate, the 
mean becomes 

Cr = 51. 767, .0032. 

Even this result is probably too high, for it includes ratios which are 
certainly erroneous, and which yet exert appreciable weight. From the 
ratios which are reasonably concordant a better mean is derivable, as 
follows : 

From (l) Cr 51.741, dr .0065 

From (2).. " =51.734, db .0818 

From (14) " =51.776, .0055 

From (3) and (15) " = 51.698, d= .0191 

From (4) " =51.904, .1055 

From (10) " = 51.729, dr .0183 

From (18) <c = 51.659, .0085 

From (i i) and (17) ' =. 51.762, dr .0102 



General mean Cr = 51.742, dr .0034 

If = 16, this becomes 52.136, a value which is probabty not very 
far from the truth. 



250 THE ATOMIC WEIGHTS. 



MOLYBDENUM. 

If we leave out of account the inaccurate determination made by 
Berzelius,* we shall find that the data for the atomic weight of molyb- 
denum lead to two independent estimates of its value one near 92, the 
other near 96. The earlier results found by Berlin and by Svanberg and 
Struve lead to the lower number; the more recent investigations, to- 
gether with considerations based upon the periodic law, point conclu- 
sively to the higher. 

The earliest investigation which we need especially to consider is that 
of Svanberg and Struve. f These chemists tried a variety of different 
methods, but finally based their conclusions upon the two following : 
First, molybdenum trioxide was fused with potassium carbonate, and 
the carbon dioxide which was expelled was estimated ; secondly, molyb- 
denum disulphide was converted into the trioxide by roasting, and the 
ratio between the weights of the two substances was determined. 

By the first method it was found that 100 parts of MoO 3 will expel the 
following quantities of C0 2 : 

3L4954 
3 * -3749 
31-4705 

Mean, 31.4469, .0248 

The carbon dioxide was determined simply from the loss of weight 
when the weighed quantities of trioxide and carbonate were fused to- 
gether. It is plain that if, under these circumstances, a little of the 
trioxide should be volatilized, the total loss of weight would be slightly 
increased. A constant error of this kind would tend to bring out the 
atomic weight of molybdenum too low. 

By the second method, the conversion by roasting of MoS 2 into Mo0 3 , 
Svanberg and Struve obtained these results. Two samples of artificial 
disulphide were taken, A and B, and yielded for each hundred parts the 
following of trioxide : 

89-79191 A 
89.7291 / 

89.6436] 
89.7082 I 
89.7660 j-B. 
- 89.7640 | 
89-8635] 



Mean, 89.7523, .0176 



Three other experiments in series B gave divergent results, and, al- 
though published, are rejected by the authors themselves. Hence it is 



* Poggend. Annalen, 8, i. 1826. 

t Journ. fur Prakt. Chem., 44, 301. 1848. 



MOLYBDENUM. 



251 



not necessary to cite them in this discussion. We again encounter in 
these figures the same source of constant error which apparently vitiates 
the preceding series, namely, the possible volatilization of the trioxide. 
Here, also-, such an error would tend to reduce the atomic weight of 
molybdenum. 

From the CO 2 series Mo 91.25 



From the MoS., series. 



Mo = 92.49 



Berlin,* a little later than Svanberg and Struve, determined the atomic 
weight of molybdenum by igniting a molybdate of ammonium and 
weighing the residual MoO 3 . Here, again, a loss of the latter by vola- 
tilization may (and probably does) lead to too low a result. The salt 
used was (Nll 4 ) 4 Mo ft O tt .BH,O, and in it these percentages of Mo0 3 were 
found : 

81.598 

81.612 

81.558 

81-555 



Mean, 81.581, .0095 

Hence Mo = 91.559. 

Until 1859 the value 92 was generally accepted on the basis of the fore- 
going researches, but in this year Dumas f published some figures tend- 
ing to sustain a higher number. He. prepared molybdenum trioxide 
by roasting the disulphide, and then reduced it to metal by ignition in 
hydrogen. At the beginning the hydrogen was allowed to act at a com- 
paratively low temperature, in order to avoid volatilization of trioxide; 
but at the end of the operation the heat was raised sufficiently to insure 
a complete reduction. From the weighings I calculate the percentages 
of metal in MoO 3 : 



.448 grm. MoO 3 gave .299 grm. Mo. 
.484 " .323 

.484 .322 

.498 .332 

559 " -373 

.388 " .258 



66.741 per cent, 
66.736 " 
66.529 " 
66.667 " 
66.726 " 
66.495 " 



Mean, 66.649, 3 



In 1868 the same method was employed by Debray.J His trioxide 
was purified by sublimation in a platinum tube. His percentages are 
as follows : 



5.514 grm. MoO 3 gave 3.667 grm. Mo. 
7.910 " 5.265 

9.031 " 6.015 " 



66.503 per cent. 
61.561 
66.604 " 



Mean, 66.556, =b .020 



* Journ. fur Prakt. Chem., 49, 444. 1850. 
f Ann. Chem. Pharm., 105, 84, and 113, 23. 
J Compt. Rend., 66, 734. 



252 THE ATOMIC WEIGHTS. 

For the same ratio we have also a single experiment by Rammelsberg,* 
who, closely following Dumas' method, found in molybdenum trioxide 
66.708 per cent, of metal. As this figure falls within the limits of Dumas' 
series, we may assign it equal weight with one experiment in the latter. 

Debray also made two experiments upon the precipitation of molyb- 
denum trioxide in ammoniacal solution by nitrate of silver. In his re- 
sults, as published, there is curious discrepancy, which, I have no doubt, 
is due to a typographical error. These results I am therefore compelled 
to leave out of consideration. They could not, however, exert a very 
profound influence upon the final discussion. 

In 1873, Lothar Meyer f discussed the analyses made by Liechti and 
Kemp J of four chlorides of molybdenum, and in the former edition of 
this work the same data were considered in detail. The analyses, how- 
ever, were not intended as determinations of atomic weight, and since 
good determinations have been more recently published, the work on 
the chlorides will be omitted from further consideration. It is enough 
to state here that they gave values for Mo ranging near 96, both above 
and below that number, with an extreme range of over eight-tenths of a 
unit. 

In 1893 the determinations by Smith and Maas appeared, represent- 
ing an entirely new method. Sodium molybdate, purified by many re- 
crystallizations and afterwards dehydrated, was heated in a current of 
pure, dry, gaseous hydrochloric acid. The compound MoO 3 .2HCl was 
thus distilled off, and the sodium molybdate was quantitatively trans- 
formed into sodium chloride. The latter salt was afterwards carefully 
examined, and proved to be free from molybdenum. The data, with all 
weights reduced to a vacuum standard, are subjoined : 



NaCl. Per cent. NaCL 

1.14726 .65087 5 6 .733 

.89920 .5 I02 3 5 6 -743 

.70534 .40020 5 6 .739 

7793 .40182 56.760 

1.26347 .71695 56.745 

1.15217 .65367 56.734 

.90199 .51188 5675 

.81692 .46358 . 56.747 

.65098 .36942 56.748 

.80563 .45717 56.747 

Mean, 56.745, .0017 

In 1895, Seubert and Pollard || determined the atomic weight of mo- 

* Berlin Monatsbericht, 1877, p. 574- 
f Ann. Chem. Pharm., 169, 365. 1873. 
I Ann. Chem. Pharm., 169, 344. 
\ Journ. Amer. Chem. Soc., 15, 397. 1893. 
|| Zeitsch. Anorg. Chem., 8, 434. 1895. 



MOLYBDENUM. 253 

lybdenum by two methods. First, the carefully purified trioxide, in 
weighed amounts, was dissolved in an excess of a standard solution of 
caustic soda. This solution was standardized by means of hydrochloric 
acid, which in turn had been standardized gravimetrically as silver 
chloride. Hence, indirectly, the ratio 2AgCl : Mo0 3 was measured. Sul- 
phuric acid and lime water were also used in the titrations, so that the 
entire process was rather complicated. Ignoring the intermediate data, 
the end results, in weights of MoO 3 and AgCl, were as follows. The third 
column gives the Mo0 3 proportional to 100 parts of AgCl : 



MoO 3 . AgCl. Ratio. 

3.6002 7. ! 79 50.206 

3.5925 7.i5 6 9 50-196 

3-73" 7.43 4 50-214 

3.8668 7.7011 50.211 

3.9361 7- 8 407 50.201 

3.8986 7.7649 50.208 

3.9630 7.8941 50.202 

3-9554 7.8806 50. 192 

3.9147 7-7999 5. i 9 

3.8543 7.6767 50.208 

3.9367 7.8437 50-190 



Mean, 50.202, .0018 

The second method adopted by Seubert and Pollard was the old one 
of reducing the trioxide to metal by heating in a current of hydrogen. 
The weights and percentages of metal are subjoined : 



Mo. Per rent. 
1.8033 i. 2021 66.661 

1.9345 1.1564 66.670 

3.9413 2.6275 66.666 

1.5241 i. 0160 66.662 

4.0533 2.7027 66.679 



Mean, 66.668, .0022 

This mean may be combined with" the results of previous investigators, 
thus : 

Dumas 66.649, .0300 

Debray 66.556, .0200 

Rammelsberg 66.708, db .0680 

Seubert and Pollard. 66.668, .0022 

General mean 66.665, 0022 

Here the data of Seubert and Pollard alone exert any appreciable 
influence. 

Neglecting all determinations made previous to 1859, there are now 



254 THE ATOMIC WEIGHTS. 

three ratios from which to compute the atomic weight of molybdenum, 

viz : 

(i.) Percentage Mo in MoO 3 , 66.665, =b .0022. 
(2.) 2AgCl : MoO 3 : : 100 : 50.202, .0018 
(3.) 2NaCl : Ma. 2 MoO 4 : 56.745, .0017 : 100. 

These involve the following values : 

O = 15.879, .0003 AgCl 142.287, .0037 

Na = 22.881, .0046 NaCl = 58.060,^.0017 



Hence for the atomic weight in question 

From (i) ......................... Mo = 95.267, .0072 

From (2) ......................... " = 95.225, .0064 

From (3) ........................ " 95.357, .0126 

General mean ............... Mo = 95.259, .0045 

With = 16, Mo = 95.985. 

This value is essentially that derived from Seubert and Pollard's data 
alone. Reducing the latter to a vacuum would affect the result very 
slightly so slightly that the correction may be ignored. 



TUNGSTEN. 255 



TUNGSTEN. 

The atomic weight of tungsten has been determined from analyses or 
the trioxide, the hexchloride, and the tungstates of iron, silver, and 
barium. 

The composition of the trioxide has been the subject of many investi- 
gations. Malaguti * reduced this substance to the blue oxide, and from 
the difference between the weights of the two compounds obtained a 
result now known to be considerably too high. In general, However, 
the method of investigation has been to reduce W0 3 to W in a stream 
of hydrogen at a white heat, and afterwards to reoxidize the metal, thus 
getting from one sample of material two results for the percentage of 
tungsten. This method is probably accurate, provided that the trioxide 
used be pure. 

The first experiments which we need consider are, as usual, those of 
Berzelius.f 899 parts WO 3 gave, on reduction, 716 of metal. 676 of 
metal, reoxidized, gave 846 W0 3 . Hence these percentages of W in 
W0 3 : 

79.644, by reduction. 
79.905, by oxidation. 

Mean, 79.7745, .0880 

These figures are far too high, the error being undoubtedly due to the 
presence of alkaline impurity in the trioxide employed. 

Next in order of time comes the work of Schneider, J who with char- 
acteristic carefulness, took every precaution to get pure material. His 
percentages of tungsten are as follows : 

Reduction Series. 

79.336 
79-254 
79.312 
79.326 
79-350 



Mean, 79.3156 
Oxidation Series. 



793 2 4 
79.328 



Mean, 79-3 2 7 
Mean of all, 79.320, =b .0068 



* Journ. fiir Prakt. Chem., 8, 179. 1836. 

fPoggend. Aiinalen, 8, i. 1826. 

J Journ. fiir Prakt. Chem., 50, 152. 1850. 



256 THE ATOMIC WEIGHTS. 

Closely agreeing with these figures are those of Marchand,* published 
in the following year : 

Reduction Series. 

79.307 
79.302 



Mean, 79.3045 

Oxidation Series. 
79.321 
79.35 2 



Mean, 79.3365 
Mean of all, 79.3205, =b .0073 

The figures obtained by v. Borch f agree in mean tolerably well with 
the foregoing. They are as follows : 

Reduction Series. 
79.310 
79.212 
79.289 

79.313 
79.225 

79-290 
79.302 



Mean, 79- 2 77 
Oxidation Series. 

79-359 
79-339 



Mean, 79.349 
Mean of all, 79.293, .0108 

Dumas J gives only a reduction series, based upon trioxide obtained 
by the ignition of a pure ammonium tungstate. The reduction was 
effected in a porcelain boat, platinum being objectionable on account of 
the tendency of tungsten to alloy with it. Dumas publishes only 
weighings, from which I have calculated the percentages : 



2.784 grm. 


WO 3 gave 2.208 grm. \V 


7Q. 's IO 


per cent. 


2,994 


2.373 " 


79.259 


" 


4.600 


3.649 " 


79.326 


11 


.985 


.781 


79.289 


11 


.917 


.727 " 


79.280 


" 


.917 


.728 " 


79-389 


" 


1.717 


1.362 " 


79-324 


" 


2.988 


2.370 " 


79-3*7 


" 






Mean, 79.312, 


.009 



* Ann. Cheni. Pharni., 77, 261. 1851. 

t Journ. fur Prakt. Chem., 54, 254. 1851. 

JAnn. Chem. Pharni. , 113, 23. 1860. 



TUNGSTEN. 257 

The data furnished by Bernoulli* differ widely from those just given. 
This chemist undoubtedly worked with impure material, the trioxide 
having a greenish tinge. Hence the results are too high. These are the 
percentages of W : 

Reduction Series. 

79.55 6 
79.526 

79-553 
79.558 
79-549 
78.736 



Mean, 79.413 

Oxidation Series. 

79.55 
79.656. 

79-555 
79-554 



Mean, 79.581 
Mean of all, 79.480, .056 

Two reduction experiments by Persozf give the following results : 

1-7999 S rm - WO 3 g av e 1.4274 g rm - w - 79-34 per cent. 

2.249 " 1-784 " 79.3 2 4 " 

Mean, 79.314, .007 

Next in order is the work done by Roscoe. J This chemist used a 
porcelain boat and tube, and made six weighings, after successive reduc- 
tions and oxidations, with the same sample of 7.884 grammes of trioxide. 
These weighings give me the following five percentages, which,*for the 
sake of uniformity with foregoing series, I have classified under the 
usual, separate headings : 

Reduction Series. 




Mean, 79.263 

Oxidation Series. 
79.230 
79 299 



Mean, 79.2645 
Mean of all, 79.264, .0146 



*Poggend. Annalen, in, 573. 1860. 
t Zeit. Anal. Chem., 3, 260. 1864. 
\ Ann. Chem. Pharm., 162,368. 1872. 

17 



258 THE ATOMIC WEIGHTS. 

In Wadd ell's experiments* especial precautions were taken to pro- 
cure tungstic oxide free from silica and molybdenum. Such oxide, 
elaborately purified, was reduced in hydrogen, with the following results : 

1.4006 grm. WO 3 gave 1.1115 W. 79-359 per cent. 

.9900 " .7855 " 79-343 " 

1.1479 -9" " 79-362 " 

.9894 .7847 " 79-3 11 

4.5639 3.6201 " 79.320 " 

79-339, .0069 

The investigation by Pennington and Smith f started from the sup- 
position that the tungsten compounds studied by their predecessors had 
not been completely freed from molybdenum. Accordingly, tungstic 
oxide, carefully freed from all other impurities, was heated in a stream 
of gaseous hydrochloric acid, so as to volatilize all molybdenum as the 
compound Mo0 3 .2HCl. The residual WO 3 , was then reduced in pure 
hydrogen, and the tungsten so obtained was oxidized in porcelain 
crucibles. Care was taken to exclude reducing gases, and the trioxide 
was finally cooled in vacuum desiccators over sulphuric acid. The oxida- 
tion data are as follows, with the usual percentage column added. The 
weights are reduced to a vacuum : 

Tungsten. . Oxygen Gained. Percentage. 

.862871 .223952 79-394 

.650700 .168900 79.392 

.597654 .155*43 79-390 

.666820 .173103 79.391 

.428228 .111168 79.390 

.671920 .174406 79.392 

-590220 .153193 79-394 

.568654 .147588 79-394 

1.080973 .280600 79.392 

Mean, 79.392, dr .0004 

With O = 16, this series gives W = 184.92. 

The very high value for tungsten found by Pennington and Smith, 
nearly a unit higher than that which was commonly accepted, seems to 
have at once attracted the attention of Schneider,^ who criticised the 
paper somewhat fully, and gave some new determinations of his own. 
The tungsten trioxide employed in this new investigation was heated in 
gaseous hydrochloric acid, and the absence of molybdenum was proved. 
The data obtained, both by reduction and by oxidation, are as follows: 

*Am. Chem. Journ., 8, 280. 1886. 

tRead before the Amer. Philos. Soc., Nov. 2, 1894. 

J Jourii. fur Prakt. Chem. (2), 53, 288. 1896. 



TUNGSTEN. 



259 



Reduction Series. 
2.0738 grm. WO 3 gave 1.6450 W. 
4.0853 " 3-2400 " 

6.1547 " 4.8811 " 



79-323 P er 

79.309 

79.307 



Oxidation Series. 

1.5253 grm. W gave 1.9232 WO 3 . 79-3 11 P er cent. 

3.1938 " 4-0273 " 79.304 " 

4.7468 " 5.9848 " 79.314 



Mean of all, 79.311, .0018 

Hence with O = 16, W = 184.007. 

In order to account for the difference between this result and that of 
Pennington and Smith, an impurity of molybdenum trioxide amounting 
to about one per cent, would be necessary. Schneider suggests that the 
quantities of material used by Pennington and Smith were too small, and 
that there may have been mechanical loss of small particles during the 
long heatings. Such losses would tend to raise the atomic weight com- 
puted from the experiments. On the other hand, the losses could hardly 
have been uniform in extent, and the extremely low prooable error of 
Pennington and Smith's series renders Schneider's supposition improb- 
able. The error, if error exists, must be accounted for otherwise. 

Since Schneider's paper appeared, another set of determinations by 
Shinn * has been published frond Smith's laboratory. Attempts to verify 
the results obtained by Smith and Desi having proved abortive, and other 
experiments having failed, Shinn resorted to the oxidation method and 
gives the subjoined data. The percentage column is added by myself: 

J 



.22297 grm. W gave .28090 \VO 3 . 
.17200 " .21664 " 

.10989 " 

.10005 " 



79-377 
79-394 
79-377 
79-417 

Mean, 79.391, *oo66 

This figure is very close to that found in Pennington and Smith's series, 
and therefore serves as a confirmation. The discordance between these 
results and Schneider's is still to be explained. 

There are still other experiments by Riche,f which I have not been 
able to get in detail. They cannot be of any value, however, for they 
give to tungsten an atomic weight of about ten units too low. We may 
therefore neglect this series, and go on to combine the others : 

Berzelius 79-7745, .0880 

Schneider, 1850 79-32O, .0068 

Marchand 79. 3205, zfc .0073 

v. Borch 79-293, rb .oio8 

Dumas 79.3 12, dz .0090 



* Doctoral thesis., University of Pennsylvania, 1896. " The atomic mass of tungsten." 
t Journ. fur Prakt. Chem., 69, 10. 1857. 



260 THE ATOMIC WEIGHTS. 

Bernoulli 79.480, db .0560 

Persoz 79-314, .0070 

Roscoe 79.264, .0146 

Waddell 79-339, db .0069 

Pennington and Smith 79. 392, .0004 

Schneider, 1896 79-31 r, .0018 

Shinn 79. 39 1 , .0066 



General mean 79-388, db .00039 

Here the work of Pennington and Smith vastly outweighs everything 
else; and if their supposition as to the presence of molybdenum in all 
the previous investigations is correct, this result is to be accepted. 

The rejection of the figures given by Berzelius and by Bernoulli would 
exert an unimportant influence upon the final result. There is, there- 
fore, no practical objection to retaining them in the discussion. 

In 1861 Scheibler* deduced the atomic weight of tungsten from 
analyses of barium metatungstate, Ba0.4W0 3 .9H 2 0. In four experi- 
ments he estimated the barium as sulphate, getting closely concordant 
results, which were, however, very far too low. These, therefore, are re- 
jected. But from the percentage of water in the salt a better result was 
attained. The percentages of water are as follows : 

13-053 
13-054 
13-045 
13.010 
13.022 



Mean, 13.0368, .0060 

The work of Zettnow,t published in 1867, was somewhat more com- 
plicated than any of the foregoing researches. He prepared the pure 
tungstates of silver and of iron, and from their composition determined 
the atomic weight of tungsten. 

In the case of the iron salt the method of working was this : The 
pure, artificial FeW0 4 was fused with sodium carbonate, the resulting 
sodium tungstate was extracted by water, and the thoroughly washed, 
residual ferric oxide was dissolved in hydrochloric acid. This solution 
was then reduced by zinc, and titrated for iron with potassium perman- 
ganate. Corrections were applied for the drop in excess of perman- 
ganate needed to produce distinct reddening, and for the iron contained 
in the zinc. 11.956 grammes of the latter metal contained iron corre- 
sponding to 0.6 cc. of the standard solution. The permanganate was 
standardized by comparison with pure ammonium-ferrous sulphate, 
Am 2 Fe(S0 4 ) 2 .6H 2 O, so that, in point of fact, Zettnow establishes directly 
only the ratio between that salt and the ferrous tungstate. From Zett 
now's four experiments in standardizing I find that 1 cc. of his solution 

* Journ. fur Prakt. Chem., 83, 324. 
t Poggend. Annalen, 130, 30. 



TUNGSTEN. 261 

corresponds to 0.0365457 gramme of the double sulphate, with a prob- 
lable error of .0000012. 

Three sets of titrations were made. In the first a quantity of ferrous 
tungstate was treated according to the process given above ; the iron 
isolation was diluted to 500 cc., and four titrations made upon 100 cc. at 
la time. The second set was like the first, except that three titrations 
[were made with 100 cc. each, and a fourth upon 150 cc. In the third 
(set the iron solution was diluted to 300 cc., and only two titrations upon 
llOO cc. each were made. In sets one and two thirty grammes of zinc 
[were used for the reduction of each, while in number three but twenty 
grammes were taken. Zettnow's figures, as given by him, are quite com- 
plicated ; therefore I have reduced them to a common standard. After 
applying all corrections the following quantities of tungstate, in grammes, 
correspond to 1 cc. of permanganate solution : 



.028301 1 
.028291 
.028311 
.028301 j 
.028367 



First set. 



Second set. 

.028367 

.028367 _, 

.028438 I 
.028438 J 

Mean, .0283549, .0000115 

With the silver tungstate, Ag 2 W0 4 , Zettnow employed two methods. 
In two experiments the substance was decomposed by nitric acid, and 
the silver thus taken into solution was titrated with standard sodium 
chloride. In three others the tungstate was treated directly with com- 
mon salt, and the residual silver chloride collected and weighed. Here 
again, on account of some complexity in Zettnow's figures, I am com- 
pelled to reduce his data to a common standard. To 100 parts of AgCl 
the following quantities of Ag 2 WO 4 correspond : 

By First Method. 
161.665 
161.603 



Mean, 161.634, .021 

By Second Method. 
161.687 
161.651 
161.613 



Mean, 161.650, .014 
General mean from both series, 161.645, .012 



262 



THE ATOMIC WEIGHTS. 



For tungsten hexchloride we have two analyses by Roscoe, published 
in the same paper with his results upon the trioxide. In one experi- 
ment the chlorine was determined as AgCl ; in the other the chloride 
was reduced by hydrogen, and the residual tungsten estimated. By 
bringing both results into one form of expression we have for the per- 
centage of chlorine in WC1 6 : * 

53.588 
53-632 



Mean, 53.610, d= .015 

The work done by Smith and Desif probably ought to be considered 
in connection with that of Pennington and Smith on the trioxide. 
Smith and Desi started with tungsten trioxide, freed from molybdenum 
by means of gaseous hydrochloric acid. This material was reduced in 
a stream of carefully purified hydrogen, and the water formed was col- 
lected in a calcium chloride tube and weighed. To the results found I 
add the percentage of water obtained from 100 parts of WO 3 . Vacuum 
weights are given. 



WO* 

.983024 

.998424 

i .008074 

.911974 

997974 
1.007024 



H.,0. 

.22834 
.23189 
.23409 
.21184 
.23179 
.23389 



Percent. 

23.228 
23.226 
23.221 
23.229 
23.226 
23.226 



Mean, 23.226, .0008 



There are now six ratios from which to calculate the atomic weight of 
tungsten : 

(I.) Percentage of W in WO 3 , 79.388, .00039 

(2.) Percentage of H 2 O in BaO.4WO 3 .9H 2 O, 13.0368, db .0060 

(3.) WO 3 : 3H 2 O : : 100 : 23.226, db .0008 

(4.) Am 2 Fe(SO 4 ) 2 .6H 2 O : FeWO 4 : : .0365457, d= .0000012 : .0283549, db .0000115 

(5.) 2AgCl : Ag 2 WO 4 : : 100 : 161.645, - 12 

(6.) Percentage of Cl in WC1 6 , 53.610, .015 



These are reduced with 

O = 15.879, d= .0003 
Ag= 107.108, dr .0031 
C1 = 35.179, . 00 48 
N = 13.935, =b .0021 



S = 31.828, d- .0015 
Ba = 136.392, .0086 
Fe = 55-597, .0023 
AgCl = 142.287, .0037 



* The actual figures are as follows : 

I9-5700 grm. WC1 6 gave 42.4127 grm. AgCl. 

10.4326 4.8374 grm. tungsten. 

fRead before Amer. Philos. Soc., Nov. 2, 1894. 



URANIUM. 263 

Hence there are six values for the atomic weight of tungsten, as follows : 

From (0 W 183.485, .0051 

From (2) . " = 182.638, .1248 

From (3) " = 183 298, dr .0088 

From (4) " = 183.035, .1229 

From (5) " == 182.268, db .0663 

From (6) " = 182.647, .0820 



General mean W = 183.429, .0044 

If = 16, W = 184.827. The rejection of all values except the first 
and third raises the mean by 0.009 ; that is, four of the ratios count for 
almost nothing, and the work done in Smith's laboratory dominates all 
the rest. The questions raised by Schneider in his latest determination, 
however, are not yet answered, and farther investigation is required in 
order to fully establish the true atomic weight of tungsten. 



URANIUM. 

The earlier attempts to determine the atomic weight of uranium were 
all vitiated by the erroneous supposition that the uranous oxide was 
really the metal. The supposition, of course, does not affect the weigh- 
ings and analytical data which were obtained, although these, from their 
discordance with each other and with later and better results, have now 
only a historical value. 

For present purposes the determinations made by Berzelius,* by Arf- 
vedson,f and by Marchand J may be left quite out of account. Berzelius 
employed various methods, while the others relied upon estimating the 
percentage of oxygen lost upon the reduction of U 3 O 8 to U0 2 . Rammels- 
berg's results also, although very suggestive, need no full discussion. 
He analyzed the green chloride, UC1 4 ; effected the synthesis of uranyl 
sulphate from uranous oxide; determined the amount of residue left 
upon the ignition of the sodio and bario-uranic acetates; estimated the 
quantity of magnesium uranate formed from a known weight of UO 2 , 
and attempted also to fix the ratio between the green and the black 
oxides. His figures vary so widely that they could count for little in 
the establishing of any general mean ; and, moreover, they lead to esti- 
mates of the atomic weight which are mostly below the true value. For 
instance, twelve lots of U S O 8 from several different sources were reduced 
to UO 2 by heating in hydrogen. The percentages of loss varied from 3.83 
to 4.67, the mean being 4.121. These figures give values for the atomic 

*Schweigg. Journ., 22, 336. 1818. Poggend. Annalen, i, 359. 1825. 
t Poggend. Annalen, i, 245. Berz. Jahr., 3, 120. 1822. 
I Journ. fiir Prakt. Chem., 23, 497. 1841. 

g Poggend. Annalen, 55, 318, 1842 ; 56, 125, 1842 ; 59, 9, 1843 ; 66, 91, 1845. Journ. fiir Prakt. Chem., 
29, 324- 



264 



THE ATOMIC WEIGHTS. 



weight of uranium ranging from 184.33 to 234.05, or, in mean, 214.53. 
Such discordance is due partly to impurity in some of the material 
studied, and illustrates the difficulties inherent in the problem to be 
solved. Some of the uranoso-uranic oxide was prepared by calcining the 
oxalate, and retained an admixture of carbon. Many such points were 
worked up by Rammelsberg with much care, so that his papers should 
be scrupulously studied by any chemist who contemplates a redetermi- 
nation of the atomic weight of uranium. 

In 1841 and 1842 Peligot published certain papers* showing that the 
atomic weight of uranium must be somewhere near 240. A few years 
qater the same chemist published fuller data concerning the constant in 
luestion, but in the time intervening between his earlier and his final 
researches other determinations were made by Ebelmen and by Wer- 
theim. These investigations we may properly discuss in chronological 
order. For present purposes the early work of Peligot may be dismissed 
as only preliminary in character. It showed that what had been pre- 
viously regarded as metallic uranium was in reality an oxide, but gave 
figures for the atomic weight of the metal which were merely approxi- 
mations. 

Ebelmen 's f determinations of the atomic weight of uranium were 
based upon analyses of uranic oxalate. This salt was dried at 100, 
and then, in weighed amount, ignited in hydrogen. The residual ura- 
nous oxide was weighed, and in some cases converted into U 3 8 by heating 
in oxygen. The following weights are reduced to a vacuum standard : 

10.1644 grm. oxalate gave 7.2939 grm. UO 2 . 



12.9985 
11.8007 

9.99 2 3 
11.0887 
10.0830 

6.7940 
16.0594 



9-33 12 
8.4690 

7- I 73 I 
7.9610 

7.2389 
4.8766 
11.5290 



Gain on oxidation, .3685 

.3275 
.2812 
.3105 



453' 



Reducing these figures to percentages, \ve may present the results in 
two columns. Column A gives the percentages of UO 2 in the oxalate, 
while B represents the amount of U 2 3 formed from 100 parts of U0 2 : 
A. , B. 

71-924 

71.787 103.949 

71.767 103.867 

71.621 103.920 

71.794 103.900 

71-793 

71.778 

71.790 103930 



Mean, 71.782, =b .019 



Mean, 103.9:3, =b .009 



*Compt. Rend., 12, 735. 1841. Ann. Chim. Phys. (3), 55. 1842. 
t Journ. fur Prakt. Cheni., 27, 385. 1842. 



URANIUM. 265 

Wertheim's* experiments were even simpler in character than those 
of Ebelmen. Sodio-uranic acetate, carefully dried at 200, was ignited, 
leaving the following percentages of sodium uranate : 

67.51508 
67.54558 
67.50927 

Mean, 67.52331, .0076 

The final results of Peligot'sf investigations appeared in 1846. Both 
the oxalate and the acetate of uranium were studied and subjected to 
combustion analysis. The oxalate was scrupulously purified by repeated 
crystallizations, and thirteen analyses, representing different fractions, 
were made. Seven of these gave imperfect results, due to incomplete 
purification of the material; six only, from the later crystallizations, 
need to be considered. In these the uranium was weighed as U 3 8 , and 
the carbon as CO 2 . From the ratio between the C0 2 and U 3 8 the atomic 
weight of uranium may be calculated without involving any error due 
to traces of moisture possibly present in the oxalate. I subjoin Peligot's 
weighings, and give, in the third column, the U 3 O 8 proportional to 100 
parts of C0 2 : 

CO 2 . U. A & . Ratio. 

.456 grm. 4.649 grm. 319.299 

.369 " 4.412 " 322.279 

2.209 " 7.084 " 320.688 

.019 " 3.279 " 3 2I -786 

.069 " 3.447 " 322.461 

.052 " 3.389 " 322.148 

Mean, 321.443, .338 

From the acetate, U0 2 (C 2 H 3 2 ) 2 .2H 2 0, the following percentages of 
U 3 8 were obtained : 

5.061 grm. acetate gave 3.354 grm. U 3 O 8 . 66.2715 per cent. 

4.601 " 3-57 " 66.4421 " 

1.869 " 1.238 " 66.2386 " 

3.817 " - 2.541 " 66.5706 " 

10.182 " 6.757 " 66.3622 " 

4.393 2.920 " 66.4694 ' " 

2.868 " 1.897 " 66.1437 



Mean, 66.3569, .038 



The acetate also yielded the subjoined percentages of carbon and of 
water. Assuming that the figures for carbon were calculated from known 

* Journ. fur Prakt. Chem., 29, 209. 1843. 
fCompt. Rend., 22, 487. 1846. 



266 THE ATOMIC WEIGHTS. 

weights of dioxide, with C = 12 and O = 16, 1 have added a third column, 

in which the carbon percentages are converted into percentages of C0 2 : 

H.,0. C. CO* 

21.60 11.27 4 J .323 

21. 16 11.30 41-433 

21.10 11.30 41-433 

2 1. 2O II.IO 4O.7OO 



Mean, 21.265, .187 Mean, 11.24 Mean, 41.222, zh .092 

From these data we get the following values for the molecular weight 
of uranyl acetate : 

From percentage of U 3 O 8 423.183, .4781 

From percentage of CO 2 423.842, =b .9462 

From percentage of H 2 O : 420.386, dr 2.9033 

General mean 423.257, =h .4222 

In the posthumous paper of Zimmermann. edited by Kriiss and Alibe- 
goff,* the atomic weight of uranium is determined by two methods. 
First, U0 2 , prepared by several methods, is converted into U 3 O 8 by heat- 
ing in oxygen. To begin with, U 3 8 was prepared, and reduced to U0 2 
by ignition in hydrogen. When the reduction takes place at moderate 
temperatures, the U0 2 is somewhat pyrophoric, but if the operation is 
performed over the blast lamp this difficulty is avoided. After weighing 
the UO 2 , the oxidation is effected, and the gain in weight observed. The 
preliminary U 3 O 8 was derived from the following sources : A, from ura- 
nium tetroxide ; B, from the oxalate ; C, from uranyl nitrate ; D, by 
precipitation with mercuric oxide. l"he full data, lettered as indicated 
above, are subjoined : 

UO^, U- A O%. Per cent, of Gain. 

8.9363 9.2872 3-927 

7.9659 8.2789 3.929 

12.4385 12.9270 3.927 

f 12.8855 i3-39'3 3.925 

B. -j 5.7089 5.9331 3.927 

( 9.6270 10.0051 3.928 

13.1855 13-7036 3-929 

9.9973 10.3901 3.929 

15.8996 16.5242 3.928 

7-4326 7.7245 3.927 

Mean, 3.9276, .0003 
Ebelmen found, 3.913, d= .009 

General mean, 3.9276, .0003 

Iii short, Ebelmen's mean vanishes when combined with Zimmer 
lann's. 

* Ann. d. Chern., 232, 299. 1886. 



URANIUM. 267 

Zimmerrnann's second method was essentially that of Wertheim, 
namely, the ignition of the double acetate UO 2 (C 2 H 3 2 ) 2 .NaC 2 H 3 2 , the 
residue being sodium uranate, Na 2 U 2 7 . 

Double Acetate. Uranate. Per cent. Uranate. 

4.272984 2.886696 67.557 

5.272094 3-560770 67.540 

2.912283 1.967428 67.556 

2.149309 67.555 

Mean, 67.552, dz .0027 
Wertheim found, 67.523, dz .0076 



General mean, 67.549, dz .0025 

All the data for uranium now sum up thus : 

(i.) Per cent. UO 2 from uranyl oxalate, 71.782, dz .019 

(2.) 6C0 2 : U 3 8 : : 100 : 321.443, dz .338 

(3.) Molecular weight of uranyl acetate, 423.842, .4222 

(4.) 3UO 2 : U 3 O 8 : : 100 : 103.9276, dz .0003 

(5.) Per cent. Na 2 U 2 O 7 from UO 2 .Na(C 2 H 3 O 2 ) 3 , 67.549, dz .0025 

Computing with = 15.879, .0003 ; C = 11.920, .0004, and Na = 
22.881, .0046, we have 

From (I) = 235.948, dz .1938 

From (2) ; . " = 238.462, dz .2953 

From (3) " =238.541, dz-4223 

From (4) " = 237.770, dz .0055 

From (5) " = 237.902, dz .0283 



General mean ... U = 2 37-774, 4= .0054 

If = 16, U = 239.586. 

In this case Zimmermann's data control the final result. All the other 
determinations might be rejected without appreciable effect. 



268 THE ATOMIC WEIGHTS. 



SELENIUM. 

The atomic weight of this element was first determined by Berzelius,* 
who, saturating 100 parts of selenium with chlorine, found that 179 of 
chloride were produced. Further on these figures will be combined with 
similar results by Dumas. 

We may omit, as unimportant for present purposes, the analyses of 
alkaline selenates made by Mitscherlich and Nitzsch. f and pass on to 
the experiments published by Sacc J in 1847. This chemist resorted to 
a variety of methods, some of which gave good results, while others were 
unsatisfactory. First, he sought to establish the exact composition of 
Se0 2 , both by synthesis and by analysis. The former plan, according to 
which he oxidized pure selenium by nitric acid, gave poor results ; better 
figures were obtained upon reducing Se0 2 with ammonium bisulphite 
and hydrochloric acid, and determining the percentage of selenium set 
free : 

.6800 grm. SeO 2 gave .4828 grm. Se. 71.000 per cent. 

3.5227 " 2.5047 " 71.102 " 

4.4870 3-193 " 71.161 " 

Mean, 71.088, .032 

In a similar manner Sacc also reduced barium selenite, and weighed 
the resulting mixture of barium sulphate and free selenium. This pro- 
cess gave discordant results, and a better method was found in calcining 
BaSe0 3 with sulphuric acid, and estimating the resulting quantity of 
BaSO 4 . In the third column I give the amounts of BaS0 4 equivalent to 
100 of BaSe0 3 : 

5573 g rm - BaSeO 3 gave .4929 grm. BaSO 4 . 88.444 

.9942 .8797 " 88.383 

.2351 " .2080 " 88.473 

.9747 " .8621 " 88.448 



Mean, 88.437, .013 

Still other experiments were made with the selenites of silver and lead ; 
but the figures were subject to such errors that they need no further dis- 
cussion here. 

A few years after Sacc's work was published, Erdmann and Marchand 
made with their usual care a series of experiments upon tHe atomic 
weight under consideration. They analyzed pure mercuric selenide, 
which had been repeatedly sublimed and was well crystallized. Their 

* Poggend. Annalen, 8, i. 1826. 

t Poggend. Annaleu, 9, 623. 1827. t 

} Ann. d. Chim. et d. Phys. (3), 21, 119. 

I Jour, fiir Prakt. Chem., 55, 202. 1852. 



SELENIUM. 269 

method of manipulation has already been described in the chapter upon 
mercury. These percentages of Hg in HgSe were found : 

71.726 

7r-73i 

71.741 



Mean, 71.7327, .003 

The next determinations were made by Dumas,* who returned to the 
original method of Berzelius. Pure selenium was converted by dry 
chlorine into SeCl 4 , and from the gain in weight the ratio between Se 
and Cl was easily deducible. I include Berzelius' single experiment, 
which I have already cited, and give in a third column the quantity of 
chlorine absorbed by 100 parts of selenium : 

.709 grm. Se absorb 3.049 grm. Cl. 178.409 

.810 " 3.219 " 177.845 

.679 " 3.003 " 178.856 

.498 " 2.688 " 179-439 

944 " 3.468 " 178.395 

.887 " 3.382 " 179.226 

935 " 3.452 " 178.398 

1 79.000 Berzelius. 

Mean, 178.696, .125 

The question may here be properly asked, whether it would be possi- 
ble thus to form SeCl 4 , and be certain of its absolute purity ? A trace of 
oxychloride, if simultaneously formed, would increase the apparent 
atomic weight of selenium. In point of fact, this method gives a higher 
value for Se than any of the other processes which have been adopted, 
and that value has the largest probable error of any one in the entire 
series. A glance at the table which summarizes the discussion at the 
end of this chapter will render this point sufficiently clear. 

Still later. Ekman and Pettersson f investigated several methods for 
the determination of this atomic weight, and finally decided upon the 
two following : 

First, pure silver selenite, Ag. 2 Se0 3 was ignited, leaving behind metallic 
silver, which, however, sometimes retained minute traces of selenium. 
The data obtained were as follows : 

Ag^SeO^. Ag. Per cent. Ag. 

5.2102 3-2787 62 -93 

5.9721 3-7597 62.95 

7.2741 4-5803 62.97 

7.5390 4.7450 62.94 

6.9250 4.3612 62.98 

7.3455 4.6260 62.98 

6.9878 4.3992 62.95 

Mean, 62.957, d= .005 

*Ann. Chetn. Pharm., 113, 32. 1860. 

-f Ber. d. Deutsch. Chem. Gesell., 9, 1210. 1876. Published in detail by the society at Upsala. 



270 THE ATOMIC WEIGHTS. 

Secondly, a warm aqueous solution of selemous acid was mixed with 
HC1, and reduced by a current of S0 2 . The reduced Se was collected 
upon a glass filter, dried, and weighed. 

SeO. 2 , Se. Per cent. Se. 

11.1760 7-9573 7i.i99 

11.2453 8.0053 7 I - J 85 

24.4729 17-4232 7i.i93 

208444 i 4- 8383 71.187 

31.6913 22.5600 7i- I 9 I 

Mean, 71.191, .0016 
Sacc found, 71.088, db .0320 



General mean, 71.1907, rb .0016 

There are now five series of figures from which to deduce the atomic 
weight of selenium : 

(I.) Per cent, of Se in SeO 2 , 71.1907, *ooi6 

(2.) BaSeO 3 : BaSO 4 : : 100 : 88.437, .013 

(3.) Per cent, of Hg in HgSe, 71.7327, d= .003 

(4.) Se : C1 4 : : 100 : 178.696, .125 

(5.) Per cent, of Ag in Ag 2 SeO 3 , 62.957, .005 

From these, computing with 

O = 15.879, dz .0003 s = 31.828, .0015 

Ag = 107.108, .0031 Ba = 136.392, .0086 

Cl = 35.179, rb .0048 Hg 3= 198.491, dz .0083, 

five values for Se are calculable, as follows : 

From (i) Se = 78.477, dc .0049 

From (2) , " i= 78.006, .0410 

From (3) " = 78.217, .0095 

From (4) " = 78.740, .0561 

From (5) " = 78.405, .0201 



General mean Se = 78.419, .0042 

If = 16, this becomes Se = 79.016. 



TELLURIUM. 271 



TELLURIUM. 

Particular interest attaches to the atomic weight of tellurium on ac- 
count of its relations to the periodic law. According to that law, tellurium 
should lie between antimony and iodine, having an atomic weight greater 
than 120 and less than 126. Theoretically, Mendelejeff assigns it a value 
of Te = 125. but all of the best determinations lead to a mean number 
higher than is admissible under the currently accepted hypotheses. 
Whether theory or experiment is at fault remains to be discovered. 

The first, and for many years the only, determinations of the constant 
in question were made by Berzelius.* By means of nitric acid he oxi- 
dized tellurium to the dioxide, and from the increase in weight deduced 
a value for the metal. He published only his final results, from which, 
if O = 100, Te = 802.121. The three separate experiments give Te = 
801.74, 801.786, and 802.838, whence we can calculate the following per- 
centages of metal in the dioxide : 

80.057 

80.036 

80.034 

Mean, 80.042, .005 

The next determinations were made by von Hauer,f who resorted to 
the analysis of the well crystallized double salt TeBr 4 .2KBr. In this 
compound the bromine was estimated as silver bromide, the values 
assumed for Ag and Br being respectively 108.1 and 80. Recalculating, 
with our newer atomic weights for the above-named elements, we get 
from von Hauer's analyses, for 100 parts of the salt, the quantities of AgBr 
which are put in the third column : 

2.000 grm. K 2 TeBr 6 gave 69.946 per cent. Br. 164.460 

6.668 " 69.8443 " 164.221 

2.934 69.9113 " 164.379 

3.697 " 70.0163 " 164.626 

i. ooo " 69.901 " 164.355 

Mean, 164.408, =b .045 

From Berzelius' series we may calculate Te = 127.366, and from von 
Hauer's Te = 126.454. Dumas, J by a method for which he gives abso- 
lutely no particulars, found Te = 129. 

In 1879, with direct reference to Mendelejeff 's theory, the subject of 
the atomic weight of tellurium was taken up by Wills. The methods 

*Poggend. Annalen, 28, 395. 1833. 
t Sitzungsb. Wien Akad., 25, 142. 
j Ann. Chim. Phys. (3), 55, 129. 1859. 
I Journ. Chem. Soc., Oct., 1879, p. 704. 



272 THE ATOMIC WEIGHTS. 

of Berzelius and von Hauer were employed, with various rigid precau- 
tions in the way of testing balance and weights, and to ensure purity of 
material. In the first series of experiments tellurium was oxidized by 
nitric acid to form Te0 2 . The results gave figures ranging from Te = 
125.64 to 128.66 : 

2.21613 grm. Te gave 2.77612 grm. TeO 2 . 79.828 per cent. Te. 

1.45313 1.81542 " 80.044 " 

2.67093 " 3-33838 " 80.007 

477828 " 5.95748 " 80.207 " 

2.65029 " 3-3I33 1 " 79-989 



Mean, 80.015, .041 

In the second series tellurium was oxidized by aqua regia to Te0 2 , with 
results varying from Te == 127.10 to 127.32 : 

2.85011 grm. Te gave 3.56158 grm. TeO 2 . 80.024 per cent. Te. 

3.09673 3-86897 " 80.040 " 

5-93 6 5 " 6.36612 " 80.012 " 

3.26604 4.08064 " 80.037 " 

Mean, 80.028, .004 

By von Hauer's process, the analysis of TeBr 4 .2KBr, Will's figures give 
results ranging from Te = 125.40 to 126.94. Reduced to a common 
standard, 100 parts of the salt yield the quantities of AgBr given in the 
third column : 

1.70673 grm. K 2 TeBr 6 gave 2.80499 grm. AgBr. 164.349 

1.75225 " 2.88072 " .164.398 

2.06938 " 3-40739 " 164.657 

3.29794 5-43 22 8 " 164.717 

2.46545 " 405742 " 164.571 



Mean, 164.538, .048 

Combined with von Hauer's mean, 164.408, .045, this gives a general 
mean of 164.468, .033. Hence Te = 126.502. 

The next determinations in order of time were those of Brauner.* 
This chemist tried various unsuccessful methods for determining the 
atomic weight of tellurium, among them being the synthetic preparation 
of -silver, copper, and gold tellurides, and the basic sulphate, Te 2 S0 7 . 
None of these methods gave sufficiently concordant results, and they 
were therefore abandoned. The oxidation of tellurium to dioxide by 
means of nitric acid was also unsatisfactory, but a series of oxidations 
with .aqua regia gave data as follows. The third column contains the 
percentage of tellurium in the dioxide : 

* Journ. Chem. Soc., 55, 382. 1889. 



TELLURIUM. 273 

Te. TeO. 2 . Percent. Te. 

2.3092 2.9001 79.625' 

2-8153 3-533 2 79-68i 

4.0176 5-347 79-798 

3.1613 3-9 6 85 79.660 

.8399 1.0526 79-793 

Mean, 79.711, .0239 

Hence Te = 124.709. 

In a single analysis of the dioxide, by reduction with S0 2 , 2.5489 
grammes Te0 2 gave 2.0374 of metal. If we give this experiment the 
weight of one observation in the synthetic series, the percentage of tel- 
lurium found by it becomes 

79.93 2 , -0534. 
Hence Te = 126.494. 

Brauner's best results were obtained from analyses of tellurium tetra- 
bromide, prepared from pure tellurium and pure bromine, and after- 
wards sublimed in a vacuum. This compound was titrated with standard 
solutions of silver, and three series of experiments, made with samples 
of bromide of different origin, gave results as follows. The TeBr 4 equiva- 
lent to 100 parts of silver appears in the third column : 

First Series. 

TeBr^. Ag. Ratio. 

2.14365 2.06844 103.636 

1.76744 1.70531 103.643 

1.47655 1.42477 103.634 

1.23354 1.19019 103.642 

Second Series. 

TeBr. Ag. Ratio. 

3.07912 2.97064 103.651 

5.47446 5- 2 8i57 103.652 

3-30927 3.I93I3 103.637 

7.26981 7.01414 103.645 

3.52077 3-39667 103.654 

Third Series. 
TeBr. Ag. Ratio. 

2.35650 2.27363 103.645 

1.51931 1.46564 103.662 

1.43985 1.38942 103.630 



Mean of all as one series, 103.644, .0018 
18 



274 THE ATOMIC WEIGHTS. 

Hence Te = 126.668, .0290. A reduction of the weighings to a 
vacuum raises this by 0.07 to 126.738. 

Still another series of analyses, made with fractionated material, gave 
values for tellurium running up to as high as 137. These experiments 
led Brauner to believe that he had found in tellurium a higher homo- 
logue of that element, a view which he has since abandoned.* Brauner 
also made a series of analyses of tellurium dibromide, but the results 
were unsatisfactory. 

In the series of determinations by Gooch and Rowland f an alkaline 
solution of tellurium dioxide was oxidized by means of standard solu- 
tions of potassium permanganate. This was added in excess, the excess 
being measured, after acidification with sulphuric acid, by back titration 
with oxalic acid and permanganate. Two series are given, varying in 
detail, but for present purposes they may be treated as one. The ratio 
Te0 2 : : : 100 : x is given in the third column. 

TeO-i Taken. O Required. Ratio. 

.1200 .01202 10.017 

.0783 .00785 10.026 

.0931 .00940 10.097 

' .1100 .01119 10.149 

.0904 .00909 10.055 

.1065 .01078 10.122 

.0910 -00915 10055 

.0910 .00910 lo.ooo 

.0911 .00924 10.143 

.0913 .00915 IO.O22 

.09I2 -00915 10.033 

.0914 .00923 10.098 

Mean, 10.068, .0100 

Hence Te = 125.96. 

In Staudenmaier's \ determinations of the atomic weight of tellurium, 
crystallized telluric acid, H 6 Te0 6 was the starting point. By careful 
heating in a glass bulb this compound can be reduced to Te0 2 , and by 
heating in hydrogen, to metal. In the latter case finely divided silver was 
added to prevent volatilization of tellurium. The telluric acid was frac- 
tionally crystallized, but the different fractions gave fairly constant results. 
I therefore group Staudenmaier's data so as to bring them into series 
more suitable for the present discussion. 

* Journ. Chem. Soc., 67, 549. 1895. 

f Atfler. Journ. Sci., 58, 375. 1894. Some misprints in the original publication have been kindly 
corrected by Professor Gooch ; hence the differences between these data and the figures formerly 
given. 

JZeitseh. Anorg. Chem., 10, 189. 1895. 



TELLURIUM. 275 

First. H 6 Te0 6 to Te0. 2 . 

Loss in Weight. Per cent. TeO. 2 . 

1.7218 .5260 69.451 

2.8402 .8676 69.453 

4.0998 1.2528 69.442 

3.0916 .9450 69.433 

1.1138 .3405 69.429 

4.9843 1.5236 69.432 

4.6716 1.4278 69.437 



Mean, 69.440, .0024 

Hence Te = 126.209. 

Second. H 6 Te0 6 to Te. 

// 6 7><9 6 . Loss hi Weight. Percent. Te. 

1.2299 .5471 55.517 

1.0175 -45 26 55-5'S 

2.5946 I.I549 55-488 



Mean, 55.508, .0068 

Hence Te = 126.303. 

Staudenmaier also gives four reductions of Te0 2 to Te, in presence of 
finely divided silver. The data are as follows : 

. 7><9. 2 . Loss in Weight. Per cent. Te. 

.9171 .1839 79.948 

i 9721 .3951 79.966 

2-4115 -4835 7995 

1.0172 .2041 79-935 

Mean, 79.950, .0043 

Hence Te = 126.636. 

The last series, giving the percentage of tellurium in the dioxide, com- 
bines with previous series thus : 

Berzelius 80.042, .0050 

Wills, first series 80.015, d= .0410 

Wills, second series 80.028, .0040 

Brauner, synthesis 79. 7 r I , .0239 

Brauner, analysis 79-93 2 , .534 

Staudenmaier 79-95i .004 3 

General mean 80.001, =t .0025 

The very recent determinations byChikashige* were made by Brauner's 
method, giving the ratio between silver and TeBr 4 . In all essential par- 
ticulars the work resembles that of Brauner. except that the tellurium, 

* Journ. Chetn. Soc., 69, 8Si. 1896. 



276 THE ATOMIC WEIGHTS. 

instead of being extracted from metallic tellurides, was derived from 
Japanese native sulphur, in which it exists as an impurity. This differ- 
ence of origin in the material studied gives the chief interest to the 
investigation. The data are as follows : 



Ag. Ratio. 

4.1812 4.0348 103.628 

4.3059 4-1547 103.639 

4.59 2 9 4.43 ! 9 103.633 



Mean, 103.633, .0023 
Brauner found, 103.644, .0018 



General mean, 103.640, it .0014 

Now, to sum up, the subjoined ratios are available for computing the 
atomic weight of tellurium : 

(I.) Percentage Te in TeO 2 , 80.001, =b .0025 
(2.) Percentage Te in H 6 TeO 6 , 55.508, .0068 
(3.) Percentage TcO 2 in H 6 TeO 6 , 64.440, .0024 
(4.) Ag 4 : TeBr 4 : : 100 : 103.640, .0014 
(5.) K 2 TeBr g : 6AgBr : : 100 : 164.468, =b .0330 
(6.) TeO 2 : O : : 100 : 10.068, =b .0100 

To reduce these ratios we have 

O = 15.879,^.0003 K = 38.817, .0051 

Ag = 107.108, .0031 AgBr = 186.452, rb .0054 

Br = :: 79-344, . -0062 

For the atomic weight of tellurium six values appear, as follows : 

From (i) Te = 127.040, .0165 

From (4) " = 126.650, rb .0302 

From (5) " = 126.502,1^.1430 

From (2) " =126.303,^.0246 

From (3) " = 126.209, zb .0138 

From (6) " = 125.960,^.1574 



General mean Te = 126.523, rb .0092 

If = 16, Te = 127.487. 

A careful consideration of the foregoing figures, and of the experi- 
mental methods by which they were obtained, will show that they are 
not absolutely conclusive with regard to the place of tellurium under 
the periodic law. The atomic weight of iodine, calculated in a previous 
chapter, is 125.888. Wills 1 values for Te, rejecting his first series as rela- 
tively unimportant, range from 125.40 to 127.32 ; that is, some of them 
fall below the atomic weight of iodine, although none descend quite to 
the 125 assumed by Mendelejeff. 

Some of Brauner's data fall even lower; and the same thing is true in 



FLUORINE. 277 

Gooch and Rowland's series, of which the mean gives Te = 125.96, a 
value very little above that of iodine. 

In considering the experimental methods, reference may properly be 
made to the controversy regarding the atomic weight of antimony. It 
will be seen that Dexter, estimating the latter constant by the conver- 
sion of the metal into Sb 2 4 , obtained a value approximately of Sb = 122. 
Dumas, working with SbCl 3 , obtained nearly the same value. Schneider 
and Cooke, on the other hand, have established an atomic weight for 
antimony near 120, and Cooke in particular has traced out the constant 
errors which lurked unsuspected in the work of Dumas. Now in their 
physical aspects tellurium and antimony are quite similar. The oxida- 
tion of tellurium to dioxide resembles in many particulars that of anti- 
mony, and may lead to error in the same way. In each of the six tel- 
lurium ratios there is still uncertainty, and a positive measurement, free 
from objections, of the constant in question is yet to be made. 



FLUORINE. 

The atomic weight of fluorine has been chiefly determined by one 
general method, namely, by the conversion of fluorides into sulphates. 
The work of Christensen, however, is on different lines. Excluding the 
early results of Davy,* we have to consider first the experiments of 
Berzelius, Louyet, Dumas, De Luca, and Moissan with reference to the 
fluorides of calcium, sodium, potassium, barium, and lead. 

The ratio between calcium fluoride and sulphate has been determined 
by the five investigators above named, and by one general process. The 
fluoride is treated with strong sulphuric acid, the resulting sulphate is 
ignited, and the product weighed. In order to insure complete trans- 
formation special precautions are necessary, such, for instance, as re- 
peated treatment with sulphuric acid, and so on. For details like these 
the original papers must be consulted. 

The first experiments in chronological order are those of Berzelius,f 
who operated upon an artificial calcium fluoride. He found, in three 
experiments, for one part of fluoride the following of sulphate : 

1-749 
1.750 
I-75I 

Mean, 1.750, .0004 

Louyet's researches J were much more elaborate than the foregoing. 
He began with a remarkably concordant series of results upon fluor spar, 

* Phil. Trans., 1814, 64. 

f Poggend. Annalen, 8, i. 1826. 

I Ann. Chim. Phys. (3), 25, 300. 1849. 



278 THE ATOMIC WEIGHTS. 

in which one gramme of the fluoride yielded from 1.734 to 1.737 of sul- 
phate. At first he regarded these as accurate, but he soon found that 
particles of spar had been coated with sulphate, and had therefore 
escaped action. In the following series this source of error was guarded 
against. 

Starting with fluor spar, Louyet found of sulphate as follows: 

.742 

744 

745 

744 

7435 
7435 



Mean, 1.7437, .0003 



A second series, upon artificial fluoride, gave : 

i.743 
1.741 



Mean, 1.7417, .0004 

Dumas * published but one result for calcium fluoride. .495 grm. gave 
.864 grm. sulphate, the ratio being 1 : 1.7455. 

De Lucaf worked with a very pure fluor spar, and published the fol- 
lowing results. The ratio between CaS0 4 and one gramme of CaF 2 is 
given in the third column : 



.9305 grm. CaF 2 gave 1.630 grm. CaSO 4 . 

.836 " 1.459 " 1.7452 

.502 " .8755 " 1.7440 

.3985 " .6945 " 1.7428 

If we include Dumas' single result with these, we get a mean of 
1.7459, .0011. 

MoissanJ unfortunately gives no details nor weighings, but merely 
states that four experiments with calcium fluoride gave values for F rang- 
ing from 19.02 to 19.08. To S he assigned the value 32.074, and probably 
Ca was taken as 40. With these data his extreme values as given 
may be calculated back into uniformity with the ratio as stated above, 
becoming 

1-7444 
1.7410 



Mean, 1.7427 



*Ann. Chem. Pharm., 113, 28. 
t Compt. Rend., 51, 299. 1860. 
I Compt. Rend , in, 570. 1890. 



FLUORINE. 279 

If we assign this equal weight with Berzelius' series, the data for this 
ratio combine thus : 

Berzelius 1.7500, .0004 

Louyet, first series 1.7437, .0003 

Louyet, second series 1.7417, .0004 

De Luca with Dumas 1.7459, .0011 

Moissan 1.7427, .0004 



General mean 1.7444, .00018 

For the ratio between the two sodium salts we have experiments by 
Dumas, Louyet, and Moissan. According to Louyet, one gramme of 
NaF gives of Na 2 S0 4 

1.686 

1.683 

1.685 



Mean, 1.6847, .0006 

The weighings published by Dumas are as follows : 

.777 grm. NaF give 1.312 grm. Na 2 SO 4 . Ratio, 1.689 

1.737 " 2.930 " " 1.687 

Mean, 1.688, .0007 

Moissan says only that five experiments with sodium fluoride gave 
. F = 19.04 to 19.08. This was calculated with Na = 23.05 and S'= 32.074. 
Hence, reckoning backward, the two values give for the standard ratio 



1.6873 

Mean, 1.6881 

Giving this equal weight with Dumas' mean, we have 

Louyet 1 .6847, =fc .0006 

Dumas 1.688, .0007 

Moissan 1.6881, .0007 



General mean 1 .6867, .00038 

Dumas also gives experiments upon potassium fluoride. The quantity 
of sulphate formed from one gramme of fluoride is given in the last 
column : 

1.483 grm. KF give 2.225 g rm - K 2 SO 4 . 1.5002 

1.309 " 1.961 " 1.4981 

Mean, 1.499^ .0007 

The ratio between barium fluoride and barium sulphate was measured 



280 THE ATOMIC WEIGHTS. 

by Louyet and Moissan. According to Louyet, one gramme of BaF., 
gives of BaS(\ 

L33 2 

1.331 

1.330 

Mean, 1.331, =b .0004 

Moissan, in five experiments, found F 19.05 to 19.09. Assuming 
that he put Ba = 137, and S 32.074 as before, these two extremes 
become 



1-3305 
Mean, 1.3308 

Giving this equal weight with Louyet's mean, we get the subjoined 
combination : 

Louyet I-33I, .0004 

Moissan 1 .3308, db .0004 



General mean i-339> .00028 

The experiments with lead fluoride are due to Louyet, and a new 
method of treatment was adopted. The salt was fused, powdered, dis- 
solved in nitric acid, and precipitated by dilute sulphuric acid. The 
evaporation of the fluid and the ignition of the sulphate was then effected 
without transfer. Five grammes of fluoride were taken in each opera- 
tion, yielding of sulphate : 

6.179 

6.178 

6.178 

Mean, 6.1783, d= .0002 

In Christensen's determinations* we find a method adopted which is 
radically unlike anything in the work of his predecessors. He started 
out with the salt (NH 4 ) 2 MnF 5 . When this is added to a mixture, in 
solution, of potassium iodide and hydrochloric acid, iodine is set free, 
and may be titrated with sodium thiosulphate. One molecule of the 
salt (as written above), liberates one atom of iodine. In four experi- 
ments Christensen obtained the following data : 

3.1199 grm. Am. 2 MnF 5 gave 2.12748 I. 68.191 per cent. 

3.9190 " 2.67020 " 68.135 " 

3.5005 " 2.38429 " 68.113 " 

1.2727 " .86779 " 68.185 " 

Mean, 68.156, .0128 

* Journ. fiir Prakt. Chem. (2), 35, 541. Christensen assigns to the salt double the formula here 
given. 



FLUORINE. 2j31 

The ratios from which to compute the atomic weight of fluorine are 
now 

(I.) CaF 2 : CaSO 4 : : i.o : 1.7444, .00018 
(2.) 2NaF : Na 2 SO 4 : : i.o : 1.6867, .00038 
(3.) 2KF : K 2 SO 4 : : i.o : 1.4991, .0007 
(4.) BaF 2 : BaSO 4 : : i.o : 1.3309, .00028 
(5.) PbF 2 : PbSO 4 : : 5.0 : 6.1783, .0002 
(6.) Am 2 MnF 5 : I : : 100 : 68.156, .0128 

To reduce them we have 

l 5-&79, db .0003 K 38.817, dr .0051 

S = 31.828, .0015 Ca = 39.764, =h .0045 

N = 13.935, =t .0021 Ba = 136.392, zfc .0086 

1 125.888, .0069 Pb = 205.358, .0040 
Na 22.881, rh .0046 Mn= 54-571, i: .0013 

And the values derived for fluorine are as follows: 

From (i) F= 18.844, d- .0048 

From (2) " = 18.948, dr .0108 

From (31 " = 18.877, .0276 

From (4) " = 18.869, .0192 

From (5) " = 18.997, dr .0047 

From (6) " = 18.853, .0073 



General mean F = 18.912, .0029 

If O = 16, F = 19.056. 

In all probability these values for fluorine average a trifle too high. 
It is difficult to be certain that a fluoride has been completely converted 
into sulphate, and an incomplete conversion tends to raise the apparent 
atomic weight of fluorine. This possible source of error exists in all of 
the ratios except the last one, but the fair concordance of the results 
obtained seems to indicate that the uncertainty cannot be very large. 



282 THE ATOMIC WEIGHTS. 



MANGANESE. 

The earliest experiments of Berzelius* and of Arfvedsonf gave values 
for Mn ranging between 56 and 57, and therefore need no farther con- 
sideration here. The first determinations to be noticed are those of 
Turner J and a later measurement by Berzelius. who both determined 
gravimetrically the ratio between the chlorides of manganese and silver. 
The manganese chloride was fused in a current of dry hydrochloric acid, 
and afterwards precipitated with a silver solution. I give the MnCl 2 
equivalent to 100 parts of AgCl in the third column : 

4.20775 grm. MnG 2 == 9.575 grm. AgCl. 43-945 \ 

, _ _ > 

3.063 = 6.96912 43-95-' 

12.47 grains MnQ 2 = 28.42 grains AgCl. 43.878 Turner. 

Mean, 43.924, .015 

Many years later Dumas || also made the chloride of manganese the 
starting point of some atomic weight determinations. The salt was fused 
in a current of hydrochloric acid, and afterwards titrated with a standard 
solution of silver in the usual way. One hundred parts of Ag are equiva- 
lent to the quantities of MnCl 2 given in the third column : 

3.3672 grm. MnCl 2 = 5.774 grm. Ag. 5 8 -3i7 

3.0872 " 5.293 " 58.3 26 

2.9671 " 5-0875 " 58.321 

1.1244 1.928 " 58.320 

1.3134 " 2.251 " 58.321 

Mean, 58.321, =h .001 

An entirely different method of investigation was followed by von 
Hauer,^]" who, as in the case of cadmium, ignited the sulphate in a stream 
of sulphuretted hydrogen, and determined the quantity of sulphide thus 
formed. I subjoin his weighings, and also the percentage of MnS in 
MnS0 4 as calculated from them : 

4.0626 grm. Mn?O 4 gave 2.3425 grm. MnS. 57-66o per cent. 

4.9367 " 2.8442 " 57.613 " 

5.2372 " 3- OI 9 2 " 57.649 c< 

7.0047 " 4.0347 " 57.600 " 

4.9175 " 2.8297 " 57-543 

4-8546 " 2.7955 57.585 " 

4.9978 2.8799 " 57.625 

4 6737 " 2.6934 " 57.629 

4.7240 2.7197 " 57.57 2 

Mean, 57.608, =fc .008 



* Poggend. Anualen, 8, 185. 1826. 

t Berz. Jahresbericht, 9, 136. 1829. 

| Trans. Roy. Soc. Ediub., ir, 143. 1831. 

I Lehrbuch, 5 Aufl., 3. 1224. 

|| Ann. Chem. Pharm., 113, 25. 1860. 

If Journ. fur Prakt. Chem., 72, 360. 1857. 



MANGANESE. 283 

This method of von Hauer, which seemed to give good results with 
cadmium, is, according to Schneider,* inapplicable to manganese, for the 
reason that the sulphide of the latter metal is liable to be contaminated 
with traces of oxysulphide. Such an impurity would bring the atomic 
weight out too high. The results of two different processes, one carried 
out by himself and the other in his laboratory by Rawack, are given by 
Schneider in this paper. 

Rawack reduced manganoso-manganic oxide to manganous oxide by 
ignition in a stream of hydrogen, and weighed the water thus formed. 
From his weighings I get the values in the third column, which repre- 
sent the Mn 3 4 equivalent to one gramme of water: 

4.149 grm. Mn 3 O 4 gave 0.330 grm. II 2 O. 12.5727 

4.649 " .370 " 12.5643 

6.8865 .5485 " 12.5552 

7.356 " .5855 " 12.5636 

8-9445 -7135 " 12.5361 

11.584 .9225 " 12.5572 

Mean, 12.5582, .0034 

Here the most obvious source of error lies in the possible loss of water. 
Such a loss, however, would increase the apparent atomic weight of 
manganese ; but we see that the value found is much lower than that^ 
obtained either by Dumas or von Hauer. 

Schneider himself effected the combustion of manganous oxalate with 
oxide of copper. The salt was not absolutely dry, so that it was neces- 
sary to collect both water and carbon dioxide. Then, upon deducting 
the weight of water from that of the original material, the weight of 
anhydrous oxalate was easily ascertained. Subtracting from this the 
CO ? , we get the weight of Mn. If we put CO 2 = 100, the quantities of 
manganese equivalent to it will be found in the last column : 

1.5075 grm. oxalate gave .306 grm. H 2 O and .7445 grm. CO 2 . 61.3835 

2.253 .4555 " *- ll 35 " 61.4291 

3.1935 -652 1-5745 " 61.4163 

5.073 " 1.028 ." 2.507 " 61.3482 



Mean, 61.3943, =b .0122 

Up to this point the data give two distinct values for Mn one near 
54, the other approximately 55 and with no sure guide to preference 
between them. The higher value, however, has been confirmed by later 
testimony. 

In 1883 Dewar and Scott f published the results of their work upon 
silver permanganate. This salt is easily obtained pure by recry stall iza- 
tion, and has the decided advantage of not being hygroscopic. Two sets 

* Poggend. Annalen, 107, 605. 
tProc. Roy. Soc., 35, 44. 1883. 



284 THE ATOMIC WEIGHTS. 

of experiments were made. First, the silver permanganate was heated 
to redness in a glass hulb, first in air, then in hydrogen. Before weigh- 
ing, the latter gas was replaced by nitrogen. The data are as follows : 



^g + MnO. Per cent. Ag + MnO. 

5-8696 4.63212 78.917 

5-4988 4-3359 1 78.852 

7.6735 6.05395 78.894 

13-10147 10.31815 78.756 

12.5799 {9.9.065 78.782 

(9.91435 , 78.811 



Mean, 78.835, .0174 

The duplication of the last weighing is not explained. 

In the second series the permanganate was dissolved in dilute nitric 
acid, reduced by sulphur dioxide, potassium nitrite, or sodium formate, 
and titrated with potassium bromide. The AgMn0 4 equivalent to 100 
KBr appears in the third column. 

AgMnO. KBr. Ratio. 

6.5289 3-42385 190.686 

7.5378 3-9553 190.575 

6.1008 3.20166 * 90.559 

5.74647 3-00677 191.117 

6.16593 3. 23602 190.540 

5.11329 2.6828 190.596 

5.07438 2.66204 190.624 

13.4484 7.05602 190.604 

12.5799 6.60065 190.588 

12.27025 6.43808 190.584 

Mean, 190.647, .0361 

Vacuum weights are given throughout. To the first series of experi- 
ments the authors attach little importance, and numbers 1 and 4 of the 
second series they also regard as questionable. These experiments rep- 
resent the use of sulphur dioxide as the reducing agent, and were attended 
by the formation of an insoluble residue, apparently of a sulphide. Ex- 
cluding them, the remaining eight experiments of the second series give 
in mean 

KBr : AgMnO 4 : : 100 : 190.584, db .0062, 

which will be used for the present calculation. Dewar and Scott also 
made determinations with manganese chloride and bromide. With the 
first salt they found Mn = 54.91, and with the second, Mn = 54.97 ; but 
they give no details. 

Marignac's work upon the atomic weight of manganese also appeared 
in 1883.* He prepared the oxid.e, MnO, by ignition of the oxalate and 



^Arch. vSci. Phys. et Nat. (3), 10. 21. 1883. 



MANGANESE. 285 

subsequent reduction of the resulting Mn 3 O 4 in hydrogen. The oxide, 
with various precautions, was then converted into sulphate. The per- 
centage of MnO in MnS0 4 is appended : 

2.6587 grrn. MnO gave 5.6530 MnSO 4 . 47.032 per cent. 

2.5185 " 5-3600 " 46.987 " 

2.5992 5-5 2 95 " 47.oo6 " 

2.8883 6.1450 " 47.002 " 

Mean, 47.007, + .0025 

J. M. Weeren, in 1890,* published determinations made by two meth- 
ods, the one Marignac's, the other von Hauer's. From manganese sul- 
phate he threw down the hydrated peroxide electrolytically,and the latter 
compound was then reduced in hydrogen which had been proved to be 
free from oxygen. The resulting monoxide was cooled in a stream of 
purified nitrogen. After the oxide had been treated with sulphuric acid, 
converted into sulphate, and weighed, a few drops of sulphuric acid and 
a little sulphurous acid were added to it, after which it was reheated and 
weighed again. This process was repeated until four successive weigh- 
ings absolutely agreed. The results of this set of experiments were as 
follows, with vacuum standards : 

15.2349 grm. MnO gave 32.4142 MnSO 4 . 47.005 per cent. 

13.9686 " 29.7186 " 47.004 " 

13.7471 29.2493 " 47.000 " ^ 

15.5222 " 33.0246 " 47.001 " 

14.9824 " 3 I -8755 " 47.002 " 

14.6784 " 3 -2304 " 47.000 

Meanj 47.002, .0006 

Marignac's mean, combined with this, hardly affects either the per- 
centage itself or its probable error. Fortunately, both Marignac and 
Weeren are completely in agreement as to the ratio, and either set of 
measurements would be valid without the other. In order, therefore, to 
give Marignac's work some proper recognition, we can assume a general 
mean of 47.004, =b .0006, without danger of serious error. 

The manganese sulphate produced in the foregoing series of experi- 
ments was used, with many precautions, for the next series carried out 
by von Hauer's method. It was transferred to a porcelain boat, dried at 
260 to avoid errors due to retention of water taken up in the process of 
transfer, and then heated to constant weight in a stream of hydrogen 
sulphide. Before weighing, the sulphide was heated to redness in hy- 
drogen and cooled in the same gas. The results, with vacuum weights, 
were as follows : 

* Atom-Gewichtsbestimmung des Mangans. Inaugural Dissertation, Halle, 1890. 



286 THE ATOMIC WEIGHTS. 

16.0029 g rm - MnSO 4 gave 9.2228 MnS 57.632 per cent. 
16.3191 " 9.4048 " 57.631 

15.9307 9.1817 " 57-634 " 

15-8441 9-131$ " 57.634 " 

16.2783 9.3819 " 57.635 " 

17.0874 9-8477 " 57.633 " 

Mean, 57.633, .0004 
von Hauer found, 57.608, =b .0080 

Hence the general mean is identical with Weeren's to the third deci- 
mal place, which is unaffected by combination with von Hauer's data. 
We have now to consider the following ratios for manganese : 

(i.) 2AgCl : MnCl 2 : : 100 : 41.924, =b .0150 

(2.) 2Ag : MnCl 2 : : loo : 58.321, d= .0010 

(3.) 1J 2 O : Mn 3 O 4 : : 100 : 1255.82, .340 

(4. ) 2L'O 2 : Mn : : 100 : 61.3943, .0122 

(5.) AgMnO 4 : Ag -f MnO : : 100 : 78.835, .0174 

(6.) KBr : AgMnO 4 : : 100 : 190.584, .0062 

(7.) MnSO 4 : MnO : : 100 : 47.004, .0006 

(8.) MnSO 4 : MnS : : 100 : 57.633, .0004 

Computing with the subjoined preliminary data 

O 15.879,^.0003 K = 38.817,^.0051 

Ag = 107.108, .0031 C = 1 1.920, .0004 

Cl = 35.179, dr .0048 S 31.828,^.0015 
Br = 79-344, .0062 AgCl = 142.287, -0037 

these ratios reduce as follows : 

First, for the molecular weight of manganese chloride, two values are 
deducible. 

From (i) MnCl 2 124.996, d= .0428 

From (2) " = 124.933, .0042 

General mean MnO 2 124.934, .0042 

Hence Mn = 54.576, .0075. 

For manganese there are seven independent values, as follows : 

From molecular weight MnCl 2 Mn = 54.576, .0075 

From (3) " = 5.3.667, ..0203 

From (4) " = 53.633, .0107 

From (5) " = 54.450, .1511 

From (6) " = 54.572, .0173 

From (7) " 54.601, .0018 

From (8) " = 54-575, dr .0022 

General mean Mn = 54.571, =fc .0013 

If = 16, this becomes Mn = 54.987. 

In this case five of the separate values are well in accord, and the re- 
jection of the two aberrant values, which have high probable errors, is 



IRON. 287 

not necessary. Their influence is imperceptible. Weeren's marvelously- 
concordant data seem to receive undue weight, but they are abundantly 
confirmed by the evidence of other experimenters. In short, the atomic 
weight of manganese appears to be quite well determined. 



IRON. 

The atomic weight of iron has been mainly determined from the com- 
position of ferric oxide, with some rather scanty data relative to other 
compounds. 

Most of the earlier data relative to the percentage of metal and oxygen 
in ferric oxide we may reject at once, as set aside by later investigations. 
Among this no longer valuable material there is a series of experiments 
by Berzelius, another by Dobereiner, and a third by Capitaine. The 
work done by Stromeyer and by Wackenroder was probably good, but 
I am unable to find its details. The former found 30.15 per cent, of 
oxygen in the oxide under consideration, while Wackenroder obtained 
figures ranging from a minimum of 30.01 to a maximum of 30.38 per 
cent.* 

In 1844 Berzelius f published two determinations of the ratio in ques- 
tion. He oxidized iron by means of nitric acid, and weighed the oxide 
thus formed. He thus found that when = 100 Fe 350.27 and 
350.369. 

Hence the following percentages of Fe in Fe 2 3 : 

70.018 
70.022 



Mean, 70.020, .0013 

About the same time Svanberg and Norlin { published two elaborate 
series of experiments ; one relating to the synthesis of ferric oxide, the 
other to its reduction. In the first set pure piano-forte wire was oxidized 
by nitric acid, and the amount of oxide thus formed was determined. 
The results were as follows : 



1.5257 grm. 


Fe gave 2.1803 


grm. Fe 2 O s . 


69.977 per cent. Fe. 


2.4051 


3-4390 


" 


69.936 


it 


2.3212 


3-3 r 94 


it 


69.928 


(( 


2.32175 


3.383 


" 


, 69.968 


a 


2.2772 


3.2550 


(t 


69.960 


" 


2.4782 


3.5418 


" 


69.970 


" 


2.3582 


3.3720 


< < 


69.935 


" , 








Mean, 69.9534, 


.0050 



* For additional details concerning these earlier papers I must refer to Oudemans' mono- 
graph, pp. 140, 141. 

t Ann. Chem. Pharm., 30, 432. Berz. Jahresb., 25, 43. 
I Berzelius' Jahresbericht, 25, 42. 



288 THE ATOMIC WEIGHTS. 

Iii the second series ferric oxide was reduced by ignition in a current 
of hydrogen, yielding the subjoined percentages of metal : 

2.98353 grm. Fe 2 O 3 gave 2.08915 grm. Fe. 70.025 per cent. 

2.41515 i.6oro 70.015 " 

299175 " 2.09455 " 70.014 " 

3.5783 2.505925 70.030 " 

4.1922 2.9375 70.072 " 

3.1015 " 2.17275 " 70.056 " 

2.6886 " 1.88305 " 70.036 " 



Mean, 70.0354, .0055 

It is evident that one or both of these series must be vitiated by con- 
stant errors, and that these probably arise from impurities in the mate- 
rials employed. Impurities in the wire taken for the oxidation series 
could hardly have been altogether avoided, and in the reduction series 
it is possible that weighable traces of hydrogen may have been retained 
by the iron. At all events, it is probable that the errors of both series 
are in contrary directions, and therefore in some measure compensatory. 

In 1844 there was also published an important paper by Erdmann 
and Marchand.* These chemists prepared ferric oxide by the ignition 
of pure ferrous oxalate, and submitted it to reduction in a stream of 
hydrogen. Two sets of results were obtained with two different samples 
of ferrous oxalate, prepared by two different methods. For present pur- 
poses, however, it is not necessary to discuss these sets separately. The 
percentages of iron in Fe 2 3 are as follows : 

70.013 ] 
69.962 | 

69.979 }-A. 

70.030 I 

69.977 J 

70.044 1 

70.015 j-B. 

70.055 J 

Mean, 70.0094, =b .0080 

In 1850 Maumene'sf results appeared. He dissolved pure iron wire 
in aqua regia, precipitated with ammonia, filtered off the precipitate, 
washed thoroughly, ignited, and weighed, after the usual methods of 
quantitative analysis. The percentages of Fe in Fe 2 3 are given in the 
third column : 

1.482 grm. Fe gave 2.117 grm. Fe 2 O 3 . 70.005 per cent. 

1.452 2.074 " 70.010 " 

1.3585 " 1.941 " 69.990 

1.420 " 2.0285 " 70.002 " 

1.492 2.1315 " 69.998 " 

1-554 " 2.22O " 7O.OOO " 



Mean, 70.0008, =h .0019 



* Journ. fiir Prakt. Chem., 33, i. 1844. 
tCompt. Rend., Oct. 17, 1850. 



IRON. 289 

Two more results, obtained by Rivot* through the reduction of ferric 
oxide in hydrogen, remain to be noticed. The percentages are : 

69.31 
69-35 

Mean, 69.33, .013 

We have thus before us six series of results, which we may now com- 
bine : 

Berzelius 70.020, .0013 

Erdmann and Marchand 70.0094, =b .0080 

Svanberg and Norlin, oxidation 69.9534, .0050 

Svanberg and Norlin, reduction 70.0354, .0055 

Maumene 70.0008, .0019 

Rivot 69.33, - OI 3 



General mean 70.0075, .0010 

From this we get Fe = 55.596. 

Dumas' f results, obtained from the chlorides of iron, are of so little 
weight that they might safely be omitted from our present discussion. 
For the sake of completeness, however, they must be included. 

Pure ferrous chloride, ignited in a stream of hydrochloric acid gas, 
was dissolved in water and titrated with a silver solution in the usual 
way. One hundred parts of silver are equivalent to the amounts of Fed, 
given in the third column : 

3.677 grm. FeCl. 2 = 6.238 grm. Ag. 58.945 

3.924 " =6.675 " 58.787 

Mean, 58.866, .053 

Ferric chloride, titrated in the same way, gave these results : 

1.179 g rm - FeCl 3 = 2.3475 grm. Ag. 50.224 

1.242 " =2.471 " 5- 26 3 

Mean, 60.2435, .0132 

These give us two additional values for Fe, as follows : 

From FeC! 2 Fe = 55.742 

From FeCl s " = 55.907 

A series of determinations of the equivalent of iron, made by students 
by measuring the hydrogen evolved when the metal is dissolved in an 
acid, was published by Torrey in 1888. J The data have, of course, slight 

* Ann. Chem. Pharm., 78, 214. 1851. 
f Ann. Chem. Pharm., 113, 26. 1860. 
I Am. Chem. Journ., 10, 74. 

19 



290 THE ATOMIC WEIGHTS. 

value, but may be considered as being in some measure confirmatory. 

They are as follows : 

56.40 

55.6o 
55-3* 
55.5 6 
55.48 

55-5 
55.86 
56.06 
56.22 
55-So 
55-78 
55.6o 
55.70 
55-94 



Mean, 55-777, .0532 

These values undoubtedly depend on Regnault's value for the weight 
of hydrogen. Correcting by the later value, as found in the chapter of 
this work relating to the density ratio H : 0, the mean becomes Fe = 
55.608, zh .0532. Here the probable error in the weight of the hydrogen 
is ignored, as being of no practical significance. 

The four ratios for iron are now as follows : 

(i.) Per cent. Fe in Fe 2 O 3 , 70.0075, .0010 

(2.) Ag 2 : FeG 2 : : loo : 58.866, .0530 

(3.) Ag 3 : FeC) 3 : : 100 : 50.2435, .0132 

(4.) H:Fe:: I : 55.608,^.0532 

Reducing these with 

O = 15.879, .0003 

Ag = 107.108, .0031 

Cl = 35.179, .0048 



we have 



From (i) Fe = 55.596, .0023 

From (2) " = 55.742, .1140 

From (3) " = 55.907, .0450 

From (4) " = 55.608, =b .0532 



General mean Fe = 55.597, .0023 

If O = 16, then Fe = 56.021. Here all the values are absorbed prac- 
tically by the first, the other three having no real significance. 



NICKEL AND COBALT. 291 



NICKEL AND COBALT. 

On account of the close similarity of these metals to each other, their 
atomic weights, approximately if not actually identical, have received 
of late years much attention. 

The first determinations, and the only ones up to 1852, were made by 
Rothhoff,* each with but a single experiment. For nickel 188 parts of 
the monoxide were dissolved in hydrochloric acid ; the solution was 
evaporated to dryness, the residue was dissolved in water, and precipi- 
tated by silver nitrate. 718.2 parts of silver chloride were thus formed ; 
whence Ni = 58.613. The same process was applied also to cobalt, 269.2 
parts of the oxide being found equivalent to 1029.9 of AgCl ; hence Co = 
58.504. These values are so nearly equal that their differences were 
naturally ascribable to experimental errors. They are, however, entitled 
to no special weight at present, since it cannot be certain from any evi- 
dence recorded that the oxide of either metal was absolutely free from 
traces of the other. 

In 1852 Erdmann and Marchand f published some results, but with- 
out details, concerning the atomic weight of nickel. They reduced the 
oxide by heating in a current of hydrogen, and obtained values ranging 
from 58.2 to 58.6, when = 16. Their results were not very concordant, 
and the lowest was probably the best. 

In 1856, incidentally to other work, Deville J found that 100 parts of 
pure metallic nickel yielded 262 of sulphate ; whence Ni = 58.854. 

To none of the foregoing estimations can any importance now be at- 
tached. The modern discussion of the atomic weights under considera- 
tion began with the researches of Schneider in 1857. This chemist 
examined the oxalates of both metals, determining carbon by the com- 
bustion of the salts with copper oxide in a stream of dry air. The carbon 
dioxide thus formed was collected as usual in a potash bulb, which, in 
weighing, was counterpoised by a similar.bulb, so as to eliminate errors 
due to the hygroscopic character of the glass. The metal in each oxalate 
was estimated, first by ignition in a stream of dry air, followed by intense 
heating in hydrogen. Pure nickel or cobalt was left behind in good con- 
dition for weighing. Four analyses of each oxalate were made, with the 
results given below. The nickel salt contained three molecules of water, 
and the cobalt salt two molecules : 

* Cited by Berzelius. Poggend. Annaleti, 8, 184. 1826. 
t Journ. fiir Prakt. Chem., 55, 202. 1852. 
t Ann. Chim. Phys. (3), 46, 182. 1856. 
t Poggend. Annalen, 101, 387. 1857. 



292 THE ATOMIC WEIGHTS. 



1.1945 grm. gave .528 grm. CO 2 . 44.203 per cent. 

2.5555 " 1.12625 " 44- 72 " 

3.199 " 1.408 44.014 " 

5.020 " 2.214 44.104 " 

Mean, 44.098, .027 

The following percentages of nickel were found in this salt 

29.107 
29.082 
29.066 
29.082 



Mean, 29.084, dz .006 



rm. gave .781 grm. CO 2 . 47-753 P er cent. 

1.107 " .5295 " 47-832 " 

2.309 " i.ioi 47-683 " 

3.007 1-435 47.722 " 

Mean, 47-7475, .0213 

The following were the percentages found for cobalt : 

32-552 
32.619 
32.528 
32.523 



Mean, 32.5555, .0149 

In a later paper* Schneider also gives some results obtained with a 
nickel oxalate containing but two molecules of water. This gave him 
47.605 per cent, of C0 2 , and the following percentages of nickel : 

3 I -4"5 
31-4038 



Mean, 31.4076, d= .0026 

The conclusion at which Schneider arrived was that the atomic weights 
of cobalt and nickel are not identical, being about 60 and 58 respectively. 
The percentages given above will be discussed at the end of this chapter 
in connection with all the other data relative to the constants in ques- 
tion. 

The next chemist to take up the discussion of these atomic weights 
was Marignac, in 1858.f He worked with the chlorides and sulphates 

*Poggend. Annalen, 107, 616. 

t Arch, des Sci. Phys et Nat. (nouv. serie), i, 372. 1858. 



NICKEL AND COBALT. 293 

of nickel and cobalt, using various methods, but publishing few details, 
as he did not consider the determinations final. The sulphates, taken 
as anhydrous, were calcined to oxides. From the ratio NiS0 4 : NiO, he 
found Ni = 58.4 to 59.0, and from five measurements of the ratio 
CoS0 4 : Co, Co = 58.64 to 58.76. If oxygen is taken as 16, these give for 
the percentages of oxide in sulphate : 

CoO in CoSOv NiO in 

48.267 48.187 

48.307 48.387 



Mean, 48.287, d= .0135 Mean, 48.287, .0675 

The chlorides were dried at 100, but found to retain water; and in 
most cases were then either fused in a stream of chlorine or of dry, 
gaseous hydrochloric acid, or else calcined gently with ammonium 
chloride. The determinations were then made by titration with a 
standard solution of silver in nitric acid. Three experiments with an- 
hydrous CoCl, gave Co = 58.72 to 58.84. Three more with CoCl 2 dried 
at 100 gave Co = 58.84 to 59.02. Three with anhydrous NiCl 2 gave 
Ni = 58.80 to 59.00. If the calculations were made with Ag = 108 and 
Cl = 35.5, then these data give as proportional to 100 parts of silver : 




60.093 
60.185 

Mean, 60.139, .0310 
, Mean, 60.118, .0192 

In one more experiment NiCl. 2 was precipitated with a known quan- 
tity of silver. The filtrate was calcined, yielding NiO ; hence the ratio 
,Ag- 2 : NiO, giving Ni = 59.29. This experiment needs no farther atten- 
tion. 

In short, according to Marignac, and contrary to Schneider's views, 
the two atomic weights are approximately the same. Marignac criticises 
Schneider's earlier paper, holding that the nickel oxalate may have con- 
tained some free oxalic acid, and that the cobalt salt was possibly con- 
taminated with carbonate or with basic compounds. In his later papers 
Schneider rejects these suggestions as unfounded, and in turn criticises 
Marignac. The purity of anhydrous NiS0 4 is not easy to guarantee, and, 
according to Schneider, the anhydrous chlorides of cobalt and nickel are 
liable to be contaminated with oxides. This is the case even when the 
chlorides are heated in chlorine, unless the gas is carefully freed from 
all traces of air and moisture. 



294 



THE ATOMIC WEIGHTS. 



Dumas' * determinations of the two atomic weights were made with 
the chlorides of nickel and cobalt. The pure metals were dissolved in 
aqua regia, the solutions were repeatedly evaporated to dryness, and the 
residual chlorides were ignited in dry hydrochloric acid gas. The last 
two estimations in the nickel series were made upon NiCL 2 formed by 
heating the spongy metal in pure chlorine. In the third column I give 
the NiCl 2 or CoCl 2 equivalent to 100 parts of silver : 

.9123 grm. NiCl 2 = 1.515 grm. Ag. 60.218 

2.295 " 3-8ii5 " 60.212 

3.290 5.464 " 60.212 

1.830 " 3.041 " 60.178 

3.001 " 4.987 " 60.176 



Mean, 60.1992, .0062 



2 352 grm. CoCl 2 = 3.9035 grm. Ag. 60.254 

4.210 6.990 " 60.229 

3.592 " 5.960 " 60.268 

2.492 " 4.1405 " 60.186 

4.2295 " 7.0255 " 60.202 



Mean, 60.2278, .on 

These results give values for Co and Ni differing by less than a tenth 
of a unit ; here, as elsewhere, the figure for Ni being a trifle the lower. 
Combining these data with Marignac's, we have 

Agi : NiC^ : : 100 : x. 

Marignac 60. 139, .0310 

Dumas 60.199,^.0062 



General mean 60. 194, db .0061 

Ag^ : CoCl 2 : : TOO : X, 

Marignac 60.118, .0192 

Dumas 60 228, .0110 



General mean 60.200, dr .0095 

In 1863 f the idea that nickel and cobalt have equal atomic weights 
was strengthened by the researches of Russell. He found that the black 
oxide of cobalt, by intense heating in an atmosphere of carbon dioxide, 
became converted into a brown monoxide of constant composition. The 
ordinary oxide of nickel, on the other hand, was shown to be convert- 
ible into a definite monoxide by simple heating over the blast lamp. 
The pure oxides of the two metals, thus obtained, were reduced by 
ignition in hydrogen, and their exact composition thus ascertained. 

*Ann. Chem. Pharm., 113, 25. 1860. 
f Journ. Chem. Soc. (2), i, 51. 1863. 



NICKEL AND COBALT. 



295 



Several samples of each oxide were taken, yielding the following data. 
The separate samples are indicated by lettering : 

Nickel 




c. 



D. 



B. 






CoO. 

2. 1211 

2.0241 

I 2.1226 

I L9947 

{3.0628 

2.1167 

I.77I7 

1.7852 
1.6878 
2.2076 
| 2.6851 

(2.1, 



46I 
f 3.4038 

E. J 2.2778 
(2.1837 



Ni. 

1.6364 

.6468 

5838 

7342 

7952 
.6761 

.79" 
.6845 
.9030 

.7179 

5788 

1.6379 
2.0873 



Cobalt. 

Co. 
1.6670 

L5907 
1.6673 

1.5678 

2.4078' 

.6638 

.3924 
.4030 

.3264 

735 
2.1104 
1.6868 
2.6752 

i.79 01 
1.7163 



Percent. Ni. 

78.597 
78.584 
78.608 
78.581 
78.589 
78.583 
78.616 
78.590 
78.588 
78.590 
78.594 
78.597 
78.588 



Mean, 78.593, .0018 



Percent. Co. 

78.591 
78.588 

78.550 
78.598 
78.614 
78.603 
78.591 
78.591 
78.588 
78.592 
78.597 
78.598 
78.595 
78.589 
78.596 



Mean, 78.592, .0023 



These percentages are practically identical, and lead to essentially the 
same mean value for each atomic weight. 

In a later paper Russell* confirmed the foregoing results by a different 
process. He dissolved metallic nickel and cobalt in hydrochloric acid 
and measured the hydrogen evolved. Thus the ratio between the metal 
and the ultimate standard was fixed without the intervention of any 
other element. About two-tenths of a gramme of metal, or less, was 



* Journ. Chem. Soc. (2), 7, 494. 1867. 



296 



THE ATOMIC WEIGHTS. 



taken in each experiment. The data obtained were as follows ; the last 
column giving the weight of hydrogen, computed from its volume, 
yielded by 100 parts of cobalt or nickel : 



Wt. Ni. 
f .0906 
.1017 
.1990 
A. <{ .0997 
.1891 

.1859 

.1838 



B. - .1806 

.2026 

C. .1933 
.1890 

D. -j .1942 

.1781 




Nickel. 

Vol. H in cc. 

153-62 
172.32 
337.o6 
168.93 
319.86 

314.75 
311-25 

318.75 
305.28 

333-81 
325.93 
319.77 
328.15 
301.09 



Cobalt. 

Vol. H in cc. 
321.36 
312.95 
319-63 
328.96 

3 2 8.43 
329.55 
290.17 

308.97 
318.60 

3H.73 
3 5-4o 



Ratio. 
3.420 
3.418 
3-4i6 

3.417 
3.412 

3.415 
3.4i6 

3.398 
3-409 
3-404 
3.401 

3-412 
3.408 
3-410 

Mean, 3.411, .001 



Ratio. 

3-395 
3.398 
3-397 
3-398 
3403 
3-401 
3-401 
3-404 
3.405 
3.410 
3.407 



Mean, 3.4017, .0009 



The weight of the hydrogen in these determinations was doubtless 
computed from Regnault's data concerning the density of that gas. Cor- 
recting by the new value for the weight of a litre of hydrogen, .089872 
gramme, the ratios become: 

For nickel 3-42H, .0010 

For cobalt 3.4112, =b .0009 

Some time after the publication of Russell's first paper, but before the 
appearance of his second, some other investigations were made known. 



NICKEL AND COBALT. 297 

Of these the first was by Sommaruga,* whose results, obtained by novel 
methods, closely confirmed those of Schneider and antagonized those 
of Dumas, Marignac, and Russell. The atomic weight of nickel Som- 
maruga deduced from analyses of the nickel potassium sulphate, 
K 2 Ni(S0 4 ) 2 .6H 2 0, which, dried at 100, has a perfectly definite compo- 
sition. In this salt the sulphuric acid was determined in the usual way 
as barium sulphate, a process to which there are obvious objections. In 
the third column are given the quantities of the nickel salt proportional 
to 100 parts of BaS0 4 : 

0.9798 grm. gave 1.0462 grm. BaSO 4 . 93-653 

1.0537 " 1.1251 " 93.654 

1.0802 " LI535 " ' 93-645 

1.1865 " 1.2669 " 93.654 

3.2100 " 3.4277 " 93649 

3.2124 " 3.43 3 " 93. 6 48 

Mean, 93.6505, rt .001 

For cobalt Sommaruga used the purpureocobalt chloride of Gibbs 
and Genth. This salt, dried at 110, is anhydrous and stable. Heated 
hotter, CoCl 2 remains. The latter, ignited in hydrogen, yields metallic 
cobalt. In every experiment the preliminary heating must be carried 
on cautiously until arnmoniacal fumes no longer appear : 

.6656 grm. gave .1588 grm. Co. 23.858 per cent. 

1.0918 " .2600 " 23.814 " 

.9058 " .2160 " 23.846 

L5895 " .3785 " 23.813 " 

2.9167 " .6957 " 23.847 " 

1.8390 .4378 " 23.806 " 

2.5010 " .5968 " 23.808 

Mean, 23.827, .006 

Further along this series will be combined with a similar one by Lee. 
It may here be said that Sommaruga's paper was quickly followed by 
a critical essay from Schneider,f endorsing the former's work and object- 
ing to the results of Russell. 

In 1867 still another new process for the estimation of these atomic 
weights was put forward by Winkler, J who determined the amount of 
gold which pure metallic nickel and cobalt could precipitate from a 
neutral solution of sodio-auric chloride. 

In order to obtain pure cobalt Winkler prepared purpureocobalt 
chloride, which, having been four or five times recrystallized, was ignited 
in hydrogen. His nickel was repeatedly purified by precipitation with 
sodium hypochlorite. From material thus obtained pure nickel chloride 

* Sitzungsb. Wien. Akad., 54, 2 Abth., 50. 1866. 
1 Poggend. Annalen,/i30, 310. 
1 Zeit. Anal. Chem., 6, 18. 1867. 



298 THE ATOMIC WEIGHTS. 

was prepared, which, after sublimation in dry chlorine, was also reduced 
by hydrogen. One hundred parts of gold are precipitated by the quanti- 
ties of nickel and cobalt given in the third columns respectively. In the 
cobalt series I include one experiment by Weselsky, which was published 
by him in a paper presently to be cited : 

.4360 grm. nickel precipitated .9648 grm. gold. 45.191 

4367 .9666 " 45.179 

5189 " I.I457 " 45-29I 

.6002 " 1.3286 " 45.175 



Mean, 45.209, .019 

.5890 grm. cobalt precipitated 1.3045 grm. gold. 45.151 

3 '47 .6981 " 45.080 

5829 1.2913 45- HI 

Sni 1.1312 " 45.182 
.5821 1.2848 " 45.307 

559 " 1.241 " 45.044 Weselsky. 

Mean, 45.151, .025 

Weselsky 's paper,* already quoted, relates only to cobalt. He ignited 
the cobalticyanides of ammonium and of phenylammonium in hydrogen, 
and from the determinations of cobalt thus made deduced its atomic 
weight. His results are as follows : 

7575 S rm - (NH 4 ) 6 Co a Cy 12 S ave - l66 S rm - Co - 21.914 per cent. 
5 J 43 " .113 " 21.972 " 



Mean, 21.943, .029 

.8529 grm. (C 6 H 8 N) 6 Co 2 Cy 12 gave .1010 grm. Co. 11.842 per cent. 
.6112 " .0723 " 11.829 " 

.7 J 4 .0850 " 11.905 " 

.9420 .1120 " 11.890 " 

Mean, 11.8665, .0124 

Next in order is the work done by Lee f in the laboratory of Wolcott 
Gibbs. Like Weselsky, Lee ignited certain cobalticyanides and also 
nickelocyanides in hydrogen and determined the residual metal. The 
double cyanides chosen were those of strychnia and brucia, salts of very 
high molecular weight, in which the percentages of metal are relatively 
low. A series of experiments with purpureocobalt chloride was also 
carried out. In order to avoid admixture of carbon in the metallic resi- 
dues, the salts were first ignited in air, and then in oxygen. Reduction 
by hydrogen followed. The salts were in each case covered by a porous 
septum of earthenware, through which the hydrogen diffused, and which 
served to prevent the mechanical carrying away of solid particles ; fur- 

* Ber. d. Deutsch. Chem. Gesell., 2, 592. 1868. 
t Am. Journ. Sci. and Arts (3), 2, 44. 1871. 



NICKEL AND COBALT. 299 

thermore, heat was applied from above. The results attained were very 
satisfactory, and assign to nickel and cobalt atomic weights varying from 
each other by about a unit ; Ni being nearly 58, and Co about 59, when 
O = 16. The exact figures will appear later. The cobalt results agree 
remarkably well with those of Weselsky. The following are the data 
obtained : 

Brucia nickelocyanide, Ni. A Cy Vi (^C^H^N^O^ & H 6 .10H 2 0. 

Salt. Ni. Percent. Ni. 

.3966 .0227 5.724 

.5638 .0323 5.729 

.4000 .0230 5-75 

.3131 -01795 5-733 

.4412 .0252 5.712 

.4346 .0249 5.729 



Mean, 5.7295, .0034 

Strychnia nickelocyanide, Ni 9 Cy l2 ( C 2l H^N 2 2 \H 6 .8H 2 0. 

Salt. Ni. Per cent. AY. 

.5358 .0354 6.607 

.5489 .0363 6.613 

.3551 -0234 ' 6.589 

4495 - 02 97 6 - 6 7 

.2530 .0166 6.561 

.1956 .0129 6.595 

Mean, 6.595, .005 

Brucia cobalticyanide, Co 2 Cy l2 ( C 2Z H 26 N 2 0^> 6 H 6 .20H 2 0. 

Salt. Co. Percent. Co. 

.4097 .0154 3.759 

3951 .0147 3-720 \ 

5456 .0204 3.739 

.4402 .0165 3.748 

.4644 .0174 3-747 

.4027 .0151 3.749 



Mean, 3.7437, .0036 

Strychnia cobalticyanide, Co. 2 Cy l2 (C 2l H 22 N 2 0,\H 6 .8H. 2 0. 

Salt. Co. Percent. Co. 

.4255 -0195 4.583 

.4025 .0185 4.596 

3733 .0170 4-554 

-4535 -0207 4.564 

-2753 -0126 4.577 

.1429 -0065 4.549 



Mean, 4.5705, =b .005 



300 THE ATOMIC WEIGHTS. 

Parpureo-cobalt chloride, C 



Salt. Co. Percent. Co. 

9472 .2233 23.575 

.8903 .2100 23.587 

.6084 .1435 23.586 

.6561 .1547 23.579 

.6988 .1647 23.569 

.7010 .1653 23.581 



Mean, 23.5795, .0019 
The last series may be combined with Sommaruga's, thus : 

Sommaruga 23.817, .006 

Lee 23.5795, .0019 



General mean 23.6045, .0018 

Baubigny's * determinations of the atomic weight of nickel are limited 
to two experiments upon the calcination of nickel sulphate, and his data 
are as follows : 

6.2605 grm. NiSO 4 gave 3.9225 NiO. 48.279 per cent. 

4.4935 " 2.1695 " 48.281 



Mean, 48.280 

Zimmermann's work, published after his death by Krtiss and Alibe- 
goff,f was based, like Russell's, upon the reduction of cobalt and nickel 
oxides in hydrogen. The materials used were purified with great care, 
and the results were as follows: 





Nickel 




1 






mo. 


Ni, 


Percent. Ni. 


6.0041 


4.7179 


78.578 


6 4562 


5-0734 


78.582 


8.5960 


6.7552 


78.585 


4.7206 


3.7096 


78.583 


8.2120 


6.4536 


78.587 


9-1349 


7.1787 


78.585 


IO.OI56 


7.8702 


78.579 


4.6482 


3.6526 


78.580 


8.9315 


7.0184 


78.580 


10.7144 


8.4196 


78.582 


3.0036 


2.3602 


78.579 






Mean, 78.582, .0006 



* Compt. Rend., 97, 951. 1883. 
f Ann. der Chem., 232, 324. 1886. 



NICKEL AND COBALT. 301 

Cobalt. 

CoO. Co. Per cent. Co. 

6.3947 5-0284 78.634 
6.6763 5.2501 78.638 
5.6668 4.45 60 78.633 
2.9977 2.3573 78.637 
8.7446 6.8763 78-635 
3.2625 2.5655 78.636 

6.3948 5.0282 78.630 
8.2156 6.4606 78.638 
9.4842 7.458o 78.636 
9.9998 7.8630 78.632 

Mean, 78.635, .0002 

Shortly after the discovery of nickel carbonyl, NiC 4 O 4 , Mond, Langer, 
and Quincke*made use of it with reference to the atomic weight of 
nickel. The latter was purified by distillation as nickel carbonyl, then 
converted into oxide, and that was reduced by hydrogen in the usual 
way. 

NiO. Ni. Per cent. Ni. 

.2414 .1896 78.542 

.3186 .2503 78.562 

.3391 .2663 78.531 

Mean, 78.545, .0061 

Schutzenberger's experiments,t published in 1892, were also few in 
number. First, nickel sulphate, dehydrated at 440, was calcined to 
oxide. 

3.505 grm. NiSO 4 gave 1.690 NiO. 48.217 per cent. 

26008 " 1.2561 " 48.297 " 

Mean, 48.257, .027 

Second, nickel oxide was reduced in hydrogen, as follows : 

1.6865 grm. NiO gave 1.3245 Ni. 78.535 per cent. 

1.2527 " .9838 " 78.533 " 

Mean, 78.534 

Iii one experiment with cobalt oxide, 3.491 grm. gave 2.757 Co, or 
78.975 per cent. In view of the many determinations of this ratio by 
other observers, this single estimation may be neglected. The experi- 
ments on nickel sulphate, however, should be combined with those of 
Marignac and Baubigny, giving the latter equal weight with Schutzen- 
berger's, thus : 

*Journ. Chem. Soc., 57, 753. 1890. 
tConipt. Rend., 114, 1149. 1892. 



302 



THE ATOMIC WEIGHTS. 

Marignac 48.287, .0675 

Baubigny 48.280, .027 

Schutzenberger 48.257, .027 



General mean. ..... 48.269, .018 

From this point on the determination of these atomic weights is com- 
plicated by the questions raised by Kriiss as to the truly elementary 
character of nickel and cobalt. If that which has been called nickel 
really contains an admixture of some other hitherto unknown element, 
then all the determinations made so far are worthless, and the investiga- 
tions now to be considered bear directly upon that question. First in 
order comes Remmler's research upon cobalt.* This chemist, asking 
whether cobalt is homogeneous, prepared cobaltic hydroxide in large 
quantity, and made a series of successive ammoniacal extracts from it, 
twenty-five in all. Each extract represented a fraction, from which, by 
a long series of operations, cobalt monoxide was prepared, and the latter 
was reduced in hydrogen after the manner of Russell. The actual deter- 
minations began with the second fraction, and the data are subjoined, 
the number of the fraction being given with each experiment : 



CoO. 


Co. 


Percent. Co. 


2 09938 


.07837 


78.859 


3 i52i 


.11814 


78.650 


4 .22062 


.17360 


78.687 


5 390H 


.30681 


78.647 


6 .28820 


.22661 


78.629 


7 3434 


.26968 


78.615 


8 43703 


.34321 


78.532 


9 9H77 


.71864 


78.560 


10 63256 


.49661 


78.508 


ii 32728 


.25701 


78.529 


12 .38042 


.29899 


78.595 


13 16580 


.13027 


78.571 


14 I.OI6O7 


79873 


78.610 


15 I-3I63S 


1-03545 


78.661 


16 91945 


.72315 


78.650 


17 53 IQ o 


.41773 


78.668 , 


18 82381 


.64728 


78.572 


19 81139 


.63754 


78.574 


20 76698 


.60292 


78.610 


21 LI3693 


.89412 


78.643 


22 2.OO259 


1-57495 


78.646 


23 1.04629 


.82185 


78.549 


24 48954 


.38466 


78.576 


25 69152 


.54326 


78.560 






Mean, 78.613, .0099 



*Zeit. Anorg. Chem., 2, 221. Also more fully in an Inaugural Dissertation, E)rlangen, 



NICKEL AND COBALT. 303 

Considered with reference to the purpose of the investigation, this 
mean and its probable error have no real significance. But it is very 
close to the means of other experimenters, and a study of the variations 
represented by the several fractions seems to indicate fortuity rather 
than system. Remmler regards his results as indicating lack of homo- 
geneity in his material ; but it seems more probable that such differences 
as exist are due to experimental errors and to impurities acquired in the 
long process of purification to which each fraction was submitted, rather 
than to any uncertainty regarding the nature of cobalt itself. For either 
interpretation the data are inconclusive, and I therefore feel justified in 
treating the mean like other means, and in combining it finally with 
them. 

From the same point of view that is, with reference to the supposed 
heterogeneity of nickel Kruss and Schmidt * carried out a series of frac- 
tionations of the metal by distillation in a stream of carbon monoxide. 
Nickel oxide, free from obnoxious impurities, was first reduced. to metal 
by heating in hydrogen, after which the current of carbon monoxide was 
allowed to flow. The latter, carrying its small charge of nickel tetra- 
carbonyl was then passed through a Winkler's absorption apparatus con- 
taining pure aqua regia, from which, by evaporation, nickel chloride was 
obtained, and from that, by reduction in hydrogen, the nickel. Ten 
such fractions were successively prepared and studied ; first, by prepa- 
ration of NiO and its reduction in hydrogen ; and, secondly, in some 
cases, by the reoxidation of the reduced metal, so as to give a synthetic 
value for the ratio Ni : 0. The data obtained are as follows, the successive 
fractions being numbered : 

Reduction of NiO. 
NiO. Ni. Per cent. Ni. 



J 1 .3722 


.2926 


78.614 


' 1 .7471 


.5870 


78.571 


2 { .7659 
I .7606 


.60085 
.5961 


78.450 
78.372 


0.0175 


.7984 


78.467 


3. -j 1.2631 


.99065 


78.430 


(1.2582 


.9868 


78.429 


4- -! ' 5I93 


.4076 


78.490 


\ .9200 


.7215 


78.424 


f -4052 


.3179 


78.455 


'* 1 . 6 5 J 8 


.5111 


78.414 


6 I * 5623 


4399 


78.232 


' 1 .5556 


4350 


78.294 


( -9831 


.7724 


78.568 


7- -j .9765 


.7646 


78.300 


(. -9639 


7557 


78.400 



*Zeit. Anorg. Chem., 2, 235. 1892. 



304 



THE ATOMIC WEIGHTS. 




2. 



3- 



5- 



Ni. 
.5870 
6011 

.7988 

9913 

.9868 

.4093 
.7216 

394 



6. 



.4415 
.4350 
7752 

7- 1 .7667 
.7558 
4555 
445 6 
.44415 
4423 
2508 
2467 



4538 
.4451 
.4438 
.4272 
.2491 
.2467 
.3904 
.3891 



Oxidation qf Ni. 

NiO. 

7471 

7659 

.7606 
1.0175 
1.2631 
1.2582 

.5193 
.9200 
.4052 
.6518 
5 62 3 
555 6 
.9831 



1 



10. 



( .3918 
1.3891 



.9639 

5756 

.56765 

.5663 

.5642 

.3174 

.3H8 

.4976 

.4961 



78.839 
78.411 
78.368 
78.400 
78.481 
78.367 
78.457 
78.432 

Mean, 78.444, =h .0166 



Per cent. Ni. 

78.571 
78.372 
78.359 
78.506 
78.482 
78.429 
78.818 

78.435 
78.825 
78.414 

78.517 
78.294 

78.853 

78.515 
78.411 

79-135 
78.499 
78.43 
78.394 
79-015 
78.367 

78.738 
78.432 



Mean, 78.557, .0319 



To these data of Kriiss and Schmidt the remarks already made con- 
cerning Remmler's work seem also to apply. The variations appear to 
be fortuitous, and not systematic, although the authors seem to think 
that they indicate a compositeness in that substance which has been 
hitherto regarded as elementary nickel. There is doubtless something 
to be said on both sides of the question ; but if Kriiss and Schmidt are 
right, all previous atomic weight determinations for cobalt and nickel 
are invalidated. In view of all the evidence, therefore, I prefer to regard 
their varying estimations as affected by accidental errors, and to treat 
their means like others. On this basis, their work combines with previ- 



NICKEL AND COBALT. 305 

ous work as follows, Schulzenberger's measurements of the ratio NiO : Ni 
being assigned equal weight with those of Mond, Langer, and Quincke : 

Russell 78.593, .0018 

Zimmermann 78.582, .0006 

Mond, Langer, and Quincke 78.545, .0061 

Schutzenberger 78.534, .0061 

Kriiss and Schmidt, reduction series 78.444, .0166 

Kriiss and Schmidt, oxidation series 78.557, zh .0319 

General mean 78-57, db .0006 

In 1889 Winkler * published a short paper concerning the gold method 
for determining the atomic weights in question, but gave in it no actual 
measurements. In 1893 f he returned to the problem with a new line 
of attack, and at the same time he takes occasion to criticise Kriiss and 
Schmidt somewhat severely. He utterly rejects the notion that either 
nickel or cobalt contain any hitherto unknown element, and ascribes the 
peculiar results obtained by Kriiss and Schmidt to impurities derived 
from the glass apparatus used in their experiments. For his own part 
he now works with pure nickel and cobalt precipitated electrolytically 
upon platinum, and avoids the use of glass or porcelain vessels so far 
as possible. With material thus obtained he operates by two distinct 
but closely related methods, both starting with the metal, nickel or 
cobalt, converting it next into neutral chloride, and then measuring the 
chloride gravimetrically in one process, volumetrically in the other. 

After precipitation in a platinum dish, the nickel or cobalt is washed 
with water, rinsed with alcohol and ether, and then weighed. It is next 
dissolved in pure hydrochloric acid, properly diluted, and by evapora- 
tion to dryness and long heating to 150 converted into anhydrous chlo- 
ride. The nickel chloride thus obtained dissolves perfectly in water, 
but the cobalt salt always gave a slight residue in which the metal was 
electrolytically determined and allowed for. In the redissolved chloride, 
by precipitation with silver nitrate, silver chloride is obtained, giving a 
direct ratio between that compound and the nickel or cobalt originally 
taken. The gravimetric data are as follows, with the metal equivalent 
to 100 parts of silver chloride given in a final column : 

Nickel 



Ni. 


Aga. 


Ratio. 




.3011 


1.4621 


20.594 




.2242 


1.0081 


20.605 




.5166 


2.5108 


20.570 




.4879 


2.3679 


20.605 




3827 


1.8577 


20.601 




3603 


75i7 


20.568 








Mean, 20.590, 


.0049 



* Ber. Deutsch. Chem. Gesell., 22, 891. 
fZeit. Anorg. Chem., 4, 10. 1893. 
20 



306 



THE ATOMIC WEIGHTS. 



Co. 

.3458 
3776 

4493 
.4488 
.2856 
.2648 



Cobalt. 

AgCl. Ratio. 

1.6596 20.836 

1.8105 20.856 

2.1521 20.877 

2.1520 20.855 

1.3683 20.873 

1.2768 20.886 

Mean, 20.864, .0050 



In the volumetric determinations the neutral chloride, prepared as 
before, was decomposed by means of a slight excess of potassium car- 
bonate, and in the potassium chloride solution, after removal of the 
nickel or cobalt, the chlorine was measured by titration by Volhard's 
method with a standard solution of silver. The amount of silver thus 
used was comparable with the metal taken. 

Nickel. 



Ni. 
.1812 
.1662 
.2129 
.2232 
.5082 
1453 



Co. 

.177804 
.263538 
.245124 
.190476 
.266706 
263538 



Af. 

.6621260 
.6079206 
7775252 
.8162108 

.8556645 
. 53 r 5 4<> 



Cobalt. 



.6418284 
.9514642 
.8855780 
.6866321 
.9629146 
.9503558 



Ratio. 
27.366 

27.339 
27.382 
27.346 
27.386 
27.338 

Mean, 27.359, - OO 59 



Ratio. 
27.702 
27.699 
27.679 

27.741 
27.696 

27-73 1 



Mean, 27.708, .0064 



In view of the possibility that the cobalt chloride of the foregoing ex- 
periments might contain traces of basic salt; Winkler, in a supplement- 
ary investigation,* checked them by another process. To the electrolytic 
cobalt, in a platinum dish, he added a quantity of neutral silver sulphate 
and then water. The cobalt gradually went into solution, and metallic 
silver was precipitated. The weights were as follows : 



Co. 

2549 
.4069 



Ag. 

.9187 
1.4691 



* Zeit. Anorg. Chem., 4, 462. 1893. 



NICKEL AND COBALT. 307 

On examination of the silver it was found that traces of cobalt were 
retained less than 0.5 mg. in the first determination and less than 0.2 
mg. in the second. Taking these amounts as corrections, the two experi- 
ments give for the ratios Ag. 2 : Co : : 100 : x the subjoined values : 

27.706 
27.687 

These figures confirm those previously found, and as they fall within 
the limits of the preceding series, they may fairly be included in it, when 
all eight values give a mean of 27.705, .0050. 

Still another method, radically different from all of the foregoing pro- 
cesses, was adopted by Winkler in 1894.* The metals were thrown down 
electrolytically upon platinum, and so weighed. Then they were treated 
with a known excess of a decinormal solution of iodine in potassium 
iodide, which redissolved them as iodides. The excess of free iodine was 
then determined by titration with sodium thiosulphate, and in that way 
the direct ratio between metal and haloid was ascertained. The results 
were as follows, with the metal proportional to 100 parts of iodine given 
in the third column : 

Cobalt. 

WL Co. Wt. I. 

2.128837 
2.166750 

First series \ .5290 2.254335 

2.908399 
2.861617 

2.209694 

Second series.. ^ .5267 2.246037 

2.268736 

Mean, 23.462, .0027 
Nickel. 

Wt. Ni. Wt. I. Ratio. 

.5144 2.217494 23.251 

.4983 2.148502 23.246 

First series.. .. ^ .5265 2.268742 23.260 

.6889 2.970709 23.243 

.6876 2.965918 23.237 

f.5120 2.205627 23.267 

Second series. . 1 .5200 2.240107 23.267 

(.5246 2.259925 23.267 





Mean, 23.255, .0091 

In these experiments, as well as in some previous' series, a possible 
source of error is to be considered in the occlusion of hydrogen by the 



* Zeitsch. Anorg. Chem., 8, i. 1894. 



308 THE ATOMIC WEIGHTS. 

metals. Accordingly, in a supplementary paper, Winkler* gives the 
results of some check experiments made with iron, which, however, was 
not absolutely pure. The conclusion is that the error, if existent, must 
be very small. 

In 1895 Hempel and Thiele's work on cobalt appeared. f First, cobalt 
oxide, prepared from carefully purified materials, was reduced in hydro- 
gen. The weights of metal and oxygen are subjoined, with the percent- 
age of cobalt in the oxide deduced from them : 

Co. O. Percentage. 

.90068 .24429 78.664 

.79159 .21445 78.686 

1.31558 .357i6 78.648 



Mean, 78.666, .0074 

This mean combines with former means as follows : 

Russell ........... . ..................... 78.592, d= .0023 

Zimmermann ............................ 78-635, .0002 

Retnmler ............................ .*. , 78.613, .0099 

Hempel and Thiele ...................... 78.666, .0074 



General mean 78.633, .0002 

In their next series of experiments, excluding a rejected series, Hempel 
and Thiele weighed cobalt, converted it into anhydrous chloride, and 
noted the gain in weight. In four of the experiments the chloride was 
afterwards dissolved, precipitated with silver nitrate, and then the silver 
chloride was weighed. The data are as follows : 

Co. Cl Taken Up. AgCl. 

.7010 - 8 453 

3138 -3793 

.2949 .3562 1.4340 

.4691 .5657 2.2812 

.5818 .7026 2.8303 

.5763 .6947 

.5096 .6142 2.4813 

From these weights we get two ratios, thus : 



C7 2 : Co : 100 : X, 


2AgCl : Co : : IOO : x. 


82.929 


20.565 


82.731 


20.564 


82.791 


20.556 


82.924 


20.538 


82.807 




82.957 


Mean, 20.556, .0043 


82.970 




Mean, 82.873, .0241 



* Zeitsch. Anorg. Chem., 8, 291. 1895. 
fZeitsch. Aiiorg. Chem., n, 73. 



NICKEL AND COBALT. 309 

The second of these ratios was also studied by Winkleiyand the two 
series combine as follows : 

Winkler 20.864, =b .0050 

Hempel and Thiele.^. 20.556, rb .0043 

General mean 20.687, =b - OO 33 

Hempel and Thiele apply to it a correction for silver chloride retained 
in solution, but its amount is small and not altogether certain. For 
present purposes the correction may be neglected. 

For the atomic weight of nickel we now have ratios as follows : 

(I.) Per cent, of Ni in NiC,O 4 .3H 2 O, 29.084, .006 

(2.) Per cent, of CO 2 from NiC 2 O 4 .2H 2 O, 44.098, rb .027 

(3.) Per cent, of Ni in NiC 2 O 4 .2H 2 O, 31.408, .0026 

(4.) Per cent, of CO 2 from NiC 2 O 4 .2H 2 O, 47.605, =h .053 

(5.) Per cent, of Ni in brucia nickelocyanide, 5.7295, .0034 

(6.) Per cent, of Ni in strychnia nickelocyanide, 6.595, =fc .005 

(7.) Per cent, of NiO in NiSO 4 , 48.269, rb .018 

(8.) Per cent, of Ni in NiO, 78.570, .0006 

(9.) Ag 2 : NiCl 2 : : 100 : 60.194, rb .0061 

(10.) 2AgCl : Ni : : 100 : 20.590, rb .0049 

(n.) Ag 2 : Ni : : 100 : 27.359, $9 

(12.) Au 2 : Ni 3 : : 100 : 45.209, .019 

(13.) BaSO 4 : K 2 Ni(SO 4 ) 2 .6H 2 O : : 100 : 93.6505. .001 

(14.) Ni : H 2 : : 100 : 3.4211, .001 

(15.) I 2 : Ni : : IOO : 23.255, .0091 

To the reduction of these ratios the following atomic and molecular 
weights are applicable : 

O = 15.879, db .0003 I = 125.888, rb .0069 

C = 11.920, rb .0004 K 38.817,1^.0051 

N = 13.935, rb .0021 Ba = 136.392, .oo86 

S = 31.828, rb. 0035 Au = 195.743, rb .0049 

Ag = 107.108, rb .0031 AgCl= 142.287, rb .0037 
Cl = 35- T 79, .0048 

Since the proportion of water in the oxalates is not an absolutely cer- 
tain quantity, the data concerning them can be best handled by employ- 
ing the ratios between carbon dioxide and the metal. Accordingly, ratios 
(1) and (2) give a single value for Ni, and ratios (3) and (4) another. In 
all, there are thirteen values for the atomic weight in question : 

From (i) and (2) Ni = 57.614, rb .0372 

From (5) " =57.625, rb. 0343 

From (3) and (4) " = 57.635, rb .0644 

From (6) " = 57.687, rb .0439 

From (8) " = 58.218, rb .0020 

From (7) " 58.268, .0428 

From (13) " = 58.448, rb .0206 



310 THE ATOMIC WEIGHTS. 

From (14) Ni 58.456, .0316 

From (15) , " = 58.551, rb .0231 

From (9) " = 58.587, =b .0179 

From (10) . . . " = 58.594, .0141 

From (u)... . "=58.607,^.0128 

From (12.) " = 58.994, zb .0248 

General mean Ni = 58.243, .0019 

If = 16, this becomes Ni = 58.687. 

It is quite evident here that ratio (8), which includes the marvelously 
concordant determinations of Zimmermann, far outweighs all the other 
data. Whether so excessive a weight can justifiably be assigned to one 
set of measurements is questionable, but the general mean thus reached 
is not far from midway between the highest and lowest of the values, and 
hence it may fairly be entitled to provisional acceptance. No one of the 
individual values rests upon absolutely conclusive evidence, so that no 
one can be arbitrarily chosen to the exclusion of the others. Further 
investigation is evidently necessary. 

For cobalt we have sixteen ratios, as follows : 

(i.) Per cent, of Co in CoC 2 O 4 .2H 2 O, 32.5555, .0149 

(2.) Per cent, of CO 2 from CoC 2 4 .2H 2 O, 47-7475, =b .0213 

(3.) Per cent, of Co in CoO, 78.633, .0002 

(4.) Per cent, of Co in purpureocobalt chloride, 23.6045, .0018 

(5.) Per cent, of Co in phenylammonium cobalticyanide, 11.8665, .0124 

(6.) Per cent, of Co in ammonium cobalticyanide, 21.943, .029 

(7.) Per cent, of Co in brucia cobalticyanide, 3.7437, zb .0036 

(8.) Per cent, of Co in strychnia cobalticyanide, 4.5705, zb .005 

(9.) Per cent, of CoO in CoSO 4 , 48.287, .0135 

(10.) Ag 2 : CoCl 2 : : 100 : 60.200, .0095 

(n.) 2AgCl : Co : : 100 : 20.687, zb .0033 

(12.) Ag 2 : Co : : 100 : 27.705, .0050 

(13.) Au 2 : Co 3 : : 100 : 45.151, .025 

(14.) Co : H 2 : : 100 : 3.4110, .0009 

(15.) T 2 : Co : : 100 : 23.462, .0027 

(16.) C1 2 : Co : : 100 : 82.873, .0241 

From these, using the atomic weights already cited under nickel, and 
combining ratios (1) and (2), we get 

From (16) Co = 58.308, zb .0187 

From (9) " =. 58.321, .0288 

From (3) " = 58.437, .0014 

From (i o) "= 58.600, .0228 

From (14) " = 58.630, .0286 

From (5) " = 58.639, db .0619 

From (8) " = 58.696, =b .0642 

From (6) " 58.736, .0808 

From (4) " =58.774, .0071 

From (7) " = 58.791, .0566 



RUTHENIUM. 311 

From (i i) Co = 58.870, .0094 

From (13) " 58.920, .0327 

From (15) " = 59. 7 2 , .0075 

From (12) " = 59.349, .0108 

From (i) and (2) " = 59-5 62 , .0382 

General mean , Co = 58.487, .0013 

If = 16, this becomes Co = 58.932. 

Here again the oxide ratio, because of Zimmermann's work, receives 
excessive and undue weight. The arithmetical mean of the fifteen values 
is Co = 58.781. Between this and the weighted general mean the truth 
probably lies, but the evidence is incomplete, and more determinations 
are needed. 



RUTHENIUM. 

The atomic weight of this metal has been determined by Claus and 
by Joly. Although Claus* employed several methods, we need only 
consider his analyses of potassium rutheniochloride, K 2 RuCl 5 . The salt 
was dried by heating to 200 in chlorine gas, but even then retained a 
trace of water. The percentage results of the analyses are as follows^ 

Ru. 2KCI. C/ 3 . 

28.96 40.80 30.24 

28.48 41.39 30.22 

28.91 41.08 30.04 

Mean, 28.78 41.09 30.17 

Reckoning directly from the percentages, we get the following dis- 
cordant values for Ru : 

From percentage of metal Ru = 102.45 l 

From percentage of KC1 " = 106.778 

From percentage of C1 3 " = 96.269 

These results are obviously of little importance, especially since the 
best of them is not in accord with the position of ruthenium in the 
periodic system. The work of Joly is more satisfactory. f Several com- 
pounds of ruthenium were analyzed by reduction in a stream of hy- 
drogen with the following results : 

* Journ. fur Prakt. Chem., 34, 435. 1845. 
fCompt. Rend., 108, 946. 



312 THE ATOMIC WEIGHTS. 

First, reduction of Ru0 2 : 



Ru. Per cent. Ru. 
2.1387 1.6267 76.060 

2.5846 1.9658 76.058 

2.3682 i. 8016 76.075 

2.8849 2 - J 939 76.046 



Mean, 76.060, rb .0040 



Second, reduction of the salt RuCl 3 .NO.H 2 : 

Per cent. Ru. 

39-78 
39.66 

Mean, 39.72, . 0405 

Third, reduction of RuCl 3 .N0.2NH 4 Cl : 

Per cent. Ru. 
29.44 
29.47 



Mean, 29.455, .0101 

Computing with = 15.879, .0003 ; N = 13.935, .0021, and Cl = 
35.179, =h .0048, these data give three values for ruthenium, as follows: 

1. From RuO 2 Ru = 100.922, .0178 

2. From RuCl 3 .NO.H 2 O " = 100.967, . 1 102 

3. From RuCl 3 .NO.2AmCl " = 100.868, .0387 

General mean Ru = 100.913, .0160 

If = 16, Ru=101.682. 



RHODIUM. 313 



RHODIUM. 

Berzelius * determined the atomic weight of this metal by the analysis 
of sodium and potassium rhodiochlorides, Na 3 RhCl 6 , and K 2 RhCl 5 . The 
latter salt was dried by heating in chlorine. The compounds were ana- 
lyzed by reduction in. hydrogen, after the usual manner. Reduced to 
percentages, the analyses are as follows : 

In Na,RhCl 6 . 

Rh. 3 NaCl. <T/ 3 . 

26.959 45.853 27.189 

27.229 45-3 01 27.470 

...... ...... 27.616 

Mean, 27.094 Mean, 45.577 Mean, 27.425 

In K 



Rh. 2KCI. CI 3 . 

28.989 41-450 29.561 

From the analyses of the sodium salt we get the following values for 
Rh: 

P'rom per cent, of metal .................... Rh = 104.191 

From per cent, of NaCl .................... " = 102.449 

From per cent, of C1 3 ..................... " = 105.103 

From ratio between C1 3 and Rh ......... ..... " = 104.263 

From ratio between NaCl and Rh ...... ..... " = 103.544 

These are discordant figures ; but the last one fits in fairly well with 
the values calculated from the potassium compound, which are as 
follows : 

From per cent, of metal .................... Rh 103.499 

" From per cent, of KC1 ..................... " = 103.648 

From per cent, of C1 3 ...................... " = 103.485 

From Rh : C1 3 ratio ........................ '- = 103.495 

From Rh : KC1 ratio ....... . ............. " = 103.540 



Mean Rh = 103.533 

If = 16, this becomes Rh = 104.323. 

Jorgensen's determination,! so far as I can ascertain, was published 
only as a preliminary note, to the effect that the atomic weight of rho- 
dium is 103, nearly. No details are given. 

* Poggend. Annalen, 13, 435. 1828. 
t Journ. fur Prakt. Chem. (2), 27, 486. 



314 THE ATOMIC WEIGHTS. 

Seubert and Kobbe * determine the atomic weight by igniting rhodium 
pentamine chloride in hydrogen, and weighing the residual metal. Their 
results are given below : 



3 . Rh. Per cent. Rh. 

1.8585 .6496 34-953 

I -556o .5435 34.929 

1.5202 .5310 34-93 

2. 01 1 1 .7031 34.961 

1.8674 .6528 34.958 

2-4347 .8513 34-965 

2.3849 .8338 34.962 

2.5393 .8881 34-974 

1.4080 .4920 34-943 

1.4654 .5123 34.960 



Mean, 34-954, -0032 

In the sixth experiment the ammonium chloride formed was collected 
in a bulb tube, and estimated by weighing as silver chloride. 3.5531 
grms. of AgCl were obtained. 

Computing with N =13.935, .0021 ; Cl =35.179, -0048, and AgCl = 
142.287, .0037, we have 

From per cent, of metal ............ Rh = 102.215, .0143 

From AgCl ratio ................ " = 102.287, =b .0324 



General mean Rh = 102.227, .0131 

If = 16, Rh = 103.006. 

In the second of these values the probable error given is only that due 
to the antecedent atomic weights of N, Cl, and AgCl. It is therefore 
lower than it should be. The two values, however, are fairly in agree- 
ment, and the result is satisfactory. 

* Ann. d. Chem., 260, 318. 1890. 



PALLADIUM. 315 



PALLADIUM. 

The first work upon the atomic weight of palladium seems to have 
been done by Berzelius. In an early paper* he states that 100 parts of 
the metal united with 28.15 of sulphur. Hence Pd = 113.06, a result 
which is clearly of no present value. 

In a later paper f Berzelius published two analyses of potassium pal- 
ladiochloride, K 2 PdCl 4 . The salt was decomposed by ignition in hydro- 
gen, as was the case with the double chlorides of potassium with platinum, 
osmium, and iridium. Reducing his results to percentages, we get the 
following composition for the substance in question : 

Pd. 2KCL C/ 2 . 

32.726 46.044 21.229 

32.655 45-741 21.604 

Mean, 32.690 Mean, 45.892 Mean, 21.416 

From these percentages, calculating directly, very discordant results 
are obtained : 

From percentage of metal Pd = 106.53 

From percentage of KC1 " = 104.13 

From percentage of C1 2 (loss) " = 1 10.20 

Obviously, the only way to get satisfactory figures is to calculate from 
the ratio between the Pd and 2KC1, eliminating thus the influence of 
water in the salt. The two experiments give, as proportional to 100 
parts of KC1, the following of Pd : 

71-075 
7i. 39 1 

Mean, 71.233, .1066 

Hence Pd = 105.419. 

In 1847 Quintus Icilius J published a determination, which need be 
given only for the sake of completeness. He ignited potassium palladio- 
chloride in hydrogen, and found the following amounts of residue. His 
weights are here recalculated into percentages : 

64.708 
64.965 
64.781 



Mean, 64.818 

From this mean, Pd= 111.258. This result has no present value. 

*Poggend. Annalen, 8, 177. 1826. 
t Poggend. Annalen, 13, 454. 1828. 

I "Die Atomgewichte vom Pd, K, Cl, Ag, C, und H, nach der Methode der kleinsten Quadrate 
berechnet." Inaug. Diss. Gottingen, 1847. Contains no other original analyses. 



316 



THE ATOMIC WEIGHTS. 



In 1889 Keiser's first determinations of this constant appeared.* Find- 
ing the potassium palladiochloride to contain u water of decrepitation," 
he abandoned its use, and resorted to palladiammonium chloride, 
Pd(NH 3 Cl) 2 , as the most available compound for his purpose. This 
salt, heated in hydrogen, yields spongy palladium, which was allowed 
to cool in a current of dry air, in order to avoid gaseous occlusions. The 
salt itself was dried, previous to analysis, first over sulphuric acid, and 
then in an air bath at a temperature from 120 to 130. Two series of 
experiments were made, the second series starting out from palladium 
produced by the first series. The data are as follows : 



Pd(NH,Cl},. 
.83260 
.72635 
.40280 
57940 
.89895 
.48065 

56015 

.82658 
2.40125 
1.10400 

933 10 



First Series. 
Pd. 

41965 
.86992 
.70670 
.79562 
.95650 
74570 
.78585 
.92003 
1.20970 
.55629 
.47010 



Percent. Pd. 
50.402 

50-391 
50.378 
50.375 
50.370 
50-363 
50.370 
50-369 
50.378 
50.389 
50.380 



Reduced to vacuum this becomes 50.360, 

Second Series. 



Pd. 

1.31900 
1.12561 

.87445 
.85210 
.86825 

.56535 

.59200 

1.22280 



2.61841 
2.23420 

73553 
.69160 
.72403 

.12222 

17457 
2.42760 



Mean, 50.379, .0008 



Per cent. Pd. 

50.374 
50-381 
50.385 
50.372 
50.362 
50.378 
50.401 
50-37I 



Mean, 50.378, 
Reduced to vacuum, 50.359 



.0028 



The reductions to vacuum are neglected by Keiser himself, but are here 
added in order to secure uniformity with later results by the same author. 
The mean of both series, thus corrected, gives Pd 105.74. 

Bailey and Lamb f made experiments upon several compounds of pal- 
ladium, but finally settled upon palladiammonium chloride, like Keiser. 



*Am. Chem. Journ., n, 398. 1889. 
t Journ. Chem. Soc., 61, 745. 1892. 



PALLADIUM. 317 

Two preliminary experiments, however, with potassium palladiochloride 
are given, in which the salt was reduced in hydrogen, and both Pd and 
KC1 were weighed. The data are as follows, with the ratio (calculated 
as with Berzelius' experiments) given in a third column : 

2KCI. Pd. Ratio. 

1.49767 1.05627 70.528 

.90484 .63738 70.441 

Mean, 70.485, ,0290 

Hence Pd = 104.312. 

The palladiammonium chloride was studied by two methods. First, 
weighed quantities of the salt were reduced in hydrogen, the ammonium 
chloride so formed was collected in an absorption apparatus, and then 
precipitated with silver nitrate. The weights found were as follows, with 
the Pd(NH 3 Cl) 2 proportional to 100 parts of silver chloride given in the 
third column : 



AgCl. Ratio. 

24276 1.682249 73.879 

08722 1.468448 % 74.040 

47666 2.000164 73.828 

34887 1.837957 73.390 

74569 2.362320 73-898 



Mean, 73.807, .0742 



Hence Pd = 105.808. Bailey and Lamb regard this as too high, and 
suspect loss of NH 4 C1 during the operation. 

The second series of data resemble Reiser's. The salt was reduced in 
hydrogen, and the spongy palladium was weighed in a Sprengel vacuum. 
The data are as follows : 

Pd(NHzCr}v Pd. Per cent. Pd. 

A f 1.890597 -947995 50-H3 

' ( 1.874175 .940271 50.170 

( 1.307076 .654687 50.088 

B ! 1.340045 .633207 50.238 

'1 1-905536 .955950 5- l6 7 

1 1.685582 .846472 50.218 

1.691028 .849120 50.213 

2.112530 1.059690 50.162 

2.110653 1.057910 50.122 

1.969100 .988155 50.184 



Mean, 50.171, .0099 

Hence Pd = 104.943. Bailey and Lamb's weighings are all reduced 
to a vacuum. 



Ml: 



318 THE ATOMIC WEIGHTS. 

Keller and Smith,* reviewing Reiser's work, find that palladiam- 
monium chloride, prepared as Keiser prepared it, may retain traces of 
foreign metals, and especially of copper. Accordingly, they prepared a 
quantity of the salt, after a thorough and elaborate process of purifica- 
tion, dried it with extreme care, and then determined the palladium by 
electrolysis in silver-coated .platinum dishes. The precipitated palladium 
was dried under varying conditions, concerning which the original me- 
moir must be consulted, and was proved to be free from occluded hydro- 
gen. By this method two sets of experiments were made to determine 
the atomic weight of palladium ; but for present purposes the two may 
fairly be treated as one. The data obtained are as follows, but the 
weights do not appear to have been reduced to a vacuum : 

Pd(NH^Cl\. Pd. Percent. Pd. 

C i. 29960 .65630 50-504 

A. J 1.05430 .53 2 53 50.51 

(i.92945 -97455 50509 

f i. 94722 .98343 50.504 

1.08649 .54870 50.502 

28423 .64858 50.503 

68275 . .85010 S-5 1 9 

1.69113 -85431 5o.5 J 7 

1.80805 .91310 50.502 

Mean, 50.508, =b .0014 

Hence Pd 106.368, a result notably higher than Reiser's. 

Reller and Smith account for the difference between their determina- 
tions and Reiser's partly by the assumption that the materials used by 
the latter were not pure, and partly by considerations based on the pro- 
cess. In order to clarify the latter part of the question they made three 
sets of experiments by Reiser's method, slightly varying the conditions. 
First, the chloride was not pulverized before ignition, and slight decrepi- 
tation took place, while dark stains of palladium appeared in the reduc- 
tion tube, indicating loss by volatilization. Secondly, the chloride was 
prepared from crude palladium exactly as described by Reiser, but was 
pulverized before reduction. No decrepitation ensued, but traces of pal- 
ladium were volatilized. The third series, also on finely pulverized 
material, was like the second ; but the palladiammonium chloride was 
purified by Reller and Smith's process. The three series, here treated 
as one, are as follows : 

Pd(NH z Cl) v Pd. Per cent. Pd. 

.62955 -3 r 743 50-422 

First series.... J -77*70 .38942 5 O-397 

.83252 .41918 50.350 

9955 .49895 50.371 

*Amer. Cheni. Journ., 14, 423. 1892. 




PALLADIUM. 319 

Pd(NH. A Cl}r Pd. Percent. Pd. 

.51468 5-372 

55590 50.388 

Second series. J ' 666 9 O -33590 50.367 

43733 50-360 

71255 50.382 

.58050 50.376 

.48502 50.403 

Third series...^ "*<* 4 9 2 94 50.401 

47517 50.4H 

43405 50-430 

Mean, 50.388, .0043 

The three series seem to be fairly in agreement between themselves, 
and with Reiser's work, but diverge seriously from the electrolytic data. 

Keller and Smith also attempted to determine the atomic weight of 
palladium by heating the palladiammonium chloride in sulphuretted 
hydrogen, and so converting it into the sulphide, PdS. These data were 
obtained : 

Pd(NH. i Cl)^ PdS. Percent. CdS. 

.71699 .47066 65.644 

1.31688 .86445 65.659 



Mean, 65.651, .0051 

Hence Pd =-. 106.55. This result, however, is affected by the work of 
Petrenko-Kritschenko,* who has shown the existence of the sulphide 
PdS to be uncertain. 

Joly and Leidie,f in their determinations of this atomic weight, re- 
turned to the potassium palladiochloride, K 2 PdCl 4 . In their first series 
of experiments the salt was dried in vacuo at ordinary temperatures. It 
was then electrolyzed in a solution acidulated with hydrochloric acid, 
both the deposited palladium and the potassium chloride being weighed. 
The palladium was dried, ignited in a stream of hydrogen, and cooled in 
an atmosphere of carbon dioxide. The results were as follows, with the 
column added by me giving the Pd equivalent to 100 parts of KC1 : 
K,PdCl,. Pd. 2 KCl. Ratio. 

1.0255 .3919 -5520 70.996 

1.2178 .3937 .5551 70.924 

1.2518 .4048 .5687 71.016 

Mean, 70.979, =b .0188 

This series was rejected by the authors, because the salt was found to 
contain water in one case 0.23 per cent. This error, however, should 

*Zeit. Anorg. Chem., 4, 251. 1893. 

t Compt. Rend., 116, 147. 1893. 



320 THE ATOMIC WEIGHTS. 

not invalidate the Pd : KC1 ratio. In a second series the palladiochlo- 
ride was dried in vacuo at 100, giving the following data : 



Pd. zKCl. Ratio. 

1.3635 .4422 .6186 7M84 

3.0628 .9944 i.39 2 9 7 I -39 I 

1.4845 .4816 .6782 71.011 

1.7995 -5838 .8206 7M43 



Mean, 71.257, db .0736 

These experiments seem to be less concordant than the preceding set. 
It must be noted, however, that the authors reject the KC1 determina- 
tions and compute directly from the ratio between the salt and the metal. 
But the ratio here chosen agrees best with the determinations made by 
other observers, giving for this series the mean value Pd = 105.455, and 
is, moreover, uniform with the data given by Berzelius and by Bailey 
and Lamb. 

Joly and Leidie also give two experiments made by reducing the 
K 2 PdCl 4 in hydrogen, with the subjoined results : 



Pd. 2KCL Ratio. 

2.4481 -7949 1.1168 7LI77 

1.8250 .5930 .8360 70 933 



Mean, 71.055, rb .0823 

Combining these data with previous series, we have 

Berzelius 7 I -233, .1066 

Bailey and Lamb 70.485, .0290 

Joly and Leidie, first 70.979, .0188 

Joly and Leidi, second 7 I - 2 57, =b -736 

Joly and Leidie, third 71.055, .0823 

General mean 70.865, d= .0150 

In view of the discordance among the determinations hitherto cited 
and because of the criticisms made by Keller and Smith, Keiser, jointly 
with Miss Mary B. Breed,* repeated his former work, with some varia- 
tions and added precautions to ensure accuracy. His general method 
was the same as before, namely, the reduction of palladiammonium 
chloride by a stream of hydrogen. First, palladium was purified by 
distillation as PdCl 2 at low red heat in a current of chlorine. From this 
chloride the palladiammonium salt was then prepared. Upon heating 
the compound gently in a stream of hydrogen, decomposition ensued 
absolutely without decrepitation or loss of palladium by volatilization. 
Neither source of error existed. The results obtained were these : 

*Am. Chetn. Journ., 16, 20. 1894. 



PALLADIUM. 321 

Pd(NH,Cl\. Pd. Per cent. Pd. 

1.60842 .80997 50-358 

2.08295 1.04920 50.371 

2.02440 1-01975 50.373 

2.54810 1.28360 50.375 

I-75505 .88410 50-375 



Mean, 50.370, .0023 
Reduced to vacuum, 50.351 

In a second series of experiments, palladium was purified as in the 
earlier investigation, but with special care to eliminate rhodium, iron, 
copper, gold, mercury, etc. The palladiammoniura salt prepared from 
this material gave as follows : 

Pd(NH. A Cl} r Pd. Per cent. Pd. 

1.50275 .75685 50.364 

1.23672 .62286 50-365 

1-34470 .67739 50.375 

i .49S9 .75095 50-379 



Mean, 50.371, i .0026 
Reduced to vacuum, 50.352 

Here, again, no loss from decrepitation or volatilization occurred, 
although evidence of such loss was carefully sought for. The data thus 
obtained may now be combined with the previous series, thus : 

Keiser, first series 50.360, dr .0008 

Keiser, second series 5-359, =b .0028 

Bailey and Lamb 50. 171, .0099 

Keller and Smith, electrolytic 50.508, rh .0014 

Keller and Smith, hydrogen series 50.388, dr .0043 

Keiser and Breed, first series 5O-35 1 , =b .0023 

Keiser and Breed, second series 5-35 2 > .0026 



General mean 50.388, dr .00062 

For palladium, ignoring the work of Quintus Icilius, the subjoined 
ratios are now available : 

(i.) 2KC1 : Pd : : 100 : 70.865, dr .0150 
(2.) Per cent. Pd in Pd(NH 3 Cl),, 50.388, dr .00062 
(3.) 2AgCl : Pd(NH 3 Cl) 2 : : 100 : 73.807, dr .0742 
(4.) Pd(NH 3 Cl) 2 : PdS : : 100 : 65.651, dr .0051 

The antecedent data are 

Cl = 35.179, i .0048 S = 3 1." 828, +3 .0015 

K = 38.817, .0051 AgCl = 142.287, .0037 

N = 13.935, dr .C02I 

21 



THE ATOMIC WEIGHTS. 

Hence, for the atomic weight of palladium, we have 

From (i) Pd = 104.874, it .0243 

From (2) " 105.858, .0200 

From (3) " = 105.808, .2117 

From (4) " = 106.550, =b .0491 



General mean I'd 105.556, .0147 

With O = 16, Pd = 106.364. 

Taking the values separately, the second is probably the best ; but in 
view of the work done by Bailey and Lamb on one side, and by Keller 
and Smith on the other, it cannot be accepted unreservedly. Until the 
cause of variation in the results is clearly determined, it is better to take 
the general mean of all the data, as given above. 



OSMIUM. 

The atomic weight of this metal has been determined by Berzelius, by 
Fremy, and by Seubert. 

Berzelius * analyzed potassium osmichloride, igniting it in hydrogen 
like the corresponding platinum salt. 1.3165 grammes lost .3805 of 
chlorine, and the residue consisted of .401 grm. of potassium chloride, 
with .535 grm. of osmium. Calculating only from the ratio between the 
Os and the KC1, the data give Os = 197.523. 

Fremy's determination f is based upon the composition of osmium 
tetroxide. No details as to weighings or methods are given ; barely the 
final result is stated. This, if = 16, is Os = 199.648. 

When the periodic law came into general acceptance, it became clearly 
evident that both of the foregoing values for osmium must be several 
units too high. A redetermination was therefore undertaken by Seubert,J 
who adopted methods based upon that of Berzelius. First, ammonium 
osmichloride was reduced by heating in a stream of hydrogen. The 
residual osmium was weighed, and the ammonium chloride and hydro- 
chloric acid given off were collected in a suitable apparatus, so that the 
total chlorine could be estimated as silver chloride. The weights were 
as follows : 

Am 2 OsCl B . Os. 6AgCl. 

1.8403 7996 3.5897 

2.0764 .9029 4.0460 

2.1501 .9344 . 4.195 

2.1345 .9275 4.1614 

*Poggend. Annalen, 13, 530. 1828. 

fCompt. Rend., 19, 468. Journ. fiir Prakt. Chem., 31, 410. 1844. 

J Bericnte Deutsch. Chem. Gesell., 21, 1839. l888 - 



OSMIUM. 323 

Hence we have for the percentage of osmium and for the osmichloride 
proportional to 100 parts of AgCl 

Per cent. Os. AgCl : Salt. 

43.446 51.266 

43.484 $1.32 

43-458 51-254 

43-453 5L293 



Mean, 51.283, .0099 



In a later paper * two more reductions are given, in which only osmium 
was estimated. 

Sail. Os. Percent. Os. 

2.6687 1.1597 43.45 6 

2.6937 1.1706 43-457 

These determinations, included with the previous four as one series, 
give a mean percentage of Os in Am 2 OsCl 6 of 43.459, .0036. 

Secondly, potassium osmichloride was treated in the same way, but 
the residue weighed consisted of Os + 2KC1. From this the potassium 
chloride was dissolved out, recovered by evaporating the solution, and 
weighed separately. The volatile portion, 4HC1, was also measured by 
precipitation as silver chloride. In Seubert's first paper these data are 
given : 

Os. 2KCI. 4AgCl. 



2.5148 ..... .7796 2.9837 

2.1138 .8405 .6547 2.5076 

Hence, with salt proportional to 100 parts of AgCl in the last column 
we have 

Per cent. Os. Per cent. KCl. AgCl : Salt. 

...... 31.000 84.091 

39.762 3 .973 84.102 



Mean, 84.097, .0030 

In his second paper Seubert gives fuller data relative to the potassium 
osmichloride, but treats it somewhat differently. The salt was reduced 
by a stream of hydrogen as before, but after that the boat containing the 
Os -{- 2KC1 was transferred to a platinum tube, in which, by prolonged 
heating in the gas, the potassium chloride was completely volatilized. 
The determinations of 4C1 as 4 AgCl were omitte \. Two series of data 
are given, as follows : 

*Ann. d. Chem., 261, 258. 



324 THE ATOMIC WEIGHTS. 



Os. Percent. Os. 

1.1863 .4691 39-543 

.9279 -3667 39-5*9 

1.0946 .433 39-558 

1.6055 .6351 39.558 

4495 .1778 39-555 

.8646 .3417 39.521 

.7024 .2781 39-593 

1.2742 .504! 39-562 

1.0466 -4H 1 39.566 



Mean, 39.553, rb .0052 

KfisClv 2KCL Percent. KCl. 

2.2032 .6820 3O.955 

2.0394 .6312 30.950 

2.7596 .8544 30.961 

2.4934 .77io 30.922 

2.8606 .8843 30.913 

2.8668 .5768 30.898 

1.2227 .3778 30899 



Mean, 30.931 

t/ 3 '- C 
'130.973 



, 31.000 
Earlier set. ' J 



Mean of all nine determinations, 30.941, dr .0079 

The single percentage of osmium in the earlier memoir is obviously to 
be rejected. 

The ratios to examine are now as follows : 

(i.) Per cent. Os in Am 2 OsC) 6 , 43.459, dr .0036 

(2.) 6AgCl : Am 2 OsCl 6 : : loo : 51.283, dr .0099 

(3.) 4AgCl : K 2 OsCl 6 : : IOO : 84.097, .0030 

(4.) Per cent. Os in K 2 OsCl 6 , 39.553, dr .0052 

(5.) Per cent. KCl in K 2 OsCI 6 , 30.951, dr .0079 

To reduce these ratios we have 

Cl = 35.179, db .0048 KCl = 74.025, .0019 

K =38.817, rb .0051 AgCl= 142.287, rb .0037 

N = 13.935, .0021 

Hence there are five independent values for osmium, as follows : 

From (i) Os = 190.111, rb .0300 

From (2) " = 190.870, .0901 

From (3) " = 189.928, =b .0371 

From (4) " = 188.914, =b .0243 

From (5) " = 189.571, =b .0928 



General mean Os == 189.546, .0163 

If = 16, Os = 190.990. 



IRIDIUM. 325 

These figures serve to fix the place of osmium below iridium in the 
periodic classification of the elements, but are not concordant enough to 
be fully satisfactory. More determinations are evidently needed. 



IRIDIUM. 

The only early determination of the atomic weight of iridium was 
made by Berzelius,* who analyzed potassium iridichloride by the same 
method employed with the platinum and the osmium salts. The result 
found from a single analysis was not far from Ir = 196.7. This is now 
known to be too high. I have not, therefore, thought it worth while to 
recalculate Berzelius' figures, but give his estimation as it is stated in 
Roscoe and Schorlemmer's " Treatise on Chemistry." 

In 1878 the matter was taken up by Seubert,f who had at his disposal 
150 grammes of pure iridium. From this he prepared the iridichlorides 
of ammonium and potassium (NH 4 ) 2 IrCl 6 and K 2 IrCl 6 , which salts were 
made the basis of his determinations. The potassium salt was dried by 
gentle heating in a stream of dry chlorine. 

Upon ignition of the ammonium salt in hydrogen, metallic iridium 
was left behind in white coherent Iamina3. The results obtained were as 
follows : 

Ir. Per cent. Jr. 



1-3164 .5755 43725 

1.7122 .7490 43-745 

1.2657 .5536 43-739 

1.3676 .5980 43.726 

2.6496 1.1586 43-739 

2.8576 1.2489 43-705 

2.9088 1.2724 43-74 2 



Mean, 43-732, .0035 

The potassium salt was also analyzed by decomposition in hydrogen 
with special precautions. In the residue the iridium and the potassium 
chloride were separated after the usual method, and both were estimated. 
Eight analyses gave the following weights : 



KJrCl* 


C/ 4 , Loss. 


Ir. 


KCl. 


1.6316 


.4779 


.6507 


5030 


2.2544 


.6600 


.8993 


6953 


2.1290 


.6238 


.8488 


.6560 


1.8632 


5457 


743 


.5745 


2.6898 


.7878 


1.0726 


.8291 


2-3719 


.6952 


9459 


.7308 


2.6092 


.7641 


1.0406 


.8040 


2.5249 


7395 


1.0070 


7775 



* Poggend. Annalen, 13, 435. 1828. 

fBer. Deutsch. Chem. Gesell., n, 1767. 1878. 



326 THE ATOMIC WEIGHTS. 

Hence we have the following percentages, reckoned on the original 
salt: 

Ir. 2 KCL Cl,. 

39.881 30.829 29.290 
39.890 30. 842 29.277 
39.868 30-813 29.300 

39.876 30-835 29.289 

39.877 30-825 29.287 
39.879 3.8n 29.310 

39.882 30.814 29.285 

39.883 30.792 29.288 

Mean, 39.880, =fc .0015 Mean, 30.820, .0037 Mean, 29.291, =b .0024 

Joly * studied derivatives of iridium trichloride. The salts were dried 
at 120, and reduced in hydrogen. With IrCl 3 .3KC1.3H 2 he found as 

follows : 

Salt. Ir. KCl. 

1.5950 .5881 .6803 

1.6386 -6037 .7000 

2.6276 .9689 1.1231 

These data, if the weight of the salt itself is considered, give discordant 
results, but the ratio Ir : 3KC1 : : 100 : x is satisfactory. The values of x 

are as follows : 

115.677 

115.952 



Mean, 115.848, .0583 

The ammonium salt, IrCl 3 .3NH 4 Cl, gave the subjoined data : 

Wt. of Salt. Wt. of Ir. Per cent. Ir. 

1.5772 .6627 42.017 

1.6056 .6742 41.990 



Mean, 42.003, .0094 

To sum up, the ratios available for iridium are these : 

(i.) Per cent. Ir in Am 2 IrC) 6 , 43.732, .0035 
(2.) Per cent. Ir in K 2 IrCl 6 , 39.880, .0015 
(3.) Per cent. KCl in K 2 IrC) 6 , 30.820, .0037 
(4.) Per cent. C1 4 in K 2 IrCl 6 , 29.291, =b .0024 
(5.) Per cent. Ir in Am 3 IrCl 6 , 42.003, .0094 
(6.) Ir : 3KC1 : : 100 : 115.848, .0583 

The data for computation are 

O == 15.879, i .0003 N = 13.935, .o 21 

Cl = 35.179, .0048 KG] = 74.025, .0019 

K =. 38.817, .0051 H = i 

*Compt. Rend., no, 1131. 1890. 



PLATINUM. 327 

And the six independent values for the atomic weight of iridium be- 
come 

From (i) Ir = 191.935, .0300 

From (2) " = 191.511, .0221 

From (3) " = 191.604, .0485 

From (4) " = 191.641, .0622 

From (5) " = 191-833, .0641 

From (6) , " = 191.695, .0966 



General mean Ir = 191.664, .0154 

If 0=16, Ir= 193.125. 



PLATINUM. 

The earliest work upon the atomic weight of this metal was done by 
Berzelius,* who reduced platinous chloride and found it to contain 73.3 
per cent, of platinum. Hence Pt = 193.155. In a later investigation f 
he studied potassium chloroplatinate, K 2 PtCl 6 . 6.981 parts of this salt, 
ignited in hydrogen, lost 2.024 of chlorine. The residue consisted of 
2.822 platinum and 2.135 potassium chloride. From these data we may 
calculate the atomic weight of platinum in four ways : 

1. From loss of Cl upon ignition Pt = 196.637 

2. From weight of Pt in residue " = 195.897 

3. From weight of KC1 in residue " = 195.384 

4. From ratio between KCl and Pt " = 195.690 

The last of these values is undoubtedly the best, for it is not affected 
by errors due to the possible presence of moisture in the salt analyzed. 

The work done by Andrews J is even less satisfactory than the foregoing, 
partly for the reason that its full details seem never to have been pub- 
lished. Andrews dried potassium chloroplatinate at 105, and then 
decomposed it by means of zinc and water. The excess of zinc having 
been dissolved by treatment with acetic and nitric acids, the platinum 
was collected upon a filter and weighed, while the chlorine in the filtrate 
was estimated by Pelouze's method. Three determinations gave as fol- 
lows for the atomic weight of platinum : 




Mean, 197.887 

Unfortunately, Andrews does not state how his calculations were made. 

*Poggend. Annalen, 8, 177. 1826. 
fPoggend. Annaleti, 13, 468. 1828. 
I British Assoc. Report, 1852. Chera. Gazette, 10, 



328 THE ATOMIC WEIGHTS. 

In 1881 Seubert* published his determinations, basing them upon 
very pure chloroplatinates of potassium and ammonium. The ammo- 
nium salt, (NH 4 ) 2 PtCl 6 . was analyzed by heating in a.stream of hydrogen, 
expelling that gas by a current of carbon dioxide, and weighing the 
residual metal. In three experiments the hydrochloric acid formed 
during such a reduction was collected in an absorption apparatus, and 
estimated by precipitation as silver chloride. Three series of experi- 
ments are given, representing three distinct preparations, as follows : 

Series I. 
Am. 2 PtCl 6 . Pt. Percent. Pt, 

2.1266 .9348 43-957 

1.7880 .7858 43.948 

1.8057 .7938 43-960 

2.6876 1.1811 43-946 

4 7^74 2.0959 43-963 

2.0325 .8935 43.961 

Mean, 43.956, =b .002 

Series II. 
Am^PtCl^. Pt. Per cent. Pt. 

3- 46o .3363 43-87 1 

2.6584 .1663 43-876 

2.3334 .0238 43-872 

1,9031 .8351 43-88: 

3.1476 .3810 43.875 

2.7054 .1871 43-889 

Mean, 43.876, .001 

Another portion of this preparation, recrystallized from water, of 1,4358 
grm. gave 0.6311 of platinum, or 43.955 per cent. 





Series III. 




Am.PtCl,. 


Pt. 


Per cent. Ft. 


2.5274 


1.11*8 


43-99 


3.2758 


1.4409 


43.986 


1.9279 


.8483 


44.001 


2.0182 


.8884 


44.020 


1.8873 


8303 


43-994 


2.2270 


.9798 


43.996 


2.4852 


1.0936 


44.004 


2.5362 


i.i i 66 


44.026 


3.0822 


I-356I 


43 99 s 






Mean, 44.001, .003 



*Ber. Deufcsch. Chem. Gesell., 14, 865. 



PLATINUM. 329 

If these series are treated as independent and combined, giving each 
a weight as indicated by its probable error, and regarding the single ex- 
periment with preparation II as equal to one in the first series, we get 
a mean percentage of 43.907, .0009. On the other hand, if we regard 
the twenty-two experiments as all of equal weight in one series, the mean 
percentage of platinum becomes 43.953, .0078. Upon comparing the 
work with that done later by Halberstadt, the latter mean seems the fairer 
one to adopt. 

For the chlorine estimations in the ammonium salt, Seubert gives the 
subjoined data. I add in the last column the weight of salt proportional 
to 100 parts of silver chloride. 

Am^PtCl^. Pt. 6AgCl. Ratio. 

2.7054 1.1871 . 5.2226 51.802 

2.2748 .9958 4.3758 5L9S6 

3.0822 i-356i 5-9496 S'-SoS 

Mean, 51.864, .041 

The potassium salt, K. 2 PtCl 6 , was also analyzed by ignition in hydro- 
gen, treatment with water, and weighing both the platinum and the 
potassium chloride. The weights given are as follows : 



Pt. zKCl. 

5.0283 2.0173 i.544o 

7.0922 2.8454 2.1793 

3.5475 1.4217 1.0890 

3-2296 1.2941 .9904 

35834 1-4372 i.iooi 

4.4232 1.7746 1.3547 

4.0993 1.6444 1.2589 

4.4139 1.7713 1.3516 

Hence we have these percentages, reckoned on the original salt 

KCl. 
30.706 
30.728 
30.698 
30.666 
30.700 
30.627 
30.710 
30.621 




Mean, 40.107, .005 Mean, 30.682, .009 

As with the ammonium salt, three experiments were made upon the 
potassium compound to determine the amount of chlorine (four atoms 
in this case) lost upon ignition in hydrogen. In the fourth column I 
add the amount of K 2 PtCl 6 corresponding to 100 parts of AgCl : 



330 THE ATOMIC WEIGHTS. 



PL *AgCL Ratio. 

6.7771 2.7158 7.9725 85.006 

3.5834 L4372 4.2270 84.774 

4.4139 1.7713 5-2144 84.648 

Mean, 84.809, .071 

Halberstadt,* like Seubert, studied the chloroplatinates of potassium 
and ammonium, and also the corresponding double bromides and platinic 
bromide as well. The metal was estimated partly by reduction in hy- 
drogen, as usual, and partly by electrolysis. Platinic bromide gave the 
following results : 

I. By Reduction in H. 

PtBr^. Pt. Per cent. Pt. 

.6396 .2422 37.867 

1.7596 .6659 37.844 

.9178 .3476 37.873 

1.1594 .4388 37.847 

1.9608 .7420 37.842 

2.0865 .7898 37.853 

4.0796 1.5422 37-852 

6.8673 2.5985 37-8j9 

77. By Electrolysis. 

1.2588 .4763 37-837 

1-4937 .5649 37-819 



Mean of all ten experiments, 37.847, .0033 

The ammonium platinbromide, (NH 4 ) 2 PtBr 6 , was prepared in two 
ways, and five distinct lots were studied. With this salt, as well as with 
those which follow, the data are given in distinct series, with from one 
to several experiments in each group, but for present purposes it seems 
best to consolidate the material and so put it in more manageable form. 
The percentages of platinum and weights found are as follows : 

/. By Reduction in H. 

Pt. Percent. Pt. 



' .6272 


.1719 


27.408 


.0438 


.2865 


27.447 


.1724 


.3215 


27.422 


1 .4862 


.4076 


27.426 


.0811 


.2966 


27.435 


. .3383 


.3672 


27.437 



*Ber. Deutsch. Chem. Gesell., 17, 2962. 1884. 



PLATINUM. 



331 



PL 
.2769 
.3269 
.3611 
.6159 
.3668 

.4899 
1.1427 

3250 
.6591 
.6940 

.4705 
.6316 
.8245 

I-3329 
.4210 
5594 
5751 



Per cent. PL 
27.426 
27.390 

27-393 
27.402 

27-45* 
27.431 
27.441 
27.460 
27.459 
27.438 

27-439 
27-444 
27.435 
27.430 

27.449 
27-457 
27.465 




II. By Electrolysis. 

.4272 27.409 

.4397 27.392 

.8569 27.439 

.3180 27.386 

.7081 27.427 

.2809 27.456 

.4591 27.418 

.4591 27.418 

4397 27.392 

Mean of all thirty-two experiments, 27.429, .0027 



With potassium platinbromide Halberstadt found as follows : 



f 2.5549 
| 2.6323 

j 2.93 '5 

3-4463 

1^4.0081 

3-9554 
2.0794 

2.1735 
2.3099 

1.4085 
2.6166 
2.6729 



PL 

.6630 
.6831 
.7598 
.8939 
1.0404 
1.0266 
.5388 

.5635 
.5986 

3645 
.6772 

.6923 



/. By Reduction in H. 



2 KBr. 

.8071 
.8318 

.9259 
1.0895 
1-2653 
1.2495 

.6558 
.6849 
.7297 

.4446 
.8279 
.8469 



Per cent. PL Per cent. KBr. 



25.940 
25.947 
25.910 
25-938 
25.957 
25.954 
25.911 
25.926 
25.914 
25.880 
25.881 
25.900 



3L590 
31-599 
31-584 
3L6I3 
31.568 

31-589 
3L538 
31.5" 
3L590 

3L565 
31.640 
31.684 



332 



THE ATOMIC WEIGHTS. 



$: 2 /^r 6 . 


Pt. 


sKBr. 


Percent. Pt. 


2. 21 10 


5726 


.6997 


25.898 


3.1642 


.8188 


9983 




1.9080 

1.6754 


4947 
4341 


.6025 
.5286 


25.927 
25-915 


1.3148 


3403 


.4160 


25.882 


L5543 


.4025 


.4911 


25-895 



By Electrolysis. 

Per cent. KBr. 
3L647 
3L550 
31-577 
3L550 
3^.640 

31.596 

Mean of eighteen experiments, 25.915, .0040 31.591, .0068 

For ammonium platinchloride Halberstadt gives the following data : 
/. By Reduction in H. 

Pt. 

.4.662 

.6087 

.6617 
1.0227 

.6059 

.7638 
1.2068 
1.4019 

2-4035 

J-532I 




Per cent. Pt. 

43-964 
43.962 



43.95 6 
43.880 
43.906 
44.011 
43-971 
43-984 
43.951 



9474 
1.1069 
1.5101 

5345 
1-6035 

1.9271 
1.1046 
1.4179 



//. By Electrolysis. 
.4161 
.4865 
.6634 
.2347 
.7044 

.8459 
.4858 
6233 



43.920 
43.951 
43.930 

43-9 10 
43-928 

43.894 
43-979 
43-959 



Mean of eighteen experiments, 43.943, .0054 
Seubert found, 43.953, .0078 

General mean, 43.946, .0044 

For potassium platinchloride Halberstadt's data are 
/. By Reduction in H. 



K.PtCl,. 


Pt. 


2KCI. 


Percent. Pt. 


Per cent. KCL 


f 1.6407 


.6574 


.5029 


40.069 


30-651 


1 1-9352 

{' 


7757 


5921 


40.084 


30.600 


L5793 


.6334 


.4836 


40.106 


30.621 


1.6446 


6595 


.5049 


40. 101 


. 30.700 


1.0225 
2.4046 


.4102 
.9641 


3133 

.7388 


40.117 
40.094 


30.640 
30.724 


f 5.8344 


2.3412 


1.7005 


40.127 


30.688 


(7.1732 


2.8776 


2.1998 


40.116 


30.666 



PLATINUM. 333 

77. By Electrolysis. 

PL 2KCL Per cent. Pt. Per cent. KCl. 

1.2354 .4953 .3792 40.092 30.695 

2.5754 1.0318 .7898 40.063 30.667 

L0933 .4387 .3355 40.126 30.668 

1.3560 .5438 .4167 40.103 30.730 

L7345 .6956 .5298 40.104 30.545 

2.0054 .8038 .6147 40.081 30.652 

2.0666 .8291 .6356 40.117 3O.755 

1.2759 .5"8 .3908 40.112 30.629 

1.9376 .7763 .5927 40.065 30.589 

2.3972 .9608 .7355 40.080 30.681 

1.2.7249 1.0929 .8364 40.108 30.691 



Mean of nineteen experiments, 40.098, rb .0031 30.663, .0080 
Seubert found, 40. 107, .0050 30.682, .0090 

General mean ,.40.101, d= .0026 30.671, .0060 

The work of Dittmar and M'Arthur* on the atomic weight of platinum 
is difficult to discuss and essentially unsatisfactory. They investigated 
potassium platinchloride, and came to the conclusion that it contains 
traces of hydroxyl replacing chlorine and also hydrogen replacing 
potassium. It is also liable, they think, to carry small quantities of 
potassium chloride. In their determinations, which involve corrections 
indicated by the foregoing considerations, they are not sufficiently ex- 
plicit, and give none of their actual weighings. They attempt, however, 
to fix the ratio 2KC1 : Pt, and after a number of discordant, generally 
high results, they give the following data for the atomic weight of plati- 
num based upon the assumption that 2KC1 = 149.182 : 

195.54 
195.48 
195.60 
195.37 



Mean, 195.50, .0330. 

Dittmar and M'Arthur also discuss Seubert's determinations, seeking 
to show that the latter also, properly treated, lead to a value nearer to 
195.5 than to 195. Seubert at once replied to them,f pointing out that 
the concordance between his determinations by very different methods 
(a concordance verified by Halberstadt's investigation) precluded the 
existence of errors due to impurities such as Dittmar and M'Arthur 
assumed. 

* Trans. Roy. Soc. Edinburgh, 33, 561. 1887. 
tBer. Deutsch. Chem. Gesell., 21, 2179. 1888. 



334 THE ATOMIC WEIGHTS. 

The ratios from which to compute the atomic weight of platinum are 
now as follows, rejecting the work of Berzelius and of Andrews : 

(i.) Percentage of Pt in ammonium platinchloride, 43.946, .0044 
(2.) Percentage of Pt in ammonium platinbromide, 27.429, db .0027 
(3.) Percentage of Pt in potassium platinchloride, 40.101, .0026 
(4.) Percentage of Pt in potassium platinbromide, 25.915, .0040 
(5.) Percentage of Pt in platinic bromide, 37.847, =b .0033 
(6.) Percentage of KC1 in potassium platinchloride, 30.671, .0060 
(7.) Percentage of KBr in potassium platinbromide, 31.591, =b .0068 
(8.) 6AgCl : Am 2 PtCl 6 : : 100 : 51.864, rb .041 
(9.) 4AgCl : K 2 PtCl 6 : : loo : 84.809, .071 
(10.) 2KC1 : Pt : : 149.182 : 195.50, dr .033 

Computing with the subjoined atomic and molecular weights 
Cl = 35.179, .0048 KC1 = 74.025, rb .0019 

Br = 79.344, .0062 KBr = 118.200, rb .0073 

K = 38.817, rb .0051 . AgCl = 142.287, .0037 

N = 13.935, .0021 

we have the following ten values for platinum : 

From (i) Pt = 193.603, rb .0336 

From (2) "= 193.493, .0248 

From (3) " = 193.283, =b .0254 

From (4) " = 193.684, db .0344 

From (5) " = 193.261, rfc .0248 

From (6) " = 193 938, rb .0746 

From (7) " = 194-538, =b . 1276 

From (8) " = 195.836, rb .3515 

From (9) " = 193.980, .4054 

From (10) " = 194.017, db .0331 

General mean . Pi = 193.443, .0114 

If = 16, Pt = 194.917. 

Of these ten values the first five are obviously the most trustworthy. 
Their general mean is Pt = 193.414, .0124 ; or, if = 16, Pt = 194.888. 
This result is preferable to the mean of all, even though the latter varies 
little from it. The five high values carry very little weight because of 
their larger probable errors. 



CERIUM. 335 



CERIUM. 

Although cerium was discovered almost at the beginning of the present 
century, its atomic weight was not properly determined until after the 
discovery of lanthanum and didymium by Mosander. In 1842 the in- 
vestigation was undertaken by Beringer,* who employed several methods. 
His cerium salts, however, were all rose-colored, and therefore were not 
wholly free from didymium ; and his results are further affected by a 
negligence on his part to fully describe his analytical processes. 

First, a neutral solution of cerium chloride was prepared by dissolving 
the carbonate in hydrochloric acid. This gave weights of eerie oxide and 
silver chloride as follows. The third column shows the amount of CeO 2 
proportional to 100 parts of AgCl : 

CeO 2 . AgCl. Ratio. 

5755 grm. 1.419 grm. 4O-557 

.6715 " 1.6595 " 40.464 

1.1300 " 2.786 " 40.560 

.5366 " i.33'6 " 40.297 

Mean, 40.469, .0415 

The analysis of the dry cerium sulphate gave results as follows. In 
a fourth column I show the amount of Ce0 2 proportional to 100 parts of 
BaS0 4 : 

Sulphate. CeO^. BaSO Ratio. 

1.379 grm. .8495 grm. 1.711 grm. 49.649 

1.276 " .7875 " 1.580 " 49.836 

1.246 " .7690 " 1.543 " 49.838 

1.553 " .9595 " 1.921 " 49.948 

Mean, 49.819, .042 

Beringer also gives a single analysis of the formate and the results of 
one conversion of the sulphide into oxide. -The figures are, however, 
not valuable enough to cite. 

The foregoing data involve one variation from Beringer's paper. 
Where I put Ce0 2 as found he puts Ce 2 O s . The latter is plainly inad- 
missible, although the atomic weights calculated from it agree curiously 
well with some other determinations. Obviously, the presence of didym- 
ium in the salts analyzed tends to raise the apparent atomic weight of 
cerium. 

Shortly after Beringer, Hermann f published the results of one experi- 
ment. 23.532 grm. of anhydrous cerium sulphate gave 29.160 grm. of 
BaS0 4 . Hence 100 parts of the sulphate correspond to 123.926 of BaS0 4 . 

*Ann. Chem. Pharm.,42, 134. 1842. 

t Journ. fur Prakt. Chem., 30, 185. 1843. 



336 THE ATOMIC WEIGHTS. 

In 1848 similar figures were published by Marignac,* who found the 
following amounts of BaS0 4 proportional to 100 of dry cerium sulphate : 




Mean, 122.40, .138 

If we give Hermann's single result the weight of one experiment in 
this series, and combine, we get a mean value of 122.856, .130. 

Still another method was employed by Marignac. A definite mixture 
was made of solutions of cerium sulphate and barium chloride. To this 
were added, volumetrically, solutions of each salt successively, until 
equilibrium was attained. The figures published give maxima and 
minima for the BaCl 2 proportional to each lot of Ce. 2 (SO 4 ) 3 . In another 
column, using the mean value for BaCl 2 in each case, I put the ratio 
between 100 parts of this salt and the equivalent quantity of sulphate. 
The latter compound was several times recrystallized : 



BaCl v Ratio. 

First crystallization ...... ii.ongrm. 11.990 12.050 grm. 91.606 

First crystallization. : ____ 13.194 " i4-3 6 5 T 4-425 " 91-657 



Second crystallization.. . . 


13.961 


15.225 15.285 


91.518 


Second crystallization.. . . 


12.627 " 


13.761 13.821 " 


9L559 


Second crystallization.. . . 


11.915 " 


12.970 13.030 " 


91-654 


Third crystallization 


14.888 < 


16.223 16.283 " 


91.602 


Third crystallization 


14.113 " 


I5.383 I5-423 " 


9L755 


Fourth crystallization.. . . 


13.111 " 


14.27014.330 " 


91.685 



Fourth crystallization 13.970 J 5-223 15.283 " 91.588 

Mean, 91.625, .016 

Omitting the valueless experiments of Kjerulf,f we come next to the 
figures published by Bunsen and Jegel J in 1858. From the air-dried 
sulphate of cerium the metal was precipitated as oxalate, which, ignited, 
gave Ce0 2 . In the filtrate from the oxalate the sulphuric acid was esti- 
mated as BaSO 4 : 

1.5726 grm. sulphate gave .7899 grm. CeO 2 and 1.6185 S rm - BaSO 4 . 
1.6967 " .8504 " 1.7500 " 

Hence, for 100 parts BaSO 4 , the CeO a is as follows : 

48.804 
48.575 



Mean, 48.689, d= .077 



*Arch. Sci. Phys. et Nat. (i), 8, 273. 1848. 

t Ann. Chem. Pharra., 87, 12. 

J Ann. Chem. Pharni., 105, 45. 1858. 



CERIUM. 337 

One experiment was also made upon the oxalate : 



353 S rm - oxalate gave .1913 CeO 2 and .0506 H 2 O. 

Hence, in the dry salt, we have 63.261 per cent, of CeO 2 . 

In each sample of Ce0 2 the excess of oxygen over Ce 2 3 was estimated 
by an iodometric titration ; but the data thus obtained need not be fur- 
ther considered. 

In two papers by Rammelsberg* data are given for the atomic weight 
of cerium, as follows. In the earlier paper cerium sulphate was analyzed, 
the cerium being thrown down by caustic potash, and the acid precipi- 
tated from the nitrate as barium sulphate : 

.413 grm. Ce 2 (SO 4 ) 3 gave .244 grm. Ce0 2 and .513 grm. BaSO 4 . 

Hence 100 BaSO 4 = 47.563 Ce0 2 , a value which may be combined with 
others, thus ; this figure being assigned a weight equal to one experi- 
ment in Bunsen's series : 

Beringer ............................... 49.819, .042 

Kunsen and Jegel ......................... 48.689, .077 

Rammelsberg ..... ....................... 47-5^3> -t- . 108 



General mean 49.360, =b .035 

It should be noted here that this mean is somewhat arbitrary, since 
Bunsen and Rammelsberg's cerium salts were undoubtedly freer from 
didymium than the material studied by Beringer, 

In his later paper Rammelsberg gives these figures concerning cerium 
oxalate. One hundred parts gave 10.43 of carbon and 21.73 of water. 
Hence the dry salt should yield 48.862 per cent, of CO 2 , whence Ce = 
137.14. 

In all of the foregoing experiments the eerie oxide was somewhat col- 
ored, the tint ranging from one shade to another of light brown according 
to the amount of didymium present. Still, at the best, a color remained, 
which was supposed to be characteristic of the oxide itself. In 1868, 
however, some experiments of Dr. C. Wolff were posthumously made 
public, which went to show that pure ceroso-ceric oxide is white, and 
that all samples previously studied were contaminated with some other 
earth, not necessarily didymium but possibly a new substance, the re- 
moval of which tended to lower the apparent atomic weight of cerium 
very perceptibly. 

Cerium sulphate was recrystallized at least ten times. Even after 
twenty recrystallizations it still showed spectroscopic traces of didymium. 
The water contained in each sample of the salt was cautiously estimated, 
and the cerium was thrown down by boiling concentrated solutions of 

* Poggend. Annalen, 55, 65 ; 108, 44. 

t Amer. Journ. Science and Arts (2), 46, 53. 



338 



THE ATOMIC WEIGHTS. 



oxalic acid. The resulting oxalate was ignited with great care. I de- 
duce from the weighings the percentage of Ce0 2 given by the anhydrous 
sulphate : 

CeO.^ 

.76305 grin. 

.7377 

.70665 " 



Sulphate. 
1.4542 grm. 
1.4104 " 
1.35027 " 



Water. 



. 19419 grrn. 
.1898 " 
.1820 " 



Percent. 
60.559 
60.437 
60.487 



Mean, 60.494 



After the foregoing experiments the sulphate was further purified by 
solution in nitric acid and pouring into a large quantity of boiling water. 
The precipitate was converted into sulphate and analyzed as before : 

Sulphate. Water. CeO.>. 

L4327 g rm - . 2 733 g rm - -69925 grm. 

1.5056 " .2775 " .7405 " 

1.44045 " .2710 " .7052 " 



Per cent. CeO. 2 . 
60.311 
60.296 
60.300 



Mean, 60.302 

From another purification the following weights were obtained : 

1.4684 grm. .1880 grm. .7717 grm. 60.270 per cent. 

A last purification gave a still lower percentage : 

t.3756 grm. .1832 grm. .7186 grm. 60.265 per cent. 

The last oxide was perfectly white, and was spectroscopically free from 
didymium. In each case the Ce0 2 was titrated iodometrically for its 
excess of oxygen. It will be noticed that in the successive series of de- 
terminations the percentage of Ce0 2 steadily and strikingly diminishes 
to an extent for which no ordinary impurity of didymium can account. 
The death of Dr. Wolf interrupted the investigation, the results of which 
were edited and published by Professor F. A. Genth. 

In the light of more recent evidence, little weight can be given to these 
observations. All the experiments, taken equally, give a mean percent- 
age of Ce0 2 from Ce 2 (S0 4 ) 3 of 60.366, .0308. This mean has obviously 
little or no real significance. 

The experiments of Wolf attracted little attention, except from Wing,* 
who partially verified certain aspects of them. This chemist, incidentally 
to other researches, purified some cerium sulphate after the method of 
Wolf, and made two similar analyses of it, as follows : 

Sulphate. Water. CeO. 2 . Percent. CeO. 2 . 

1.2885 grm. .1707 grm. .6732 grm. 60.225 

1.4090 " .1857 " .7372 " 60.263 

Mean, 60 244 



* Am. Journ. Sci. (2), 49, 358. 1870. 



CERIUM. 339 

The cerio oxide in this case was perfectly white. The cerium oxalate 
which yielded it was precipitated boiling by a boiling concentrated solu- 
tion of oxalic acid. The precipitate stood twenty-four hours before 
filtering. 

In 1875 Buehrig's * paper upon the atomic weight of cerium was issued. 
He first studied the sulphate, which, after eight crystallizations, still 
retained traces of free sulphuric acid. He found, furthermore, that the 
salt obstinately retained traces of water, which could not be wholly ex- 
pelled by heat without partial decomposition of the material. These 
sources of error probably affect all the previously cited series of experi- 
ments, although, in the case of Wolf's work, it is doubtful whether they 
could have influenced the atomic weight of cerium by more than one or 
two tenths of a unit. Buehrig also found, as Marignac had earlier shown, 
that upon precipitation of cerium sulphate with barium chloride the 
barium sulphate invariably carried down traces of cerium. Furthermore, 
the eerie oxide from the filtrate always contained barium. For these 
reasons the sulphate was abandoned, and the atomic weight determina- 
tions of Buehrig were made with air-dried oxalate. This salt was placed 
in a series of platinum boats in a combustion tube behind copper oxide. 
It was then burned in a stream of pure, dry oxygen, and the carbonic 
acid and water were collected after'the usual method. Ten experiments 
were made; in all of them the above-named products were estimated, 
and in five analyses the resulting eerie oxide was also weighed. By de- 
ducting the water found from the weight of the air-dried oxalate, the 
weight of the anhydrous oxalate is obtained, and the percentages of its 
constituents are easily determined. In weighing, the articles weighed 
were always counterpoised with similar materials. The following weights 
were found : 

Oxalate. Water. CO 2 . CeO. z . 

9.8541 grm. 2.i987grm. 3.6942 grm 

9.5368 " 2.1269 " 3-5752 " 

9.2956 " 2.0735 " 3.4845 " 

10.0495 " 2.2364 " 3-774 " 

10.8249 " 2.4145 " 4.0586 " 

9.3679 " 2.0907 " 3-5 118 " 4-6150 grm. 

9.7646 " 2.1769 " 3.6616 " 4.8133 " 

9.9026 " 2.2073 " 3.7139 s " 4-8824 " 

9.9376 " 2.2170 " 3.7251 " 4-8971 " 

9.5324 " 2.1267 " 3-5735 " 4-6974 " 



These figures give us the following percentages for C0 2 and Ce0 2 in the 
anhydrous oxalate : 

* Journ. fi'ir Prakt. Chem., 120, 222. 1875. 



340 THE ATOMIC WEIGHTS, 

CO. r CeO,. 

48.256 

48.249 

48.248 

48.257 

48.257 

48.258 63417 
48.257 63.436 
48.262 63.446 

48.249 63.429 
48.253 63.430 



Mean, 48.2546 .001 Mean, 63.4316, =b .0032 

These results could not be appreciably affected by combination with 
the single oxalate experiments of Jegel and of Rarnmelsberg, and the 
latter may therefore be ignored. 

Robinson's work, published in 1884,* was based upon pure cerium 
chloride, prepared by heating dry cerium oxalate in a stream of dry, 
gaseous hydrochloric acid. This compound was titrated with standard 
solutions of pure silver, prepared according to Stas, and these were 
weighed, not measured. In the third column I give the ratio between 
CeCl 3 and 100 parts of silver : 

CeCl 3 . Ag. Ratio. 

5.5361 7.26630 76.189 

6.0791 7-98377 76 172 

6.4761 8.50626 76.133 

6.98825 9.18029 76.122 

6.6873 8.78015 76.164 

7.0077 9.20156 76.158 

6.9600 9- r 393 76.150 



Mean 

Reduced to a vacuum this becomes 76.167. 

In a later paper, f Robinson discusses the color of eerie oxide, and 
criticises the work of Wolf. He shows that the pure oxide is not white, 
and makes it appear probable that Wolf's materials were contaminated 
with compounds of lanthanum. He also urges that Wolf's cerium sul- 
phate could not have been absolutely definite, because of defects in the 
method by which it was dehydrated. 

Brauner,J in 1885, investigated cerium sulphate with extreme care, 
and appears to have obtained material free from all other earths and 
absolutely homogeneous. The anhydrous salt was calcined with all 

* Chemical News, 50, 251. Nov. 28, 1884. Proc. Roy. Soc., 37, 150. 
t Chemical News, 54, 229. 1886. 
t Sitzungs. Wien. Akad., Bd. 92. July, 1885. 



CERIUM. 341 

necessary precautions, and the data obtained, reduced to a vacuum, were 
as follows : 

Ce. 2 (SO\. CeO r Percent. CeO 2 . 

2.16769 1.31296 60.5693 

2.43030 1.47205 60.5707 

2.07820 1.25860 60.5620 

2.21206 1.33989 60.5721 

1.28448 .77845 60.6043 

1.95540 1.18436 60.5687 

2.46486 1.49290 60.5673 

2.04181 1.23733 6o -5997 

2.17714 1.31878 60.5739 

2.09138 1.26654 60.5605 

2.21401 1.34139 60.5863 

2.44947 1.48367 60.5711 

2.22977 1.35073 60.5771 

2.73662 1.65699 60.5486 

2.62614 1.59050 60.5642 

1.67544 1.01470 60.5632 

1.57655 -95540 60.6007 

2.72882 1.65256 60.5600 

2.10455 1.27476 60.5716 

2 - IO 735 1.27698 60.5965 

2-43557 I-475 1 ? 60.5692 

3.01369 1.82524 60.5649 

4.97694 3.0I37 2 60.5537 

Mean, 60 5729, .0021 

This mean completely outweighs the work done by Wolf and Wing, 
so that upon combination the latter practically vanish. Wing's mean is 
arbitrarily given equal weight with Wolf's, and the combination is as 
follows : 

Wolf. 60.366, .0308 

Wing 60. 244, =b .0308 

Brauner 60.5729, .0021 



General mean 60.566, d= .0021 

In 1895 several papers upon the cerite earths were published by Schutz- 
^nberger.* In the first of these a single determination of atomic weight 
is given. Pure Ce0. 2 , of a yellowish white color, was converted into sul- 
phate, which was dried in a current of dry air at 440. This salt, dis- 
solved in water, was poured into a hot solution of caustic soda, made 
from sodium, and, after filtration and washing, the filtrate, acidulated 
with hydrochloric acid, was precipitated with barium chloride. The 
trace of sulphuric acid retained by the cerium hydroxide was recovered 
by re-solution and a second precipitation, and added to the main amount. 

* Compt. Rend., 120, pp. 663, 962, and 1143. 1895. 



342 THE ATOMIC WEIGHTS. 

100 parts of Ce,(S0 4 ) 3 gave 123.30 of BaS0 4 . This may be assigned equal 
weight with one experiment in Marignac's series, giving the following 
combination : 

Hermann 123 926, .238 

Marignac 122.40, .138 

Schutzenherger 123.30, .238 



General mean ..................... 122.958, . 1 139 

Schutzenberger, criticising Brauner's work, claims that the latter was 
affected by a loss of oxygen during the calcination of the cerium dioxide. 

In his second and third papers Schutzenberger describes the results 
obtained upon the fractional crystallization of cerium sulphate. Prepa- 
rations were thus made yielding oxides of various colors canary yellow, 
rose, yellowish rose, reddish, and brownish red. These oxides, by syn- 
thesis of sulphates, the barium-sulphate method, etc., gave varying values 
for the atomic weight of cerium, ranging from 135.7 to 143.3. Schutzen- 
berger therefore infers that cerium oxide from cerite contains small 
quantities of another earth of lower molecular weight ; but the results as 
given are not sufficiently detailed to be conclusive. The third paper is 
essentially a continuation of the second, with reference to the didymiums. 

Schutzenberger's papers were promptly followed by one from Brauner,* 
who claims priority in the matter of fractio nation, and gives some new 
data, the latter tending to show that cerium oxide is a mixture of at least 
two earths. One of these, of a dark salmon color, he ascribes to a new 
element, " meta-cerium." The other he calls cerium, and gives for it a 
preliminary atomic weight determination. The pure oxalate, by Gibbs y 
method, gave 46.934 per cent, of Ce0 2 , and, on titration with potassium 
permanganate, 29.503 and 29.506 per cent, of C 2 O 3 . Hence Ce = 138.799. 
In mean, this ratio may be written 

3 C 2 3 : 2Ce0 2 : : 29.5045 : 46-934, 

and to each of its numerical terms we may roughly assign the probable 
error .001. This is derived from the average of the two titrations, and 
is altogether arbitrary. 

The ratios, good and bad, for cerium now are 

(i.) Ce 2 (SO 4 \ s : 3BaSO 4 : : 100 : 122.958, d= .1139 

(2.) 3BaSO 4 : 2CeO 2 : : 100 : 49-36o, .035 

(3.) 3 BaCl 2 : Ce 2 (S0 4 ) 3 : : loo : 91.625, .016 

(4.) 3AgCl : CeO 2 : : loo : 40.469, .0415 

(5.) Percentage CeO 2 from Ce 2 (SO 4 ) 3 , 60.566, .0021 

(6.) Percentage CeO 2 from Ce 2 (C 2 O 4 > ) 3 , 63.4316, + .0032 

(7.) Percentage CO 2 from Ce 2 (C 2 O 4 ) 3 , 48.2546, =b .001. 

(8.) 3Ag : CeCl 3 : : IOO : 76.167, .0065 

(9-) 3 C 2 3 : 2Ce 2 : : 2 9.5 45, .001 : 46.934, -ooi 



*Chem. News, 71, 283. 



CERIUM. 343 

To reduce these ratios we have 

O = I5.879,:t.OOO3 C = II.92O, .OOO4 

Cl = 35.179, d= .0048 S = 31.828, zb .0015 

Ag = 107.108, dz .0031 Ba = 136.392, .0086 

i42.287, .0037 



From the ratios, with these intermediate data, we can get two values 
for the molecular weight of Ce 2 (S0 4 ) 3 , and five for that of Ce0 2 . For 
cerium sulphate we have 

From (i) ................... Ce 2 (SO 4 ) 3 = 565.404, . 1670 

From (3) ................... " = 568.304, db . 1054 

General mean ......... Ce z (SO 4 ) 3 = 567.478, .0891 

Hence Ce == 140.723, .0451. 
For eerie oxide the values are 

From (2) ...... ' ................. CeO 2 171.577, .1218 

From (4) ........... . ........... " = 172.746,^.1772 

From (5) ....................... " =r 170.879, .0115 

From (6) ....................... " =172.125,^.0177, 

From (9) ...................... " = 170.557, .0076 

General mean ............. CeO 2 = 170.827, .0060 

And Ce = 139.069, .0061. 

For cerium itself, four independent values are now calculable, as 
follows : 

From molecular weight of sulphate. . . Ce = 140.723, .0451 

From molecular weight of dioxide ... " = 139.069, rb .0061 

From ratio (8) .................... " = 139.206, .0263 

From ratio (7) ............... ..... " = 140.516, .0047 

General mean ............... Ce = 140. 1 13, =b .0036 

If = 16, Ce = 141.181. 

It must be admitted that this combination is of very questionable 
utility. Its component means vary too widely from each other, and in- 
volve too many uncertainties. Furthermore, Schutzenberger and Brau- 
ner both impugn the homogeneity of the supposed element, as it has 
hitherto been recognized. Even if no " meta-elements " are involved in 
the discussion, it seems clear, on chemical grounds, that the two lower 
values are really preferable to the two higher, and that ratio (7) receives 
excessive weight. The general mean obtained is probably a full unit too 
high. The value 139.1 is perhaps nearly correct. 



344 THE ATOMIC WEIGHTS. 



LANTHANUM. 

Leaving out of account the work of Mosander. and the valueless ex- 
periments of Choubine, we may consider the estimates of the atomic 
weight of lanthanum which are due to Hermann, Rammelsberg, Marig- 
nac, Czudnowicz, Holzmann, Zschiesche, Erk, Cleve, Brauner, Bauer, 
and Bettendorff. 

From Rammelsberg* we have but one analysis. .700 grm. of lantha- 
num sulphate gave .883 grm. of barium sulphate. Hence 100 parts of 
BaS0 4 are equivalent to 79.276 of La 2 (S0 4 ) 3 . 

Marignac.f working also with the sulphate of lanthanum, employed 
two methods. First, the salt in solution was mixed with a slight excess 
of barium chloride. The resulting barium sulphate was filtered off and 
weighed; but, as it contained some occluded lanthanum compounds, its 
weight was too high. In the filtrate the excess of barium was estimated, 
also as sulphate. This last weight of sulphate, deducted from the total 
sulphate which the whole amount of barium chloride could form, gave 
the sulphate actually proportional to the lanthanum compound. The 
following weights are given : 



, BaCl r ist BaSO,. 2 d BaSO,. 

4.346 grm. 4.758 grm. 5.364 grm. .115 grm. 

4-733 " 5.178 " 5-848 " .147 " 

Hence we have the following quantities of La,,(S0 4 ) 3 proportional to 
100 parts of BaS0 4 . Column A is deduced from the first BaS0 4 and 
column B from the second, after the manner above described : 



A. 


B. 




81.022 
80.934 


83.281 
83.662 




Mean, 80.978, .030 
From A 


Mean, 83.471, - 
La 


b.I28 

n8 4.7 


From B . . 




147. n 



A agrees best with other determinations, although, theoretically, it is 
not so good as B. 

Marignac's second method, described in the same paper with the forego- 
ing experiments, consisted in mixing solutions of La.,(S0 4 \. 5 with solutions 
of BaCl. 2 , titrating one with the other until equilibrium was established. 
The method has already been described under cerium. The weighings 

* Poggend. Annalen, 55, 65. 

t Arch. Sci. Phys. et Nat. (i), n, 29. 1849. 



LANTHANUM. 



345 



give maxima and minima for BaCl 2 . In another column I give La.,(S0 4 ) 3 
proportional to 100 parts of BaCl 2 , mean weights being taken for the 
latter : 

Ratio. 
91.004 
90.968 
91-297 
9'.332 
9 r -3 62 

9L475 
91.364 
91.615 
91.482 

Mean, 91.322, .048 

Hence La = 140.2. 

Although not next in chronological order, some still more recent work 
of Marignac's * may properly be considered here. The salt studied was 
the sulphate of lanthanum, purified by repeated crystallizations. In two 
experiments the salt was calcined, and the residual oxide weighed ; in 
two others the lanthanum was precipitated as oxalate, and converted into 
oxide by ignition. The following percentages are given for La 2 O 3 : 

"'5 I By calcination. 



La.,(SO 


BaCl v 


1 1. 644 g 


m. 12.765 12.825 


12.035 


' I 3-i95 I 3-265 


10.690 


' 11.669 11-749 


12.750 


13.920 14.000 


io.757 


11.734 11.814 


12.672 


13-813 13.893 


9.246 


10.080 10.160 


10.292 


11.204 1 1.264 


10.192 


( ii. in 11.171 



57.58 
57.50 

57-55 



jPpt. 



as oxalate. 



Mean, 57-5475, - OII 5 

The atomic weight determinations of Holzmann f were made by analy- 
ses of the sulphate and iodate of lanthanum, and the double nitrate of 
magnesium and lanthanum. In the sulphate experiments the lantha- 
num was first thrown down as oxalate, which, on ignition, yielded oxide. 
The sulphuric acid was precipitated as BaSO 4 in the filtrate. 



5'57 
.3323 
.4626 



.9663 grm. 
.6226 " 
.8669 " 



1.1093 grm. 
.7123 " 
.9869 " 



These results are best used by taking the ratio between the BaS0 4 , put 
at 100, and the La, 2 0. r The figures are then as follows : 

46.489 
46652 
46.873 



Mean, 46.671, .075 



* Ann. Chim. Phys. (4), 30, 68. 1873. 
t Journ. fur Prakt. Chem., 75, 321. 1858. 



346 THE ATOMIC WEIGHTS. 

In the analyses of the iodate the lanthanum was thrown down as oxa- 
late, as before. The iodic acid was also estimated volumetrically, but 
the figures are hardly available for present discussion. The following 
percentages of La 2 3 were found : 

23-454 
23.419 
23.468 

Mean, 23.447, .0216 

The formula of this salt is La 2 (I0 3 ) 6 .3H 2 0. 

The double nitrate, La 2 (N0 3 ) 6 .3Mg(N0 3 ) 2 .24H 2 0, gave the following 
analytical data : 



Salt. H^O. MgO. 

53 2 7 g rm - I 569grm. .0417 grm. .1131 grm. 

5931 " -1734 " -0467 " .1262 " 

.S 662 " .1647 " -0442 " .1197 " 

3757 " .0297 " .0813 " 

.3263 <( .0256 l< .0693 " 

These weighings give the subjoined percentages of La 2 3 : 

21.231 

21.278 
21.141 

21.640 
21.238 



Mean, 21.3056, .058 

These data of Holzmann give values for the molecular weight of La 2 s 
as follows : 

From sulphate , La 2 O 3 = 322.460 

From iodate " 320.726 

From magnesian nitrate " = 322.904 

Czudnowicz* based his determination of the atomic weight of lantha- 
num upon one analysis of the air-dried sulphate. The salt contained 
22.741 per cent, of water. 

.598 grm. gave .272 grm. La 2 O 3 and .586 grm. BaSO 4 . 

The La 2 3 was found by precipitation as oxalate and ignition. The 
BaSO 4 was thrown down from the filtrate. Reduced to the standards 
already adopted, these data give for the percentage of La 2 O 3 in the anhy- 
drous sulphate the figure 58.668. 79.117 parts of the salt are propor- 
tional to 100 parts of BaSO 4 . 

* Journ. fur Prakt. Chem., So, 33. 1860. 



LANTHANUM. 347 

Hermann * studied both the sulphate and the carbonate of lanthanum. 
From the anhydrous sulphate, by precipitation as oxalate and ignition, 
the following percentages of La 2 O 3 were obtained : 




Mean, 57.654, .016 

The carbonate, dried at 100, gave the following percentages : 

68.47 La 2 3 . 

27.67 C0 2 . 

3.86 H 2 0. 

Reckoning from the ratio between C0 2 and La 2 O 3 , the molecular weight 
of the latter becomes 324.254. 

Zschiesche's f experiments consist of six analyses of lanthanum sul- 
phate, which salt was dehydrated at 230, and afterwards calcined. I 
subjoin his percentages, and in a fourth column deduce from them the 
percentage of La 2 3 in the anhydrous salt : 

H^O. SO 3 . La-iO^ La z O 3 in Anhydrous Salt. 

22.629 33-470 43.909 56.745 
22.562 33.306 44.132 5 6 .9 6 4 
22.730 33.200 44.070 57-34 
22.570 33-333 44.090 56.947 
22.610 33.160 44.24 57- I 5 

22.630 33-05 1 44-3 10 57.277 

Mean, 57.021, .051 

Erk J found that .474 grm. of La 2 (S0 4 ) 3 ,by precipitation as oxalate and 
ignition, gave .2705 grm. of La 2 3 , or 57.068 per cent. .7045 grm. of the 
sulphate also gave .8815 grm. of BaS0 4 . Hence 100 parts of BaS0 4 are 
equivalent to 79.921 of La 2 (S0 4 ) 3 . 

From Cleve we have two separate investigations relative to the atomic 
weight of lanthanum. In his first series strongly calcined La 2 3 , spec- 
troscopically pure, was dissolved in nitric acid, and then, by evaporation 
with sulphuric acid, converted into sulphate : 

1.9215 grm. La 2 O 3 gave 3.3365 grm. sulphate. 57-59 P er cent. 



2.0570 


3.5705 


57.6ii 


it 


1.6980 " 


2.9445 


57.667 


< < 


2.0840 " 


3.6170 


57.6i7 





1.9565 , " 


3.396o 


57.612 


11 






Mean, 57.619, 


rb .0085 



* Journ. fur Prakt. Chem., 82, 396. 1861. 

t Journ. fur Prakt. Chem., 104, 174. 

I Jenaisches Zeitschrift, 6, 306. 1871. 

g K. Svensk. Vet. Akad. Handlingar, Bd. 2, No. 7. 1874. 



348 THE ATOMIC WEIGHTS. 

From the last column, which indicates the percentage of La 2 O 3 in 
La 2 (S0 4 ) 3 , we get, if SO, =* 80, La = 139.15. 

In his second paper,* published nine years later, Cleve gives results 
similarly obtained, but with lanthanum oxide much more completely 
freed from other earths. The data are as follows, lettered to correspond 
to different fractions of the material studied : 

B - ' 8 39 S rm . La 2 O 3 gave 1.4600 sulphate. 57.466 per cent. 

fi.i86i 2.0643 " 57458 " 

c I -8993 " L5645 " 57.482 

' | .8685 1.5108 " 57.486 " 

I .8515 " 1.4817 " 57.468 " 

D I .6486 " 1.1282 " 57.490 " 

' 1 .7329 1.2746 57oOO " 

E. 1.2477 2.1703 " 57.490 

F | 1.1621 2.0217 " 57.481 

' i 1-5749 " 2.7407 " 57-463 " 

G | 1.3367 2.3248 " 57.497 " 

.4455 " 2.5146 " 57-484 " 



Mean, 57.480, dz .0040 

Hence with S0 3 = 80, La = 138.22. 

From Brauner we also have two sets of determinations, both based upon 
the conversion of pure La 2 O 3 into La 2 (S0 4 ) 3 . 

In his first paper, Brauner f gives only two syntheses, as follows: 

1-75933 g rm - La 2 O 3 gave 3.05707 La a (SO 4 ) 3 . 57-5 6 6 per cent. 

.92417 " 1.60589 " 57-549 

Mean, 57-5575 

This mean we may regard as of equal weight with Marignac's, and 
assign to it the same probable error. 

In Brauner's second paper J six experiments are given ; but the weights 
are affected by a misprint in the second determination, which I am un- 
able to correct. Only five of the syntheses, therefore, are given below. 

7850 grm. La 2 O 3 gave 1.3658 La 2 (SO 4 ) 3 . 57-476 per cent. 

2.1052 " 3-6633 " 57.467 " 

i. ooio " I-74H " 57-5 2 5 

1.3807 " 2.4021 " 57-479 " 

1.5275 " 2.6588 " 57.451 



Mean, 57.480, db .0084 

Brauner's weighings are all reduced to a vacuum. 

Both Bauer and Bettendorff made their determinations of the atomic 

* K. Sveiisk. Vet. Akad. Handlingar, No. 2, 1883. 

t Journ. Chem. Soc., Feb., 1882, p. 68. 

I Sitzuugsb. Wien. Akad., June, 18*2, Bd. 86, II Abth. 



LANTHANUM. 349 

weight of lanthanum by the same general method as the preceding 
Bauer's data * are as follows : 

.6431 grm. La 2 O 3 gave 1.1171 sulphate. 57.569 per cent. 

.7825 " 1.3613 " 57.482 " 

1.0112 " I.757I " 57-549 " 

.7325 " 1.2725 " 57.564 " 

Mean, 57.541, =b .0136 

Bettendorff found f- 

.9146 grm. La 2 O 3 gave 1.5900 sulphate. 57-522 per cent. 

-9395 " '.6332 " 57.525 " 

.9133 " I-5877 " 57.523 " 

1.0651 1.8515 " 57.526 " 

Mean, 57.524, .0006 

We may now combine the similar means into general means, and de- 
duce a value for the atomic weight of lanthanum. For the percentage of 
oxide in sulphate we have estimates as follows. The single experiments 
of Czudnowicz and of Erk are assigned the probable error and weight of 
a single experiment in Hermann's series : 

Czudnowicz 58.668, =b .027 

Erk 57.o68, .027 

Hermann 57-654, rfc .016 

Zschiesche 57-O2I, .051 

Marignac 57-5475, .01 15 

Cleve, earlier series 57-6i9, .0085 

Cleve, later series 57-48o, .0040 

Brauner, earlier series 57-5575, =b - OI ! 5 

Brauner, later series 57.480, .0084 

Bauer 57-541, db .0136 

Bettendorff. 57-524, .0006 



General mean 57.522, .00059 

This result is practically identical with that of Bettendorff, whose work 
seems to receive excessive weight. The figure, however, cannot be far 
out of the way. 

For the quantity of La 2 (S0 4 ) 3 proportional to 100 parts of BaSO 4 . we 
have five experiments, which may be given equal weight and averaged 
together : 

Marignac , 81.022 

Marignac 80.934 

Rammelsberg 79.276 

Czudnowicz 79. 1 1 7 

Erk 79.921 

Mean, 80.054, .270 

* Freiburg Inaugural Dissertation, 1884. 
i Ann. d. Chem., 256, 168. 



350 THE ATOMIC WEIGHTS. 

Iii all, there are six ratios from which to calculate : 

(i.) Percentage of La. 2 O 3 in La 2 (SO 4 ) 3 , 57.522, .00059 

(2.) 3BaCl. 2 : La 2 (SO 4 ) 3 : : ioo : 91.322, .048 Marignac 

(3.) 3BaSO 4 : La 2 (SO 4 ) 3 : : ioo : 80.054, .270 

(4.) 3BaSO 4 : La 2 O 3 : : ioo : 46.671, .075 Holzmann 

(5.) Percentage of La 2 O 3 in iodate, 23.447, dr .0216 Holzmann 

(6.) Percentage of La 2 O 3 in magnesian nitrate, 21.3056, .058 Holzmann 

Hermann's single experiment on the carbonate is omitted from this 
scheme as being unimportant. 

For the reduction of these data we have 

O= 15.879, zh. 0003 N :: 13.935, .0021 

Cl 35.179, .0048 C = 11.920, .0004 
I = 125.888, .0069 Mg = 24. ioo, =b .001 1 

S = 31.828, -0015 Ba == 136.392, .0086 

For lanthanum sulphate two values are obtainable : 

From (2) La 2 (SO 4 ) 3 = 566.425, .2999 

From (3) " = 556.542,^1.8729 



General mean Ln 2 (SO 4 ) 3 = 566. 182, rh .2961 

Hence La = 140.075, .1481. 

For the oxide there are four independent values, as follows : 

From (i) La 2 O 3 = 322.825, .0090 

From (4) " = 322.460,^.5215 

From (5) " =320.726,^.3159 

From (6) " = 322.904, .9107 

A glance at these figures shows that the first alone deserves considera- 
tion, and that a combination of all would vary inappreciably from it. 
Taking, then, La 2 3 = 322.825, =fc .0090, we get- 
La = 137.594, =b .0046; 

or, with = 16, La = 138.642. 

If we take the concordant results of Cleve's and Brauner's later series, 
which give the percentage of La 2 3 in La 2 (S0 4 ) 3 as 57.480, then La = 
137.316. Possibly this value may be better than the other, but the evi- 
dence is not conclusive. 



THE DIDYMIUMS. 351 



THE DIDYMIUMS. 

Leaving Mosander's early experiments out of account, the atomic 
weight of the so-called u didymium " was determined by Marignac, Her- 
mann, Zschiesche, Erk, Cleve, Brauner, and Bauer. All of these data 
now have only historical value, and may be disposed of very briefly. 

Marignac* determined the ratios between didymium sulphate and 
barium sulphate, between silver chloride and didymia, and between 
didymium sulphate and didymium oxide. The other determinations all 
relate to the sulphate-oxide ratio. Leaving all else out of account, the 
earlier data for the percentage of Di 2 O 3 in Di 2 (SO 4 ) 3 are as follows. The 
atomic weight of Di in the last column is based upon SO 3 = 80 : 

Per cent. Z?/ 2 Oj. At. Wt. Di. 

Marignac, f five experiments 58.270 ! 43-56 

Hermann, J one experiment 58.140 142.67 

Zschiesche,^ five experiments .... 57-9 2 6 141.21 

Erk, || two experiments 58.090 i4 2 -33 

Cleve, ^[ six experiments 58.766 147.02 

Brauner,** three experiments 58.681 146.42 

The discordance of the determinations is manifest, and yet up to 1883 
the elementary nature of didymium seems to have been undoubted. In 
that year, however, Cleve and Brauner both showed, independently, that 
the didymia previously studied by them contained samaria, and that 
source of disturbance was eliminated. 

In Brauner 's investigation ft the didymium compounds were carefully 
fractionated, and the determinations of atomic weight were made by 
synthesis of the sulphate from the oxide in the usual way. Neglecting 
details, his first series gave results as follows : 

Per cent. Di^O y At. Wt. 

5 8 -5 6 I45-36 

58-526 145.50 

58.5 145-31 

58-515 I45-42 

58.53 1 145-53 

*Two papers: Arch. Sci. Phys. et Nat. (i), n, 29. 1849. Ann. Chim. Phys. (3), 38, 148. 1853. 
f Ann. Chim. Phys. (3), 38, 148. 1853. 
| Journ. fur Prakt. Chem., 82, 367. 1861. 
\ Journ. fi'ir Prakt. Chem., 107, 74. 
|| Jenaisches Zeitschrift, 6, 306. 1871. 
f K. Svensk. Vet. Akad. Handl., Bd. 2, No. 8. 1874. 
** Berichte, 15, 109. 1882. 

ft Journ. Chem. Soc., June, 1883. The values given are as computed by Brauner, with O = 16 
and S = 32.07. 



352 THE ATOMIC WEIGHTS. 

Another determination, with material refractionated from that used in 
his investigation of the previous year, gave 58.512 per cent. Di. 2 3 and 
Di = 145.40. 

These determinations, although concordant among themselves, are 
still about a unit lower than those published in 1882, indicating that in 
the earlier research some earth of higher molecular weight was present. 
Accordingly, another series of fractionations was carried out, and the 
several fractions of " didyrnia " obtained gave the following values : 
Fraction. Per cent. Di^O^. At.Wt.^Di." 

i 58.355 H4.32 

2 58.479 i45- 16 

3 5 8 -5o 145-39 

4 58.755 i47.io 

c J 59.071 149.35 

' ' 1 59-086 149.46 

The last fraction is evidently near samaria (Sm = 150), and this earth 
was proved to be present by a study of the absorption spectra of the 
material investigated. 

Similar results, but in some respects more explicit, were obtained by 
Cleve,* who also found that his earlier research had been vitiated by the 
presence of samaria. He gives two series of syntheses of sulphate from 
oxide, with two different lots of material, after eliminating samaria, and 
obtains, computing with S0 3 = 80, values for Di as follows : ' 

First Series. 

Per cent. Di 2 O 3 . At. Wt. Di. 

58.088 142.31 

58.113 142.49 

58.047 142-03 

58.099 142.39 

58.104 142.42 

58.098 142.38 

58.104 142.42 

58.103 142.42 

58.070 142.19 

58.079 142.25 

Second Series. 

Percent. >/ 2 6> 3 . At. Wt. Di. 

58.125 142.57 

58-093 H2.35 

58.088 142.31 

58.111 142.47 

58.056 142.10 
58.097 142.38 

58.057 142.10 

In short, the atomic weight of this " didymium " is not far from 142. 

*Bull. Soc. Chim., 39, 289. 1883. Ofv. K. Vet. Akad. Forhandl., No. 2, 1883. 



THE DIDYMIUMS. 353 

Bauer's little known determinations* were also made by the synthesis 
of the sulphate. They have corroborative value and are as follows : 

Per cent. >/ 2 <9 3 . At. Wt. Di. 

58.285 I43-56 

58.100 142.40 

58.133 142.64 

58.098 142.38 

In 1885 all of the foregoing determinations were practically brushed 
aside by Auer von Welsbaeh,f who by the most laborious fraction ations 
proved that the so-called " didymia " was really a mixture of oxides, 
whose metals he names neodidymium and praseodidymium, names 
which are now commonly shortened into neodymium and praseodymium. 
One of these metals gives deep rose-colored salts, the other forms green 
compounds, and the difference of color is almost as strongly marked as 
in the cases of cobalt and nickel. Their atomic weights, determined by 
the sulphate method, are given by Welsbach a 

Pr = 143.6 
Nd = 140.8 

No further details as to these determinations are cited, and whether 
they rest upon = 16, S0 3 = 80, or = 15.96 is uncertain. Fuller deter- 
minations are evidently needed. 

* Freiburg Inaugural Dissertation, 1884.. 
t Monatsh. Chem., 6. 4QO. 1885. 



23 



354 THE ATOMIC WEIGHTS. 



SCANDIUM. 

Clove,* who was the first to make accurate experiments on the atomic 
weight of this metal, obtained the following data : 1.451 grm. of sulphate, 
ignited, gave .5293 grm. of Sc 2 3 . .4479 grin, of Sc 2 3 , converted into 
sulphate, yielded 1.2255 grm. of the latter, which, upon ignition, gave 
.4479 grin, of Sc 2 3 . Hence, for the percentage of c 2 3 in Sc 2 (S0 4 ) s we 
have : 

36.478 

36.556 

36.556 

Mean, 36.530, .0175 

Hence, if SO, = 79.465, Sc = 44.882. 

Later results are those of Nilson,t who converted scandium oxide into 
the sulphate. I give in a third column the percentage of oxide in sul- 
phate : 

.3379 grm. Sc 2 3 gave .9343 grm. Sc 2 (SO 4 ) 3 . 36.166 per cent. 

.3015 .8330 36.194 

.2998 " .8257 " 36.187 " 

.3192 " .8823 " 36-178 " 



Mean, 36.181, db .004 

Hence Sc == 43.758. 

Combining the. two series, we have 

Cleve 36.530, =b .0175 

Nilson 36. 1 8 1 , .0040 



General mean 36. 190, .0039 

Hence, with SO, = 79.465, .00175, 

Sc = 43.784, .0085. 

If = 16, Sc 44.118. 

As between the two values found, the presumption is in favor of the 
lower. The most obvious source of error would be the presence in the 
scandia of earths of higher molecular weight. 

*Compt. Rend., 89, 419. 
fCompt. Rend., 91, 118. 



YTTRIUM. 355 



YTTRIUM. 

All the regular determinations of the atomic weight of yttrium depend 
upon analyses or syntheses of the sulphate. A series of analyses of the 
oxalate, however, by Berlin,* is sometimes cited, and the data are as fol- 
lows. In three experiments upon the salt Yt/C 2 4 ) 3 3H,0 the subjoined 
percentages of oxide were found : 

45-70 
45-^5 
45-72 



Mean, 45.69, dz .0141 

Hence with = 15.879 and C = 11.920, 



Yt == 88.943. 

Ignoring the early work of Berzelius,f the determinations to be con- 
sidered are those of Popp, Delafontaine, Bahr and Bunsen, Cleve, and 
Jones. 

Popp t evidently worked with material not wholly free from earths of 
higher molecular weight than yttria. The yttrium sulphate was dehy- 
drated at 200 ; the sulphuric acid was then estimated as barium sul- 
phate, and after the excess of barium in the filtrate had been removed 
the yttrium was thrown down as oxalate and ignited to yield oxide- 
The following are the weights given by Popp : 

Sulphate. BaSO. Y^O 3 . H. 2 O. 

1.1805 grm. *-3 l 45 g rm - -4742 grni. .255 grm. 

1.4295 1.593 " -5745 " -308 " 

.8455 " .9407 " .3392 " .1825 " 

1.045 " 1.1635 " .4195 " .2258 " 

Eliminating water, these figures give us for the percentages of Yt 2 3 in 
Yt 2 (SOj 3 the values in column A. In column B I put the quantities of 
Yt 2 3 proportional to 100 parts of BaS0 4 : 

A. B. 

51.237 36.075 

51.226 36.064 

51.161 36.058 

51-209 36.055 

Mean, 51.208, .on Mean, 36.063, .003 

From B, Yt = 101.54. The values in A will Be combined with similar 
data from other experimenters. 

* Forhandlingar ved de Skaiidinaviske Naturforskeres, 8, 452. 1860. 

f lyehrbuch, V Aufl., 3, 1225. 

I Ann. Chem. Pharm., 131, 179. 1804. 



356 THE ATOMIC WEIGHTS. 

In 1865 Delafontaine* published some results obtained from yttrium 
sulphate, the yttrium being thrown down as oxalate and weighed as 
oxide. In the fourth column I give the percentages of Yt 2 3 reckoned 
from the anhydrous sulphate : 



Sulphate. 


Yt 2 <9 3 . 


H.jp. 


Percent. ] 


9545 S rm - 


.371 grm. 


.216 grm. 


50.237 


2.485 " 


.9585 " 


.565 " 


49.9 22 


2.153 " 


.827 


4935 " 


49.834 



Mean, 49.998, =b .081 

In another paper f Delafontaine gives the following percentages of 
Yt. 2 3 in dry sulphate. The mode of estimation was the same as before : 

48.23 
48.09 
48-37 

Mean, 48.23, .055 

Bahr and Bunsen, J and likewise Cleve, adopted the method of con- 
verting dry yttrium oxide into anhydrous sulphate, and noting the gain 
in weight. Bahr and Bunsen give us the two following results. I add 
the usual percentage column : 

Yt. 2 3 . Yt^SO^ Percent. F/ 2 6> 3 . 

.7266 grm. L4737 grm. 49.34 

.7856 " L5956 " 49-235 

Mean, 49.2695, .0233 

Cleve's first results are published in a joint memoir by Cleve and 
Hoeglund, and are as follows : 



Percent. 

1. 4060 grm. 2. 8925 grm. 48.608 

1.0930 " 2.2515 " 48.545 

1.4540 " 2.9895 " 48.637 

1.3285 " 2.7320 " 48.627 

2.3500 " 4-833 " 48.624 

2.5780 " 5.3055 " 48.591 



Mean, 48.605, =h .0096 

In a later paper Cleve || gives syntheses of yttrium sulphate made with 
yttria, which was carefully freed from terbia. The weights and percent- 
ages are as follows : 

*Ann. Chem. Pharm., 134, 108. 1865. 

t Arch. Sci. Phys. et Nat. (2), 25, 119. 1866. 

J Ann. Chem. Pharm., 137, 21. 1866. 

g K. Svenska Vet. Akad. Handlingar, Bd. i, No. S. 1873. 

|j K. Svenska Vet. Akad. Handlingar, No. 9, 1882. See also Bull. Soc. Chim., 39, 120. 1883. 



YTTRIUM. 357 

yt. 2 O 3 . y/ 2 (S0 4 ) 3 . Percent. Yt. t O z . 

.8786 1.8113 48/507 

.8363 .7234 48.526 

.8906 .8364 48.497 

.7102 .4645 48.494 

.7372 .5194 48.519 

.9724 .0047 48.506 

.9308 .9197 48.487 

.8341 .7204 48.483 

1.0224 2.1073 48.5*7 

.9384 i.934i 48.519 

9744 2.0093 48.494 

1.53*4 3.1586 48.484 

Mean, 48.503, .0029 

Hence Yt = 88.449. 

The y ttria studied by Jones* had been purified by Rowland's method- 
thai is, by precipitation with potassium ferrocyanide and certainly con- 
tained less than one-half of one per cent, of other rare earths as possible 
impurities. Two series of determinations were made one by ignition of 
the sulphate, the other by its synthesis. The results were as follows, with 
the usual percentage column added : 

First Series. Syntheses. 



Yt^Oy 


Yt^SO^. 


Percent. Yt 2 O s . 


.2415 


.4984 


48.455 


.41 12 


.8485 


48.462 


.2238 


.4617 


48.473 


3334 


.6879 


48.466 


.3408 


.7033 


48.457 


.3418 


.7049 


48.489 


.2810 


.5798 


48.465 


.3781 


.7803 


48.456 


4379 


.9032 


48.483 


.4798 


.9901 


48.460 






Mean, 48.467, .0025 




Second Series. Analyst. 


58. 


Yt z (SO 4 ) 3 . 


Yt,0,. 


Percent. Yt. 2 O 3 . 


.5906 


.2862 


48.459 


.4918 


.2383 


48.455 


.5579 


.2705 


48.485 


.6430 


.3"7 


48.478 


.6953 


.3369 


48.454 


1.4192 


.6880 


48.478 


.8307 


.4027 


48.477 


.7980 


.3869 


48.484 


.8538 


.4*39 


48.477 


1.1890 


.5763 


48.469 






Mean, 48.472, .0024 



* Anier. Chem. Journ., 17, 154. 1895. 



358 THE ATOMIC WEIGHTS, 

From syntheses Yt = 88. 287 

From analyses " = 88.309 

These data of Jones were briefly criticised by Delafontaine,* who re- 
gards a lower value as more probable. In a brief rejoinder f Jones 
defended his own work; but neither the attack nor the reply needs 
farther consideration here. They are referred to merely as part of the 
record. 

For the percentage of yttria in the sulphate we now have eight series 
of determinations, to be combined in the usual way : 

Popp 51.208, rb .01 10 

Delafontaine, first 49,998, rb .0810 

Delafontaine, second 48.230, .0550 

Bahr and Bunsen 49.2695, rb .0233 

Cleve, earlier 48.605, db .0096 

Cleve, later 48.503, .0029 

Jones, syntheses 48.467, rb .0025 

Jones, analyses 48.472, rb .0024 



General mean 48.532, rb .0015 

Hence, if = 15.879, .0003, and S = 31.828, .0015, 

Yt = 88.580, rb .0053. 

If = 16, Yt = 89.255. 

If only the four series by Cleve and by Jones are considered, the mean 
percentage of yttria in the sulphate becomes 48.481. Hence Yt = 88.350, 
or, with = 16, 89.023. 

This result is preferable to that derived from all the data, for it throws 
out determinations which are certainly erroneous. Cleve's early series 
might also be rejected, but its influence is insignificant. 

*Chem. News, 71, 243. 
fChem. News, 71, 305. 



SAMARIUM, GADOLINIUM. ETC. 



SAMARIUM, GADOLINIUM, ERBIUM, AND YTTERBIUM. 

The data relative to the atomic weights of these rare elements are 
rather scanty, and all depend upon analyses or syntheses of the sul- 
phates. 

SAMARIUM. 

Atomic weight given by Marignac,* without details, as 149.4, and by 
Brauner,f as 150.7 in maximum. The first regular series of determina- 
tions was by Cleve, J who effected the synthesis of the sulphate from the 
oxide. Data as follows : 



Sm 2 O 3 . Sm.i(SOJ 3 . Per cent. 

1.6735 2.8278 59- l8 

i.97o6 3.3301 59- '75 

I.II22 1.8787 59-201 

1.0634 1.7966 S9- 1 9 

.8547 1.4440 59.J90 

7447 1-2583 59-183 



Mean, 59.1865, .0025 

Hence Sm = 149.038. 

Another set of determinations by Bettendorff, after the same general 
method, gave as follows: 

Sm.,O. A . Sm^SO^. Per cent. Sm. 2 O 3 . 
1.0467 1.7675 59-219 

1.0555 1.7818 59. 2 38 

1.0195 1.7210 59.225 

Mean, 59,227, .0038 

Hence Sm = 149.328. v 

Combining the two series, we have 

Cleve .................................. 59. 1865, = .0025 

Bettendorff ............................. 59.227, .0038 



General mean 59.1 99, =h .002 r 

Hence, if S0 3 = 79.465, .00175, 

Sm = 149. 127, =b .01 15. 

If 0=16, Sm = 150.263*. 

According to Demarcay.|| samaria contains an admixed earth whose 
properties are yet to be described. 

* Arch. Sci. Phys. et Nat. (3), 3, 435. 1880. 

t Journ. Chem. Soc., June, 1883. 

1 Journ. Chem. Soc., August, 1883. Conipt. Rend., 97, 94. 

gAnn. Chem. Pharm., 263, 164. 1891. 

j| Compt. Rend., 122, 728. 1896. 



360 THE ATOMIC WEIGHTS. 

GADOLINIUM. 

This element, discovered by Marignac, must not be confounded with 
the mixture of metals from the gadolinite earths to which Nordenskiold 
gave the same name. Several determinations of its atomic weight have 
been made, but Bettendorff's only were published with proper details.* 
He effected the synthesis of the sulphate from the oxide, and his weights 
were as follows. The percentage of Gd 2 O 8 in Gd 2 (SOJ 3 is given in the 
third column : 






Gd. 2 O. A . Gd^SO^. Percent. G 

1.0682 1-7779 60.082 

1.0580 1.7611 60.076 

1.0796 1.7969 60.081 



Mean, 60.080, .0013 

Hence, with S0 3 = 79.465, Gd = 155.575. 
If = 16, Gd 156.761, 

Boisbaudranf found Gd = 155.33, 156.06, 155.76, and 156.12. The last 
he considers the best, but gives no details as to antecedent values. He 
also quotes Marignac, who found Gd 156.75, and Cleve, who found 
154.15, 155.28, 155.1, and 154..77. Probably these all depend upon 

S0 3 = 80. 

ERBIUM. 

Since the earth which was formerly regarded as the oxide of this metal 
is now known to be~a mixture of two or three different oxides, the older 
determinations of its molecular weight have little more than historical 
interest. Nevertheless the work done by several investigators may prop- 
erly be cited, since it sheds some light upon certain important problems. 

First, Delafontaine's J early investigations may be considered. A sul- 
phate, regarded as erbium sulphate, gave the following data. An oxalate 
was thrown down from it, which, upon ignition, gave oxide. The per- 
centages in the fourth column refer to the anhydrous sulphate. In the 
last experiment water was not estimated, and I assume for its water the 
mean percentage of the four preceding experiments : 

Sulphate. r 2 O 3 . ff. 2 O. Per cent. Er z O 3 . 

.827 grm. .353 grm. .177 grm. 54. 308 

1.0485 " .4475 " .226 " 54.407 

.803 " .3415 " .171^ " 54.035 

1.232 " .523 " .264" " 54.028 

1.1505 " .495 " 54-76o 



Mean, 54.308, zb .0915 

Hence Er = 117.86. 

* Ann. Chem. Pharm., 270, 376. 1892. 

t Compt. Rend., in, 409. 1890. 

J Ann. Chem. Pharm., 134, 108. 1865. 



ERBIUM, YTTERBIUM, ETC. 361 

Bahr and Bunsen * give a series of results, representing successive puri- 
fications of the earth which was studied. The final result, obtained by 
the conversion of oxide into sulphate, was as follows : 

.7870 grm. oxide gave 1.2765 grm. sulphate. 61.653 P er cent, oxide. 

Hence Er = 167.82. 

Hoeglund, f following the method of Bahr and Bunsen, gives these 

results : 

Er. 2 O,. Er^(SO^. A . Per cent. Er. 2 O 3 . 

1 .8760 grm. 3.0360 grm. 61.792 

1.7990 " 2.9100 " 61.821 

2.8410 " 4-5935 " 61.848 

1.2850 " 2.0775 " 61.853 

1.1300 " 1.827 " 61.850 

.8475 " r -37Q " 61.861 

' Mean, 61.8375, .0063 
Hence Er = 169.33. 

According to Thalen,t spectroscopic evidence shows that the " erbia " 
studied by Hoeglund \vas largely ytterbia. 
Humpidge and Burney give data as follows : 

1.9596 grm. Er 2 (SO 4 ) 3 gave 1.2147 g rm - Er. 2 O 3 . 61.987 per cent. 
1.9011 " 1.1781 " 61.965 " 

Mean, 61.976, -0074 

Hence Er= 170.46. 

The foregoing data were all published before the composite nature of 
the supposed erbia was fully recognized. It will be seen, however, that 
three sets of results were fairly comparable, while Delafontaine evidently 
studied an earth widely different from that investigated by the others. 
Since the discovery of ytterbium, some light has been thrown on the 
matter. The old erbia is a mixture of several earths, to one of which, a 
rose-colored body, the name erbia is now restricted. For the atomic 
weight of the true erbium Cleve || gives three determinations, based on 
syntheses of the sulphate after the usual method. His weights were as 
follows, with the percentage ratio added : 

Er. 2 O 3 . Er.i(SO^ y Per cent. Er. 2 O 3 . 
1.0692 1.7436 61.321 

1.2153 1.9820 61.317 

.7850 1.2808 61.290 

Mean, 61.309, d= .0068 

Hence, with S0 3 = 79.465, Er == 165.059. 
If =16, Er= 166.316. 

*Ann. Chem. Pharm., 137, 21. 1866. 

fK. SvenskaVet. Akad. Handlingar, Bd. i, No. 6. 

I Wiedemann's Beibliitter, 5, 122. 1881. 

# Journ. Chem. Soc., Feb., 1879, p. 116. 

|| K. Svensk. Vet. Akad. Handlingar, No. 7, 1880. Abstract in Compt. Rend., 91, 382. 



362 THE ATOMIC WEIGHTS. 

It is not worth while to combine this result with the earlier determi- 
nations, for they are now worthless. 



YTTERBIUM. 



For ytterbium we have one very good set of determinations by Nilson.* 
The oxide was converted into the sulphate after the usual manner : 



1.0063 g rm - 

1.0139 " 

.8509 " 

.7371 " 

1.0005 " 

.8090 " 

1.0059 " 



Percent. Y&. 2 O 3 . 

.6186 giro. 62.171 

.6314 " 62.149 

.3690 " 62.155 

.1861 " 62.145 

.6099 " 62.147 

.3022 " 62.126 

.6189 <( 62.134 



Mean, 62.147, .0036 



Hence, with S0 3 = 79.465, Yb = 171.880. 
If O = 16, Yb = 173.190. 



TERBIUM, THULIUM, HOLMIUM, DYSPROSIUM, ETC. 

For these elements the data are both scanty and vague. Concerning 
the atomic weights of holmium and dysprosium, practically nothing has 
been determined. To thulium, Clevef assigns a value of Tm = 170.7, 
approximately, but with no details as to weighings. Probably the value 
was computed with S0 3 = 80. 

For terbium, ignoring older determinations, Lecoq de Boisbaudran has 
published two separate estimates.]! First, for two preparations, one with 
a lighter and one with a darker earth, he gives Tb = 161.4 and 163.1 
respectively. In his second paper he gives Tb = 159.01 to 159.95. These 
values probably are all referred to S0 3 = 80. 

*Compt. Rend., 91, 56. 1880. Berichte, 13, 1430. 

t Compt. Rend., 91, 329. 1880. 

J Compt. Rend., 102, 396, and in, 474. 



ARGON AND HELIUM. 363 



ARGON AND HELIUM. 

The true atomic weights of these remarkable gases are still in doubt, 
and so far can only be inferred from their specific gravities. 

For argon, the discoverers, Rayleigh and Ramsay,* give various deter- 
minations of density, ranging, with hydrogen taken as unity, from 19.48 
to 20.6. In an addendum to the same paper, Ramsay alone gives for 
the density of argon prepared by the magnesium method the mean value 
of 19.941. In a later communication f Rayleigh gives determinations 
made with argon prepared by the oxygen method, and puts the density 
at 19.940. 

For the density of helium, Ramsay J gets 2.18, while Langlet finds 
the somewhat lower value 2.00. 

From one set of physical data both gases appear to be m on atomic, but 
from other considerations they are supposably diatomic. Upon this 
question controversy has been most active, and no final settlement has 
yet been reached. If diatomic, argon and helium have' approximately 
the atomic weights two and twenty respectively; if monatomic, these 
values must be doubled. In either case helium is an element lying be- 
tween hydrogen and lithium, but argon is most difficult to classify. With 
the atomic weight 20, argon falls in the eighth column of the periodic 
system between fluorine and sodium, but if it is 40 the position of the gas 
is anomalous. A slightly lower value would place it between chlorine 
and potassium, and again in the eighth column of Mendelejeff's table; 
but for the number 40 no opening can be found. 

It must be noted that neither gas, so far, has been proved to be abso- 
lutely homogeneous, and it is quite possible that both may contain ad- 
mixtures of other things. This consideration has been repeatedly urged 
by various writers. If argon is monatomic, a small impurity of greater 
density, say of an unknown element falling between bromine and rubid- 
ium, would account for the abnormality of its atomic weight, and tend 
towards the reduction of the latter. If the element is diatomic, its classi- 
fication is easy enough on the basis of existing data. Its resemblances 
to nitrogen, as regards density, boiling point, difficulty of liquefaction, 
etc., lead me personally to favor the lower figure for its atomic weight, 
and the same considerations may apply to helium also. Until further 
evidence is furnished, therefore, I shall assume the values two and twenty 
as approximately true for the atomic weights of helium and argon. 

* Phil. Trans., 186, pp. 220 to 223, and 238. 1,895. 

fChem. News, 73, 75. 1896. 

JJourn. Chem. Soc., 1895, p. 684. 

\ Zeitsch. Anorg. Chem., 10, 289. 1895. 



364 



THE ATOMIC WEIGHTS. 



TABLE OF ATOMIC WEIGHTS. 

The following table contains the values for the various atomic weights 
found or adopted in the preceding calculations. As the table is intended 
for practical use, the figures are given only to the second decimal, the 
third being rarely, if ever, significant. In most cases even the first deci- 
mal is uncertain, and in some instances whole units may be in doubt. 

H = i. 0=16. 

Aluminum 26.91 27.11 

Antimony 11 9-S 2 I2O 43 

Argon ? ? 

Arsenic 74-44 75- 01 

Barium 136.39 r 37-43 

Bismuth 206. 54 208. 1 1 

Boron 10.86 10.95 

Bromine 79-34 79-95 

Cadmiu'm ni.io lll -95 

Caesium l 3 l -&9 132.89 

Calcium 39-76 40.07 

Carbon..., 11.92 12.01 

Cerium I39-IO 140.20 

Chlorine 35 .18 35-45 

Chromium 5!-74 5 2 - J 4 

Cobalt 58.49 58.93 

Columbium 93-Q2 93-73 

Copper 63. 12 63.60 

Erbium 165.06 166.32 

Fluorine 18.91 19.06 

Gadolinium , 155-57 156.76 

Gallium 69.38 69.91 

Germanium 7 r -93 72.48 

Glucinum 9.01 9.08 

Gold 195-74 i97- 2 3 

Helium ? ? 

Hydrogen .... i.ooo 1.008 

Indium 112.99 Ir 3-^5 

Iodine 125.89 12685 

Iridium 191.66 '93- 12 

Iron.. 55-6o 56.02 

Lanthanum T 37-59 138.64 

Lead , 205.36 206.92 

Lithium 6.97 7.03 

Magnesium 24.10 24.28 

Manganese 54-57 54-99 

Mercury 198.49 200.00 

Molybdenum 95. 26 95-99 

Neodymium 139-7 140.80 

Nickel 58.24 58.69 



TABLE OF ATOMIC WEIGHTS. 365 



Nitrogen ........................... r 3-93 1 4>4 

Osmium ............... ............ J ^>9-SS I 9-99 

Oxygen ........................... 15.88 16.00 

Palladium .......................... IO 5-56 106.36 

Phosphorus ......................... 30.79 3 J .O2 

Platinum ........................... 193-41 l 94-%9 

Potassium ................... ....... 38.82 39. 1 1 

Praseodymium ................ ..... 142.50 143.60 

Rhodium ........................... 102.23 103.01 

Rubidium.. ....................... 84.78 85.43 

Ruthenium ......................... 100.91 101.68 

Samarium .......................... I 49- I 3 150.26 

Scandium ..... ...... .............. 43-78 44-12 

Selenium ........................... 78.42 79.02 

Silicon ............................. 28. 1 8 28.40 

Silver .............................. 107. 1 1 107.92 

Sodium ............................ 22.88 23.05 

Strontium ......................... 86.95 87.61 

Sulphur ............................ 31.83 32.07 

Tantalum .......................... 181.45 182.84 

Tellurium .......................... 126.52 127.49 

Terbium ........................... 158.80 160.00 

Thallium ................. ........... 202.61 204.15 

Thorium .......................... 230.87 232.63 

Thulium ........... ................ 169.40 170.70 

Tin ..... , ...... ................. 118.15 119.05 

Titanium ........................... 47-79 48. 1 5 

Tungsten ......................... J83-43 ^4. 83 

Uranium ........................... 237.77 239.59 

Vanadium ........................ 5-99 5 r -38 

Ytterbium ......................... 171.88 ! 73-i9 

Yttrium ........ . ................... 88.35 89.02 

Zinc. ... ........................... 64.91 65.41 

Zirconium .......................... 89. 72 90.40 



INDEX TO AUTHORITIES. 



Agamennone X 4> 2 5 

Allen 89 

Allen and Pepys 24 

AlibegofF 266, 300 

Anderson 130 

Andrews 1 18, 327 

Arago 24, 58, 72 

Arfvedson 84, 263, 282 

Aston 52, 172 

Awdejew , . . . ; 132 



Bahr 137 

Bahr and Bunsen 356, 361 

Bailey 197, 231 

Bailey and L,amb. 316 

Balard 44 

Baubigny 93, 148, 180, 244, 300 

Bauer 349, 353 

Becker I 

Beringer 335 

Berlin 238,251,355 

Bernoulli 257 

Berzelius. . 5,8, 24, 34, 38, 43, 44, 50, 58, 

72, 82, 84,91, IOI, IIO, 112, 121, 123, 

127, 132, 135, 146, 171, 176, iSS, 196, 

204, 209, 211, 213, 2l6, 236, 238, 250, 

255. 263, 268, 271, 277, 282, 257, 313, 

315, 322, 325, 327, 355 

Bettendorff 349, 359, 360 

Biot and Arago 24, 58, 72 

Blomstrand 234, 236 

Boisbaudran 181, 360, 362 

Bongartz 226 

Bongartz and Classen 200, 201 

Borch, von 256 

Boussingault 24, 58 

Brauner. .272, 274, 340, 342, 348, 351, 359 

Breed 320 

Bucher 1 60 

Buehrig ... 339 

Buff 24, 72 

Bunsen 87, 89, 356, 361 

Bunsen and Jegel 336 

Burney 361 



Burton 151 

Burton and Vorce , . . . 142 



Capitaine 287 

Cavendish 24 

Chikashige 275 

Choubine 344 

Christensen 280 

Chydenius 204 

Clark 9 

Clarke 159 

Classen 200, 201, 231, 232 

Claus . . 31 r 

Cleve. . 206, 347, 348, 351, 352, 354, 356' 
359, 360, 361, 362 

Cleve and Hoeglund 356 

Commaille 91 

Cooke 27, 8r, J57, 221, 222, 224 

Cooke and Richards 13 

Crafts 25, 58 

Crookes 185 

Czudnowicz. 211, 346 



Davy 24 

Debray 133, 251 

Delafoutaine 205, 356, 358, 360 

De Luca 278 

Demarcay 359 

Detnoly 191 

De Saussure 24, 72 

Desi 262 

Deville 291 

Deville and Troost 235 

Dewar and Scott _ , 283 

Dexter 217 

Diehl 84 

Dittmar 85 

Dittmar and Henderson 12, 19 

Dittmar and M' Arthur 333 

Dobereiner 127, 287 

Duloug and Berzelius 8, 24, 58, 72 

Dumas. . 9, 39, 45, 50, 51, 72, 80, 91, no^ 
112, 113, 119, 129, 140, 156, 176, 188, 
199, 201, 209, 213, 217, 229, 251, 256, 
269, 278, 279, 282, 289, 294 

(367) 



368 



THE ATOMIC WEIGHTS. 



Dumas and Boussingault. . 24, 58 

Dumas and Stas 76 



Ebelmen 264 

Ekman and Pettersson 269 

Erdmanii 146 

Erdmann and Marchand. ..IT, 76, 110, 
in, 166, 268, 288, 291 

Erk 347, 351 

Ewan and Hartog 171 



Faget 37 

Favre 147 

Fourcroy 24 

Fownes 72 

Fremy 322 

Friedel 77 



Gay-Lussac 32, 135, 146 

Genth 338 

Gerhardt 36 

Gibbs 298, 342 

Gladstone and Hibbard . . 152 

Ginelin 84 

Godeffroy 87, 90 

Gooch and Rowland 274 

Gray 98 



Hagen 84 

Halberstadt 330 

Hampe 92 

Hardin 34, 63, 74, 163, 167 

Hartog 171 

Hauer, von 156, 271, 283 

Hebberling 184 

Hempel and Thiele 308 

Henry 6 

Hermann 84, 196, 206, 234, 236, 

335, 347, 351 

Heycock 88 

Hibbard 152 

Hibbs 67, 68, 215 

Hinrichs 6 

Hoeglund 356, 361 

Holzmann 345 

Hoskyns-Abrahall 171 

Howland 274 

Humboldt and Gay-Lussac 32 

Humpidge and Burney 361 

Huntington 46, 157 



Isnard 176 



Jacquelain 136, 146, 238 

Jegel 336 

Johnson 17 

Johnson and Allen 89 

Jolly 59 

Joly 311, 326 

Joly and Leidie 319 

Jones 159, 3^7, 358 

Jorgensen 313 



Keiser 15, 150, 316 

Keiser and Breed* 320 

Keller and Smith 318 

Kemp 252 

Kessler 214. 216, 218, 224, 241, 242 

Kirwan 24 

Kjerulf 336 

Klatzo 132 

Kobbe 314 

Kralovanzky 84 

Kriiss 102 

Kriiss and Alibegoff 266, 300 

Kriiss and Moraht 133 

Kriiss and Nilson . 207 

Kriiss and Schmidt 303 



Lagerhjelm 229 

Lamb 316 

Lamy 184 

Langer 301 

Langlet 363 

Laurent . 34, 171 

Laurie 103 

Lavoisier 24, 58, 72 

Le Conte 25 

Leduc 20, 27, 32, 59, 78 

Lee 298 

Lefort 240 

Leidie 319 

Lenssen 156 

Lepierre 186 

Levol 102 

Liebig 44 

Liebig and Redtenbacher 72 

Liechti and Kemp ... 252 

Lougchamp ,. . 127, 135 



INDEX TO AUTHORITIES. 



369 



Lorimer and Smith 159 

Louyet 277, 279, 280 

Lowe 231 

Lowig 44 

M 

Maas 252 

M'Arthur 333 

Macdonnell I3 6 

Malaguti 255 

Mallet 84, 105, 150, 177 

Marchand 1 1 , 72, 76, 1 10, 1 1 1, 

166, 256, 263, 268, 288, 291 

Marchand aud Scheerer 138 

Marignac. . 34, 35, 36, 3 8 , 39, 4i, 43, 44, 
45, 47, 48, 49, 60, 62, 65, 74, no, 114, 

II.5, Il8, 121, 122, 123, 129, 141, 148, 

196, 230, 235, 236, 284, 292, 336, 344, 

345, 35i, 359, 3 6 o. 

Mather 176 

Maumene 34, 36, 39, 43, 75, 288 

Meineke 244 

Meyer... , 252 

Meyer and Seubert i, 5, 6 

Millon 48, 167 

Millon and Commaille 91 

Mitscherlich 72 

Mitscherlich and Nitzsch 268 

Moberg 239 

Moissan 278, 279, 280 

Mond, Langer, and Quincke 301 

Morabt 133 

Morley 12, 21, 27, 32 

Morse and Burton 151 

Morse and Jones 159 

Morse and Reiser 150 

Mosander 190, 335, 344, 351 

Mulder 6 

Mulder and Vlaanderen 199 

N 

Nilson 207, 354, 362 

Nilson and Pettersson 133 

Nitzsch 268 

Nordenfeldt 137 

Nordenskiold 360 

Norlin 287 

Noyes 16, 17 



Ostwald i, 6, 57, 71, 83, 131 

Oudemans , 6 

24 



Parker 142 

Partridge 157 

Peligot 238, 264, 265 

Pelouze 35, 51,60, 

113, 118, 188, 209, 213 

Penfield 186 

Pennington and Smith 258 

Penny 35, 39, 5o, 62, 64, 66, 67 

Pepys 24 

Persoz 257 

Petrenko-Kritscbenko 319 

Petterssou 133, 269 

Pfeifer 225 

Piccard 87 

Pierre 191 

Pollard . . 252 

Popp 355 

Popper 225 

Q 

Quincke 301 

Quintus Icilius 315 



Rammelsberg. . . 234, 252, 263, 337, 344 

Ramsay 149, 363 

Ramsay and Aston 52, 172 

Rawack 283 

Rawson 244 

Rayleigh. . 14, 16, 25, 26, 58, 59, 98, 363 

Rayleigb nnd Ramsay 363 

Rayleigh and Sidgewick 98 

Redtenbacher 72 

Regnault 24, 25, 72 

Reich and Ricbter 182 

Remmler 302 

Reynolds and Ramsay 149 

Richards 13, 46, 82, 92, 93, 94, 96, 

97, 115, 119, 121, 123, 124, 154 

Richards and Parker 142 

Richards and Rogers 141, 152, 153 

Riche 259 

Richter . . . , 182 

Rimbacb 1 74 

Rivot 289 

Robinson 340 

Rogers 141, 152, 153 

Roscoe 77, 211, 257, 262 

Rose 190, 217, 234, 236 

Rothhoff 291 

Russell , 294, 295 



370 



THE ATOMIC WEIGHTS. 



Sacc 268 

Salvetat 1 10, 1 13, 1 18 

Scheerer 135, 136, 138, 139 

Scheibler 260 

Schiel 188 

Schmidt 203, 303 

Schneider 216, 224, 229, 232, 255, 

258, 282, 291, 292, 297 

Schrotter 209 

Schutzeuberger 301 , 34 1 

Scott 3 2 , 283 

Sebelien 1,7 

Sef strom ...* 166 

Seubert i, 322, 323, 325, 328, 333 

Seubert and Kobbe 314 

Seubert and Pollard 252 

Shaw 98 

Shinn 259 

Sidgewick 98 

Siewert , 243 

Smith 159, 258, 318 

Smith and Desi 262 

Smith and Maas 252 

Sommaruga 297 

Spring 6 

Stas. . 6, 37, 38, 40, 41, 42, 44, 45, 47, 48, 
49, 5i, 52, 57, 61, 62, 64, 65, 66, 71, 
73, 76, 78, 80, 82, 83, 85, 128, 130, 131 

Staudenmaier 274 

Strecker 73 

Stromeyer 84, 156, 287 

Struve 81, 82, 123, 250 

Svanberg 130, 167 

Svanberg and Nordenfeldt 137 

Svanberg and Norlin 287 

Svanberg and Struve. 82, 250 



Terreil 177 

Thalen 361 

Thiele 308 

Thomsen. . 13, 22, 30, 57, 69, 71, 83, 131 

Thomson 24, 58 

Thorpe 192 

Thorpe and Laurie 103 



Thorpe and Young ... 1 89 

Tissier 176 

Torrey 151, 180,289 

Troost 84, 235 

Turner.. 38, 64, 121, 122, 123, 128, 166, 

167, 282 



Unger 221 



Van der Plaats. . . 6, 57, 71, 77, 83, 131, 
149, 200, 210 

Van Geuns . . 5 

Vanni 98 

Vauquelin 24 

Vlaanderen 199 

Vogel 6 

Vorce 142 

W 

Wackeuroder. ... 287 

Waddell 258 

Wallace 44, 213 

Warrington 33 

Weber 217 

Weeren 132, 285 

Weibull 196 

Wells and Penfield 186 

Welsbach 353 

Wertheim 265 

Werther 184 

Weselsky 298 * 

Wildenstein 241 

Wills 271 

Wing 338 

Winkler. . . . 182, 195, 297, 305, 306, 307 

Wolf. 337, 340 

Woskresensky 72 

Wrede 24, 72 



Young 



189 



Zettuow 260 

Zimmermann 266, 300 

Zschiesche 347, 351 




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