Silver nitrate cannot be used because it becomes reduced to nitrate even
at a temperature of 0°C., as was shown by its reducing action on
potassium permanganate, and by the reaction with meta-diamido benzene
after the reaction had been completed. The main difficulty with the
method is that air must be excluded in order to prevent oxidation and
solution of some of the precipitated silver. The silver is perfectly
free from cadmium if an excess of silver sulphate is used and the
precipitated metal digested with it for some time. Since this part of
the work was done, a paper by Mylius and Fromm (Ber. 1894, 630) appeared
in which one of the reactions studied was that of cadmium on silver
sulphate. They also found the resulting silver free from cadmium. The
method seems very promising, but the work had to be discontinued for
lack of time.
Conclusion.
I. The work on the oxalate and sulphide methods described in this paper
is of no value for determining the atomic weight of cadmium. It does not
even enable us to fix an approximate value.
II. There are a number of errors in the chloride and bromide methods as
they were used in this work, but they are not very large and partially
compensate each other. Their results, 112.383 and 112.396 respectively,
may be regarded as approximations to the true value.
III. The synthesis of cadmium sulphate as carried out is of especial
value in fixing a _minimum_ value for the atomic weight of cadmium. The
result is 112.35, agreeing closely with that obtained by the bromide and
chloride methods.
IV. There is an error in the oxide method due to products of
decomposition of the nitrate being retained. Direct experiments gave .39
of a unit for this when platinum crucibles were used and .24 of a unit
when porcelain ones were used. The calculated errors for porcelain and
platinum crucibles are .30 and .51 of a unit respectively, if 112.38 is
assumed as the atomic weight of Cadmium.
V. The average of the chloride, bromide, and sulphate methods is 112.38.
This result is to be regarded as _tentative_ and not as final since the
main object of this work has been to find the cause of the discrepancy
in some methods employed in determining this constant, rather than to
make an atomic weight determination.
Biographical Sketch.
John Emery Bucher was born near Hanover, Pa., August 17, 1872. He
entered Lehigh University in 1888 and graduated in 1891. During the past
three years he has been a graduate student in the Johns Hopkins
University.
Subjects: Chemistry, Mineralogy and Mathematics.
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