An examination of some methods employed in determining the atomic weight of Cadmium — John Shaqi
An examination of some methods employed in determining the atomic weight of CadmiumBucher, John Emery
History
An examination of some methods employed in determining the atomic weight of Cadmium
Bucher, John Emery
Cadmium; Thesis (Ph. D.)
The weighed cadmium chloride was dissolved by placing the boat
containing it in an Erlenmeyer flask containing water. The boat was then
washed, dried and replaced in its weighing-tube. On weighing again, the
loss in weight is equal to the weight of cadmium chloride taken. All
samples gave a perfectly clear solution except those used for
determinations XX and XXI. A drop of nitric acid (1:3) was added to each
solution except in determination XIV where the cubic centimetres were
added, and in XVI where ten cubic centimeters were added. A solution of
silver nitrate was then added to precipitate the chlorine. This as well
as the subsequent washing was done in a dark-room illuminated by a
single gas light whose rays had to pass through a strong solution of
neutral potassium chromate. The precipitate was contracted by warming on
the water-bath. It was then collected in the prepared Gooch crucibles
and washed. Before filtering, the flask containing the precipitate and
mother-liquor was allowed to cool. Silver chloride is soluble in water
to a considerable extent but is reprecipitated by adding an excess of
either silver nitrate or hydrochloric acid. Stas (Ann. de Chem. et Phys.
[4], 25, 22; [5], 3, 145; [5], 3, 289.) investigated this very
thoroughly. Cooke also did some work on it and used a dilute solution of
silver nitrate to wash the chloride thus preventing solution (Proc.
Amer. Acad. 17, 7.). In the above work, therefore, a solution containing
0.10 grammes of silver nitrate per liter was first used, followed by one
only one-tenth as strong, and finally pure water was used. Only two or
three washings could be made with water as the chloride went into
solution after this owing to the removal of the silver nitrate. The last
silver nitrate solution used is so weak that any error introduced by not
washing it out completely is insignificant. After washing, the silver
chloride was dried at temperatures varying from 150°C. to 300°C. to
constant weight. A glass air-bath was used in order to prevent products
from the burning gas from coming in contact with the chloride. It was
then weighed. The quantity of silver nitrate used in the determinations
was varied very much. The excess over what was required to precipitate
the chloride is given in the table of results in those cases in which it
is known. The quantity of water used in each determination is also given
where it is known. It is given in the number of cubic centimetres used
per gramme of cadmium chloride and does not include wash water. All
weighings are reduced to the vacuum standard on the basis that Sp. Grs.
of CdCl_{2} = 3.94 and AgCl = 5.5. The results are:
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