Preparation of Pure Cadmium.
“Cadmium met. puriss. galv. reduc”, obtained from Schuchardt, was used
for preparing pure cadmium. It was heated to redness in a current of
hydrogen which had been purified by washing with both acid and alkaline
solutions of potassium permanganate. This treatment converted the
metallic powder into a bar which could be distilled in a vacuum. The
metal was then distilled nine times in the same manner that Morse and
Burton, Amer. Chem. Jour. 12, 219, had distilled zinc. All distillations
were made slowly except the last one, which was made quite rapidly.
Preparation of Nitric Acid.
Whenever pure nitric acid was required, it was purified by distilling
against a platinum dish and collecting the distillate in a smaller one
of the same metal. The nitric acid used was dilute and free from
chlorine.
Purification of Water.
The water used in this work was purified by distilling twice from an
alkaline solution of potassium permanganate, always rejecting the first
part of the distillate. Whenever water was needed in the preparation of
a pure compound e.g. cadmium oxalate, oxalic acid, cadmium nitrate,
etc., it was subjected to the additional process of being distilled
against a large platinum dish which was kept cool by placing ice inside
it.
Purification of Oxalic Acid.
Commercial oxalic acid was heated with a fifteen percent solution of
hydrochloric acid until all was dissolved. The solution was then warmed
for twenty four hours. On cooling, crystals of oxalic acid separated out
and these were washed with a little cold water to remove the mother
liquor. They were then dissolved in hot ninety-five percent alcohol and
allowed to crystallize slowly on cooling. The acid was next crystallized
from ether in which it is only sparingly soluble. After this it was
boiled with water until the odor of ethyl acetate had disappeared.
Finally it was recrystallized three times from water and dried in the
air at ordinary temperatures.
Preparation of Cadmium Oxalate.
A weighed piece of cadmium was dissolved in nitric acid and the excess
of acid evaporated off. The nitrite was then dissolved in a large
quantity of water and an equivalent amount of oxalic acid in solution
added. The oxalate separated in a few moments as a crystalline
precipitate. It was collected on a porcelain filter and washed
thoroughly to remove nitric acid and ammonium nitrate. A considerable
amount of ammonium nitrate was formed during the solution of the cadmium
in nitric acid. The oxalate was finally dried in an air-bath for fifty
hours, at 150°C.