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Each two apertures receive the glass tubes used in gas washing bottles, while the third holds a dropping funnel. It is filled with dilute hydrochloric acid, and after the expulsion of the air by a current of gas, plentiful quantities of chromous acetate are passed into the bottles.
When the current of gas has been passed in for some time, the hydrochloric acid is let enter, which dissolves the chromous acetate, and thus, in the absence of air, produces a solution of blue chromous chloride. It is advisable to use an excess of chromous acetate or an insufficient quantity of hydrochloric acid, so that there may be no free hydrochloric acid in the liquid.
The solution of chromous chloride must therefore be freed from the zinc by filtration in the absence of air. For this purpose the reduction is carried on in a flask fitted up like a washing bottle. The long tube is bent down outside the flask, and is here provided with a small bulb tube containing glass wool or asbestos.
The blue chromous chloride solution thus obtained is poured into a saturated solution of sodium acetate in an atmosphere of carbonic acid. A red precipitate of chromous acetate is formed, which is washed by decantation in water containing carbonic acid. This salt is relatively stable, and can be preserved for an indefinite time in a moist condition in stoppered bottles filled with carbonic acid.
In this manner a chromous acetate is obtained perfectly free from zinc. For the absorption of oxygen the compound just described is decomposed with hydrochloric acid in the following simple washing apparatus: Upon a shelf there are fixed side by side two ordinary preparation glasses, closed with caoutchouc stoppers, each having three perforations.
If the two apertures of the washing apparatus are fitted with small pinch cocks, it is ready for use, and merely requires to be connected with the gas apparatus in action in order to free the gas generated from oxygen. As but little chromous salt is decomposed by the oxygen such a washing apparatus may serve for many experiments.
N.W. Shedd, M.I.T. OTTO, BARON V.D. PFORDTEN. The author makes use of a solution of chromous chloride, which he prepares as follows: He first heats chromic acid with concentrated hydrochloric acid, so as to obtain a strong green solution of chromic chloride free from chlorine. This is then reduced with zinc and hydrochloric acid.
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