The preparation of Cd₄Br₇.

The anhydrous bromide of cadmium was prepared by dissolving the carbonate in an aqueous solution of hydrobromic acid, evaporating the bromide to dryness on the water bath and heating the residue in a current of dry hydrobromic acid gas. When the bromide was heated with an excess of the metal in an atmosphere of nitrogen it conducted itself in general like the chloride. When the molten bromide and the metal came in contact the salt quickly became deep red in color. After heating for some time considerable dissociation was produced by raising the temperature. This was more apparent in the preparation of the bromide than with the chloride. On cooling, the mass possessed a greenish tint which disappeared when cold, the bromide then being very nearly the same color as the corresponding chloride. Also like the chloride it appeared to be homogeneous and free from metal. Two determinations of cadmium and two of bromine were made, using the product as soon as prepared.

First determination of cadmium:

Amount ofsubstance used .3736  gr.
” ”cadmium found.16658 ”
Cadmium.
44.59 per cent.

Second determination of cadmium:

Amount ofsubstance used .35930 gr.
” ”cadmium found.16013 ”
Cadmium.
44.57 per cent.

First determination of bromine:

Amount ofsubstance used .66640 gr.
” ”bromine found.36953 ”
Bromine.
55.45 per cent.

Second determination of bromine:

Amount ofsubstance used .56035 gr.
” ”bromine found.31085 ”
Bromine.
55.47 per cent.

The percentage of cadmium and bromine found agrees very closely with that of a compound of the formula Cd₄Br₇. The relation of cadmium to bromine in this would be:

When this compound was heated for a long time with an excess of the metal its composition was not appreciably changed.

The compound Cd₄Br₇ is a strong reducing agent: giving with nitric acid oxides of nitrogen, with dilute hydrochloric, sulphuric or acetic acid, free hydrogen, and with mercuric chloride, mercurous chloride or metallic mercury. The action of water on the bromide by means of which cadmous hydroxide was formed, was not studied as carefully as with the chloride but appeared to be essentially the same.