Part 10

Cadmium. Bromine. 44.44 per cent. 55.56 per cent.

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.

The Preparation of Cd₁₂I₂₃.

Cadmic iodide was prepared in the same manner as the bromide. It was dried in a stream of hydriodic acid gas at as low temperature as possible to lessen the decomposition of the hydriodic acid. When the anhydrous iodide was heated with an excess of metal in an atmosphere of nitrogen the red color of the iodide became intensified. Heating was continued until there was evidence of dissociation, which, under the same conditions, was less marked than with the chloride and much less than with the bromide. Owing to the high specific gravity of the iodine compound some difficulty was experienced in obtaining a preparation free from metal. This difficulty was finally overcome by keeping the material just above its melting temperature for a long time and constantly jarring the flask. During the process of cooling a decidedly greenish tint was observed which disappeared as the process was continued. When cold the substance resembled the chloride and bromide. Two determinations of cadmium were made in the first preparation.

First determination:

Amount of substance used .55540 gr. ” ” cadmium found .17456 ”

Cadmium. 31.43 per cent.

Second determination:

Amount of substance used .47535 gr. ” ” cadmium found .14980 ”

Cadmium. 31.51 per cent.

As these results did not correspond to the composition represented by the formula Cd₄I₇, which our experience with the chloride and bromide had led us to expect, we reheated the material for several hours with an excess of the metal. Two analyses of the product gave:

Cadmium. Iodine. 31.44 per cent. 68.65 per cent. 31.39 68.68

showing that the iodide had taken up during the first heating all the metal which it could retain. The analytical results suggest the formula Cd₁₂I₂₃, in which the calculated percentages are:

Cadmium. Iodine. 31.53 per cent. 68.47 per cent.

In its conduct towards dilute hydrochloric and acetic acids and water the substance behaves like the corresponding chloride and bromide.

The Preparation of Cadmous Hydroxide and Oxide.

When the substance Cd₄I₇ is treated with water a complicated reaction takes place. The general character of the reaction appears to be the same with the chloride, bromide and iodide. The decomposition of the chloride was studied more thoroughly than that of the other compounds.

When the finely powdered chloride is treated with water it yields cadmic chloride which passes into solution, a small quantity of a white flocculent material which may be cadmic hydroxide but which in no case could be entirely freed from traces of chlorine, and a highly lustrous crystalline substance which rapidly lost its crystalline appearance and passed over into a grayish white amorphous compound, which when freed from chlorine was found to be cadmous hydroxide, of the formula Cd(OH). The separate products resulting from the treatment with water were analyzed.

First Analysis:

Amount of Cd₄Cl₇ treated with water 1.45970 gr. Cadmium found in flocculent precipitate .02318 ” ” ” ” crystalline substance .09614 ” ” ” ” solution in water .81970 ” Total cadmium found .93902 ”

Chlorine found in crystalline compound .00371 gr. ” ” ” solution in water .51671 ” Total chlorine found .52042 ”

Approximately seven-eighths of the total cadmium dissolved as cadmic chloride while the remainder was contained in the flocculent precipitate and in the gray crystalline compound.

Second Analysis:

Amount of Cd₄Cl₇ treated with water 1.0794 gr. Cadmium found in flocculent precipitate .01469 ” ” ” ” solution in water .60795 ”

Chlorine found in solution in water .38491 ”

The percentage of cadmium in the white precipitate is less in this analysis than in the former. The cadmium in solution is again about seven-eighths of the total and the chlorine present in the same solution shows that the cadmium was all combined as cadmic chloride.

All attempts to determine the composition of the gray crystalline compound failed, owing to the rapidity with which it decomposed with water. Even with the most rapid work it could not be isolated in the undecomposed condition.