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 ofsubstance used .55540 gr.
” ”cadmium found.17456 ”
Cadmium.
31.43 per cent.

Second determination:

Amount ofsubstance 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:

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:

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 Cd₄Cl₇treated with water 1.45970gr.
Cadmium found inflocculent precipitate  .02318 ”
” ”” crystalline substance .09614 ”
” ”” solution in water .81970 ”
Total cadmium found   .93902 ”
Chlorine found incrystalline 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 Cd₄Cl₇treated with water 1.0794 gr.
Cadmium found inflocculent precipitate  .01469 ”
” ”” solution in water .60795 ”
Chlorine found insolution 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.

Analyses of the partially decomposed crystals gave variable proportions of metal and halogen but never less than eight equivalents of the former to one of the latter.

While the decomposition of Cd₄Cl₇ with water cannot at present be fully explained, yet it is clear from the analyses that one eighth of the total cadmium is thrown down as a white precipitate and a crystalline compound which as will be seen passes over into cadmous hydroxide. One half of the cadmous chloride is oxidized to cadmic chloride taking the chlorine from the other half.

The compound Cd₄Cl₇ was treated directly with absolute alcohol with the hope of obtaining the crystalline substance in an undecomposed condition. Although a substance of the same general appearance as that formed in the presence of water was obtained yet it decomposed so readily that a satisfactory analysis could not be made.

Notwithstanding the rapidity with which the decomposition of the crystalline compound begins, long continued washing was necessary in order to completely remove the chlorine. The extraction of the last traces of the halogen is hastened by the use of warm instead of cold water. The temperature of the water must not exceed 50°C. In water whose temperature approaches the boiling point the hydroxide is slowly decomposed with liberation of metal.

The new hydroxide is a strong reducing agent. It dissolves in dilute acids; yielding with nitric acid oxides of nitrogen, with hydrochloric or sulphuric acid free hydrogen. After washing with warm water until all the chlorine had disappeared, it was dried over phosphorus pentoxide and analyzed.

First determination of cadmium.

Amount ofsubstance used .0968  gr.
” ”cadmium found .08415 ”
Cadmium.
86.93 per cent.

Second determination of cadmium.

Amount ofsubstance used .09806 gr.
” ”cadmium found .08522 ”
Cadmium.
86.91 per cent.

The calculated percentage of cadmium in Cd(OH) is:

Cadmium.
86.79 per cent.

The determination of water in cadmous hydroxide was made by placing a small specimen tube containing the hydroxide in a Kjeldahl flask which was heated in a bath of concentrated sulphuric acid. During the heating a slow current of dry nitrogen was passed over the substance.

First determination of water.

Amount ofsubstance used .08434 gr.
” ”water found .00609 ”
Water.
7.22 per cent.

Second determination of water.

Amount ofsubstance used .08895 gr.
” ”water found .00600 ”
Water.
6.74 per cent.

Third determination of water.

Amount ofsubstance used .11766 gr.
” ”water found .00856 ”
Water.
7.25 per cent.

Average amount of water = 7.07 per cent.

The calculated percentage of water in Cd(OH) is, 6.99.

At the temperature at which concentrated sulphuric acid gives off dense white fumes cadmous hydroxide gives off all its water and passes over into a heavy yellow powder. At 150°C not a trace of water was liberated. Under the microscope the yellow powder was found to consist of minute translucent crystals.

First determination of cadmium.

Amount ofsubstance used .08064 gr.
” ”cadmium found .07511 ”
Cadmium.
93.14 per cent.

Second determination of cadmium.

Amount ofsubstance used .10846 gr.
” ”cadmium found .10106 ”
Cadmium.
93.17 per cent.

The calculated percentage of metal in Cd₂O is 93.32 per cent.

If water of too high temperature is employed in washing the subhydroxide, the presence of free metal in it can be detected under the microscope and by rubbing between agate surfaces. If the yellow suboxide is strongly heated it breaks up into a mixture of oxide and metal which possesses a distinctly green color. Towards acids the suboxide conducts itself like the subhydroxide.

It is a fact of some interest in connection with the periodic arrangement of the elements, that the tendency toward the formation of a lower series of compounds which becomes so strongly developed in mercury begins to exhibit itself in some slight degree in cadmium.