Part 11

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 of substance used .0968 gr. ” ” cadmium found .08415 ”

Cadmium. 86.93 per cent.

Second determination of cadmium.

Amount of substance 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 of substance used .08434 gr. ” ” water found .00609 ”

Water. 7.22 per cent.

Second determination of water.

Amount of substance used .08895 gr. ” ” water found .00600 ”

Water. 6.74 per cent.

Third determination of water.

Amount of substance 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 of substance used .08064 gr. ” ” cadmium found .07511 ”