Part 9

A third preparation was made like the first and second and analyzed.

Analysis:

Amount of chloride used .2832 gr. ” ” cadmium found .18244 ” ” ” chlorine ” .10123 ”

Cadmium. Chlorine. 64.42 per cent. 35.74 per cent.

When the new substance is heated it fuses to a red liquid and then breaks up into metal and the chloride of cadmium. Its reactions are in general those of a strong reducing agent. Treated with nitric acid, oxides of nitrogen are liberated. With dilute hydrochloric, sulphuric and acetic acids it gives free hydrogen. In the presence of dilute acids it reduces mercuric to mercurous chloride, or to metallic mercury.

Three determinations of the reducing power of the substance were made with a freshly prepared specimen, by dissolving weighed portions in hydrochloric acid and measuring the hydrogen liberated.

The following results were obtained:

Hydrogen found. Hydrogen calculated for Cd₄Cl₇. 1ˢᵗ determination 15.67 c.c. 15.65 c.c. 2ⁿᵈ ” 11.80 c.c. 11.82 c.c. 3ʳᵈ ” 23.00 c.c. 23.03 c.c.

An examination of the analyses shows beyond question that the substance formed by the action of metallic cadmium on the molten anhydrous chloride is of definite composition. The proportion of cadmium to chlorine could not be changed even when the substance was heated with the metal for twenty hours, while a very short time was sufficient for its formation when the metal and chloride were melted together.

It may be possible that a substance possessing these properties is not a definite chemical compound but a mixture of cadmous and cadmic chlorides or a solution of one in the other.

If it were a solution it is difficult to see why the composition of the solution should be so constant, since the solubility of a substance is generally altered by a change in temperature. The different preparations were not made at exactly the same temperature yet the composition of the different preparations was the same.

If the substance was a mixture of the two chlorides, when treated with water the cadmic chloride would most probably dissolve directly leaving the cadmous chloride to be acted upon by the water. The decomposition by water will however be seen not to be as simple as would be expected under these conditions.

From the above considerations it appears highly probable that the substance is a definite chemical compound of cadmic and cadmous chlorides. If cadmic chloride can form a chemical compound with the chloride of another element there appears to be no reason why it should not form a compound with another chloride of cadmium, as with cadmous chloride.

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 of substance used .3736 gr. ” ” cadmium found .16658 ”

Cadmium. 44.59 per cent.

Second determination of cadmium:

Amount of substance used .35930 gr. ” ” cadmium found .16013 ”

Cadmium. 44.57 per cent.

First determination of bromine:

Amount of substance used .66640 gr. ” ” bromine found .36953 ”

Bromine. 55.45 per cent.

Second determination of bromine:

Amount of substance 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: