Estimation of Rhodium

Rhodium is conveniently estimated by precipitation with magnesium from solutions of its salts. The precipitate is washed with dilute sulphuric acid to remove excess of magnesium, dried, ignited in a current of hydrogen, cooled in carbon dioxide and weighed as metal.

Rhodium may also be estimated by reduction of its salts with hydrazine hydrate in hot alkaline solution, the concentration of the rhodium not being too great. The hydrosol first formed rapidly coagulates, yielding a metallic, glistening precipitate, gas being evolved the while in consequence of the catalytic action of the metal on the hydrazine. The precipitate is dried at 105° C., ignited in air, followed by hydrogen, and finally by carbon dioxide, in which gas it is cooled. The rhodium thus obtained is free from alkali.