Colloidal Osmium

Osmium Hydrosol or Colloidal Osmium is readily prepared by reducing potassium osmate, K₂OsO₄, with hydrazine hydrate in the presence of some protective colloid such as gum acacia or lysalbate (or protalbate) of sodium. The reduction may be effected with acrolein if desired.

Colloidal osmium may also be obtained by reduction of colloidal osmium dioxide. The last named is prepared by reduction with hydrazine hydrate of potassium osmate solution suspended in lanolin, which serves as protective colloid. The product is dissolved in petroleum, precipitated with alcohol and reduced in a current of hydrogen at 50° to 60° C. A solution containing 21 per cent, of osmium has been obtained in this manner.

Colloidal osmium readily undergoes oxidation; it catalytically assists the oxidation of unsaturated compounds by gaseous hydrogen. In this respect it is stated to be even more effective than the finely divided metal, but less active than either platinum or iridium. Carbon monoxide combines with oxygen, yielding the dioxide, when shaken at ordinary temperatures with the hydrosol of osmium.