Note 31 bis — Chapter XXIV · COPPER, SILVER, AND GOLD

Schottländer (1893) obtained gold in a soluble colloid form (the solution is violet) by the action of a mixture of solutions of cerium acetate and NaHO upon a solution of AuCl3. The gold separates out from such a solution in exactly the same manner as Ag does from the solution of colloid silver mentioned above. There always remains a certain amount of a higher oxide of cerium, CeO2, in the solution—i.e. the gold is reduced by converting the cerium into a higher grade of oxidation. Besides which Krüss and Hofmann showed that sulphide of gold precipitated by the action of H2S upon a solution of AuKCy2 mixed with HCl easily passes into a colloid solution after being properly washed (like As2S3, CuS, &c., Chapter I., Note 57).