This compound early attracted the attention of the alchemists, who no doubt supposed, when they saw it come from their crucibles, that they had taken a long stride toward the discovery of the philosopher's stone, and that one step more would enable them to convert tin into veritable gold. So they called this strange gold-like compound aurum musivum, or mosaic gold. It is in reality a disulphide of tin, and is made as follows: -
1. Melt 12 oz. of tin and add to it 3 oz. of mercury; triturate this amalgam with 7 oz. of sulphur and 3 oz. or sal ammoniac. Put the powder into a mattrass,* bedded rather deep in sand, and keep it for several hours in a gentle heat, which is afterwards to be raised and continued for several hours longer. If the heat has been moderate, and not continued too long, the golden-colored, scaly, porous mass, called aurum musivum, will be found at the bottom of the vessel; but if it has been too strong, the aurum musivum fuses to a black mass, of a striated texture.
2. Melt together, in a crucible over a clear fire, equal parts of sulphur and the white oxide of tin. Keep them constantly stirred with the stem of an earthenware pipe or glass rod till they assume the appearance of a yellow flaky powder. In stirring the mixture avoid the use of an iron rod, as it would destroy the compound.
* A mattrass is a glass flask with a long neck. Any thin bottle of green glass will answer if it is bedded well in sand, so that it may not be exposed to sudden changes of temperature. We have made very fine mosaic gold in two common clay crucibles placed mouth to mouth and luted together. (See article Lute.) In the upper crucible we bored a small hole for the escape of vapors, and the whole was placed inside a larger crucible, the space between being filled with sand. No metallic vessel will answer.
Mosaic gold is used as a color or bronze for coating plaster-of-paris images, and also as a gold varnish on toys, and likewise for the sparkles or spangles in that which is called gold sealing-wax. Of late years, however, the manufacture of bronze-powders has been so much improved that they have driven the mosaic gold entirely out of the market. In the laboratory it is still used for coating the rubbers of electrical machines, as it produces powerful excitations, requires no grease, and does not stick to the glass.