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Veins of sulphide of mercury, cinnabar, or vermilion have been found in other parts of the Protectorate: we suspected their presence at Apatim, and collected specimens, still to be assayed. The natives have an idea that when 'the gold turns white' it is uncanny to work the place; moreover, silver is always removed from the person when miners approach the gold-diggings.
We must remember that the particles of gold in the stone may be enveloped with a film of auriferous sulphide, by which they are protected from the solvent actions of the mercury.
When, for example, I ask for the cause of gunpowder and am told that it is sulphur, charcoal, and nitre, or for a cause of sulphuric acid and am given sulphide of iron and oxygen, it is clear that considered separately these ingredients are not causes at all.
When, finally, a precipitation of aluminum oxide takes place the liquid is almost free from iron. From time to time, the solution, in which the aluminum oxide is suspended, is tested for iron by ammonium sulphide, and the current is interrupted when no further reaction is observed. The hot solution is then directly submitted to the action of the electric current.
It occurs as metallic arsenic, which is of a steel-grey colour, brittle, and gives off a garlic-like odour when heated; as arsenious acid; in the form of two sulphides the red sulphide, or realgar, and the yellow sulphide, or orpiment; and as arsenite of copper, or Scheele's green. It also exists as an impurity in the ores of several metals iron, copper, silver, tin, zinc, nickel, and cobalt.
The tissues assume a greenish-black colour from the formation in them of a sulphide of iron resulting from decomposition of the blood pigment. Under certain conditions the dead part may undergo changes resembling more closely those of ordinary post-mortem decomposition.
The whole dissolves; the excess of acid is driven off by evaporation at a boiling heat, and the residue, diluted with water, is saturated with hydrogen sulphide. The iron remains in solution, while the mixed lead and tin sulphides precipitated are allowed to digest for a long time in an alkaline sulphide.
Sulphide of ammonium gives sulpho-cyanide of ammonium. This develops a blood-red colour with perchloride of iron, bleached by corrosive sublimate. Root and leaves. Poisonous property depends upon an alkaloid, aconitine. Aconite is one of the constituents of St. Jacob's Oil. Symptoms.
This calcium sulphide remains as an insoluble mass when the carbonate of soda is extracted from the black ash, and forms the chief constituent of the alkali waste, which until the year 1880 could be seen in large heaps around chemical works.
But when we find large nuggety masses of high carat gold in the beds of dead rivers, another origin has to be sought. As previously stated, there is fair reason to assume that at least three salts of gold have existed, and, possibly, may still be found in Nature silicate, sulphide, and chloride.
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