Professor Black in the Academy. HOW GOLD CAME INTO THE BEEFS.

Thames Star, Volume XVII, Issue 5256, 21 November 1885, Page 2

Professor Black in the Academy.

HOW GOLD CAME INTO THE BEEFS.

Professor Black lectured last evening on the agency by which the gold was placed in the reefs, being the same agency which placed the quartz there. There were divergent opinions on the subject, he said, but as we usually find the gold and the quartz together it may be taken for granted that they are both placed there by the same causes. Chlorine is one of the principal factors by which gold is found in the reefs, from the fact that being easily dissoluble in water, whenever it comes into contact with gold it combines freely with it, and carries it along with itself wherever it goes. The question might be aiked, where was the gold before it came into the reef? Sea water has been found to contain about one grain of gold to one ton of sea water, and from this fact it might be taken for granted that nil the formation of rooks that are found at the bottom of the sea must contain gold in greater or lesser quantities. The theory of the chlorine agency just mentioned might be questioned from the fact that on analysis it has been found that the underground water does not contain any chlorine, but from this it must not necessary follow that chlorine has not, in some previous period of the formation of the subterranean rocks, existed there. The lecturer showed this by supposing that there was a little gold scattered.without any variation throughout a large extent of country composed of mica schist rocks, and supposing the fissures he bad before referred to last evening were there, and "water containing a solution of chlorine and gold, in combination chloride of gold, flowing through this country, and wherever it came across fissures where quartz was in process of formation, the gold was precipitated and deposited in the growing quartz reef.—An experiment was here made by the Professor, showing by the action of muriatic acid on black oxide of manganese that chlorine is a heavy gas of a greenish yellow color, and with a very offensive smell. Chlorine was. therefore formed by the action of muriatic acid on black oxide of manganese.—This latter abounds in nature, but muriatic acid is very scarce, and only plentiful in the sub* stances thrown out by volcanoes. It can, however, be made from sulphuric acid and common salt, which latter exists to an unlimited extent all over the world, and by the action of water it is carried into the sea, which owes its saltness thereto. Now we have the salt, and we want to know where the sulphuric acid which helps to form the muriatic acid is to be found. This is obtained by the action of the oxygen, which is in all running water, on iron pyrites. Thus the muriatic acid being formed from sulphuric acid and salt, this acting on the black oxide of manganese which, as said before, exists in great abundance, chlorine is the result. This chlorine acts on the gold in the rocks, dissolves it, and the solution of chlorine and gold, chloride of gold is carried away by running water, until it comes with contact with some substance that has the faculty of releasing the gold from the chlorine, and allows the former to be deposited in its metallic state. This power, of all other substances, sulphate of iron possesses, and it exists in the rocks. The Professor showed as a specimen of this a piece of pure sulphate of iron taken from a reef on the Thames. There are other substances besides sulphate of iron which have the power of causing the gold in solution to be thrown down, such as sulphurous acid, organic matter, Ac, and it may be that the presence of gold in the quartz reefs may in some instances be attributed to their agency. Still another way of dissolving gold is by adding sulpheretted hydrogen to gold, when the latter is precipitated as j a black sulphide, Thia sulphide can be i dissolved by alkaline water, and the gold will be found left in a metallic state. In concluding, he gave a summary of the chief agencies by which gold can be dissolved, which were as follows:—1. Presence of iron pyrites, together with salt and black oxide of manganese exposed to the action of water and the atmosphere., 2. Quarts at a high temperature, together with muriatic acid and black oxide of manganese. 3. Saltpetre together with iron pyrites oxidising and salt. 4. Sul* pheretted hydrogen, together with alkaline water.