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For example, all the specimens of bornite and pyrrhotite examined yielded sulphuretted hydrogen with tartaric, citric, and oxalic acids, but chalcopyrite and pyrite do not.

In the easy recognition of the secondary copper sulphides, chalcocite, bornite, etc., the engineer finds a finger-post on the road to extension in depth; and the directions upon this post are not to be disregarded.

Much of the copper of commerce is made from chalcopyrite and bornite, and these ores are more difficult to work.