See Mineralogy in this Suppl.—In the third volume of Mr Nicholson's Philosophical Journal, we have a method of making artificial pyrites, which we shall give in the words of the author.

I impregnated water (says he) very strongly with carbonic acid, and introducing some iron filings, I contained the impregnation for a day or two, and afterwards allowed the water to stand in a well corked bottle for some days, till the acid had taken up as much iron as possible. I then poured it into an aerating apparatus; threw up the hepatic gas from sulphuret of potash and sulphuric acid; and after having agitated the water till it had got a good dose of the gas, I poured the water into a large balloon; this was in the evening, and next morning when I looked at it I found it covered with a pretty thick film of a most beautiful variegated pyrites. I had so little of it, that the only proof I had of its being this substance was, that it was ignited on its being placed on a hot poker.