Corresponderer: How to Make Sulphate of Iron-Copperas. Blue and Red Glass for Chemists' Bottles.

Scientific American 1, 14.1.1862

Corresponderer: How to Make Sulphate of Iron-Copperas.
Messrs. Editors: - This salt is manufactured from a native sulphuret of iron, of which there are great quantities in some parts of the United States. where it forms the principal part of the rocks of whole districts. In England it is made from iron pyrites, which are found in glubular masses in the coal strata. In making the copperas, a quantity of these pyrites are piled upon an inclined platform, and sprinkled with water from time to time. As this drains through them it carries those portions which have been rendered soluble by the action of the atmosphere, the sulphuret having absorbed oxygen, and having thereby been converted into an acidulous sulphate. These drainings are received into large stone cisterns and pumped from thence into leaden pans, where a fire is kept up under them for several days, during which time large quantities of old iron are thrown in to saturate the excess of acid and precipitate any pershulphate that may have formed. When this solution is sufficiently concentrated it is drawn out into stone cisterns, where it cools and crystallizes. In this state it is of a light green color, and is the protosulphate of iron; but by exposure to the air for some time it absorbs the oxygen, and is partially converted into the red persulphate. In a fry atmosphere it effercesces and parts with its water crystallization, and is then a dry powder, and on being dissolved again in water it is found to be composed of the persulphate and protosulphate of iron. When copperas is fresh and green it is then in the best state for deoxdizing indigo in the copperas blue vat of the cotton dyer, but when it is older, or has been oxydized, so as to appear brown or yellow, it is then better adapted for dying black than when fresh and green. The specific gravity of its concentrated solution is 1.753, and of the salt itself 1.850. It is composed of 27.26 of protoxide of iron, 36.30 of sulphuric acid, 42.43 of water in 100 parts.
R. H. Gibson.
Fisherville, N H., Dec 21m 1861.

Blue and Red Glass for Chemists' Bottles.
- It is quite customary with doctors, druggists and photographers, to employ blue glass bottles for the purpose of keeping such chemicals as the nitrate of silver, which is so easily affected with light. It is pretty generally believed that the blue color of the glass counteracts the effects of light, but according to the experiments of M. Dumey, of France, this is not so. He asserts that the blue color foes not interfere with the chemical rays of light, and that white glass and blue glass bottles are alike unfir for containing silver solutions. He states, however, that red glass bottles are perfectly reliable to use for retaining sensitive chemical substances, as this color prevents the light affecting them.

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