Читать книгу The Practical Ostrich Feather Dyer - Alexander Bartlett Paul - Страница 17

Copperas is generally prepared from the soft, white variety of iron pyrites, frequently found to a great extent in the coal measures. These, on exposure to air and moisture, decompose the latter, taking up oxygen, and are thus converted into sulphate of iron. Copperas forms pale greenish blue semi-transparent crystals, containing forty-five per cent. of water. If this be expelled, there remains a dull whitish powder. The crystals dissolve readily in one and one-half times their weight of cold water, and less than half their weight of boiling water. The direct uses of copperas have very much diminished in feather dyeing; as for dyeing black in conjunction with logwood it has been almost entirely superseded by bichromate of potash. In drabs and in saddening down light colors it is, to a certain extent, still used. It is used in quantities so small, however, that there is no serious results to be feared, as it must be used in quantity to injure the fibre.