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To Test the Purity of Alum

The usual impurity which renders alum unfit for the uses of the dyer, is the ferro-sulphate of potassa, but if iron be present in any other shape it is equally injurious. Common alum frequently contains ammonia, from urine or the crude sulphate of the gas works having been employed in its manufacture. This may tin in small quantities at a time, until about be detected by adding a little quicklime or 2 ounces tin to the pound of acid used are caustic potassa. Pure alum should form a dissolved. In this operation the temperature colorless solution with water, and give a white should not be allowed to rise. ( See No. 4124.) precipitate with pure potassa soluble in an ex-

109. Yellow Spirits are prepared in the same way, only substituting sulphuric acid for the nitric acid. This is used for the same purposes as red spirits, with the advantage of the economy of sulphuric over nitric acid .

110. Barwood Spirit is prepared by using 5 measures hydrochloric acid, 1 nitric acid and 1 water, dissolving in this 1 ounce feathered tin for every pound of the whole mixture. 14 ounces tin may be used if the red dye is required to be very deep.

111. Plumb Spirit is made by using 6 to 7 measures hydrochloric acid to 1 nitric acid and 1 water, dissolving in it 14 ounces tin for each pound of the acid mixture. This spirit is named from a preparation made with it and a decoction of logwood. A strong solution of logwood is made and allowed to cool, then to each gallon of the solution there is added from 1 to 14 pints of the spirit; the whole is well stirred and set aside to settle.

This preparation has a beautiful violet color, and silk and cotton are dyed of that shade by dipping them into this plumb liquor without any previous mordant. The depth of tint will depend on the strength of the solution. cess of the latter. It should suffer no change on the addition of tincture of galls, prussiate of potash, or sulphureted hydrogen. 116. Nitrate of Iron is used in the dyehouse for various purposes. Its principal use is for dyeing Prussian Blue, and is obtained as follows: Take 4 parts nitric acid and 1 part water in a glass or stoneware vessel; place it in a warm bath, and add clean iron so long as the acid continues to dissolve it with effervescence; take out any iron that remains undissolved, and, after settling for 1 hour, the clear solution is ready for use. The fumes given off during the operation should be guarded against, being deleterious to health and injurious to any metal or vegetal with which they come in contact. This solution should be kept in the dark, as it loses some of its strength by exposure to light.

117. Chloride of Iron is another salt used in the dye-house for dyeing silks and woolens a deep blue, and is preferred, for that purpose, to copperas. It is prepared for use thus: To 4 parts hydrochloric acid add 2 parts water, and apply a gentle heat; then add iron in pieces, or filings, so long as it continues to be dissolved; then pour off the clear liquid into a basin, and evaporate, when greenish colored crystals of chloride of iron will be ob tained. This salt crystallizes with difficulty, deliquesces in the air, and should not be ex- 112. Plumb Spirit for Woolen Dyeing. This is prepared by adding tin to nitric acid in which a quantity of chloride of ammonium (sal ammoniac) has been dissolved.

Observe, that all these spirit preparations are posed. Instead of evaporating and crystalvaried by different operators , some preferring lizing, the solution may be put in a bottle and more or less of the two acids, and also of reserved for use. the tin; but the proportions given form good 118. To make Iron Liquor. Into a working spirits, and if care be taken in their preparation not to fire them, that is, not to allow the temperature to get so high as to convert the tin into a persalt, the operator will not fail in his processes as far as the quality of the spirit is concerned.