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DYEING AND CALICO PRINTING.

for the artificial production of alizarin, to which we shall recur elsewherein full.

The preparation of pure alizarin from madder, on the large scale, is a tediousoperation. The best material to start from is an alcoholic extract of goodmadder. Some kinds of this extract are manufactured on a large scale.When properly prepared they deposit a red granular substance, very suitablefor the preparation of alizarin.

Another source is the “ Green Alizarin” of commerce, first prepared byKopp. To obtain it on the large scale madder is mixed with ten times itsweight of aqueous sulphurous acid, to which a little hydrochloric acid hasbeen added to decompose the lime-salts of the madder. The mixture isplaced in a well-covered wooden vessel, and allowed to stand from twelve totwenty-four hours, with occasional stirring. The semi-fluid mass is thrownupon a filter, the vat is washed out with a little water, and the rinsings addedto the filter; the liquid is allowed to run through, and the residue is stronglypressed. The liquid is again put in a wooden vat. The dry pressed residueis again treated with ten times its weight of sulphurous acid water, as before,the filtrate and the pressings being mixed with the first liquid. This treat-ment is repeated a third time, but the liquid obtained, being too weak to bemixed with the preceding, is saved for the second extraction of a fresh quan-tity of madder.

On adding to the sulphurous liquid about 3 to 5 per cent of sulphuric orhydrochloric acid, and heating to 6o° C., an orange flocculent precipitate falls.Its precipitation is complete in about thirty minutes. The deposit is separatedfrom the mother-liquor by decantation or filtration, and washed with a littlecold water till the washings have a faint yellow colour and display no longeran acid reaction. This precipitate is purpurin, almost chemically pure. If themother-liquor is now allowed to boil for two hours the so-called green or crudealizarin separates out, and is deposited in twenty-four to thirty hours as agreenish-black mass. It is washed by decantation with cold water two orthree times.

From this so-called “ green alizarin ” a much purer article, “ yellowalizarin,” is obtained by the following process :—1 part of green alizarin isboiled with 15 to 20 parts of rectified petroleum, boiling at 150' C. As soonas the boiling ceases the green insoluble matter separates as a sediment.After a few minutes the liquid is decanted. It contains much alizarin, part ofwhich separates out on cooling. When the temperature has fallen to aboutioo° C., dilute caustic soda-lye is added, and the mixture well agitated. Thesoda takes up all the alizarin, with a bluish-purple colour, whilst the petroleumbecomes almost colourless, and may be used again. The lye is poured intodilute sulphuric acid, when alizarin separates in yellow flocks. These arecollected on a filter, washed till perfectly free from acid, and dried. From this“ yellow alizarin ” pure alizarin can be prepared by sublimation.

Another suitable source for pure alizarin is cotton which has been dyed aTurkey-red. Several yards of this cloth are cut up and submitted to the aCtionof alcohol, at 85 per cent, mixed with strong sulphuric acid. The fatty matter,alumina, and colour are simultaneously dissolved. The liquid thus obtainedis very carefully neutralised with ammonia, by which the alumina is precipi-tated. After filtration the filtrate is concentrated on the water-bath, and