224

DYEING AND CALICO PRINTING.

brownish-yellow deposit. When this point is reached the mass is allowed tocool, dissolved in hot water, the deep blue violet liquid decanted or filteredfrom the undissolved residue, and the clear filtrate mixed with sulphuric orhydrochloric acid. Sulphurous and carbonic acids are evolved, whilst alizarinis deposited in dense brownish-yellow flakes. These, when cold, are collectedon a filter, and perfectly washed with cold water. The alizarin can serve forall purposes to which the preparations of madder were formerly applied.

Anthrachinon-bisulphuric acid is prepared from anthracen as follows :—i part of anthracen is heated in a suitable vessel with 4 parts of concen-trated sulphuric acid, at first for 3 hours to 100°, and afterwards for anotherhour to 150“. The mass, when cold, is mixed with three times its weight ofwater. If unchanged anthracen is deposited, it is collected, washed, dried,and set aside for a future operation. The strongly acid dark coloured solutioncontains anthracen-bisulphuric acid and much free sulphuric acid. It is heatedto boiling, and peroxide of manganese in powder is added to thrice the weightof the anthracen employed. The boiling is kept up till the anthracen-bisulphuric acid is converted into anthrachino-bisulphuric acid. The mixtureshould be evaporated to dryness, and the heat continued for some time. Themass is now dissolved in boiling water, and dilute milk of lime is added, tillthe liquid has an alkaline reaction. Insoluble protoxide of manganese isdeposited along with sulphate of lime, whilst anthrachino-bisulphate of limeremains in solution. All insoluble matter is removed by filtration andpressing, and the residual solution of anthrachino-bisulphate of lime isdecomposed by means of carbonate of soda. The solution is evaporated todryness, and converted into alizarin by treatment with acids.

Dale and Schorlemmer have patented a still simpler process :—1 part ofanthracen is boiled for some time with 4 to 10 parts of strong sulphuric acidIt is then diluted with water, and the solution neutralised with carbonate oflime, baryta, soda, and potash. The sulphates are then removed by filtrationor crystallisation. The resulting solution is heated to 180° to 260° C., alongwith caustic soda, to which a quantity of saltpetre or chlorate of potash,equal in weight to the anthracen originally employed, has been added, untilthe deep blue-violet colour is developed. The alizarin is then thrown downwith acids in the usual manner.

The alizarin of commerce generally forms a thin paste, containing about15 per cent of solid matters, alizarin, anthrachinon, and oxyanthrachinon.To prepare from this paste pure alizarin it may be dissolved in dilute causticsoda and filtered. The filtrate is mixed with chloride of barium, boiled,filtered, and the precipitate is well washed with water, then suspended inwater, and decomposed with hydrochloric acid. The orange-coloured preci-pitate is filtered, washed, dried, and sublimed, when pure alizarin isobtained.

The identity of artificial and natural alizarin was for a time doubted, inconsequence of experiments made with impure products. Certain chemistsfound that tissues dyed with artificial alizarin lost a considerable amount ofcolour on treatment with soda-lye. This result was probably due to thepresence of tinctorial matters other than alizarin. The artificial alizarinpaste of Gessert and of Lucius has, according to Bolley, ten to twelve timesthe tinctorial power of Italian garancin. For the properties of alizarin the