ARTIFICIAL ALIZARIN.

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pure anthracen, either in commercial anthracen or in crude green grease isthe following':—The melting-point of the sample in question is first determined.

5 to 10 grms. are sufficient for the operation. It is put between thick folds ofblotting paper, and placed under a press, between plates which have beenpreviously warmed. The anthracen remaining upon the paper after pressureis weighed. The residue, after it has been boiled with a certain quantity ofalcohol, filtered, washed with cold alcohol, and dried, is weighed as pureanthracen. It is now advisable to determine the melting-point of thepurified produdt, which will generally be 210° C.

The methods by which anthracen may be extradled from the less volatileoils and from the residual pitch need not be here described. The produces ofanthracen are very numerous, but the only one which concerns us is artificialalizarin. Its preparation, according to the earliest patent of Graebe andLiebermann, is as follows :—Purified anthracen (C I4 H I0 ) is converted intoanthrachinon, Ci 4 H80 2 , either—

1. By treating 1 part of anthracen with 2 parts of bichromate of potash

and sulphuric acid, with or without acetic acid.

2. By oxidising anthracen with bichromate of potash, both dissolved in

acetic acid.

3. By oxidising anthracen with nitric acid of medium concentration, and

simultaneous application of concentrated acetic aci,d.

The anthrachinon thus obtained is converted into C I4 H 6 Br 2 0 2 by heating1 equivalent of anthrachinon and 4 equivalents of bromine in closed vessels,for several hours, to the temperature of 80° to 130° C. The bibrom-anthrachinon is then heated in closed vessels, with concentrated soda orpotash-lye, to 180 0 to 260° C., in order to replace the bromine with peroxideof hydrogen. The mixture slowly assumes first a blue and then a violetcolour, which gradually becomes more intense. When the depth of colour nolonger increases the mass is allowed to cool, dissolved in water, filtered, andsupersaturated with sulphuric or hydrochloric acid, when alizarin separatesout in yellow flakes, which are filtered and purified by washing with water.

The third patent of the same chemists (dated November 3, i86g, andJanuary 18, 1870) directs the preparation of artificial alizarin as follows:—

One part of anthrachinon is mixed with about 3 parts of concentrated sul-phuric acid (sp. gr. i’848), and the mixture is heated in a suitable vessel till aportion poured into water dissolves completely, and leaves only traces ofunchanged(anthrachinon. It is then allowed to cool, and diluted with water.In order to remove the excess of sulphuric acid it is accurately saturated withchalk. Sulphate of lime is thrown down, and is removed by filtration andpowerful pressure, whilst anthrachino-bisulphate of lime remains in solution.As this salt is insoluble in cold water, this operation should be conducted at aboiling heat. The hot solution is mixed with a solution of carbonate of soda,likewise hot, till the readtion is alkaline. The mixture is boiled for some time,till the carbonate of lime is deposited in a heavy granular state. The solutionof anthrachino-bisulphate of soda is separated by decantation and filtration,and evaporated to dryness. To 1 part of the dry salt, 2 or 3 parts of solidsoda and a little water are added. The mixture is then heated in iron vesselsto 180° to 260° C., till the fused mass has an intense violet colour, and aportion dissolved in water and mixed with dilute sulphuric acid gives a copious