284? Mr. J. Higgin on the Colouring Matters qf Madder. 



burns away without leaving a residue. Tried with mordanted 

 cloth in the usual manner, pure xanthine has little or no effect, 

 merely giving an orange tinge to the alumina. 



The precipitate by sulphuric acid from the watery extract 

 of madder is washed, first with water acidulated with sulphuric 

 acid, and afterwards with a little pure water. About an equal 

 bulk of fine chalk is then mixed up with it, and the mixture 

 repeatedly boiled in water and filtered, till the solution, at first 

 dark-coloured, becomes a faint pink only ; the mixed solutions 

 are acidulated with sulphuric acid, and the greenish-yellow 

 L precipitate collected, washed to remove acid, and dissolved in 



/, alcohol; the solution evaporated down to one-fourth of its 



/ ^volume, and an equal measure of water added. The precipi- 



tated rubiacine may be again dissolved in hot alcohol, and 



crystallized therefrom. It has the following properties : — Spa* 



,J ■ ringly soluble in cold water, but more so in hot, — the solution 

 is amber-coloured ; very soluble in alcohol and aether. Boiling 

 alum solution dissolves it, and forms a clear orange solution 



_^ with no shade of pink ; it does not precipitate from this solu- 

 tion when cold, unless a large quantity of alizarine be also in 

 solution, when almost all the rubiacine precipitates. Sulphuric 

 acid precipitates it from the alum solution perfectly in green- 

 ish-yellow flocks. Its solution in alkalies is a fine crimson, 

 similar to archil. Concentrated sulphuric acid dissolves it 

 readily, and gives a fine orange solution ; water precipitates it 

 unchanged. The solution, if heated some time, becomes 

 brown, and water now precipitates a fine brown powder, which 

 has no colouring properties. Rubiacine is less soluble in aci- 

 dulated than in pure water ; it forms a compound with lime of 

 considerable solubility. In solution of sulphate of ammonia 

 made alkaline by ammonia, rubiacine is soluble when heated, 

 a property offering one means of separation from alizarine, 

 which is totally insoluble in that menstruum at any tempera- 

 ture. Rubiacine may be boiled a long time in dilute sulphuric 

 acid without change. Boiling solution of chlorate of potash 

 has no action on it. When heated, rubiacine fuses, blackens, 

 and gives off orange vapours, which condense in a crystalline 

 C^j^f. mass. Mordanted cloth is not dyed, when treated in the usual 

 manner, with rubiacine. 



The alizarine is contained in the insoluble chalky matter 

 left after the separation of rubiacine. This is digested with 

 dilute hydrochloric acid at a gentle heat, cooled, filtered, and 

 again treated with dilute acid, then washed on a filter till free 

 from acid ; alizarine remains, and may be crystallized from 

 alcohol. It is obtained in much greater quantity from the 

 madder which had been treated with boiling water at first. 



I, 



