194 



cliloiic acid, by filtering off the sulphide of lead. Wash the 

 latter for a short time and withdraw from it the R. acid by means 

 of boiling alcohol. Evaporate the alcoholic solution to ^, add water 

 and a little solution of baryta, thereby obtaining a white deposit, 

 which has to be removed when, after addition of more solution of 

 baryta, Ruberythrate of baryta will be j)recipitated in crimson-red 

 flocks. Collect the latter, dissolve in diluted acetic acid, neutralise 

 the solution with ammonia almost completely, and add subacetate 

 of lead, which throws down the compound of lead with a cinnabar- 

 i*ed colour. This compound has to be washed with diluted alcohol, 

 and is decomposed under alcohol with sulphuret of hydrogen. Heat 

 the whole to the boiling point, filter hot and evaporate, obtaining 

 thereby light-yellow crystals of R. acid, which have to be purified 

 by pressing and by recrystallising in a little water. — The Rube- 

 rythric acid forms yellow needles of a silky gloss, slightly bitter; 

 loses at 100*^ nothing of its weight; dissolves slowly in cold, readily 

 in hot water ; the aqueous solutions become cloudy when heated 

 with hydrochloric acid, and form on boiling a yellow jelly, which 

 conglomerates to flakes of alizarin ; dissolves in alcohol and in 

 ether with gold-yellow coloiir (Schunck's rubianic acid is insoluble 

 in ether); dissolves in aqueous alkalies with blood-red colour, the 

 solutions assuming on boiling the purple-red hue of the alkaline 

 solutions of alizarin and throwing down alizarin after the addition 

 of acids. 



Rllliiacin = C32 Hn Oio. In the root of Rubia tLnctorum, 

 perhaps combined with lime. Proceed at first, as indicated under 

 Rubian ; mix the residue, remaining after the edulcoration of the 

 rubian, with the remnant left after the evaporation of the alcohol, 

 containing verantin and rubiretin, and treat the mixture with a 

 boiling solution of chloride or of nitrate of iron. Rubiretin and 

 Rubiacin dissolve (the latter jjartly as such, partly by Oxydation 

 as rubiacate of iron-oxyd) in the liquid, while verantin remains in 

 combination with oxyd of iron. Filter the deep red-brown solution 

 after short boiling, keep the remnant for the preparation of veran- 

 tin, precipitate from the filtrate with hydrochloric acid Rubiacin, 

 rubiacic acid, and rubiretin, as a yellow (after washing, brown) 

 deposit, dissolve moist in boiling alcohol, dissolving Rubiacin and 

 rubiretin and separating the former on cooling in small, citron- 

 yellow crystals. By evaporating more of the alcohol, a mixture of 

 Rubiacin and rubiretin is obtained as a dark brown-red residue, 

 which forms on boiling with water dark -brown drops of rubiretin, 

 while Rubiacin remains suspended as a light jiowder, and is easily 

 decanted. After repeating the boiling with water several times, 

 and pouring ofi" the yellow powder which has formed, rubiretin 

 remains as a dark, i"ed-brown mass. — Forms splendid tabular 

 crystals and needles, similar to iodide of lead, of a strong, reddish- 



