Dr. Schunck on Colouring Matters. 219 



into drops in boiling water, but when cold it is brittle. It dissolves 

 in alkalies with a dark red colour, and is re-precipitated by acids 

 in yellow flocks ; indeed it bears in all respects a great resem- 

 blance to the body which I have called alpha-resin. Nevertheless 

 it seems to consist of more than one substance ; for if it be heated 

 in a glass tube over a lamp, an abundant sublimate, consisting of 

 shining yellow crystals, is obtained in the upper part of the tube : 

 these crystals very much resemble rubiacine. If it be treated with 

 a boiling solution of perchloride or pernitrate of iron, the liquid 

 becomes reddish brown, and gives after filtration a yellow precipi- 

 tate with muriatic acid, which is a proof of its containing either 

 alpha-resin or rubiacine, or both. Hence it becomes very probable 

 that rubiacine, the alpha-resin, and perhaps also the beta-resin, are 

 formed from rubian by the action of the oxygen of the air. It be- 

 comes still more probable when we consider the following facts : — If 

 an infusion of madder with cold water be allowed to stand in contact 

 with the air, it will be found that after some hours the liquid is filled 

 with a number of long hair-like crystals, which are, as I have shown 

 on a previous occasion*, rubiacine, generally mixed with a substance 

 having all the properties of beta-resin. I have had one specimen of 

 madder which gave such quantities of rubiacine on allowing the 

 infusion to stand, that it collected on the surface of the liquor as 

 a bright yellow scum, and by crystallizing it from alcohol it was 

 obtained almost in a state of purity. Now as rubiacine is insoluble 

 in cold water, it must in this case either have been formed from 

 some substance contained in the infusion by the action of the air, 

 or else it was at first held in solution by some other substance, such 

 as an alkali or alkaline earth from which it gradually became sepa- 

 rated, as by the formation of some acid in the liquid. I incline to 

 the former supposition, and think it probable that it is the rubian 

 which by its oxidation gives rise to the rubiacine. 



Xanthine. — This substance, the method of preparing which from 

 a decoction of madder after the separation of the colouring matters, 

 &c. by acid, I have described above, is of course not a pure sub- 

 stance, since after ignition it leaves a considerable quantity of fixed 

 residue : it is also probable that it contains a small quantity of sugar, 

 as I stated before. Nevertheless it produces reactions of a peculiar 

 kind, which cannot be attributed to sugar, gum, or any similar sub- 

 stance, and can only be due to a peculiar body which exists only in 

 madder. It has the following properties : — When prepared as above 

 described, it is a thick, viscid, yellow or brownish-yellow syrup, 

 resembling honey in colour and consistency, which cannot be ren- 

 dered dry even by exposing it to a heat at which it begins to be de- 

 composed. When exposed to the air, it becomes more liquid on 

 account of its attracting moisture. When heated to ignition, it swells 

 up enormously, giving off at the same time a very perceptible smell 

 of aceton and burns, leaving at last a considerable quantity of ash, 



* See the Report of the British Association for the Advancement of Science for 

 1846. 



