Dr. Schunck on Colouring Matters. 205 



mains behind when the other substances have been removed by 

 means of boiling water and alcohol ; it is soluble in caustic alkalies 

 with a dark brown colour, and seems to be the substance lo which 

 the colour of the dark brown precipitate is due : I consider it to be 

 oxidized extractive matter. Concerning the method of separating 

 the other six substances contained in the dark brown precipitate, I 

 have nothing to add to what I said in my last report, as I have not 

 been able to discover a shorter or better plan of separating them 

 than that which is there described. In regard to their nature, pro- 

 perties and composition, which I have examined more minutely, I 

 shall in this report give a number of additional details ; before 

 doing so however I shall make a few observations on the subject in 

 general. I may state, in the first place, that I have arrived at the 

 conclusion that there is only one colouring matter contained in mad- 

 der, viz. alizarine ; the other substance, which I took for a colouring 

 matter in the first instance, and which I called rubiacine, I now con- 

 sider to be no colouring matter at all, for reasons which I shall pre- 

 sently state. I have also reason to believe that the two substances 

 which in my first report I called fats, are not fats, but resins ; they 

 are coloured resins similar to many others known to chemists. Of 

 these two resins I shall call the more easily fusible one, which dis- 

 solves in a boiling solution of perchloride or pernitrate of iron, the 

 alpha-resin ; the other less easily fusible one, which forms an inso- 

 luble compound when treated with perchloride or pernitrate of iron, 

 the beta-resin. The method of preparing them is the same as that 

 which I described in my former report. After the dark brown pre- 

 cipitate produced in a decoction of madder by acids has been succes- 

 sively treated with boiling water and boiling alcohol, there remains 

 behind a dark brown substance ; on treating this substance with 

 caustic potash, it dissolves in great part with a dark brown colour ; 

 on filtering there remains on the filter a mixture of peroxide of iron 

 and sulphate of lime ; on adding a strong acid to the filtered liquid 

 a substance in dark brown flocks is precipitated, which is thrown on 

 a filter, washed and dried. This substance, when heated on platinum 

 foil, burns without much flame, and leaves a considerable ash. It 

 is easily decomposed by boiling dilute nitric acid, which converts it 

 with an evolution of nitrous acid into a yellow flocculent substance. 

 As it is insoluble in all menstrua except the alkalies, it n)ay be 

 asked, how it can be extracted from madder by means of boiling 

 water, in which it is of itself insoluble, and whether it is not pos- 

 sible that it may be formed during the process of boiling by the 

 action of the air on some substance contained in the extract. I think 

 the latter supposition very probable, and 1 shall presently describe 

 a substance of almost identical properties formed by the action of 

 the air on xanthine, the extractive matter of madder. 'J'here can how- 

 ever be no doubt that the brown colour of the precipitate, which is 

 produced by acids in a decoction of madder, is due to this substance, 

 for the other bodies contained in it are not brown, but yellow or 

 orange -coloured in a precipitate state. This dark brown precipitate 



