434 Dr. Schunck on Rubian and its Products of Decomposition. 



colour. Acetate of copper changes the colour of the alcoholic 

 solution from light yellow to brownish -yellow, and after some 

 time an orange-coloured precipitate is formed. When rubiagine 

 is treated with a boiling solution of perchloride of iron, the solu- 

 tion acquires a darker colour, but does not assume the deep 

 brownish-purple characteristic of solutions of rubiafine and 

 rubiacine in that menstruum. The liquid being filtered boiling 

 hot, deposits on cooling a quantity of yellow shining scales, but 

 the addition of muriatic acid produces no further precipitate. 

 These scales dissolve easily in boiling alcohol, and the solution 

 on cooling and standing deposits a number of small yellow grains 

 and nodules consisting of crystalline needles, which are appa- 

 rently nothing but rubiagine itself, for they are not capable of 

 sublimation, and their alcoholic solution is not precipitated by 

 acetate of lead. The greatest part of the rubiagine is left un- 

 dissolved by the perchloride of iron in the shape of a yellowish- 

 brown powder, which does not dissolve on treating it with 

 an additional quantity of the iron salt. Boiling muriatic acid 

 changes the colour of this powder to yellow, and it has then all 

 the properties of rubiagine. Rubiagine is therefore not changed 

 into rubiacic acid by the action of persalts of iron. Notwith- 

 standing the great resemblance which rubiagine bears to the 

 other bodies belonging to the same series^ its reactions prove it 

 to be a distinct substance. It is distinguished from rubianine, 

 by its insolubility in water ; from rubiadine, for which it might 

 most easily be mistaken, by its being incapable of sublimation ; 

 and from rubiafine, by its not being convertible into rubiacic acid. 

 Its behaviour towards acetate of lead, which is different from that 

 of all the other three substances, also serves to characterize it. 

 The analysis of rubiagine gave the following results : — 

 0-3800 grm., prepared directly from madder, gave 0*9490 

 carbonic acid and 0'1760 water. 



In 100 parts it contained therefore — 



Carbon 68-10 



Hydrogen 5-14 



Oxygen 26-76 



There are two formulae with which this analysis con'csponds, 

 and both of which explain the formation of the substance equally 

 well, viz. Cs^H^^Qio and C^^H^^oia. These formula require 

 respectively in 100 parts — 



C32 H" Qio. C^^ H17 013. 



Carbon .... 67*13 68*57 



Hydrogen . . . 4*89 4*41 



Oxygen .... 27*98 27*02 



