the Colouring Matters of Madder. 195 



this substance presents no characteristic properties to observa- 

 tion. It is a perfectly uncrystalline, glutinous, neutral sub- 

 stance, hardly possessing a sweet taste, and not capable of enter- 

 ing into combination with any other body. There would be 

 absolutely no means of ascertaining whether its formula is 

 C 12 H 12 O 12 , C 14 H 14 Q 14 , or C n IF O n , if it did not occupy a fixed 

 place as part of a system of bodies. It is the last member of 

 the series whose position can be determined ; but that of the 

 others being known, it falls at once into the only place it can 

 occupy. The formula of rubian being given, by its decompo- 

 sition into alizarine and water, and into rubiretine, verantine and 

 water, it only remains to ascertain the formula of the group of 

 bodies comprising rubianine, rubiadinc, rubiafine and rubiagine, 

 which mutually replace each other according to circumstances, 

 as I mentioned above. Now one of these bodies, rubiafine, gives 

 by simple oxidation with persalts of iron, rubiacic acid, without 

 losing any carbon, the rubiacic acid being inconvertible into 

 rubiafine by means of reducing agents. In rubiacate of potash, 

 the potash is to the carbon as 1 : 32 ; consequently all the bodies 

 of this group must contain 32 equivalents of carbon, and 

 the formulae then only differ from one another by certain mul- 

 tiples of HO. Hubianine, for instance, must be C 32 H 19 15 ; 

 and if this be deducted from the formula for rubian, after adding 

 to the latter 9HO, the remainder will be C 24 H 24 O 24 , which re- 

 presents two equivalents of sugar. I fear it is through no merit 

 of mine that M. Laurent has been led to adopt the same view of 

 the constitution of this substance ; for if this were the first in- 

 stance on record of the formation of sugar from other bodies, we 

 should without doubt have been entertained with disquisitions 

 by chemists of M. Laurent's school on all kinds of possible for- 

 mulae which might be attributed to it. Nevertheless there is no 

 instance of the formation of sugar from bodies of a more complex 

 nature, as in the decomposition of salicine and phloridzine, in 

 which its formula has not resulted from a similar process of 

 reasoning to mine, instead of from direct experiment. 



As regards rubiacine, M. Laurent is not to be blamed for 

 adopting a formula which leaves unexplained its formation from 

 rubian, as he was not aware of its being a derivative of the latter 

 substance. The relation, however, in which rubiacine stands to 

 rubiacic acid fixes the number of equivalents of carbon which it 

 contains at 32, and consequently determines the formula. Con- 

 cerning the true composition of rubiacic acid there can be no 

 doubt. M. Laurent's formula for the potash salt is impossible; 

 for without regarding the absurdity of assuming it to contain 

 half an equivalent of base and a fraction of an equivalent of 

 oxygen, it presupposes an error in the determination of the car- 



02 



