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



of an organic substance, which is obtained by carefully evapo- 

 rating at the ordinary temperature over sulphuric acid. It is 

 not advisable to evaporate with the assistance of heat, as the 

 solution then becomes dark brown from the action of the air. 

 After evaporation over sulphuric acid there is left at last a 

 brownish-yellow, transparent syrup, having a sweetish taste, 

 which I shall prove by its properties and composition to be a 

 species of sugar. 



I shall now describe more in detail the properties of the 

 substances just mentioned. 



Alizarine. — The alizarine obtained from the decomposition of 

 rubian exhibits all the usual properties of this well-known sub- 

 stance. Its colour is dark yellow without any tinge of brown 

 or red. The crystals possess a lustre which I have never seen 

 equalled in this substance. Its analysis gave the following re- 

 sults : — 



0-3200 grin, of the crystals, on being heated in the water- 

 bath, lost 0-0580 grm. of water = 18 - 12 per cent. According to 

 the formula C 14 H 5 4 + 3HO, they should lose 18-24 per cent. 



0-2575 grm. of the dry substance, burnt with chromate of 

 lead, gave 06550 carbonic acid and 00945 water. 



These numbers lead to the following composition : — 



Carbon 

 Hydrogen 

 Oxygen . . 



0*1050 grm. of the lead compound, prepared by precipitating 

 the alcoholic solution with sugar of lead, gave 00720 sulphate 

 of lead, equivalent to 00529 oxide of lead=50 - 44 per cent. 

 The formula C 14 H 4 3 + PbO requires 49*90 per cent, oxide 

 of lead. 



The formula here given is the same to which I was led by my 

 former experiments, and it now receives a new confirmation 

 from the relation in which it stands to that of rubian. 



The formation of alizarine from rubian admits of a very easy 

 explanation. By simply losing 14 equivs. of water, 1 equiv. of 

 rubian is converted into 4 equivs. of alizarine, as the following 

 equation shows : — 



C 56 H 34 O 30 =4(C 14 H 5 O 4 ) + 14HO. 



The action of sulphuric acid in the preparation of garancine 

 from madder now becomes more intelligible. It consists simply, 

 as far as the practical effect is concerned, in the conversion of 

 rubian into alizarine. 



MM. Wolff and Strecker, in a late paper ' On the Red 





