Dr. Schunck on Rubian and its Products of Decomposition. 205 



needles, as just mentioned. The watery solution has a light 

 yellow colour, reddens litmus paper slightly, and has a distinctly 

 bitter taste, though not so intensely bitter as that of a solution 

 of rubian. It is soluble in alcohol, but not in aether. AVhen 

 heated on platinum foil it melts and then burns with a smoky 

 flame, leaving a slight carbonaceous residue. When heated in 

 a tube it melts to a brownish-red liquid, which on being allowed 

 to cool becomes solid and crystalline, but on being heated again 

 more strongly gives fumes, which condense on the colder parts 

 of the tube to a liquid, which soon solidifies, forming a mass of 

 shining needles. When slowly heated between two watch-glasses, 

 there is formed on the upper glass a sublimate of shining orange- 

 coloured crystals, having the appearance and all the properties 

 of alizarine, while a considerable carbonaceous residue is left on 

 the lower glass. Concentrated sulphuric acid dissolves rubianic 

 acid easily even in the cold, forming a dark red solution, which on 

 being boiled becomes of a dark reddish-brown colour, without 

 evolving much sulphurous acid. If sulphuric acid be added to 

 a watery solution of rubianic acid, and the solution be boiled, 

 dark yellow or orange-coloured flocks begin to be deposited, 

 which increase as the boiling continues. On allowing to cool 

 they often separate in such quantities as to render the liquid 

 quite thick. These flocks are quite uncrystalline, though some- 

 times small yellow crystalline grains are found among them, 

 which consist of undecomposed acid, and disappear on con- 

 tinuing the action for some time longer. These flocks consist 

 of alizarine almost in a state of purity. On dissolving them in 

 alcohol and evaporating spontaneously, a quantity of beautifully 

 crystallized alizarine is obtained. The liquid filtered from the 

 flocks contains sugar, which is obtained with its usual appear- 

 ance and properties on neutralizing the acid with carbonate of 

 lead, filtering, passing sulphuretted hydrogen through the liquid, 

 filtering again, and evaporating. Muriatic acid acts in precisely 

 the same manner on rubianic acid as sulphuric acid. Nitric 

 acid dissolves rubianic acid even in the cold, forming a yellow 

 solution, which on being boiled disengages nitrous fumes and 

 becomes colourless. The solution on evaporation leaves a brown 

 syrup, which contains oxalic acid. Rubianic acid is not decom- 

 posed on being treated with boiling solutions of phosphoric, 

 acetic, oxalic or tartaric acids ; it merely dissolves in them, and 

 crystallizes out again unchanged on the solutions cooling. If 

 chlorine gas be passed through a watery solution of rubianic 

 acid, the yellow colour of the solution slowly disappears. If 

 there are any crystals of undissolved acid floating in the liquid, 

 these disappear very slowly, and the gas must be passed through 

 for a long time in order to efiect their decomposition. The 



