MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 393 
before described, and a little sugar, which was obtained from the liquid filtered from 
the lead precipitate. The sugar and the alizarine were probably secondary products 
of decomposition formed from the rubianic acid by the action of the alkali. 
Ruhianic Acid . — This substance really merits the name of an acid, for though its 
acid properties are not well marked, the fact of its giving crystallized compounds 
with the alkalies is a sufficient indication of the class in which it should be placed. 
It crystallizes from its watery solution in silky needles of a pure lemon-yellow colour, 
which when dry form a light, bulky interwoven mass. Sometimes it is slowly depo- 
sited from its watery solution in grains and masses of an indistinctly crystalline form, 
which leave an orange tinge. This difference in appearance is due to some impurity, 
which maybe removed by redissolving the acid in boiling water and adding a little ani- 
mal charcoal, when the acid crystallizes rapidly from the filtered solution in 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 ether. When heated on pla- 
tinum 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 be- 
tween 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 sometimes small yellow crystalline grains are 
found among them, which consist of undeconiposed 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 appearance 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 evapoiation leaves a brown 
syrup, which contains oxalic acid. Rubianic acid is not decomposed on being treated 
3 G 2 
