394 MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 
with boiling- solutions of phosphoric, acetic, oxalic or tartaric acids ; it merely dis- 
solves in them, and crystallizes out ag-ain 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 imdissolved acid float- 
ing in the liquid, these disappear very slowly, and the gas must be passed through 
for a long time in order to effect their decomposition. The solution now appears 
colourless, but slightly milky. No yellow flocks are formed, as in the case of rubian, 
but the solution, on standing for some time, usually deposits a quantity of brownish- 
yellow crystals. If a solution of chloride of lime be added to a watery solution of 
rubianic acid, the latter turns blood-red, but in a few moments the colour disappears, 
and the solution becomes quite colourless. 
Rubianic acid dissolves in caustic potash and soda in the cold with a lively cherry- 
red colour. If caustic potash be added to a strong watery solution of the acid, 
nothing separates on standing; but if carbonate of potash be 'employed instead of 
caustic potash, there is deposited almost immediately a quantity of dark-coloured 
crystalline needles. These needles are the potash salt. When collected on a filter, 
slightly washed with water and dried, they form a beautiful puce-coloured silky mass. 
When dried either in the water-bath or in vacuo, the colour changes to a bright red, 
but after a few minutes’ exposure to the atmosphere the original colour is restored. 
Rubianic acid is so weak an acid, that water alone is sufficient to separate it from its 
combination with potash. When the potash salt is treated with boiling water it dis- 
solves with a red colour, but the solution on cooling and standing deposits yellow 
crystals of the acid itself. Mere treatment with cold water produces to some extent 
the same effect; for if the salt be placed on a filter and washed with cold water, 
numerous small yellow specks, caused by the separation of the acid, become visible. 
When caustic or carbonate of soda are added to a boiling watery solution of the acid, 
the solution deposits on cooling a quantity of small bright red spherical grains, which 
generally form a mass so bulky as to render the liquid thick and gelatinous. When 
this mass, which consists of the soda salt, is placed on a filtei-, an almost colourless 
liquid runs through, leaving the salt on the filter in a soft spongy state, from its 
retaining mechanicall}^ a large quantity of water. The round grains of wliich it con- 
sists, though they have a somewhat crystalline appearance, are not in reality crystal- 
line. In consequence of its sparing solubility in water, which is less than that of the 
potash salt, it may he washed with cold water without dissolving. When dry it is 
dark red, and gives a red powder. It dissolves again in boiling water with a red 
colour, and the solution on cooling forms a thick jelly, which however is converted, 
on standing, into a mass of yellow crystalline grains consisting of acid. If a solution 
of rubianic acid in caustic potash or soda be supersaturated with any stronger acid, 
the solution becomes yellow without depositing anything, but after some time the 
acid separates in yellow crystals. But if the alkaline solution, containing a consider- 
able excess of alkali, be boiled, its colour changes gradually from red to purple, and 
