206 Dr. Schunck on Rubian and its Products of Decomposition* 



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 brown- 

 ish-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 stand- 

 ing ; 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 atmo- 

 sphere 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 dissolves 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 sepa- 

 ration 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 coohng a quantity of small bright red sphe- 

 rical grains, which generally form a mass so bulky as to render 

 the liquid thick and gelatinous. When this mass, which con- 

 sists of the soda salt, is placed on a filter, an almost colourless 

 liquid runs through, leaving the salt on the filter in a soft spongy 

 state, from its retaining mechanically a large quantity of water. 

 The round grains of which it consists, though they have a some- 

 what crystalline appearance, are not in reality crystalline. In 

 consequence of its sparing solubility in water, which is less than 

 that of the potash salt, it may be washed with cold water with- 

 out 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 con- 

 verted, on standing, into a mass of yellow crystalline grains con- 

 sisting 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 considerable excess of alkali, be boiled, its 



