PRODUCTS DERIVED FROBI INDIGO-BLUE, 75 



is a brittle, amorplious, brownish-yellow resia, transparent 

 in thin layers. At a temperature of ioo°C. it becomes 

 soft and semi-liquid. When heated on platinum foil, it 

 burns with a bright flame, leaving much charcoal, which, 

 on being heated, disappears without leaving any ash. It 

 is decomposed by boiling, nitric acid, yielding a product of 

 decomposition in crystalline needles. It is quite insoluble 

 in alkaline liquids, such as caustic potash, soda, and am- 

 monia, even when a reducing agent, such as protoxide of 

 tin, is added ; but it is decomposed on being heated with 

 dry soda-lime, giving off alkaline fames having a peculiar 

 penetrating odour. The body B can hardly be distin- 

 guished by its external appearance from A, with which it 

 has also many properties in common ; but it is easily soluble 

 in caustic and carbonated alkalies, yielding yellow solutions, 

 from which it is precipitated by acids in brown flocks. The 

 compounds with baryta, lime, lead, silver, and copper pre- 

 pared by double decomposition are brown or yellow, and 

 insoluble in water. When treated with boUing nitric acid 

 it behaves like A, yielding also a product of decomposition 

 crystallizing in needles. The body C is a brown powder, 

 which, on being heated, burns without previously melting ; 

 it is insoluble, like A, in watery solutions of alkalies, and 

 very little soluble in alcohol alone, but easily soluble in an 

 alcoholic solution of soda. D resembles C in most of its 

 properties, but differs from it by its solubility in caustic 

 and carbonated alkalies. E is a reddish-brown powder, 

 soluble in alkalies, and more easily -soluble in alcohol than 

 C and D, but distinguished from the others chiefly by its 

 solubility in acetate of soda. 



The composition of these bodies is, however, a matter of 

 some interest, since it is only from a knowledge of their 

 composition that any light can be thrown on the nature of 

 this curious process. I shall, therefore, proceed to give a 

 short account of the results yielded by the analysis of these 



