derived from Indigo-blue. 299 



precipitated by sulphuric acid in brown flocks, which were 

 filtered off, well washed with water, and then treated with 

 boiling alcohol, in which they dissolved completely. The alco- 

 holic solution deposited, on cooling, a brown powder, which 

 was collected on a filter, washed with a little cold alcohol, 

 and dried. To this product I apply, for the sake of distinc- 

 tion, the letter E. 



The acid liquid filtered from the mixture of substances 

 insoluble in water still contained in solution a product of de- 

 composition derived from the indigo-blue. It was evaporated 

 until crystals began to appear on its surface, and it was then 

 set aside and allowed to stand for some time, when a large 

 quantity of crystals was gradually deposited. After separa- 

 tion from the mother-liquor, these crystals appeared of a 

 brown colour ; but by recrystallization from boiling water and 

 decolorization with animal charcoal, they were rendered white 

 and pure. They were then found to have the properties and 

 composition of anthranilic acid, the well-known product formed 

 by the action of caustic alkalies on indigo-blue. The mother- 

 liquor of the crystals left, on evaporation, a thick brown syrup, 

 which seemed to be a compound of anthranilic acid and acetic 

 acid. On dissolving it in water, adding sulphuric acid to the 

 solution and evaporating, I obtained a quantity of crystals, 

 which were purified by crystallization, first from water and 

 then from boiling alcohol. They differed in appearance from 

 anthranilic acid, and consisted indeed of a compound of the 

 latter with sulphuric acid. The same compound is obtained 

 in place of uncombined anthranilic acid, if a great excess of 

 sulphuric acid beyond what is required to unite with the free 

 soda and that combined with acetic acid and the various pro- 

 ducts yielded by the process has been employed in the first 

 instance. The sulphate, being more soluble in water than 

 the free acid, does not crystallize so easily from the brown 

 syrup which the liquid always leaves on evaporation ; and 

 hence it is advisable not to use an excess of sulphuric acid in 

 the process above described for the separation of the anthra- 

 nilic acid. 



As regards their properties, the products insoluble in water 

 present very little that is of interest. The body A is a brittle, 

 amorphous, brownish-yellow resin, transparent in thin layers. 

 At a temperature of 100° C. it becomes soft and semiliquid. 

 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 nee- 

 dles. It is quite insoluble in alkaline liquids, such as caustic 



