ISATIN. 387 



salts are soluble in water, the solutions having a blue 

 color. 



Isatin, C 8 H 5 .N"0 2 , is formed by the oxidation of 

 indigo-blue. Finely powdered indigo is heated with 

 water to boiling, and to the liquid concentrated nitric 

 acid is added, until the blue color has completely dis- 

 appeared. By repeatedly boiling the mass with water, 

 the isatin formed is dissolved, and, on cooling, it 

 gradually crystallizes out. It may now be purified by 

 dissolving in potassa, precipitating with hydrochloric 

 acid and recrystallizing. 



Yellowish-red prisms, of a strong lustre ; soluble in 

 alcohol, forming a brown-red solution; in cold potassa- 

 ley forming a violet solution ; fusible ; partially sub- 

 limable without decomposition. Combines with the 

 alkaline bisulphites, forming crystallizing compounds. 



When distilled with concentrated- potassa-ley, anilin 

 passes over, hydrogen being at the same time set free. 

 Suspended in water, and treated with nitrous acid, it 

 is converted into nitrosalicylic acid (p. 346), a gas 

 being evolved at the same time; treated with ammonia 

 in an alcoholic solution, it yields a large number of 

 crystallizing compounds, the composition of which 

 shows that they have resulted from isatin by the addi- 

 tion of ammonia and the elimination of water. 



Chlorisatin, C 8 H 4 C1N0 2 . Is produced by the action 

 of chlorine gas on a boiling-hot solution of isatin in 

 water, it being thrown down under these circumstances 

 as a yellow, flocky precipitate ; further, together with 

 secondary products, by conducting chlorine into pure 

 indigo mixed with water. From the crude product 

 thus obtained, the chlorisatin is extracted by means 

 of boiling water, and separated by means of crystalli- 

 zation from dichlorisatin, C 8 H 3 C1 2 1TO 2 , which is formed 

 at the same time, and is more easily soluble in water. 

 Orange-yellow, transparent, four-sided prisms, of 

 bitter taste ; inodorous ; scarcely soluble in cold water, 

 soluble in alcohol; partially sublimable. Towards 

 bromine it conducts itself in the same way. The sub- 



