388 ISATOSULPHURIC ACID. 



stitution-products of isatin are decomposed by fusing 

 caustic potassa like isatiri, substitution-products of ani- 

 lin being formed. 



Isatosulphuric acid, C 8 H 4 N0 2 .S0 2 .OH, is formed 

 by the action of potassium bichromate and sulphuric 

 acid on sulphindigotates (indigo-carmine). Difficultly 

 crystallizable, very easily soluble acid ; monobasic. Its 

 barium salt, (C 8 H 4 NS0 5 ) 2 Ba + 4H 2 0, forms brass-red, 

 strongly lustrous, crystalline scales, but slightly soluble 

 in cofd water. 



Trioxindol (Isatic acid), C 8 H 7 N0 3 . The violet solu 

 tion of isatin in potassa-ley becomes yellow when 

 boiled, and then contains potassium isatate. The free 

 acid is exceedingly unstable ; when the attempt is 

 made to set it free by means of another acid, it breaks 

 up into isatin and water. 



The substitution-products of isatin conduct them 

 selves towards caustic potassa in like manner. They 

 yield chlorinated or brominated isatic acids, which are 

 likewise exceedingly unstable in a free condition. 



Dioxindol (Hydrindic acid), C 8 H 7 N0 2 , is formed by 

 the action of sodium-amalgam on isatin, to which is 

 added water, by reduction of the isatic acid, which is 

 at first formed. Transparent, rhombic prisms ; easily 

 soluble in water and alcohol ; fuses at 180, and decom 

 poses at 195, anilin being formed. The aqueous solu 

 tion in contact with air turns red, oxygen being taken 

 up and isatin formed. Combines with acids and bases, 

 forming salts. Treated with chlorine or bromine it 

 yields crystallizing substitution-products. Treated with 

 nitrous acid in an alcoholic solution, it is at first con 

 verted into a crystalline substance, nitrosodioxindol, 

 C 8 H 6 (NO)M) 2 , insoluble in water; fusing at 300-310 ; 

 further action converts it into ethyl benzoate and other 

 products. It yields oil of bitter almonds when gently 

 warmed with nitric acid or silver oxide. 



