40 Dr. Schuuck on the Formation of Indifjo-blue. 



vine and indirubine. The indigo-blue left undissolved hy tlie 

 boiling alcohol was purified by treating it^ according to Fritzsche's 

 method, with a warm solution of grape-sugar in alcohol to which 

 caustic soda was added, and allowing the mixture to stand in a 

 warm place until the indigo-blue was dissolved. The yellow 

 solution having been drawn off with a siphon and allowed to 

 stand exposed to the air, became first red, then purple, and then 

 deposited the indigo-blue in the shape of small crystalline scales, 

 ■which were collected on a filter and washed first with alcohol, 

 afterwards with boiling water, then digested with muriatic acid, 

 well washed with water and dried. 



The bodies insoluble in water formed by the action of acids on 

 indican are therefore six in number. I shall now give an account 

 of their properties and composition. 



Indigo-blue. 

 The indigo-blue obtained by this process has all the proper- 

 ties usually ascribed to that substance. It is insoluble in alka- 

 line liquids, but dissolves easily when a deoxidizing substance, 

 such as a salt of protoxide of tin or protoxide of iron, or grape- 

 sugar, is added at the same time, the solution exhibiting the 

 usual appearance of an indigo vat, such as the yellow colour, and 

 the blue pellicle on the surface. It is only slightly soluble in 

 boiling alcohol, to which it communicates a blue tinge, but easily 

 and completely soluble in couccnti-atcd sulphuric acid, forming 

 a blue solution from which nothing is precipitated on the addition 

 of water. By the action of boiling nitric acid it yields indigotlc 

 acid, and when treated with a strong boiling solution of caustic 

 soda, it is converted into an acid having the properties of anthra- 

 nilic acid. Its identity with indigo-blue is, however, placed 

 beyond doubt by its analysis, which yielded the following re- 

 sults : — 



I. 0*3365 grm. dried at 100° C. and burnt with oxide of cop- 

 per and chlorate of potash, gave 0"8955 grm. carbonic acid and 

 0"1305 grm. water. 



0-5175 grm. burnt with soda-lime gave 0'3775 grm. plati- 

 num*. 



II. 0-3605 grm. gave 0-9G05 grm. carbonic acid and 0-1350 

 water. 



0-5230 grm. gave 4G cubic, centims. of moist nitrogen at a 



* The double chloride which yielded this amount of platinum was 

 washed according to Ilofnianu's directions, with .xther, to which a little 

 alcohol was added, instead of with the usual mixture of alcohol and a;thcr. 

 It weighed OWY.iit grm., which if it had consisted of the double chloride of 

 ]datinum and ammonium alone, would have corresponded to 005/1 grm. of 

 nitrogen, or 11-03 per cent. The apparent excess arose without doubt 

 from the presence of aniline. 



