Dr. Scliuiick on the Formation of Indigo-blue. 41 



temperature of 12°C. and a pressure of 736-8 millims., equivalent 

 to 437 cubic ceutims. of dry nitrogen at 0^ C. and a pressure ot 

 760 millims. or 0-0534 grm. 



Hence was deduced the following composition :— 



Eqs. Calculated. I. H- 



Carbon . . 16 96 73-28 73-57 72-06 



Hydrogen . 5 5 3-81 4-30 410 



Ntrogen . 1 14 10-68 10-36 10-33 



Oxygen . . 3 _16 Jl3;23 12;77 12-96 



131 100-00 10000 100-00* 



Indirubine. 



This substance, when obtained by the process above described, 



usually appears in the form of a dark brown amorphous mass. 



On one occasion, when very pure indican had been emp oyed in 



its preparation, it was deposited from the boiling alcoholic soiu- 



* The analyses above given lead to a compositiou more nearly ap- 

 proacliinff the theoretical one than any previously on record, with the ex- 

 ception of those given bv Laurent {Ann. de Chim. et de Phys sev3, vol. ni. 

 pS which were made with snbl.med indigo-blue. To the use of he 

 latter for this purpose, however, objections may be raised on account ot the 

 difncultvof separating it from particles of carbon and traces of oilv and 

 resinous matters formed by the sublimation. Dumas m his last memoir on 

 the composition of indigo-blue {Ann. de Chim. et de Phys. ^ev. .i,vo\.u. 

 p 207), proved that the excess of carbon m the previous analyses o the 

 substance was only ap-parent, being caused by the admixture of a lit e 

 sulphur derived from the sulphate of iron which is generally used foi ts 

 imrification Havin<!; carefuUv removed this sulphur, he obtained in thiee 

 analvses 72-90, 72-8 1, and 7-2-D7 per cent, of carbon, which correspond 

 apparently with the theoretical composition. Tliese amounts are, hovvever, 

 calculated according to the old atomic weight of carbon If correc ed in 

 accordance with the new atomic weight of carbon, which was esabjished 

 bv Uumas a short time previously, they become respectively 7^^' \^ "' 

 and 71-92, the great excess iu the second determmation being probably due 

 to some misprmt. On analysing some specimens of the '"^^'^o-W"^ 

 remainin- from his previous investigation, which he mmself had pro^cd to 

 be impure, and calculating the results according to the new atomic weight 

 of cKn, Dumas obtained in four analyses, T6-6, T^'b 72-7, and /3-3 per 

 cent of carbon. The coincidence between these and the iirevious analyses 

 is of course only apparent. I have myself always found a deficiency m 

 the amount of carbon, unless care was taken to wash the precipita ed 

 inditro-blue for a considerable time. I ascribe this circumstance to the 

 indilo-blue, like all porous bodies, combining with certain substances and 

 removing tliein from their solutions in consequence of an attraction ot sur- 

 face exerted bv it. If, for instance, grajie-sugar is cmpbyed lu its puri- 

 fication a certain quantity of it is earned down by the imhgo-ldne and can 

 onlybe -emoved by confnu.ous washing with hot ^yatc.r, followed by treat- 

 St with muriatic^ acid and renewed washing with water -^ M-' -J 

 of water is foun.l to leave on evaporation a small .puintity of suui. and 

 this docs uot cease until the washing has been coutmuud for several dajb. 



