FORMATION OF INDIGO-BLUE. 197 



ug nitric acid it yields indigotic acid, and when treated 



;i strong boiling solution of caustic soda it is converted 



having the properties of anthranilic acid. Its 



tity with indigo-blue is however placed beyond doubt by 



following results: — 



I. 0.3365 grm. dried at 100° C. and burnt with oxide of 



nd chlorate of potash gave 0.8955 grm. carbonic 

 and 0.1305 water. 

 0.5 175 grm. burnt with soda-lime gave 0.3775 grm. plati- 



AMD0.* 



II. 0.3605 grm. gave 0.9605 grm. carbonic acid and 0.1350 

 water. 



0.5230 grm. gave 46 CC. of moist nitrogen at a tempera- 

 i »f 1 2° C. and a pressure of 736.8 m m - equivalent to 42.7 CC. 

 of dry nitrogen at 0° C. and a pressure of 760 mm or 0.0534 grm. 

 Hence was deduced the following composition : — 



* The double chloride which yielded this amount of platinum was washed 

 according to Hofmnnn's directions with ether, to which a little alcohol was added 

 instead of with the usual mixture of alcohol and ether. It weighed 0.fK)9*> grm., 

 which if it had consisted of the double chloride of platinum and ammonium 

 alone, would hare corresponded to 0.0571 grm. of nitrogen or 11.03 per cent. 

 The apparent excess arose without doubt from the presence of aniline. 



f The analyses above given lead to a composition more nearly approaching 

 -■oretical one than apy previously on record, with the exception of those 

 given by Laurent (Ann. de Chim. et de Pbys. Ser. III., T. which 



were made with sublimed indigo-blue. To the use of the latter for this pur. 

 pose, however, objections may be raised on account of the difficulty of separating 

 n particles of carbon and traces of oily and resinous matters formed by 

 the sublimation. Dumas in his last memoir on the composition of indigo. blue 

 (Ann. de. Chim. et de Phys. Ser. III,. T. 2, p. 207) proved that the excess 

 of carbon in the previous analyses of the substance was only apparent, being 

 caused by the admixture of a little sulphur derived from the sulphate of iron 

 which is generally used for its purification. Having carefully removed this 



