920 NEUTRAL COLOURING MATTERS. 



amounts to about ] 8 or 20 per cent of the indigo employed. 

 The density of aniline is 1.028, it boils at 442.4 (228 centig.). 

 Its smell is strongly aromatic, but at the same time disagreeable, 

 it is sparingly soluble in water, but mixes in all proportions 

 with alcohol and ether. Exposed to the air, it acquires a 

 yellow colour, and becomes resinous. The most remarkable 

 property of aniline, is its basic character. It forms salts with 

 acids, assuming an atom of water when it unites with oxygen 

 acids, and combining directly with hydracids, exactly like the 

 vege to -alkalies and ammonia. 



Oxalate of aniline is formed by mingling together alcoholic 

 solutions of aniline and oxalic acid ; it falls as a white powder, 

 which is to be washed with alcohol, from which it crystallizes 

 on cooling. Its formula is C 12 H 7 N + HO,C 2 O 3 . Hydrochlorate 

 of aniline is prepared by mixing aniline with hydrochloric acid, 

 and crystallizing the salt ;' it dissolves easily in water ; its 

 formula is C 12 H 7 N + HC1* 



Unverdorben had previously obtained, among the empyreu- 

 matic products of the dry distillation of indigo, an oily alkaline 

 body, which he had distinguished as crystalline, because it has 

 the property of forming crystallizable salts with acids. It was 

 not analysed, but there can be little doubt that it is identical 

 with aniline. 



COLOURING PRINCIPLES OF ARCHIL, LITMUS, AND CUDBEAR. 



Various lichens, which communicate no colour to pure water, 

 strike a fine blue with solution of ammonia. They contain 

 certain crystallizable principles, in themselves colourless, which 

 are thus modified by assuming the elements of ammonia. The 

 history of these principles is still incomplete, although con- 

 siderable progress has been made in their investigation by the 

 labours of Robiquet, Heeren, Dumas, Kane, and E. Schunk. 

 The limits of this work will not permit me to enter into details 

 respecting the various bodies obtained, of which I can do little 

 more than indicate the names and the composition when deter- 

 mined. 



From archil weed, the Roccella tinctoria. Dr. Kane obtained 

 the following series of substances, either existing in the lichen, 



* Fritsche in Liebig's Annalen, xxxvi, 84. 



