194 



METHODS OF ANALYSIS. 



and a few drops of hydrochloric acid, shake, and heat to boiling. Care must 

 be taken to carry along for comparison a solution of the coloring matter acidi- 

 fied with hydrochloric acid, in order not to mistake the action of the acid alone 

 for reduction. Some of the colors for instance, safranin and indulins are 

 slow to be reduced and must be allowed to stand for some time. For the 

 stannous chlorid and hydrochloric acid can be substituted a solution of tin in 

 strong hydrochloric acid. 



As soon as the group is determined it is possible to carry the work further 

 by reference to tables of coloring matter in which the physical, chemical, and 

 tinctorial properties are given ; but it is impossible for the published books to 

 keep up with the new dyes which are constantly being discovered, so that the 

 tables are never complete, although they will, as a rule, contain all the data 

 necessary. 



Classification of organic coloring matters. 



[A portion of the aqueous or alcoholic solution is treated with HC1 and SnCl 2 .] 



Schultz and Julius, Tabellarische Ubersicht dor kiinstlichen organise hen 1'arl.stofT. 

 Allen. Commercial Organic Analysis, 3d ed., 3 (1): 529-565. 



