derived from Indigo-blue. 295 



small quantity of indigo-blue by means of grape-sugar and 

 caustic soda, using water as a solvent instead of alcohol ; but 

 though the indigo-blue was kept for a long time in solution, 

 and heat was applied at the same time to assist the action, 

 it made its appearance again on exposure to the air, apparently 

 undiminished in quantity. In another experiment, in which 

 alcohol was used as the menstruum and protoxide of tin as 

 the reducing-agent, the same result was arrived at. It was 

 therefore apparent that the disappearance of the colouring- 

 matter was due to the combined action of the alcohol and 

 the grape-sugar, not to the separate action of either. By the 

 use of a great excess of these two agents, together with caustic 

 soda and the long-continued application of heat to the solu- 

 tion, I succeeded in causing several grammes of indigo-blue 

 to disappear entirely. I avoid the word decompose, because, 

 as I shall show, the colouring-matter is not decomposed, but 

 enters into new forms of combination. 



It now occurred to me that, since by the action of caustic 

 alkalies on sugar acetic and formic acids are formed, the 

 effect produced by the grape-sugar in this process might in 

 reality be due to the presence of one or both of these acids 

 rather than to that of the sugar itself. My supposition was 

 completely verified by experiment. On treating some pure 

 indigo-blue with alcohol, to which an alkaline solution of pro- 

 toxide of tin was added until it dissolved, then adding acetate 

 of soda and digesting at a moderate heat, the indigo-blue after 

 some time ceased to be deposited on exposure to the air, or 

 even agitation ; it had entirely disappeared. The same thing 

 occurred when formiate of soda was employed in the place of 

 acetate. It was evident, therefore, that in this process acetic 

 or formic acid was capable of playing the same part as grape- 

 sugar; and as the use of the latter might have tended to 

 introduce complications, in consequence of the formation of 

 secondary products, I ceased to employ it in my subsequent 

 experiments. The object of the present communication is to 

 give an account of the combined action of alcohol, acetate 

 of soda, and caustic alkali on indigo- blue, and the products 

 thereby formed. 



At the commencement of the investigation I imagined that 

 it was an essential condition that the indigo-blue should 

 be in a state of solution ; but I soon found that this was not 

 necessary. The operation succeeds equally well if indigo- 

 blue freshly precipitated or in fine powder be employed. The 

 plan which I adopted was quite simple. Pure indigo-blue 

 was introduced into a large quantity of ordinary spirits of 

 wine, and, after being well agitated, the mixture was raised 



