PRODUCTS DERIVED PROM INDIGO-BLUE. 69 



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 protoxide 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 em- 

 ployed 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 to the boiling-point. A quantity of 

 pure acetate of soda, previously deprived of its water of 

 crystallization, and a little solid caustic soda were then 

 added, and the boiling was continued for several hours. A 

 reduction of a portion of the indigo-blue took place in the 

 first instance, as was evident from the deep red colour of 

 the liquid. On agitating with air, this red colour disap- 

 peared for a moment, the indigo-blue being precipitated in 

 powder, to be again dissolved on boiling the liquid ; but 



