Dr. Scbunck on the Foi'mation of Indigo-blue. 37 



convenient to collect and treat the products formed at each stage 

 of the action separately. The iiltercd liquid, though clear at 

 first, soon became opalescent and muddy, and deposited dark 

 flocks, while the surface liecame covered with a blue pellicle. 

 After the liquid had stood in the cold for about twenty-four 

 hours, this deposit usually ceased to be formed, and the action 

 then entered on its second stage, which was manifested by the 

 separation from the filtered liquid of a brown powder, the quan- 

 tity of which was much increased by heating. This powder 

 contained little or no indigo-blue, but some indirubine, and a 

 large quantity of other products of decomposition. I think it 

 j)robable that the first deposit owed its origin to the pure indican 

 contained in the solution, while the second was formed from in- 

 dican that had undergone a change by the action of water. The 

 matter insoluble in water formed by the action of acid having been 

 collected on a filter, the acid liquid was employed for the pre- 

 paration of the other products of decomposition in a manner to 

 be hereafter described. The portion of the products insoluble 

 in water was also obtained by another method, still more expe- 

 ditious than the one just described. The leaves of the plant 

 having been finely chopped, boiling water was poured over them, 

 and the mixture having been well stirred, the liquid was strained 

 through calico and mixed with sugar of lead. This produced a 

 pale green precipitate which was separated by filtration, and the 

 liquid having been mixed with an excess of sulphuric acid, was 

 filtered from the &ul])hate of lead and heated for some time, when 

 it produced a deposit containing the same products as before. 

 Instead of sulphuric acid, I sometimes employed nitric acid, 

 avoiding however, in this case, the use of heat. J\Iore indigo- 

 blue and less of the other products of decomposition seemed to 

 be formed when nitric acid was used. 



In whatever manner the pi-oducts insoluble in water were 

 obtained, I always adopted the same method of treatment for 

 the purpose of separating them from one another, a method 

 which is indeed essentially the same as that employed by Bcr- 

 zclius for the separation of the constituents of crude indigo. 

 The whole of the acid used in the process having been carefully 

 removed by means of cold water, the mass left on the filter was 

 treated with dilute caustic soda. This dissolved a great j)ortion, 

 fonning a dark brown opakc liquid, which was filtered from the 

 insoluble matter. The latter was treated again with caustic soda, 

 the action being now assisted by heat, and the process was re- 

 peated until nothing more was dissolved. The liquid, on being 

 mixed with an excess of muriatic acid, let fall a voluminous fioe- 

 culent ])reci])itate of a brown colour, which, after being collected 

 oa a filter and washed with water, was treated witli a boiling 



