88 Dr. Schuuck on the Formation of Indigo-blue. 



solation of indican, I tried a small quantity of it by boiling witli 

 sulphuric acid, and ascertained that it gave indigo-blue and iudi- 

 rubiue ; but on heating the whole quantity to the boiling-point 

 with acid, I obtained instead of these two bodies, a substance 

 dissolving in alcohol with a brown colour. It was evident that 

 the indican, in consequence probably of the solution being very 

 dilute, had taken up the elements of water before the acid could 

 act on it, and that the latter then gave rise to the products of 

 decomposition peculiar to the hydrate. In general, however, the 

 nature of the flocks which are deposited on boiling a watery 

 solution of indican with sulphuric or muriatic acid, affords a very 

 good test of the purity of the indican. A solution is boiled in 

 a test-tube partly filled, and the flocks which are formed collected 

 on a filter, washed with water, and then treated with successive 

 portions of boiling alcohol until no more M'ill dissolve. If to the 

 first portions of alcohol a purple colour be imparted, and a fine 

 purplish-blue to the succeeding ones, then the indican may be 

 considered pure. If the colour of the alcohol is brown, and if 

 black flocks are left undissolved, the substance has undergone a 

 complete change. 



The sugar which is formed when acids act either on indican 

 or its hydrates, is obtained in a state of purity in the following 

 manner. If sulphuric acid be employed, which is preferable to 

 muriatic, the acid liquid is filtered from the flocks consisting of 

 indigo-blue and other products of decomposition, and the acid 

 is removed by means of an excess of acetate of lead. If to the 

 liquid filtered from the sulphate of lead an excess of ammonia is 

 added, the sugar is precipitated in combination with oxide of 

 lead. The precipitate, which is usually yellow and bulky, is, 

 after washing, decomposed with sulphuretted hydrogen, and 

 from the liquid filtered from the sulphuret of lead the sugar is 

 again precipitated with acetate of lead and ammonia. The 

 second precipitate, which is usually almost white, is again de- 

 composed with sulphuretted hydrogen, and the filtered liquid is 

 evaporated over sulphuric acid, when it leaves a colourless or 

 only slightly yellow syrup, which has the following properties. 

 It has a faintly sweet taste. When heated it swells up, emitting 

 the usual smell of burning sugar, and then burns leaving much 

 charcoal. With concentrated sulphuric acid it strikes a dark 

 red colour, which on heating becomes black. Boiling nitric acid 

 decomposes it M'ith an evolution of nitrous fumes. When its 

 watery solution is boiled with caustic soda, it becomes yellow 

 and deposits a few brown flocks. With sulphate of copper and 

 caustic soda it gives a blue solution, which on boiling becomes 

 yellow, and then deposits suboxide of copper. If nitrate of silver 

 be added to its watery solution while boiling, a little metallic 



