198 ME. E. SCHUNCK ON THE 



could act on it, and that the latter then gave rise to the pro- 

 ducts 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 mu- 

 riatic acid afibrds 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 boil- 

 ing alcohol until no more will 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 un- 

 dergone 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 de- 

 composition, 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 pre- 

 cipitated in combination with oxide of lead. The precipi- 

 tate, 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 pre- 

 cipitated with acetate of lead and ammonia. The second 

 precipitate which is usually almost white is again decom- 

 posed 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 pro- 

 perties. 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 



