Di'. Scliunck on the Formation of Indigo-blue. 83 



thin layers, and leaving it for some time in vacuo over sulphuric 

 acid. On attempting to dry it in the water-bath, it immediately 

 midergoes a complete alteration. Its taste is slightly bitter and 

 nauseous. Its solutions have always an acid reaction, but 

 whether this reaction is peculiar to it in an absolutely pure state, 

 I am unable to say. When heated in a tube it swells up, and 

 gives fumes which condense to a brown oily sublimate, in which, 

 after some time, a white crystalline substance is formed. When 

 boiled with caustic alkali it evolves ammonia. Its compounds 

 have a yellow colour. With caustic alkalies, baryta, and lime- 

 water, the watery solution turns of a bright yellow. The alco- 

 holic solution gives with sugar of lead a bright sulphur-yellow 

 precipitate, which is increased by the addition of ammonia. The 

 watery solution gives no precipitate with acetate of lead until 

 ammonia is also added. Its most remarkable and interesting 

 property is that of yielding indigo-blue when treated with strong 

 acids. If sulphuric or muriatic acid be added to its watery solu- 

 tion, no change whatever is perceptible for some time ; bvit on 

 heating to near the boiling-point, the solution immediately be- 

 comes sky-blue. On boiling for a short time, the solution becomes 

 opalescent. On continuing to boil, it acquires a purple colour, 

 and then, provided the solution is tolerably concentrated, a 

 copious deposit consisting of dark purplish-blue flocks is formed. 

 The liquid filtei'cd from these flocks retains a yellow colour, and 

 contains a peculiar species of sugar, to which I shall return pre- 

 sently. The flocks themselves do not consist of indigo-blue 

 only. After being collected on a filter and washed with water, 

 they appear of a dark purple colour, the filter also acquiring 

 during washing a purple tinge. If they be now treated with 

 alcohol, a part dissolves even in the cold, but to a greater extent 

 on heathig, the alcohol acquiring a beautiful purple colour. If 

 the flocks remaining undissolved be treated after filtration with 

 an additional quantity of boiling alcohol, the latter acquires a 

 more bluisli tinge. Each succeeding portion of alcohol with 

 which the flocks are boiled acquires more and more of a blue 

 colour, until at last the colour is a pure indlgo-bluc. There 

 remains In general a large quantity of indigo-blue undissolved, 

 and the alcoholic liquids, on standing, deposit the colouring 

 matter contained in them in the shape of bright l)lue flocks. 

 The purple alcoholic solution leaves, on eva])oratlon, a reddish- 

 brown residue, which bears the greatest resemblance to, if it is 

 not identical with, the indigo-red of iJcrzelius. Like the latter 

 substance, it is quite insoluble in caustic alkalies and gives, when 

 heated in a tube, j)urple fumes and a small quantity of a white 

 crystalline sublimate. I propose to call this substance Indiru- 

 bine. 1 have found that it is invariably formed along with 



