128 



Mr. E. Sclmnck on the Colouring cind [Recess^ 



the five liquids should be exactly the same, and then, after pouring them 

 into test-tubes of the same bore, comparing together the tints which they 

 exhibited, the following differences were observed : — The second was a 

 little lighter than the first ; the third, however, was much lighter ; whilst 

 the fourth was as dark as, but not darker than the first ; and the fifth ap- 

 peared hardly darker than the third ; but on being boiled a few moments 

 and allowed to cool, its tint was as dark as that of the first. Hence it fol- 

 lows that the colour of the substance owed a part of its intensity to the 

 presence of an alkaline or other base ; for had this not been the case, had 

 the extractive matter been in an uncombined state, the addition of dilute 

 acid would have caused a deepening of the tint, or at least have left it im- 

 changed instead of making it lighter, whereas the alkali would have pro- 

 duced a darkening of the colour. The addition of a large excess of acid 

 lowered the intensity of the colour in the first instance, in consequence of 

 the acid combining with the bases ; but on heating the solution it had the 

 effect of deepening the colour, from the decomposing action of the acid 

 on the now free extractive matter. 



In order to isolate the organic body, or bodies, contained in the substance, 

 some of the latter was dissolved in water, and to the solution basic acetate 

 of lead was added. This deprived the solution of its colour, giving an abun- 

 dant cream-coloured precipitate, which was filtered off, washed, suspended 

 in water, and decomposed with sulphuretted hydrogen. The filtered liquid 

 was evaporated at a gentle heat, when it left a brown glutinous residue. 

 This, when burnt, still left a considerable quantity of ash, which was yellow 

 and non-alkaline, and consisted chiefly of alumina with a little oxide of 

 iron and a trace of lime. "When treated with absolute alcohol, a great part 

 of this glutinous matter dissolved, yielding a deep yellow solution, while a 

 quantity of light-brown flocks was left undissolved. The filtered liquid 

 left on evaporation a brownish-yellow dchquescent substance, which had the 

 appearance and properties of the extractive matter soluble in alcohol. When 

 burned, it left only a slight trace of ash. When treated with boiling caustic 

 alkaline lye it evolved ammonia. It was perfectl}'- insoluble in ether, and 

 was therefore free from the extractive matter soluble in that menstruum. 

 Its watery solution, when mixed with sulphuric acid and heated for some 

 time, deposited a quantity of dark brown flocks, which, after being filtered 

 off, washed, and dried, had the appearance of a dark brown, almost black 

 powder (uromelanine), which was almost insoluble in alcohol, but dissolved 

 readily in aqueous ammonia, giving a brown solution, from which it was re- 

 precipitated by acids in brown flocks. This is the most characteristic pro- 

 perty of the extractive matter soluble in alcohol and insoluble in ether, and 

 serves to distinguish it from the one soluble in ether, which yields, by 

 decomposition with strong acids, a brown resinous substance, easily soluble 

 in alcohol (uroretine). That portion of the substance derived from the 

 precipitate with basic acetate of lead, which was left undissolved by abso- 

 lute alcohol in the shape of hght brown flocks, was easily soluble in water. 



