86 



Mr. E. Scliiinck on the Colouring and 



[Recess^ 



normal urine exhibits great diversity of tint without any corresponding dif- 

 ference in its other properties, and hence it has been inferred that these 

 differences are of Uttle physiological or pathological importance, and that 

 an investigation of their cause would not be likely to lead to any usefal 

 practical results. Our knowledge of the properties and composition of 

 these substances is therefore extremely defective, and the most discordant 

 views prevail as to their true nature. 



Fourcroy and Vauquelin * were of opinion that the smell, colour, taste, 

 and great liability to decomposition of urine, in fact all its characteristic 

 properties, were due to one constituent only, viz. urea. It is evident, how- 

 ever, that their urea must have been impure, since they obtained from it by 

 the action of caustic potash a brov>?n fatty matter and acetic acid, products 

 which could only have been derived from the extractive matter and other 

 impurities with which it was contaminated. It was afterwards shown by 

 Berzelius that urea is colourless, and possesses no remarkable smell nor 

 taste. Proust, as mentioned above, attributed the colour, as well as the 

 bitter taste and peculiar smell of urine, to his fallow resin. Prout 

 thought that the colouring-matter of healthy mine was of two kinds, one of 

 them being capable of combining with urate of ammonia and imparting to 

 it the usual tint of uric acid calculi, the other destitute of this property. To 

 Berzelius f, the great observer who has enriched almost every department 

 of chemical science with his rescrj'ches, we owe the first, it may almost be 

 said the only, investigation of tiie extractive matters of urine, the sub- 

 stances to which, as he correctly supposed, the ordinary colour of the se- 

 cretion is due. This investigation, though now almost forgotten, may still 

 be consulted with advantage, as it contains information not to be found 

 elsewhere. In its main results I have found it remarkably correct, and I 

 shall have occasion to refer to it again. Though Berzelius did not succeed 

 in obtaining his substances in a state of complete purity and free from other 

 constituents of urine, such as urea and chlorides, he nevertheless ascertained 

 the existence of several distinct urinary extractive m.atters, which were dis- 

 tinguished from one another by their behaviour towards various solvents. 

 One of these he found to be soluble in absolute alcohol, the second was only 

 soluble in alcohol of sp. gr. 0*833, while the third was insoluble in alcohol 

 of all strengths, and only soluble in water. He seems also to have obtained 

 a minute quantity of an extractive matter soluble in ether, the others being 

 insoluble in that menstruum. The extractive matter soluble in absolute 

 alcohol he proposed to name halophile, in consequence of its power of com- 

 bining with various neutral salts. According to Berzelius, these substances 

 bear a great resemblance to the extractive matters of flesh. Duvernoy 

 made some experiments on these extractive matters, and he seems to have 

 been the first to observe the remarkable deepening and change of colour 

 which is seen on adding strong acids to their watery solutions. One of the 

 methods employed by him for separating the colouring or extractive matter 

 * Annales de Chimie, t. xxxi. p. 68. t Lehrbuch der Cheinie, B. ix. 



