PROCEEDINGS 



THE ROYAL SOCIETY. 



" On a Colloid Acid, a Normal Constituent of Human Urine." By 

 WILLIAM MAUCET, M.D., F.R.S. Received May 28, 1864*. 



IN the autumn of 1862, feeling assured that, besides the known normal 

 crystalloid compounds found in urine, this secretion contained colloid 

 substances, I submitted samples of the healthy secretion, after concen- 

 tration, first, to the process of dialysis, and then to the action of reagents, 

 and finally succeeded in precipitating with alcohol a colloid substance ex- 

 hibiting a faintly acid or neutral reaction, and containing a small proportion 

 of ash. For a while my endeavours to obtain a definite compound from 

 this amorphous mass were fruitless, until, on observing that basic acetate 

 of lead produced a precipitate in its aqueous solution, I thought of examin- 

 ing this precipitate, and, by decomposing it with sulphuretted hydrogen, 

 found it to consist of an organic acid combined with lead. This new acid 

 is possessed of the properties of a colloid substance ; it may be considered 

 as having a definite combining proportion or equivalent weight, and is 

 undoubtedly destined to become of great importance in physiological che- 

 mistry. 



After having satisfied myself of the presence of a colloid acid in urine, I 

 tried every means to obtain as much of it as possible from a given volume 

 of the secretion, and prepare it in the pure condition ; and after having 

 experienced many difficulties, I adopted the following method as the simplest 

 and that yielding the most satisfactory results. 



Mode of Preparation of the Colloid Acid. 



Urine is mixed with animal charcoal and concentrated until reduced to 

 about one-fourth of its original bulk. It is filtered, and a solution of caustic 

 baryta is added until complete precipitation by this agent be effected. The 

 fluid filtered from the baryta precipitate is dialyzed without further evapo- 



* Read June 16, 1864 : see Abstract, vol. xui. p. 314, 



VOL. XIV. B 



