On Kreatinins. 



499 



precipitate produced by this reagent in normal urine has been attri- 

 buted to urea. Enough, however, has been said to prove that the 

 precipitate produced by mercuric chloride in normal urine is of a very 

 complex nature. 



Reaction of Normal Human Urine with Strong Solution of Mercuric 

 Chloride. — The Author's Researches. 



In all my experiments with a view to separate the reducing agent 

 from normal urine, I have employed a solution of mercuric chloride 

 in water, saturated at the temperature of the laboratory (16° C). 



In my first experiments I filtered the urine immediately after 

 adding to it one-fourth of its volume of the cold saturated mercuric 

 chloride solution, and always found that the filtrates still contained 

 the reducing substance in solution. 



I soon observed, however, that after separating the fiocciilent amor- 

 phous precipitate first produced by mercuric chloride, the filtrate did 

 not long remain clear, but after about half an hour a second precipi- 

 tate began to form, having a granular appearance, and continuing to 

 separate out for many days. On filtering from time to time, and 

 examining the reducing action of the filtrate, it was found that the 

 reducing power progressively diminished as more and more of the 

 mercury salt separated out from the solution. In short it soon 

 became evident that the reducing agent of normal urine may be com- 

 pletely removed from that liquid by precipitation with mercuric chlo- 

 ride. 



Although the complete precipitation of the reducing substance is 

 very slow if mercuric chloride be added alone, if we add to fresh un- 

 concentrated urine one-twentieth of its volume of a cold saturated 

 solution of sodium acetate, then one-fourth of its volume of cold 

 saturated solution of mercuric chloride, and filter immediately, the 

 filtrate deposits the whole of the normal reducing agent as mercury 

 salt in about forty-eight hours. The precipitation is known to- be 

 complete when the filtrate from the second mercury precipitate re- 

 mains clear, even on the addition of more solution of sodium acetate 

 and mercuric chloride. It will then be found that the permanently 

 clear filtrate is without reducing action upon both potassium picrate 

 and cupric oxide in boiling alkaline solutions. 



The first precipitate produced by mercuric chloride in normal urine 

 is amorphous and flocculent, and has some resemblance to coagulated 

 albumen. Finding that it contained no reducing agent, I have de- 

 ferred the study of this precipitate for the present, but a cursory 

 examination of it showed that it contained uric acid, probably as mer- 

 curic urate, besides the substance described by Dr. Greene, which is 

 precipitated by lead acetate. When decomposed by hydrogen sulphide 

 under water, the filtrate from mercuric sulphide is acid in reaction, 



