498 



Mr. G. S. Johnson. 



dialyse through animal membranes. Dr. Greene analysed this sab- 

 stance, with the following results : — 



Carbon 34' 52 



Hydrogen 5' 71 



Nitrogen 12 '58 



Oxygen 47*19 



100-00 



The empirical formula indicated by these numbers is C 16 H 30 rT 5 O 16 , 

 which requires — 



Carbon 35-03 



Hydrogen 5 '4 7 



Nitrogen 12-77 



Oxygen 4673 



100-00 



The main object of Dr. Greene's research was to prove that the 

 precipitate produced by mercuric chloride in normal urine contains a 

 large proportion of organic nitrogen, and that corrections might be 

 made, in the determination of the urea in urine by the hypobromite 

 method, by deducting so much nitrogen for every gram of mercury 

 precipitate yielded by the original urine. 



As, however, Dr. Greene rejected everything iu the precipitate by 

 mercuric chloride in normal urine which is not also precipitated by 

 lead acetate, he of course missed the normal reducing agent altogether, 

 and must have also considerably under-estimated the total nitrogen 

 contained in the mercury precipitate, for the reducing agent of normal 

 urine is highly nitrogenous, as will presently appear. 



Maly (' Ann. Chem. Pharm.,' vol. 159, p. 279) describes a method 

 for obtaining kreatinin hydrochloride from the urine of man or the 

 horse by precipitation with mercuric chloride. His method consists 

 in concentrating the urine to one-third of its original bulk, then pre- 

 cipitating by lead acetate and filtering, whereby the uric acid and 

 Greene's substance are removed. The filtrate is freed from lead by 

 sodium carbonate or sulphuretted hydrogen, neutralised after a second 

 filtration by acetic acid or sodium carbonate, and then precipitated by 

 mercuric chloride. The precipitate is washed and then decomposed 

 by hydrogen sulphide under water, &nd the filtrate is decolourised by 

 animal charcoal and evaporated. The residue, on being re-crystallised 

 once or twice from alcohol, yields pure kreatinin hydrochloride in hard 

 shining prisms (vide Watts's ' Dictionary,' Suppl. 2, p. 393). 



In spite of these researches, mercuric chloride has recently been 

 again recommended as a precipitant for albumen in urine, and the 



