THE URINE. 343 



fermentation, this titration method cannot be applied. The same 

 is true of urine containing leucin, tyrosin or medicinal preparations, 

 precipitated by mercuric nitrate. 



In cases where the urine is free from albumin or sugar and not 

 specially poor in chlorides, the quantity of urea, and also the 

 approximate quantity of mercuric nitrate necessary for the titration, 

 may be learned from the specific gravity. A specific gravity of 

 1.010 corresponds to about 10 p. m., the specific gravity 1.015 



fenerally somewhat less than 15 p. m., and the specific gravity 

 .015-1.020 about 15-20 p. m. urea. With a specific gravity higher 

 than 1.020 the urine generally contains more than 20 p. m. of urea, 

 and above this point the amount of urea increases much more 

 rapidly than the specific gravity, so that at a specific gravity of 

 1.030 it contains over 40 p. m. urea. In fevers, urine with a 

 specific gravity above 1.020 sometimes contains 30-40 p. m. urea, 

 or even more. 



PREPARATION FOR THE TITRATION. If a large amount of urea 

 is suspected from a high specific gravity, the urine must first be 

 diluted with a carefully-measured quantity of water, so that the 

 amount of urea is reduced below 30 p. m. In a special portion of 

 the same urine the amount of chlorides is determined by one of the 

 methods which will be given later, and the number of c. c. of silver- 

 nitrate solution necessary is noted. Then a larger quantity of urine, 

 say 100 c. c., is mixed with one half or, if this is not sufficient to 

 precipitate all the sulphuric and phosphoric acids, with an equal vol- 

 ume of the baryta solution, it is then allowed to stand a little while, 

 and the precipitate is filtered through a dried filter. From the fil- 

 trate containing the urine diluted with water a proper quantity, 

 corresponding to about 60 c. c. of the original urine, is measured, 

 and exactly neutralized with nitric acid added from a burette, so 

 that the exact quantity employed is known. The neutralized mix- 

 ture of urine and baryta is treated with the proper quantity of 

 silver-nitrate solution necessary to completely precipitate the chlo- 

 rides, which was ascertained by a previous determination. The mix- 

 ture containing a known volume of urine is now filtered through a 

 dried filter into a flask, and from the filtrate an amount is measured 

 corresponding to 10 c. c. of the original urine. 



EXECUTION OF THE TITRATION. Nearly the total quantity of 

 mercuric-nitrate solution to be used, and which is known from the 

 specific gravity of the urine, is added at once, and immediately 

 afterwards the quantity of soda solution necessary, as indicated by 

 the table. If the mixture becomes yellowish in color, then too much 

 mercury solution has been added and another determination must 

 be made. If the test remains white, and if a drop taken out and 

 placed on a glass plate with a dark background and stirred with a 

 drop of a thin paste of sodium bicarbonate does not give a yellow 



