124 § 86. BASES AND ACIDS WITH REAGENTS. 



0.5 c.c. of this solution of urea of known strength that 

 has been prepared. 



M. Byasson ( Chemical News Amer. Hepr.y 4, 143) pre- 

 pares this standard solution by dissolving exactly 72 

 grms. of pure red oxide of mercury, or mercuric oxide, in 

 100 grms. of nitric acid diluted with half its weight of 

 water, evaporates the solution at a gentle heat until acid 

 vapors appear, and then makes the volume up to one litre 

 at 15° C; if the dilution causes a slight turbidity, a few 

 drops of nitric acid will remove it. In this way, he states, 

 a solution will be obtained in which all the mercury is 

 present as mercuric nitrate, and with as small an excess of 

 acid as possible ; while, if prepared by dissolving mercury 

 in nitric acid, it is liable to contain mercurous nitrate. 



As this mercuric solution is also to be used, in anal- 

 yses of urine, to determine the sodic chloride, it should 

 also be titrated with reference to this. Take 10 c.c. of a 

 solution of sodic chloride containing 2"!,^ of the salt or 0.2 

 grm., add to it 3 c.c. of the standard solution of urea, 

 prepared as above, and 5 c.c. of a cold saturated solution 

 of pure sodic sulphate, and allow the mercuric solution 

 to flow from the burette into this mixture with constant 

 stirring, until there is a permanent turbidity in the liquid ; 

 the amount of mercuric solution required for this corres- 

 ponds to the 0.2 grm. of sodic chloride ; calculate the 

 amount of sodic chloride that corresponds to 1 c.c. of the 

 standard mercuric solution, and mark it on the label of 

 the bottle. 



For the determination of urea in a solution containing 

 it and free from phosphoric and hippuric acids, proceed 

 with 15 c.c, as directed for determining the standard of 

 the solution with reference to urea, after having first de- 

 termined the sodic chloride, which is commonly present, 

 by the amount of the standard solution required to pro- 

 duce permanent turbidity ; use the dry sodic carbonate to 

 maintain the neutrality of the solution, the paste of the 



