838 APPENDIX. 



with (b), and take 15 c.c. of the filtrate in a dish. Let (b) fall drop by 

 drop into the 15 c.c. in the dish, stirring constantly. Have ready a glass 

 plate with several separate drops of (c), and from time to time add a 

 drop of the urine mixture by means of a glass rod to one of the drops. 

 When a yellow color first appears in a drop of the NaC0 3 , the mercuric 

 nitrate is just in excess. Kead the burette. Calculate as follows: 



1 c.c. of mercuric solution precipitates .01 grm of urea,/, the No. of 

 c.c. used X .01 = amount of urea in 15 c.c. of filtrate, i.e., in 10 c.c. of 

 urine. But 10 c.c. of urine usually contains enough TSaCl to act on 2 c.c. 

 of mercury solution.* Hence, when reckoning the number of c.c. of 

 standing mercury solution used, a deduction of 2 c.c. must always be 

 made. 



Quantitative Estimation of Chlorides. 



Liebig's Method. The solutions required are a baryta mixture as 

 above; and (b) standard solution of mercuric nitrate, such that 1 c.c. 

 would be capable of decomposing .01 grm. of sodium chloride. 



Method. Take 40 c.c. of urine free from albumen, and add 20 c.c. of 

 (a). Filter. Take 15 c.c. of filtrate and place in a flask or dish, adding 

 a drop or two of nitric acid. Fill a burette with (I), and slowly run 

 some of this solution into the filtrate in the dish, stirring constantly. 

 As soon as a distinct cloud appears in the diluted urine, and does not 

 disappear on stirring, then all the sodium chloride in urine has been 

 decomposed. Eead burette. Calculate as follows: 



1 c.c. of mercury solution decomposed .01 grm. of NaCl, /. the 

 number of c.c. used X .01 grm. = number of grms. of NaCl in 15 c.c. of 

 filtrate, i.e., 10 c.c. of urine. 



Quantitative Estimation of Phosphates. 



The solutions required are (a} solution of sodium acetate, containing 

 100 grm. of sodium acetate, 100 c.c. of acetic acid, and 900 c.c. of distilled 

 water; (b) a solution of uranium acetate or nitrate, such that 1 c.c. will 

 precipitate .005 grm. of phosphoric acid; and (c) a solution of ferro- 

 cyanide of potassium. 



Method. Take 50 c.c. of urine. Add some (a) solution, and heat on 

 water-bath to nearly 100 C. Fill burette with (b), and allow this to 

 fall into the urine slowly. Have ready a glass 'plate with several distinct 

 drops of potassium ferro-cyanide solution. From time to time add a 

 drop of urine mixture to one of the drops; and when there FIRST ap- 

 pears a reddish-brown color in a drop of potassium ferro-cyanide, all the 

 phosphates are precipitated. Read burette. Calculate thus: 



1 c.c. precipitates .005 grm. of phosphoric acid, .*. the number of c.c. 

 used X .005 grm. = number of grms. of phosphoric acid in 50 c.c. of 



urine. 



* This is only a rough estimate. 



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