THE URINE. 379 



1-2 c. c. of the ferric-salt solution, and dilute with water to about 100 c. c. 

 Now the sulphocyanide solution is added from a burette, constantly stirring, 

 uiitil a permanent faint red coloration of the liquid takes place. The amount 

 of sulphocyanide found in the solution by this means indicates how much it 

 must be diluted to be of the proper strength. Titrate once more with 10 c. c. 

 AgNO 3 solution and correct the sulphocyanide solution by the careful addition 

 of water until 20 c. c. exactly correspond to 10 c. c. of the silver solution. 



The determination of the chlorine in the urine is performed by 

 this method in the following way : Exactly 10 c. c. of the urine 

 are placed in a flask which has a mark corresponding to 100 c. c. ; 

 5 c. c. nitric acid are added ; dilute with about 50 c. c. water, and 

 then allow exactly 20 c. c. of the silver-nitrate solution to flow in. 

 Close the flask with the thumb and shake well, slide off the thumb 

 and wash it with distilled water into the flask, and fill the flask to 

 the 100-c. c. mark with distilled water. Close again with the 

 thumb, carefully mix by shaking, and filter through a dry filter. 

 Measure off 50 c. c. of the filtrate by means of a pipette, add 3 c. c. 

 ferric-salt solution, and allow the sulphocyanide solution to flow in 

 until the liquid above the precipitate has a permanent red color. 

 The calculation is very simple. For example, if 4.6 c. c. of the 

 sulphocyanide solution were necessary to produce the final reaction, 

 then for 100 c. c. of the filtrate ( = 10 c. c. urine) 9.2 c. c. of this 

 solution are necessary. 9.2 c. c. of the sulphocyanide solution 

 corresponds to 4.6 c. c. of the silver solution, and since 20 4.6 

 = 15.4 c. c. of the silver solution were necessary to completely 

 precipitate the chlorides in 10 c. c. of the urine, then 10 c. c. con- 

 tain 0.154 grm. NaCl. The amount of sodium chloride in the 

 urine is therefore 1.54$ or 15.4 / w . If we always use 10 c. c. for the 

 determination, and always 20 c. c. AgN0 3 , and dilute with water to 

 100 c. c,, we find the amount of NaCl in 1000 parts of the urine by 

 subtracting the number of c. c. of sulphocyanide (R) required with 

 50 c. c. of the filtrate from 20. The quantity of NaCl p. m. is 

 therefore under these circumstances = 20 R, and the percentage 



. , T 20 R 

 of NaCl . 



The approximate estimation of chlorine in the urine (which 

 must be free from albumin) is made by strongly acidifying with 

 nitric acid and then adding to it, drop by drop, a concentrated 

 silver-nitrate solution (1 : 8). In a normal amount of chlorides the 

 drop sinks to the bottom as a rather compact cheesy lump. In 

 diminished amounts of chlorides the precipitate is less compact and 

 coherent, and in the presence of very little chlorine a fine white 

 precipitate or only a cloudiness or opalescence is obtained. 



Phosphates. Phosphoric acid occurs in acid urines partly as 

 double-, MH 8 P0 4 , and partly as simple-acid, M 2 HP0 4 , phosphates, 



