478 A MANUAL OF PHYSIOLOGY 



The standard solution of silver nitrate can be made by dissolving 

 29*063 grammes of pure fused silver nitrate in distilled water and 

 making up the volume of the solution accurately to i litre. The 

 solution should be kept in the dark. One c.c. of this solution corre- 

 sponds to o'oi gramme NaCl or 0*00607 gramme Cl. 



The standard solution of ammonium sulphocyanide is prepared 

 as follows : Dissolve 13 grammes pure ammonium sulphocyanide 

 (NH 4 CNS) in a litre of distilled water. Measure with a pipette into 

 a beaker 20 c.c. of the standard silver nitrate solution, and add 

 5 c.c. of the iron alum solution and 4 c.c. of pure nitric acid (specific 

 gravity 1*2). Fill a burette with the sulphocyanide solution, and run 

 it into the silver nitrate solution until a^faint permanent red tinge is 

 obtained. Note the number of c.c. of the sulphocyanide solution 

 required, and then dilute the solution till 2 c.c. of the sulphocyanide 

 solution correspond exactly to i c.c. of the silver solution, so as just 

 to allow of the end reaction with the iron solution being seen, and 

 no more. 



To carry out the method, put 10 c.c. of urine, which must be free 

 from albumin, in a stoppered flask, with a mark corresponding to 

 100 c.c., or a graduated cylinder. Add 50 c.c. of water, 4 c.c. of pure 

 nitric acid (specific gravity i'2), and 15 c.c. of the standard silver 

 solution ; shake well, fill with water to the mark, and again shake. 

 After the precipitate has settled, filter it off. Take 50 c.c. of the 

 filtrate, add 5 c.c. of the solution of iron-ammonia-alum, and run 

 in from a burette the standard solution of ammonium sulphocyanide 

 until a weak but permanent red coloration appears. 



Suppose x c.c. of the sulphocyanide solution are required, then 

 the chlorine in 10 c.c. of urine evidently corresponds to (15 #), 

 o'oi gramme NaCl. 



4. Phosphates (i) Qualitative Tests. (a) Render the urine alka- 

 line with ammonia. A precipitate of earthy phosphates (calcium 

 and magnesium phosphates) falls down. Filter. The filtrate con- 

 tains the alkaline phosphates. To the filtrate add magnesia mixture. * 

 The alkaline phosphates (sodium, potassium, or ammonium phos- 

 phates) are precipitated as ammonio-magnesic or triple phosphate. 

 (b) Add to urine half its volume of nitric acid and a little molybdate 

 of ammonium, and heat. A yellow precipitate of ammonium phos- 

 pho-molybdate shows that phosphates are present. This test is 

 given both by alkaline and earthy phosphates. 



(2) Quantitative Estimation. The quantitative estimation of phos- 

 phoric acid in urine is best done volumetrically, by titration with a 

 standard solution of uranium nitrate, using ferrocyanide of potassium 

 as the indicator. Uranium nitrate gives with phosphates, in a solu- 

 tion containing free acetic acid, a precipitate with a constant pro- 

 portion of phosphoric acid. As soon as there is more uranium in 

 the solution than is required to combine with all the phosphoric acid, 

 a brown colour is given with potassium ferrocyanide, due to the 

 formation of uranium ferrocyanide. In carrying out the method, 

 5 c.c. of a mixture of acetic acid and sodium acetate (there are 

 10 grammes of sodium acetate and 10 grammes of glacial acetic acid 

 in 100 c.c. of the mixture) are added to 50 c.c. of urine, which is 

 then heated in a beaker on the water-bath almost to boiling. The 

 standard uranium solution (which contains 35-5 grammes of uranium 

 nitrate in the litre, and i c.c. of which corresponds to 0^005 gramme 



* Magnesium chloride no grammes, ammonium chloride 140 grammes, 

 ammonia (specific gravity o'gi) 250 c.c., and water 1,750 c.c. 



