ADVANCED PHYSIOLOGICAL CHEMISTRY 473 



The Indicator. Tincture of Cochineal (Tinct. Cocci. B.P.). This gives 

 ti green colour with uranium, but not so long as any unprecipitated 

 phosphates exist in the solution. 



The Titration. Place 50 c.c. urine in a porcelain basin, add 5 c.c. 

 sodium acetate solution and cochineal until the solution is distinctly 

 red. Now bring the solution to the boil and run in the standard 

 solution from a burette, until a faint green colour persists even after 

 boiling. 



This result gives the total phosphates (i.e. alkaline and earthy). 



The Earthy Phosphates may be determined by the following 

 method : 200 c.c. urine are mixed with ammonia till strongly alkaline 

 and left standing over night. The earthy phosphates are thus pre- 

 cipitated. They are filtered off, washed with dilute ammonia, removed 

 from the filter paper to a basin by means of a wash bottle, and the 

 precipitate dissolved by boiling it with a few drops of acetic acid. 

 The resulting solution is made up to 50 c.c. and the estimation 

 carried out as above. 



By subtracting the earthy from the total phosphates, we obtain the 

 .amount of the alkaline phosphates. 



Sulphates. The volumetric method for the determination of sul- 

 phates is very unsatisfactory, on account of there being no coloured 

 indicator for the end of the reaction. It will therefore be necessary 

 to describe the gravimetric as well as the volumetric method. 



/. The Volumetric Method. The Standard Solution. 30'5 gr. crystal- 

 lised barium chloride are dissolved in a litre of distilled water ; 

 1 c.c. = 0*01 gr. of sulphuric acid S0 3 . 



The Indicator. A 20 per cent, solution of sulphate of potassium or 

 .sodium. 



The Titration. 100 c.c. urine are boiled in a flask with 5 c.c. of pure 

 hydrochloric acid so as to decompose the ethereal sulphates, which 

 otherwise do not give a precipitate with barium chloride. Now run in 

 .about 5 c.c. of the standard solution from a burette, boil and allow to 

 stand till the precipitate has settled, then add a few drops more and 

 see if the further precipitate is produced. If there be any doubt of 

 this, remove some of the clear fluid to a watch glass which is placed 

 on a piece of black glazed paper, and add a drop of the barium chloride 

 solution. If a precipitate results replace the contents of the watch 

 glass in the flask, and add more barium chloride. The titration must 

 be carried on in this method until no more precipitate is obtained with 

 barium chloride. A sample of the supernatant fluid is then mixed in 



,the normal phosphate which is insoluble in water and would not, therefore, react 

 Hvith the uranium. 



