ADVANCED CHEMICAL PHYSIOLOGY 291 



sucked dry at any time on the filter. Precipitate is washed with 

 10-20 c.c. water saturated with benzidine sulphate. The precipitate 

 and filter paper are then transferred into the original precipitation 



N 

 flask with about 50 c.c. water and titrated with ,-TT NaOH using 



phenolphthalein as indicator. 



1 c.c. ^ NaOH = 0-0049 gm. H 2 SO 4 . 



This method may also be employed to estimate the sulphate present 

 in the neutral sulphur determination. The solution which results on 

 treatment of the black residue with dilute HC1 may be treated with 

 benzidine solution as above and the sulphate determined volumetrically. 



Estimation of Phenols in Urine (Folin and Denis slightly modified). 

 Place 10 c.c. of ordinary or 20 c.c. of very dilute urine in a 50 c.c. 

 volumetric flask. Add 2-10 c.c. acid silver lactate solution (5 per- 

 cent, silver lactate in 5 per cent, lactic acid solution) until no more 

 precipitate is obtained, then add a few drops of colloidal iron and shake. 

 Fill to the mark with distilled water, shake again and filter. This 

 precipitation removes uric acid and traces of protein quantitatively. 

 Transfer 25 c.c. of the filtrate to a 50 c.c. volumetric flask and to it 

 add a sufficient quantity of saturated sodium chloride solution (con- 

 taining 10 c.c. cone. HC1 per litre) to precipitate all the silver. Fill 

 to the mark with distilled water and filter. 



To determine " free " (non- conjugated) phenols take 20 c.c. of the 

 filtrate, place in a 50 c.c. flask, add 5 c.c. of the phosphotungstic phos- 

 phomolybdic acid reagent l and 15 c.c. saturated sodium carbonate 

 solution. Dilute to mark with water at 30-35 C. and allow to stand 

 for twenty minutes. Estimate deep blue solution in a Duboscq 

 colorimeter against a standard solution of phenol. 



Total (free and conjugated) phenols are determined by transferring 

 20 c.c. of the same filtrate to a large test tube, add 10 drops of cone. 

 HC1, place small funnel in mouth of tube and then heat rapidly to 

 boiling over a free flame. Now place in a boiling water bath for ten 

 minutes. At the end of this time remove, cool, transfer contents to 

 a 100 c.c. measuring flask, add 10 c.c. of the reagent x and 25 c.c. of 

 the saturated sodium carbonate solution. Make up to volume, shake 

 and let stand for twenty minutes. Read against a standard solution 

 of phenol. 



Standard solution of phenol is a solution of pure phenol 10 mg. in 



N 

 100 c.c. -JQQ HC1. Dissolve 0-100 gm. crystallised phenol in 100 c.c. 



N 



^ HC1. Take 25 c.c. of this solution in a 250 c.c. flask, add 50 c.c. 



N N 



,-TT NaOH, heat to 65 C., add 25 c.c. ^f\ iodine solution, stopper, 



1 Reagent. Transfer to a large flask 34 gms. of ammonium molybdate 

 [(NH 4 ) t (MoO 4 )] (or 25 gms. MoO 3 ), add 140 c.c. of 10 per cent. NaOH and 

 about 150 c.c. of water. Boil for twenty minutes to get rid of ammonia, then 

 add to the solution 100 gms. sodium tungstate, 50 c.c. of 85 per cent, phos- 

 phoric acid and 100 c.c. of cone. HC1. Dilute to a volume of 700-800 c.c., 

 close the mouth of the flask with a funnel and watch glass and then boil 

 gently for not less than four hours, adding hot water from time to time to 

 replace that lost during boiling. Cool and dilute to 1,000 c.c, 



