ANALYSIS OF URINE 557 



(1) Standard Ammonium Sulphate Solution. 



Pure commercial ammonium sulphate (13-2 gm.) is purified by decomposing 

 it with caustic soda (8-0 gm.) ; the ammonia, which is liberated, is aspirated 

 into sulphuric acid (9-8 gm.), diluted with 2-3 volumes of water. The am- 

 monium sulphate is precipitated with alcohol, filtered off, dissolved in water 

 and again precipitated with alcohol. It is dried over sulphuric acid, i c.c. 

 of a solution containing 47206 gm. ammonium sulphate in 1000 c.c. corre- 

 sponds to i mgm. nitrogen. 



(2) Nessler's Reagent (see p. 615). 



(3) Standard Uric Acid Solution. 



(a) o'25 gm. of uric acid are rinsed with 25-50 c.c. of water into a 250 c.c. 

 measuring flask. 25 c.c. of '4 per cent, lithium carbonate solution are added 

 and solution of the uric acid effected by shaking occasionally for i hour. It is 

 diluted to 250 c.c. This solution will keep for about a week. 



(b) i gm. of uric acid is placed in a 1000 c.c. measuring flask and dis- 

 solved in 200 c.c. of *4 per cent, lithium carbonate solution ; 40 c.c. of 40 per 

 cent, formaldehyde solution (formalin) are added, the mixture is shaken and 

 allowed to stand for a few minutes. It is acidified with 20 c.c. of N acetic 

 acid and diluted to 1000 c.c. The solution should remain clear for 24 hours 

 and is standardised against the fresh solution (a). 5 c.c. of this solution give 

 about the same colour as the solution containing i mgm. of uric acid in i c.c. 



(4) Phosphotungstic Acid Reagent. 



ioo gm. of sodium tungstate and 80 c.c. of 85 per cent, phosphoric acid 

 solution are added to 750 gm. of water. The mixture is boiled gently for 

 2 hours under a reflux condenser, cooled and diluted to 1000 c.c. 



2 c.c. give the maximum colour with i mgm. of uric acid. 



(5) Standard Creatinine Solution. 



Creatinine zinc chloride is prepared from urine as described on p. 169. 

 It is purified by recrystallising it three times by dissolving it in 10 parts 

 of boiling 25 per cent, acetic acid, adding one- tenth of its volume of con- 

 centrated alcoholic zinc chloride solution and i '5 volumes of alcohol. The 

 precipitate is filtered off after standing for 12-16 hours and washed with 

 alcohol. It is dried in vacua over sulphuric acid. Creatinine zinc chloride 

 is readily soluble in *iN hydrochloric acid. 



1*6 1 06 gm. are dissolved in 1000 c.c. of acid, i c.c. contains i mgm. of 

 Creatinine. 



A litre of such a solution will suffice for several thousand creatinine 

 ^estimations. 



