REAGENTS AND SOLUTIONS 609 



Topfer's Reagent. 1 Dissolve 0.5 gram of di-methylaminoazobenzene 

 in 100 c.c. of 95 per cent alcohol. 



Tropseolin OO. 2 Dissolve 0.05 gram of tropaeolin 00 in zooc.c. 

 of 50 per cent alcohol. 



Uffelmann's Reagent. 3 Add a 5 per cent solution of ferric chloride 

 to a i per cent solution of carbolic acid until an amethyst-blue color is 

 obtained. 



Uranium Acetate Solution. 4 Dissolve about 35.0 grams of uranium 

 acetate in i liter of water with the aid of heat and 3-4 c.c. of glacial 

 acetic acid. Let stand a few days and filter. Standardize against a 

 phosphate solution containing 0.005 gram of PiOs per cubic centimeter. 

 For this purpose dissolve 14.721 grams of pure air-dry sodium am- 

 monium phosphate (NaNH 4 HPO4+4H2O) in water to make a liter. 

 To 20 c.c. of this phosphate solution in a 200 c.c. beaker add 30 c.c. 

 of water and 5 c.c. of sodium acetate solution (see above) and 

 titrate with the uranium solution to the correct end reaction as indi- 

 cated in the method proper, page 552. If exactly 20 c.c. of uranium 

 solution are required i c.c. of the solution is equivalent to 0.005 gram 

 P 2 O 5 . If stronger than this dilute accordingly and check again by 

 titration. 



Urease. 5 (a) Soy Bean Meal. Grind the soy bean to a powder 

 which will pass through a 2o-mesh sieve. 



(b) Solid Urease Preparation. Digest i part of soy bean meal with 

 5 parts of water at room temperature, with occasional stirring for an 

 hour, and clear the solution by filtration through paper pulp or centri- 

 f ugation. Pour this extract slowly, with stirring, into at least 10 volumes 

 of acetone. The acetone dehydrates the enzyme preparation. Filter, 

 dry in vacuum and powder. For standardization procedure see the 

 determination of urea in urine. 



(c) Enzyme Solution. Dissolve 2 grams of urease, prepared as above, 

 together with 0.6 gram of di-potassium-hydrogen phosphate and 0.4 

 gram of mono-potassium-dihydrogen phosphate in 10 c.c. of water. 

 The solution may be kept under toluol for two weeks, without losing 

 activity. 



Uric Acid Reagents. 6 (a) Silver Magnesium Solution 



3 per cent silver lactate solution 70 c.c. 



Magnesia mixture 30 c.c. 



Concentrated ammonium hydroxide solution 100 c.c. 



1 Topfer's method, p. 174. 



2 Test for free acid, p. 154. 



8 Uffelmann's reaction, p. 170. 



4 Phosphate determination, p. 552. 



5 Determination of urea, p. 491. 



6 Determination of uric acid, p. 274 and p. 510. 



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