URINE 533 



Warm the tube and contents in a water-bath at 72C. for 5-6 minutes and make 

 the reading. 



4. Turbidity Method of Folin and Denis. 1 Principle. The albumin of the 

 urine is precipitated with sulphosalicylic acid and the turbidity produced com- 

 pared with that of a standard protein solution. 



Procedure. To about 75 c.c. of water in each of two 100 c.c. volumetric flasks 

 is added 5 c.c. of a 25 per cent solution of sulphosalicylic acid. To one flask is then 

 added 5 c.c. of the standard protein solution containing 10 mg. of albumin and to 

 the other is added the albuminous urine i c.c. at a time (by means of an Ostwald 

 pipette) until the turbidity obtained seems to be reasonably near that of the 

 standard. The two flasks are then filled up to the mark with water, cautiously 

 inverted a few times to secure mixing, and are then ready for the quantitative 

 comparison just as in colorimetric work. The standard must invariably be read 

 against itself. The standard 2 containing 10 mg. of protein is set at 20 mm. The 

 unknown must not read less than 10 nor more than 30. 



Calculation. Dividing 200 by the product of the reading of the unknown and 

 the number of cubic centimeters of urine taken gives the albumin in milligrams per 

 cubic centimeter of urine. The albuminous suspensions must not be shaken but 

 mixed very carefully. The method is fairly accurate and requires but a few minutes 

 if a standard solution is at hand. The method is not apph'cable to urines deeply 

 colored with blood or bile but may be used for albuminous fluids other than urine 

 if such fluids are not highly pigmented. It must be borne in mind that different 

 proteins, as serum albumin and serum globulin, may give markedly different degrees 

 of turbidity under the same conditions. 3 



Interpretation. See page 532. 



Acetone and Acetoacetic Acid 



i. Folin-Hart Method. Principle. This method as well as the 

 two following serve the purpose of determining the acetone, and aceto- 

 acetic acid together in terms of acetone. Acetoacetic acid on heating 

 is decomposed with the formation of acetone. In this method the 

 acetone preformed and that derived from the acetoacetic acid are 

 carried over by means of an air current into a solution of iodine in potas- 

 sium hydroxide (alkaline hypoiodite solution). The acetone is here 

 absorbed and retained as iodoform. The excess iodine over that 

 necessary to combine with the acetone is determined by titration with 

 sodium thiosulphate. The method is simple and accurate if directions 

 are carefully followed. 



1 Folin and Denis: Jour. Biol. Chem., 18, 273, 1914. 



2 Standard Albumin solution. Fresh blood serum free from hemoglobin is used. 

 2 5-35 c.c. of the serum are diluted with a 15 per cent solution of chemically pure sodium 

 chloride to about 1500 c.c. The solution is mixed and filtered. By means of nitrogen 

 determinations the protein content of the filtrate is determined (protein = NX 6. 25) and 

 on the basis of the figure obtained the solution is diluted with 15 per cent sodium chloride 

 solution so that it contains 2 mg. of protein per cubic centimeter. It is best to saturate 

 the albumin solution with chloroform. The solution keeps for months. 



3 Marshall and Banks: Proceedings of the American Philosophical Society, 54, 176, 



