536 



PHYSIOLOGICAL CHEMISTRY 



of a N/io solution of iodine and add an excess of sodium hydroxide solution (15-25 

 c c. of 20 per cent). Stopper the flask and shake it for about one minute. Add 

 1-2 drops of concentrated hydrochloric acid, and note the production of a brown 

 color at the point of contact if an excess of iodine is present. In case there is no 

 such excess, the solution should be treated with N/io iodine solution until an excess 

 is obtained. Retitrate this excess of iodine with N/io sodium thiosulphate solu- 

 tion until a light yellow color is observed. At this point a few cubic centimeters 

 of starch paste should be added and the mixture again titrated until no blue color 

 is visible. This is the end-reaction. 



Calculation. Subtract the number of cubic centimeters of N/io thiosulphate 

 solution used from the volume of N/io iodine solution employed. Since i c.c. of 

 the iodine solution is equivalent to 0.967 mg. of acetone, and since i c.c. of the thio- 

 sulphate solution is equivalent to i c.c. of the iodine solution, if we multiply the 

 remainder from the above subtraction by 0.967 we will obtain the number of milli- 

 grams of acetone in the 100 c.c. of urine examined. 



Calculate the quantity of acetone in the twenty-four-hour urine specimen. 



Interpretation. See page 534. 



3. Method of Scott-Wilson. 1 Principle. The urine is distilled 

 with acid and the acetone (preformed and from acetoacetic acid by 



FIG. 168. SCOTT-WILSON APPARATUS. 



hydrolysis) collected in an alkaline solution of basic mercuric cyanide. 

 A precipitate of keto-mercuric cyanide is formed according to the 

 following equation: 



C 3 H 6 + 2Hg(CN) 2 + 3HgO = C 3 OH g5 C 4 N4 + 3H 2 



The precipitate is filtered off and its mercury content determined by 

 titration with potassium thiocyanate solution. The method is adapted 

 to the determination of acetone in small amounts, and has the ad- 

 vantage over the iodoform method that it is not affected by alcohol. 



Procedure. The apparatus for the distillation of acetone is set up as in the 

 illustration (Fig. 168). Introduce 100 c.c. of the normal urine (or a lesser quan- 



1 Scott-Wilson: Jour. PhysioL, 42, 444, 1911. 



