URINE . 555 



the reaction utilized is HgCl 2 + 4KI = K2HgI 4 + KC1, i c.c. of 0.05 M 

 HgCl 2 is equivalent in the titration to i c.c. of the 0.2 M KI. 



In preparing the two standard solutions the 0.05 M HgCl2 is standardized by 

 the sulphide method, and the iodine is standardized by titration against it. 

 A slight error appears to be introduced if the iodide solution is gravimetrically 

 standardized and used for checking the mercury solution, instead of vice versa. 



In standardizing the mercuric chloride the following procedure has been 

 found convenient : 25 c.c. of 0.05 M HgCl 2 are measured with a calibrated pi- 

 pette, diluted to about 100 c.c., and H 2 S is run in until the black precipitate floc- 

 culates and leaves a clear solution. The HgS, collected in a Gooch crucible 

 and dried at no , should weigh 0.2908 gram if the solution is accurate. 



Both by gravimetric analyses of the basic mercuric sulphate -acetone pre- 

 cipitate and by titration, the mercury content of the precipitate has been found 

 to average 76.9 per cent. On this basis, each c.c. of 0.2 M KI solution, being 

 equivalent to 10.0 mg. of Hg, is equivalent to 13.0 mg. of the mercury acetone 

 precipitate. 



Titration is not quite so accurate as weighing, but, except when the amounts 

 determined are very small, the titration is satisfactory. 



Calculation. i mg. of j3-hydroxybutyric acid yields 8.45 mg. of precipitate, 

 i mg. of acetone yields 20.0 mg. of precipitate, i c.c. of 0.2 M KI solution 

 is equivalent to 13 mg. of precipitate hi titration of the latter. 



In order to calculate the acetone bodies as /3-hydroxybutyric acid rather 

 than acetone, use the above factors multiplied by the ratio of the molecular 



/3-acid 104 

 weights j i = - g- = 1.793. la order to calculate the acetone bodies 



in terms of molecular concentration, divide the factors in the table by 58. To 

 calculate c.c. of o.i M acetone bodies per liter of urine use the above factors 



, . i- j. 10,000 



multiplied by =-- = 172.4. 



5o 



Special Factors for Calculation of Results when 25 c.c. of Urine Filtrate, 

 Equivalent to 2.5 c.c. of Urine, are used for the Determination. 



Acetone bodies, calculated as gm. 



1 The "total acetone bodies" factor is calculated on the assumption that the molecular 

 proportion of them in the form /8-hydroxybutyric acid is 75 per cent of the total, which 

 proportion is usually approximated in acetonuria. Because /3-hydroxybutyric acid yields 

 only 0.75 molecule of acetone, the factors are strictly accurate only when this proportion 

 is present, but the error introduced by the use of the approximate factors is for ordinary 

 purposes not serious. The actual errors in percentage of the amounts determined are as 

 follows: molecular proportion of acetone bodies as /3-acid 0.50, error 6.5 per cent; /3-acid 

 60.0, error 3.8 per cent; /3-acid 0.80, error 1.3 per cent. 



2 For the determination of preformed acetone see method p. 557. 



