ADVANCED CHEMICAL PHYSIOLOGY 293 



mixture should be definitely alkaline to litmus, if not add more calcium 

 hydroxide. Dilute to the 250 c.c. mark and allow to stand for at 

 least thirty minutes and then filter through a dry folded filter paper 

 into a dry flask. Some of the filtrate may be tested now to see if all 

 sugar is removed by boiling. If sugar is present a yellow precipitate 

 will be obtained instead of a white precipitate. 



25 c.c. of the filtrate is now measured into a 500 c.c. Erlenmeyer 

 flask, 100 c.c. water, 10 c.c. 17N. sulphuric acid (add 500 c.c. cone. 

 H 2 SO 4 cautiously to 450 c.c. distilled water, cool thoroughly and make 

 up to 1,000 c.c. with water ; the solution may require slight adjustment) 

 and 35 c.c. mercuric sulphate solution (73 gms. pure red mercuric 

 oxide dissolved in 1,000 c.c. of 4N. sulphuric acid). Connect a good 

 reflux condenser, best with straight condensing tube, to the Erlenmeyer 

 and heat to boiling. When boiling has properly started add 5 c.c. 

 bichromate solution (50 gms. potassium bichromate dissolved in water 

 and made up to 1,000 c.c.) through the condenser tube ; continue 

 gentle boiling for one and a half hours. Then cool and filter off the 

 yellow precipitate through asbestos in a weighed Gooch crucible. 

 Wash out the Erlenmeyer with about 200 c.c. cold water. Suck 

 asbestos dry and then transfer to a hot air oven at 110 for an hour. 

 Cool in room air and weigh. 



Calculation. Assuming that beta-oxybutyric acid forms 75 per cent, 

 of the total acetone bodies present (the usual proportion), then if 25 c.c. 

 of the filtrate, i.e. 2-5 c.c. of original urine, are used, 1 gm. of precipi- 

 tate equals 2 -48 gms. total acetone bodies as acetone per 100 c.c. urine. 



Instead of weighing the precipitate the contents of the Gooch, 

 including the asbestos, may be washed into a small beaker with as 



N 

 little water as possible. Add 15 c.c. y HC1 and heat the mixture 



until all precipitate is dissolved. Cool the solution, add 6-7 c.c. of 



M 



3M. sodium acetate solution and then run in ^~.KI rapidly from 



a burette with constant stirring. If more than a small amount of 

 mercury is present a red precipitate of HgI 2 at once forms and re- 

 dissolves as soon as 2-3 c.c. of KI in excess of the amount required 

 to form the soluble K 2 HgI 4 have been added. If only a few mg. of 

 Hg are present the excess KT ; may be added before the HgI 2 has had 

 time to precipitate, so that 'the titrated solution remains clear. In 



this case not less than 5 c.c. of the ^.KI are added as final titration 



5 



is not satisfactory if less is present. The excess KI is titrated back 

 by adding ^Q.HgCla from another burette until a permanent red 

 precipitate forms. As the reaction is HgCl 2 + 4KI = K 2 HgI 4 + 

 2KC1. 1 c.c. of ^.HgCl 2 = 1 c.c. y.KI; 1 c.c. of ^.KI = 

 13 mg. mercury acetone precipitate. 

 When 25 c.c. filtrate, i.e. 2-5 c.c. urine, are used 1 c.c. g~.KI = 



0-032g total acetone bodies, or 0-034g beta-oxybutyric acid as acetone 



M 

 per 100 c.c. urine. Standardise the 2Q.HgCl 2 by the sulphide 



precipitation method. 



