PHYSIOLOGICAL CHEMISTKY 453 



is reduced below 70 grm. per diem. Under these conditions the 

 amount of the acetone bodies is increased by exercise. 



EXPERIMENT X. Tests for Acetone. Legal's Test. Add to 

 the urine in a test tube a few drops of a fresh solution of sodium 

 nitroprusside and then caustic soda solution till definitely alkaline. 

 A permanent red colour develops, which becomes deeper and assumes 

 a purplish tint on acidifying with strong acetic acid. (Compare with 

 test for creatinin). 



Bothera's Test. Add a few drops of sodium nitroprusside solution, 

 ammonia till alkaline, and saturate the liquid with ammonium sulphate 

 crystals. A deep colour similar to that of permanganate develops 

 and reaches its maximum in 15 minutes. This test is more sensitive 

 and distinctive than Legal's. 



lodoform Test. Distil a few c.c. of the urine with a few drops 

 of dilute sulphuric acid. To the distillate add a few drops of iodine 

 in potassium iodide solution and caustic soda till the iodine colour 

 disappears. lodoform is precipitated, and is detected by the charac- 

 teristic smell. 



EXPERIMENT XL Test for Aceto-acetic Acid. To the urine add 

 ferric chloride solution in excess of that required to precipitate the 

 phosphate present. A deep red colour in the solution indicates the 

 presence of aceto-acetic acid. (Salicylic acid in the urine gives a very 

 similar colour.) 



There is no simple test for oxybutyric acid- The best procedure is based on 

 Schaffer's method for estimating oxybutyric acid, in which this substance is 

 oxidised to acetone. 50 to 100 c. c. urine which contains acetone is diluted with 

 twice its volume of water, treated with basic lead acetate and ammonia (to remove 

 possible glycuronic acid) and filtered. The filtrate is acidified with 10 c.c. 

 sulphuric acid (cone.) and boiled for half an hour, with the addition of water 

 to keep the volume constant ; this removes the acetone present. It is then 

 distilled (potassium bichromate 0*5 per cent, solution being added from a dropping 

 funnel so as to keep the volume constant) as long as reduction occurs as shown 

 by the colour. To the distillate are added a few c.c. of hydrogen peroxide (free 

 from alcohol) and caustic soda till alkaline. It is then redistilled, and the second 

 distillate tested for acetone by Rothera's test and by the iodoform test. 



/OH 



Homogentisic Acid is di-oxyphenyl-acetic acid C 6 H 3 ^-OH 



CH 2 COOH. 



It reduces Fehling's solution. When present in the urine it causes the 

 latter to become of a dark-brown colour on standing, or this change in 

 colour may be hastened by adding some alkali. It is present in the 

 urine throughout life, and it has been noticed that persons who exhibit 

 it are almost invariably the children of first cousins. It can be easily 



