THE URINE. 423 



gives the so-called GERHARDT'S reaction, showing a wine-red color 

 on the addition of a dilute, not too acid, ferric-chloride solution. 

 Treat 10-50 c. c. of the urine with ferric chloride as long as it gives 

 a precipitate, filter the precipitate of ferric phosphate, and add 

 some more ferric chloride to the filtrate. In the presence of the 

 acid a claret-red color is produced. After this heat a second, similar 

 portion of the urine to boiling until faint acid reaction, and repeat 

 the test on cooling, which should now give negative results. A third 

 portion of urine is acidified with sulphuric acid and shaken with 

 ether (which takes up the acid). Now shake the removed ether 

 with a very dilute watery solution of ferric chloride, and the watery 

 layer becomes violet-red or claret-red. The color disappears on 

 warming. 



In the absence of aceto-acetic acid the acetone may be tested for 

 directly. This may be done directly on the urine by LEGAI/S and 

 PENZOLDT'S tests. These tests, which are only approximate tests, 

 are only of value when the urine contains a considerable amount of 

 acetone. For a more accurate test we distil at least 250 c. c. of the 

 urine faintly acidified with sulphuric acid, care being taken to have 

 a good condensation. Most of the acetone is contained in the first 

 10-20 c. c. of the distillate. This distillate is tested for acetone by 

 the above tests. In testing for acetone in the simultaneous pres- 

 ence of aceto-acetic acid, first make the urine faintly alkaline, and 

 shake it carefully with ether free from alcohol and acetone in a 

 separatory funnel. The removed ether is then shaken with water, 

 which takes up the actone, and then the watery liquid is tested. 



/?-Oxybutyric Acid, C 4 H 8 3 or CH 3 .CH(OH).CH 2 .COOH. The 

 appearance of this acid in the urine was first positively shown by 

 MINKOWSKI, KiJLZ and STADELMANIST. It occurs especially in all 

 difficult cases of diabetes, but it has also been observed in scarlet 

 fever and in measles, in scurvy, and in diseases of the brain. 

 /?-oxybutyric acid is accompanied by aceto-acetic acid in the 

 urine. 



y#-oxybutyric acid forms an odorless syrup which mixes readily 

 with water, alcohol, and ether. This acid is optically active and 

 indeed laevo-gyrate, and it therefore interferes with the estimation 

 of sugar in the urine by means of polarization. It is not precip- 

 itated either by lead acetate or by ammoniacal basic lead acetate. 

 On boiling with water, especially in the presence of a mineral 

 acid, this acid decomposes into ^-CROTONIC ACID, which melts at 

 71-72 C., and water: CH 3 .CH(OH).CH 2 .COOH =H 2 + CH 3 .CH: 



