390 



APPENDIX 



Probably the most convenient test for urea is the hypobromite method, using 

 the Doremus ureometer with a side tube connected to the closed arm of the fermenta- 

 tion tube by a glass stop cock. 



The reagent is prepared by taking 70 c.c. of a 30% stock solution of NaOH, 

 diluting it with 180 c.c. water and then adding 5 c.c. of bromine, stirring until the 



bromine is dissolved. This solution if stored 

 in a cool dark place will keep about one week, 

 The urine to be tested must be free from 

 sugar and albumin and contain less than i % 

 of urea. Ordinarily the urine must be di- 

 luted two to four times to obtain a speci- 

 men containing less than i%. In using 

 this improved Doremus ureometer the closed 

 portion of the U tube is filled with the hy- 

 pobromite solution, and the urine introduced 

 by allowing it to run in from the side tube 

 by opening the glass cock arranged for that 

 purpose. After the gas has risen and the 

 instrument has stood for a short time the 

 readings may be made in grams to the liter, 

 or in percentage. 



This urea determination is only a rough 

 clinical one. 



Gerhardt's Test for Diacetic Acid. 



Add a few drops of ferric chloride solu- 

 tion to 10 to 50 c.c. of urine so long as a 

 precipitate continues to form. Then filter 

 and to the filtrate add more ferric chloride 

 solution. A bordeaux red color shows dia- 

 cetic acid. The test is sensitive. As a con- 

 trol to show that the color is not due to drug 

 elimination (antipyrine, salicylates, etc.) 

 boil a specimen which gave the test for 

 three to five minutes. If the color was due 



to drugs it will be obtained with a boiled sample while such treatment drives off the 

 diacetic acid. In Hurtley's test add 2.5 c.c. HC1 and i c.c. of i% sol. of sod. 

 nitrate to 10 c.c. urine. Shake and allow to stand 2 minutes. Now add 15 c.c. 

 strong ammonia followed by 5 c.c. of 10% sol. ferrous sulphate. The slow produc- 

 tion of a violet colour shows positive test (2 hours). Shows i part aceto-acetic 

 acid in 50,000. 



If the urine shows a well-marked Gerhardt reaction it is well to test for /?-oxy- 

 butyric acid. 



The following modification of Lange's test by Hart is a satisfactory one. The 

 principle involved is the removal of acetone and diacetic acid by heat, then oxidizing 

 /?-oxybutyric acid to acetone with hydrogen peroxide and then testing for acetone. 



FIG. 106. 



-Doremus-Hinds Ure- 

 ometer. 



