URINE. 133 



diazobenzenesulphonic acid was used by Ehrlich and has 

 since been designated by the clinicians as Ehrlich's Diazo- 

 reac ion. The fact must not be forgotten, however, that, as 

 a test for bilirubin this reagent has also been employed by 

 Ehrlich, and by others to determine the presence of sugar 

 and protein in the urine. The color obtained in the reaction 

 in the case of these two latter substances does not differ 

 greatly from that of the so-called Ehrlich's reaction, and on 

 this account the possibility of error in interpretation must 

 always be borne in mind. 



Ehrlich's diazo-reaction is usually performed as follows: 

 An equal volume of a freshly prepared solution of diazo- 

 benzenesulphonic acid is added to the urine and the mixture 

 is then rendered alkaline with an excess of NH 4 OH. An 

 orange color develops in ordinary cases, but in certain 

 urines there results a red color which may vary from a car- 

 mine to a deep ruby-red; upon shaking the solution the 

 froth also partakes of the color. Sometimes a green or 

 violet precipitate will settle out upon standing. 



The formation of the fresh diazobenzenesulphonic acid is 

 effected by the previous preparation of the two following 

 solutions : 



1. 1 grm. sulphanilic acid and 50 c.c. of cone. HC1 dis- 

 solved in a liter of water. 



2. 5.0 grm. sodium nitrite dissolved in a liter of water. 

 Just previous > to use these two solutions are mixed in 



the proportion 40 : 1 and the mixture used as above. 



The free nitrous acid which is liberated by the action of 

 the HC1 upon the NaN0 2 , reacts with the sulphanilic acid 

 with the formation of diazobenzenesulphonic acid, according 

 to the equation 



/NH 2 /N^ 



C 8 H/ +HN0 2 =C 6 H/ 

 X HS0 3 X SO 



