10 CHEMISTRY OF THE PROTEIDS CHAP. 



hereby, the substance diazobenzene-sulphanilic acid, which with the 

 unknown substance in the urine produces the red colour. 



Pauly * prepares the diazobenzene-sulphanilic acid in the following 

 way : 2 grams finely pulverised sulphanilic acid are shaken up with 3 

 ccm. water and 2 ccm. concentrated hydrochloric acid, and this mixture 

 is added in small quantities, within one minute, to a solution of 1 gram 

 of newly prepared potassium nitrite in 1 to 2 ccm. water ; after each 

 addition the mixture is cooled. The sulphanilic acid passes rapidly 

 into solution and is soon replaced by a dense, white, crystalline deposit 

 of diazobenzene-sulphanilic acid ; after a few minutes the fluid part is 

 sucked off and the crystals are then washed with a little water. 



In testing for histidin, ascertain the absence of tyrosin by means of 

 Millon's reagent ; add sodium carbonate solution to the fluid under 

 examination till the reaction is alkaline, and then add 3 to 5 ccm. of a 

 freshly-prepared solution of a few centigrams of diazobenzene-sulphanilic 

 acid in soda solution. The red colour of histidin appears usually at 

 once, and at the latest after three minutes. On diluting with distilled 

 water the red colour does not disappear (histidin) or becomes somewhat 

 more yellow (tyrosin). All other albuminous derivatives, such as 

 glycocoll, alanin, leucin, a-amino-valerianic acid, serin, lysin, ornithin, 

 asparagin, glutaminic acid, cystin, and hippuric acid give in sodium car- 

 bonate solutions lemon yellow to deep yellow colours, which disappear 

 on dilution and on acidification. a-Pyrrolidin-carboxylic acid and 

 tryptophane give negative results. 



Histidin is recognisable in dilutions of 1 : 100,000 (pale pink) to 

 1 : 20,000, in which case the colour is already a deep cherry-red in 

 thicker solutions. The diazo-reaction is also a more delicate test for 

 tyrosin than is Millon's reaction. 



9. The Glucosamin-Test of Ehrlicli 



Ehrlich 2 made in 1901 the discovery that urine turns a more 

 or less pronounced carmine-red colour by the addition of a few drops 

 of the pale yellow ^-dimethyl-amino-benzaldehyde dissolved in normal 

 hydrochloric acid. His pupil Proscher 3 obtained a substance in 

 sufficient quantity to determine its formula as C 16 H 24 6 N 2 , from 

 which Ehrlich calculated that the substance was either formyl- 



N J Herm. Pauly, Zeitschr. f. physiol. Chem. 42. 508 (1904). In a second paper, ibid. 

 44. 159 (1905), it is pointed out that the diazo-reaction does not allow us to distinguish 

 between imido-azols and the pyrirnidin-nucleus, becaxise the 4-methyl uracil, which is an 

 oxygen-containing pyrimidin, also gives the diazo-reaction. 



2 Paul Ehrlich, Die medic. Wochenschr., April 1901, No. 15. 



3 Proscher, ^Zeitschr. f. physiol. C/iem. 31. 520 (1900-1), and Deutsche med. 

 Wochensch.1903, p. 927. 



