An Improved Murexide Test 173 



AN IMPROVED MUREXIDE TEST FOR TEACHING 

 PURPOSES. 



Samuel E. Earp, Indianapolis, Indiana. 



During my class work in chemistry in medical college I directed 

 my students to follow Hoffmann and Ultzmann as a laboratory guide. 

 Directions for the murexide test were as follows : Mix concretion in 

 a small mortar, place in a porcelain dish, add a few drops of nitric acid 

 and a little water and warm carefully over a flame until the uric acid 

 is dissolved. Evaporate cautiously, almost to dryness. Already we 

 notice during the evaporation, if uric acid is present, onion-red streaks 

 on the walls of the dish which vanish suddenly if that portion of the 

 dish approaches the flame. If, when the fluid has evaporated to dry- 

 ness, we add a drop of ammonia to the residue the whole interior of the 

 dish becomes a beautiful purple-red (murexide acid-purpurate of am- 

 monia). If KOH is added to the residue it becomes violet-blue. The 

 murexide depends upon the fact that by the addition of HNO; and heat, 

 first alloxan and then alloxantine is formed which on addition becomes 

 murexide. 



It is very commonplace for 50 per cent of the class to make failures. 

 It seems difficult for them to gauge the proper amount of dilution and 

 the requisite amount of heat. I adopted the following method without 

 more than two per cent of failures. 



Heat the concretion slowly in an evaporation dish with a minimum 

 amount of water acidulated with nitric acid until the approach of dry- 

 ness. Put metal plate over low flame burner frame and upon it a 

 moistened salt of ammonium; then invert the evaporating dish over the 

 ammonium so that the fumes are confined. This operation is quickly 

 accomplished and there is little opportunity for error and too, even a 

 student who is a novice, will not fail in this method of demonstration. 



"Proc. 38th Meeting, 102^; (192;J).' 



