30 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



a red residue on evaporation (distinction from the murexide 

 reaction for uric acid). 



2. The So-called Weidel's Reaction. 1 Dissolve half of the 

 xanthine obtained in bromine-water, warming gently, evap- 

 orate the solution on the water-bath to dryness, and invert 

 the dish over another which contains some ammonia. The 

 residue becomes red. 2 



IV. PREPARATION OF SARCOLACTIC ACID. 



For this purpose the filtrate from the silver precipitate 

 III Method B may be used. Evaporate this to a sirup on the 

 water-bath. Ammonia escapes and a portion of the silver 

 separates in reduced form. Extract the residue with alcohol, 

 filter the alcoholic extract, evaporate on the water-bath, dis- 

 solve in 75 cc. of water to which 25 cc. of dilute sulphuric 

 acid have been added, and extract by shaking in a separat- 

 ing-funnel, three or four times at least, with one and a half 

 volumes of ether to which a little alcohol has been added. 

 Separate the ether, filter through a dry filter, and distil off 

 the ether. It is advantageous to distil the first extract at 

 once and use the distilled ether (adding some fresh ether) 

 for the second extraction. 



Use a small portion of the residue resulting for the Uffel- 

 mann's reaction for lactic acid (see chapter on Digestion). 

 Dissolve the remainder in water, boil with freshly precipi- 



1 The best way to perform the test according to E Fischer (Ber. 30, 

 2236 (1897) is to boil a small quantity of the finely powdered xanthine 

 with some freshly prepared chlorine-water or with some hydrochloric 

 acid and a little potassium chlorate, then cautiously evaporate the fluid 

 to dryness on platinum foil and moisten the residue with ammonia (forma- 

 tion of murexide). O. 



2 If we use, in addition to the bromine-water (originally chlorine-water 

 was . prescribed) , a trace of nitric acid, the reaction is far more beauti- 

 ful, but under these conditions other xanthine bases also give the test. 

 This form of the reaction is therefore to be discarded as liable to lead to 

 error. 



