ADVANCED PHYSIOLOGICAL CHEMISTRY 459 



PREPARATION OF UREA. 



1. From Urine. To about 400 c.c. urine add barium mixture 

 (1 vol. saturated barium nitrate solution mixed with 2 vol. baryta 

 water) until there is no further precipitate of sulphates and phosphates. 

 Filter and evaporate the nitrate, at first over a free flame, afterwards 

 on a water bath to a thin syrup. Now mix this syrup with about 

 100 c.c. methylated spirit and, after allowing the mixture to stand for 

 about half an hour so that the precipitate of inorganic salts may settle, 

 filter the alcoholic extract into an evaporating dish and evaporate it 

 nearly to dryness on a water bath. Allow the residue to cool, and 

 then add to it about double its volume of concentrated pure nitric acid, 

 meanwhile placing the basin in a dish of cold water, and stirring the 

 contents with a glass rod so as to accelerate the formation of the urea 

 nitrate. After about half an hour the crystals of urea nitrate are 

 filtered off by means of a suction filter, sucked as dry as possible, and 

 then placed between several thicknesses of filter paper between 

 which they are pressed so as to dry them. In order to convert the 

 nitrate into urea, the crystals are placed in an evaporating dish and 

 dissolved in as little water as possible ; the basin is then placed on a 

 heated water-bath, and powdered barium carbonate added with a pen- 

 knife in small quantities until the fluid reacts neutral. By this 

 treatment the urea nitrate is decomposed, the nitric acid combining 

 with barium to form barium nitrate, and the urea being thereby 

 liberated. The mixture is now filtered, the filtrate evaporated to 

 dryness and the urea taken up from the residue by extracting with 

 absolute alcohol, which does not dissolve the barium nitrate. The 

 alcoholic solution of urea is now evaporated to dryness, when a mass 

 of urea crystals is obtained. 



The above process may be considerably curtailed by omitting the 

 preliminary precipitation of phosphates, etc. with barium mixture, 

 the evaporated urine being simply mixed in a test tube with nitric 

 acid, which is kept cool by submersing it in a beaker of water. 

 The crystals of urea nitrate are then filtered off, dried between filter 

 paper and treated with barium carbonate as above described. 



2. Separation of Urea from Blood, Serous Fluids or Watery Extracts 

 of Tissues. About 100 c.c. of the fluid are mixed with four times its 

 volume of methylated spirit, vigorously shaken and allowed to stand 

 over night. By this treatment the proteids are coagulated, whereas 

 the spirit dissolves the urea. The coagulum is now^filtered off, washed 

 with spirit, and the washings are combined with the filtrate, the whole 

 being then evaporated to dryness on a water-bath. The residue is 



