UREA OR ANORMAL CYANATE OF AMMONIA. 993 



mixed together, and forms a white woolly crystalline substance. 

 This cyanate affords ammonia when treated by an alkali, and its 

 acid undergoes the usual decomposition when liberated by ano- 

 ther acid. But if heated, either dry or in solution, it loses a 

 little ammonia, still retaining, however, the elements of a neu- 

 tral cyanate, and is transformed into urea, a change the more 

 remarkable that urea is a substance belonging to the animal 

 economy. 



Urea or anormal cyanate of ammonia, C 2 O 2 N 2 H 4 =C 2 O 2 

 + 2NH 2 (Dumas). This substance, discovered by Vauquelin 

 and Fourcroy in urine, was obtained from cyanic acid and am- 

 monia by Woehler, and is the first peculiarly organic product 

 which was formed artificially. It exists in the form of lactate 

 of urea in human urine, and combined with hippuric acid in the 

 urine of the cow and elephant (Cap and Henry). Urea 

 combines with most acids without neutralising them, and is a 

 feeble base. 



The following is an advantageous process for urea from 

 human urine, without the use of alcohol. Fresh urine is evapo- 

 rated in a water-bath to about ^. or ^ of its volume, allowed to 

 cool and filtered. Oxalic acid is taken in the proportion of 

 about half an ounce to each pint of urine employed, dissolved 

 in twice its weight of hot water, and the solution slowly added 

 with continual agitation to the concentrated urine ; a large pro- 

 duction of a buff-coloured precipitate results, which is oxalate 

 of urea. The impure oxalate, when quite cold, is collected on a 

 large calico filter, slightly washed with a cold solution of oxalic 

 acid, and pressed in the hands as strongly as possible, to get 

 rid of the mother liquor containing salts, &c. The solid mass 

 of oxalate of urea is next dissolved in hot water in a capacious 

 vessel, and neutralised with chalk (whiting) rubbed up with 

 water to a thick cream. So soon as the acid reaction to test- 

 paper ceases, the whole may be thrown on a filter to drain, and 

 squeezed to avoid unnecessary loss. On digesting the solution 

 with animal charcoal, again filtering and concentrating, without 

 ebullition, to a small bulk, crystals of urea are deposited on 

 cooling ; these have a brownish colour and disagreeable smell, 

 but by a second solution in warm water, with the addition of a 

 little more bone-black and filtration, the substance is obtained 

 snow-white and inodorous. The urea obtained in this manner 



2 T T 



