UREA. 51 



manganese, are to be thoroughly mixed, and heated on an iron 

 plate to a dull red heat. The mixture smoulders into a brown 

 mass which contains cyanate of potash, carbonate of potash, and 

 sesquioxide of manganese. When cold it is to be repeatedly 

 digested in cold water, and the solution mixed with 20*5 parts of 

 crystallized suljihate of ammonia dissolved in water. Sulphate 

 of potash and cj^anate of ammonia are formed ; and this latter 

 substance, on the application of a slight heat, is converted into 

 urea. Sulphate of potash usually separates at once, in crj^stals ; 

 but, without stopping to remove them, we may evaporate the 

 fluid on the water- bath to dryness, and remove the urea by a 

 small quantity of water. On evaporatiug this aqueous solution 

 to dryness, the m'ea may be extracted with boiling alcohol of 

 80 or 90|5, whilst the sulphate of potash remains undissolved. 

 The alcohol is allowed to evaporate, and the urea separates 

 from it in crystals. In this manner a pound of ferrocyanide of 

 potassium will furnish one third of a pound of pure urea. 



The composition of urea is represented by the formula^ 

 C,, H^ N, O,^. It contains a larger proportion of nitrogen 

 (^G'TSS^) than any other organic compound. 



Urea when pvire and in crystals is white and transparent : 

 when deposited from a concentrated hot solution it is in the 

 form of fine silky needles, but by very slow or spontaneous eva- 

 poration it separates in colourless flattened four-sided prisms of 

 specific gra\dty 1-35. It is soluble in its own weight of cold, 

 and in every proportion of hot water ; in 4*5 parts of cold, and 

 in 2 parts of boiling alcohol; it is slightly soluble in ether, 

 about 1 part in 60, at a temperature of 62°. 



It deliquesces in a very moist atmosphere only, and even then 

 its chemical properties remain unchanged. In dry air it is per- 

 fectly permanent. It fuses at 250° into a colourless liquid, and 

 is decomposed by a higher temperature into ammonia, cyanate 

 of ammonia, and dry solid cyanuric acid. A concentrated watery 

 solution may be boiled and preserved for a long time without 

 any change, but if albumen, glutiu, mucus, or especially ferment, 

 should be present, it is speedily converted into carbonate of 

 ammonia. The possibility of this transformation is obvious 

 from the formula 



C^ H^ N, 0„ (urea)+2H0 = 2 (CO^, NHJ. 



' See Appendix I, Note 18. 



