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Urea

A crystalline, colorless, transparent substance, consisting of cyanate of ammonia. Fresh urine, gently evaporated to the consistence of a syrup, is to be treated with its own volume of nitric acid at 24 deg. the mixture is to be shaken and immersed in an ice-bath to solidify the crystals of nitrate of urea; these are washed with ice-cold water, drained, and-pressed between sheets of blotting paper. When they are thus separated from foreign matters, they are to be dissolved in water to which subcarbonate of potash is added, whereby the nitric acid is taken up, and the urea set at liberty. This new liquor is evaporated at a gentle heat, nearly to dryness; the residue is treated with pure alcohol, which only dissolves the urea; the solution is concentrated, and the urea crystallizes. (Thénard.) Or: Mix 28 parts of perfectly dry ferrocyanide of potassium with 14 parts of black oxide of manganese, both pure and in fine powder; then place them on a smooth iron plate, and heat them to a dull red, over a charcoal fire. When the mass begins to burn, it must be frequently stirred; after which cool and dissolve in cold water, filter, and add 20½ parts of dry sulphate of ammonia, and decant the clear from the precipitated sulphate of potassa. Concentrate at a heat below 212°, again decant, evaporate to dryness, and digest in boiling alcohol of 80%; crystals of urea will be deposited as the solution cools. (Liebig.) 4324, Nitrate of Urea. This may be prepared as in last receipt from urea; or by saturating the artificial urea (Liebig's preparation) with nitric acid.