158 BASIC BODIES. 



body, but can also be artificially prepared. When Wohler made 

 the beautiful discovery that urea was formed by the union of cyanic 

 acid and ammonia, the physiologists of that day who were still 

 imbued with ideas of vital forces, were astonished that a matter 

 which appeared only capable of formation by organic force, could 

 also be formed by the hand of the chemist from so-called inorganic 

 matters. The astonishment of the physiologists has, however, 

 gradually ceased, not only because they have for the most part 

 shaken off their adherence to irrational vital forces, but also 

 because since that time many other substances have been artificially 

 produced, which are identical with, or at all events most similar to 

 previously known organic matters. We have learned to regard 

 urea as one of the most common products of decomposition, not 

 only of natural organic bodies, but also of artificial substances. It 

 would occupy too much of our present space, were we to enumerate 

 all the cases in which urea occurs as a product of the decomposition 

 of a nitrogenous substance ; we will here only mention its formation 

 on the union of cyanogen and water, of fulminate of copper and 

 hydrosulphate of ammonia (Gladstone*), in the decomposition of 

 allantoine by nitric acid, of creatine by the alkalies, of alloxan by a 

 boiling solution of acetate of lead, &c. 



There are various ways in which urea may be obtained from 

 urine, but it is chiefly effected by nitric or oxalic acid ; it is more 

 advisable to use the alcoholic extract of urine than the residue left 

 by its direct evaporation ; if nitric acid be used, the nitrate of urea 

 must be exposed to due pressure between tiles and filtering paper, 

 and after it has been dissolved in a little water, must be decom- 

 posed with carbonate of lead or of baryta ; crystals of nitrate of 

 lead or baryta soon separate from the filtered fluid, which must be 

 evaporated and extracted with alcohol ; this alcoholic solution may 

 contain, in addition to urea, a little nitrate of lead, but it takes up 

 no nitrate of baryta; when baryta has been used, the alcoholic 

 solution must be decolorised with animal charcoal ; when the salt 

 of lead has been used, the solution is often perfectly colourless 

 after the precipitation of the metal by sulphuretted hydrogen. The 

 urea separates in a crystalline form, on the evaporation of the 

 alcoholic solution. 



In order to prepare urea from cyanate of ammonia, we raise a 



mixture of 28 parts of ferrocyanide of potassium, from which all the 



water has been expelled, and 14 parts of well-dried, good peroxide 



of manganese, to a faint red heat; (even when the mixture is suffi- 



* Ann. d. Ch. u. Phann. Bd. 6fi, S. 1-5. 



