SYNTHESIS OF UREA. 157 



tion is colored it can be decolorized by filtering it through 

 bone-black. Distill off the alcohol or allow it to evaporate 

 to obtain the urea. 



343. SYNTHETICALLY. Coarsely powder 50 grammes 

 of potassium ferrocyanid and heat in an iron dish over a 

 Bunsen flame, stirring continually, until it has become a 

 white powder and the lumps show no yellow color when 

 they are broken. If it turns brown the heat is too high. 

 Pulverize the mass as finely as possible in a mortar., mix it 

 thoroughly with half its weight of finely-powdered man- 

 ganese dioxid, and heat in an iron dish under the hood, 

 stirring meanwhile, until the mass glows and becomes thick 

 and sticky. Heat until a small test dissolved in hydro- 

 chloric acid gives no blue color with ferric chlorid. Then 

 allow it to cool ; dissolve the potassium cyanate, which has 

 thus been formed with cold water. Convert this into am- 

 monium cyanate by the addition of 38 grammes of dry 

 ammonium sulphate. Filter and evaporate upon the water- 

 bath at about 60 to 70, at which temperature ammonium 

 cyanate is converted into urea. The potassium sulphate 

 crystallizes out first, and should be removed from time to 

 time. At last evaporate to dryness and dissolve out the 

 urea with absolute alcohol as before. 



344. Mix a few of the . dry crystals with soda-lime 

 and heat in a dry test-tube. The presence of nitrogen is 

 shown by the evolution of ammonia. 



345. Warm some crystals of pure urea in a dry test- 

 tube. It melts, then decomposes, yielding ammonia, which 

 can be identified by litmus-paper. When the substance has 

 solidified, cool it, dissolve in water, make alkaline with 

 sodium hydrate, and add a few drops of copper sulphate 

 solution. The color is due to the presence of biuret, IS[II 2 - 

 CONHCONH 2 . Write the equation for its formation. 



