COMPOUNDS OF CAKBON WITH OXYGEN AND NITROGEN 409 



of carbonic anhydride. It is easily understood that such a combination 

 will take place with any ammonium carbonate under the action of salts 

 which take up the water for instance, sodium or potassium car- 

 bonate 37 as in an anhydrous state ammonia and carbonic anhydride 

 only form one compound, CO 2 2NH 3 . 38 As the normal ammonium car 

 bonate contains two ammonias, and as the amides are formed with the 

 separation of water at the expense of the hydrogen of the ammonias, 

 so this salt has its symmetrical amide, CO(NH 2 ) 2 . This must be termed 

 carbamide. It is identical with urea, CN 2 H 4 0, which, contained in the 

 urine (about 2 per cent, in human urine), is for the higher animate 

 (especially the carnivorous) the ordinary product of excretion 39 and 

 oxidation of the nitrogenous substances found in the organism, If 

 ammonium carbainate be heated to 140 (in a sealed tube, BazarofF), 

 or if carbony} chloride, COC1 2 , be treated with ammonia (Natanson), 

 urea will be obtained, which shows its direct connection with carbonic f 

 acid that is, the presence of carbonic acid and ammonia, in it. From 

 this it will be understood how urea during the putrefaction of urine is 

 converted into ammonium carbonate, CNaB^O + H 2 O = C0 2 4- 2NH 3 . 

 Thus urea, both by its origin and decomposition, is an amide of 

 carbonic acid. Representing as it does ammonia (two molecules) in 

 which hydrogen (two atoms) is replaced by the bivalent radicle of 

 carbonic acid, urea retains the property of ammonia of entering into 

 .combination, with acids (thus nitric acid forms C'N 2 H 4 O,HN0 3 ), 

 with bases (for instance, with mercury oxide), and with salts (such 

 as sodium chloride, ammonium chloride), but containing an acid 

 residue it has no alkaline properties. It is soluble in water without 

 change, but at a red heat loses ammonia and forms cyanic acid, 

 CJSTHO, 39t>is which is a nitrile of carbonic acid that is to say, is a 



*? Calcium chloride enters into double decomposition with ammonium carbamate. 

 Acids (for instance, sulphuric) take up ammonia, land set free carbonic anhydride , 

 whilst alkalis (such as potash) take up carbonic anhydride and set free ammonia, and 

 therefore, in this case for removing water only sodium or potassium carbonate can be 

 taken. An aqueous solution of ammonium carbamate does not entirely precipitate a 

 solution of CaCl 2 , probably because calcium carbamate is soluble in water, and all the 

 (NH 3 ) 2 C0 2 is not converted by dissolving into the normal salt, (NH 4 0) 2 C0 5 . 



38 It must be imagined that the reaction takes, place at first between equal volumes 

 (Chapter VII.) ; but then -carbamic acid, HO(CNH^O), is produced, which, as an acid, 

 immediately combines with the ammonia, forming NH^O^CNHoO). 



39' Urea is undoubtedly, a product of the oxidation of complex nitrogenous -matters 

 (albumin) of the animal body. It is found in the blood. It is absorbed from the- blood 

 by the kidneys. A man excretes about 80 grams of urea per day. As a derivative of 

 carbonic anhydride, into, which it is readily converted, urea is in a sense a product of 

 oxidation. 



39 i> is Its polymer, C 3 N 3 H 3 3 , is formed together with it. Cyanic acid is &. very 

 unstable, easily changeable liquid, while cyanuric acid is a crystalline solid which is very 

 stable at the ordinary temperature. 



