NJ'S OF CARBON WITH OXVCEN AND NITROGEN 897 



This ammonium carbamate is one of the most remarkable of the 

 ammonium carbonates, because it is the simplest in its composition, 

 and is easily and immediately formed by mixing two volumes of dry 

 ammonia with one volume of dry carbonic anhydride, 2JS~H 3 4-CO 2 = 

 NH,O(CONH 2 ) ; it is a solid substance, smells strongly of ammonia, 

 attracts moisture from the air, and entirely decomposes at 60. The 

 fact of this decomposition may be judged 3(i by the density of its 

 vapour, which =13 (H = l) ; this exactly corresponds with the density 

 of a mixture of 2 volumes of ammonia and 1 volume 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 carbonate. 37 As 

 ammonia and carbonic anhydride in an anhydrous state only form one 

 compound, C0 2 2NH 3 , 3H ammonium carbamate, as has been already 

 stated, may be regarded as COX 2 , where X has been replaced by the 

 residues NH 2 and NH 4 O (that is, HO in which H is replaced by 

 NH,), and therefore is still capable of losing water and forming the 

 symmetrical amide CO(NH 2 ) 2 . This must be termed carbamide. It 

 is identical with urea, CN 2 H 4 O, which, contained in the urine (about 

 2 per cent, in human urine), is for the higher animals (especially the 

 carnivorous) the ordinary product of excretion 39 of the nitrogenous 

 substances found in the organism. If ammonium carbamate be heated 

 to 140 (in a sealed -tube, Bazarnff), or if carbonyl chloride, COC1 2 , 

 be treated with ammonia (Natanson), urea will be obtained, which 



Vi N auniiuni determined the following densities of the vapour of ammonium carbamate 

 (in millimetres of mercury) : 



-10 +10 20 30 40 50 60 



5 12 30 62 124 248 470 770 



Horstmann and Isambert studied the densities corresponding with excess of NH 3 or CO.,, 

 and found, as might have been expected, that with such excess the mass of the salt 

 formed (in a solid state) increases and the decomposition (transition into vapour) 

 decreases. 



37 Calcium chloride enters into double decomposition with ammonium carbamate. 

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

 alkalis (for instance, potash) take up carbonic anhydride and set free ammonia, and 

 therefore, for removing water here only sodium or potassium carbonate may be 

 taken. 



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

 (Chapter VII.) ; but then carbamic acid, HO(CNH 2 O), is produced, which, as an acid, 

 immediately combines with the ammonia, forming NH4O(CNH 2 O). 



59 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 car- 

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

 oxidation. 



