548 AN AMERICAN TEXT- BOOK OE PHYSIOLOGY. 



,9-Oxybutyric Acid, CH 3 CHOHCH 2 COOH. — A lsevo-rotatory acid (see 

 p. 539). 



Amido- Derivatives of Carbonic Acid. 

 OC '<OH- OC <OH- 0C <NH:- 



Carbonic acid. Carbamic acid. Carbamide. 



Carbamic Acid. — This is not known free, but its calcium .salts have been 

 found, especially in herbivorous urine, and its presence in the blood as ammo- 

 nium carbamate is maintained. 1 The latter has been obtained by Drechsel 2 by 

 oxidizing glyeocoll and leuein in ammoniacal solution, and he has converted it 

 into urea by electroly.sis. From these facts he concludes that ammonium car- 

 bamate is the antecedent of urea. It must, however, be remembered that 

 ammonium carbamate is very readily decomposable, and has never been 

 directly detected in the blood. 



Ammonium carbamate is formed by the direct union of ammonia with car- 

 bonic oxide in their nascent states, and is therefore found in commercial ammo- 

 nium carbonate and as the product of the oxidation of the amido- compounds 

 above mentioned : 



2XH 3 + C0 2 =OC<g£f^ 



Water converts it into ammonium carbonate : 



oc <Snh 4 +h * = oc <£nh;- 



Carbamide, or Urea, OC(NH 2 ) 2 . — This is the principal end-product of the 

 nitrogenous portion of proteid in all mammals, being found in considerable 

 concentration in the urine. Schondorff 3 finds in the blood, liver, spleen, 

 pancreas, and brain about 0.12 per cent, of urea, while muscle contains 0.09 

 per cent., the heart 0.17 per cent., and the kidney 0.(57 per cent. In uraemia 

 it may collect in all tissues of the body, and may then be excreted in slight 

 amount by the gastric and intestinal juices. It is given off in profuse sweat- 

 ing, though only in small proportion to that lost in the urine. 



Preparation. — -(1) Like other amides, by heating ammonium carbonate; 

 further, by the electrolysis of, or by heating, ammonium carbamate: 



OC< ONH = OC< XH 2 + 2H2 °- 



ocx™^ = oc<™; + h 2 o. 



(2) Through the union of ammonia with carbonyl chloride: 



1 Drechsel: Lvdvng'a Arbeiten, 1875, S. 172; Drechsel und Abel, Archiv fur Physiologic, 1891, 

 S. 242. 



* Loc. cit. * Prfiiger's Archiv, 1899, Bd. 74, S. 307. 



