CARBAMIC ACID. 691 



In regard to other methods such as BUNSEN'S method with its many 

 modifications as suggested by PFLUGER, BORLAND and BLEIBTREU, 

 we refer to more complete handbooks. 



For the quantitative estimation of urea in blood or other animal 

 fluids, as well as in the tissues, SCHONDORFF has proposed a method 

 where the proteins and extractives are first precipitated by a mixture 

 of phosphotungstic acid and hydrochloric acid, and then the filtrate 

 made alkaline with lime. The quantity of ammonia formed on heating 

 a part of this filtrate to 150 C. with phosphoric acid and the amount 

 of carbon dioxide produced by heating the other part to 150 C. are 

 determined. In regard to the principles of this method, as well as to 

 the details, we refer to the original article (PFLUGER'S Arch., 62). SAL- 

 KOWSKI 1 has recently suggested a method for estimating the urea in 

 tissues. 



Urein is the name given by OVID MOOR to a product which he obtained by 

 extracting urine, which had been evaporated to a syrup, with absolute alcohol 

 and precipitating the urea with alcohol containing oxalic acid, or by cooling and 

 treatment with alcohol. Urein is a golden-yellow oil which is poisonous; it 

 reduces permanganate in the cold, and it forms the chief portion of the nitro- 

 genous extractives of urine. There is no doubt that urein is a mixture of several 

 substances. According to Moon, 2 the amount of urea in the urine is only about 

 one-half that ordinarily given, and he has suggested a new method for the deter- 

 mination of the true quantity of urea. The possibility that in the urine we have 

 other bodies besides urea which have been determined with the urea cannot be 

 denied a priori. From the investigations published so far it must be said that 

 MOOR'S assertions are not sufficiently grounded. 3 



yNH 2 



Carbamic Acid, CH 3 N02=CO\ . This acid is not known in the free 



state, but only as salts. Ammonium carbamate is produced by the action of 

 dry ammonia on dry carbon dioxide, but also after the addition of Na 2 C0 3 to a 

 solution which contains an ammonium salt (MACLEOD and HASKINS). Carbamic 

 acid is also produced by the action of potassium permanganate on protein and 

 several other nitrogenous organic bodies. 



The occurrence of carbamic acid in human and animal urines has already 

 been considered in connection with the formation of urea. The calcium salt 

 which is soluble in water and ammonia but insoluble in alcohol, is the most impor- 

 tant in the detection of this acid. The solution of the calcium salt in water 

 becomes cloudy on standing, but much more quickly on boiling, and calcium car- 

 bonate separates. NOLF, MACLEOD and HASKINS have made experiments as to 

 the method of formation of carbamic acid. The latter have indicated a new 

 method for the quantitative estimation of carbamates. 4 



1 Arbeiten aus dem pathol. Institute, Berlin, 1906. 



2 O. Moor, BuM. Acad. de St. Petersbourg, 14 (also Maly's Jahresber., 31, 415), 

 and Zeitschr. f. Biologic, 44 and 45, and Zeitschr. f. physiol. Chem., 40 and 48. 



3 See Kuliabko, Maly's Jahresber., 31, 415; Erben, Zeitschr. f. physiol. Chem., 

 38; Folin, ibid., 37; Gies, Journ. Amer. Chem. Soc., 25; Haskins, Amer. Journ. of 

 Physiol., 12; Lippich, Zeitschr. f. physiol. Chem., 48 and 52. 



4 Nolf, Zeitschr. f. physiol. Chem., 23; Macleod and Haskins, Amer. Journ. of 

 Physiol., 12, and Journ. of biol. Chem., 1. 



