APPENDIX. 333 



(b.) PRIMARY DIAMIDES OR UREAS. 



Urea, (NH 2 ) 2 CO, is the last product of the oxidation of the albu- 

 minous tissues of the body and of the albuminous foods. It occurs as 

 the chief nitrogenous constituent of the urine of man, and of some other 

 animals. It has been found in the blood and serous fluids, lymph, and 

 in the liver. 



Properties. Crystallizes in thin glittering needles, or in prisms with 

 pyramidal ends. Easily soluble in water and alcohol, insoluble in ether, 

 easily decomposed by strong acids, readily forms compounds with acids 

 and bases, of which the chief are (NH 2 ) 2 COHN0 3 , urea nitrate, and 

 (NH 2 ) 2 (CO), H 2 C 2 2 + H 2 0, urea oxalate. 



Constitution. It is usually considered to be a diamide of carbonic 



CO N H 



2 



H 2 V 



acid which may be written H 2 N 2 , or CO N H 2 V which is CO (H0) 2 , 



H 2 ) 



with (OH)' 2 , replaced by (NH a )' a . Some think it a monamide of carbamic 

 acid, CO, OH, NH 2 , thus CO, NH 2 NH 2 , with one atom of NH 2 , or 

 amidogen in place of one of hydroxyl OH. 



) IN" 

 TJrea is isomeric with ammonium cyanate C j- QJSTTT from which it 



was first artificially prepared. 



Kreatin, C 4 H 9 N 3 2 , is one of the primary products of muscular 

 disintegration. It is always found in the juice of muscle. It is gener- 

 ally decomposed in the blood into urea and kreatinin, and seldom, unless 

 under abnormal circumstances, appears as such in the urine. Treated 

 with either sulphuric or hydrochloric acid, it is converted into kreatinin; 

 thus 



C 4 II, N. 0, = 0, H, N 3 + H, O. 



Kreatinin, C 4 H 7 N 3 0, is present in human urine, derived from oxi- 

 dation of kreatin. It does not appear to be present in muscle. 



(c.) UREIDES. 



Ureides are a third variety of amides, and may be considered as ureas 

 in which part of the hydrogen is replaced by diatomic acid radicals. 

 Honour eides contain one acid radical and one urea residue; and diureides, 

 one acid radical and two urea residues. 



Uric Acid, C H 4 N 4 3 , occurs in the urine, sparingly in human urine, 

 abundantly in that of birds and reptiles, where it represents the chief, 

 nitrogenous decomposition product. It occurs also in the blood, spleen, 

 liver, and sometimes is the only constituent of urinary calculi. It is 

 probably converted in the blood into urea and some carbon acid. It 



