APPENDIX, 687 
3. By addition of water to cyan-amide: 
CN.NH: + H:O = CON2H:. 
4, By evaporation of ammonium cyanate in aqueous solution: 
CN(ONH,) = CON:H,. 
The last reaction possesses a historical interest, for it was by this 
method that an organic compound occurring in the animal body was 
first formed from inorganic substances in the laboratory by Wéhler in 
1828. Urea forms compounds with acids, the most interesting of which 
to the student of animal chemistry is the following: 
Urea nitrate. CH.N.O.HNOs. 
When urine is concentrated, and strong nitric acid added cautiously, 
the above crystallizes out in glistening six-sided or rhombic tablets, solu- 
ble in water, but insoluble in ether. This makes a reliable and fairly 
delicate test for the presence of urea. : 
Uric acid. CsH.N.Os. 
This metabolite occurs in the spleen and several other organs and 
tissues; sparingly in the urine of man and most mammals; abundantly 
in that of birds and serpents, in which it takes the place of urea. In its 
purest form it presents itself as a colorless crystalline powder, tasteless 
and odorless. Its crystalline forms, arising spontaneously from urine, 
are very variable and always colored. Very insoluble in cold water, 
ether, and alcohol ; readily soluble in sulphuric acid, caustic alkalies, 
and some of their salts. The most important salts of uric acid are the 
urates of sodium, potassium, and ammonium, all of which occur in urin- 
ary sediments. 
The murexid test for uric acid is as follows: Add strong nitric acid 
in very small quantity, and evaporate to dryness, when a red color 
should appear, which on addition of ammonia gives rise to a purple. 
The following equations will show the relations of uric acid to urea, etc., 
so far as laboratory reactions are concerned. We have in the body of 
the work shown that uric acid is not in all probability itself an anteced- 
ent of urea in the body: 
C:.H.N.O; + H.0 + O = G1H:N.0,. + CN2H.O. 
Uric acid. Alloxyan. Urea. 
C.N:H.0, + 2H.O = C;:H.O; + CN.H.O. 
Alloxan. Mesoxalic acid. Urea. 
CsH.N.0: + H2O + O = CsHeN.Os + COs. 
Uric acid. Allantoin. 
C.HeN.Os + H:O = CHsN.O + C:H.N.O. 
Allantoin. Urea. Allanturic acid. 
Uric acid has been made artificially by fusing together urea and glyco- 
cin (glycin, glycocoll, or amido-acetic acid) : 
/NH, 
CH C0,H 
Creatin. C.H.NsO2. 
This body may be abstracted from dead muscle, and obtained eithcr 
in a white amorphous condition or in rhombic prisms, soluble in cold 
