132 ANIMAL CHEMISTRY LECTURE VI. 



or conjugated with two atoms of urea to form a diureide, such as 

 mycomelic acid, a body having exactly the same relation to 

 oxalic acid that uric has to mesoxalic acid. 



(139.) Now, just as we can convert mesoxalic into oxalic acid 

 by burning off its excess of carbonic oxide, so may we convert 

 oxalic acid itself into carbonic acid by a precisely similar 

 oxidation, thus : 



Oxalic Oxygen Carb-anhyd. Carbonic 



C 2 H 2 4 + = C0 3 + CH 3 3 . 



The rapidity with which the oxidation of oxalic acid can be 

 effected is easily capable of experimental illustration. In this tall 

 beaker, for instance, I place some ordinary black oxide or per- 

 oxide of manganese Mn0 2 , a compound which readily parts with 

 one of its two atoms of oxygen to become converted into prot- 

 oxide of manganese MnO ; while I introduce into the flask an ounce 

 or so of commercial oxalic acid. Now, upon drenching the acid 

 with hot water and pouring the resulting mixture of solution and 

 crystals upon the oxide of manganese, we get, you perceive, a 

 most rapid oxidation of the oxalic acid, accompanied by a violent 

 effervescence of carb-anhydride gas which we shall be able to re- 

 cognise in a minute or two by its high specific gravity and by its 

 power of extinguishing flame and rendering lime-water turbid. 

 The effervescence is at first so great as to be almost unmanage- 

 able, and a very slight agitation would cause the liquid contents 

 to froth over the beaker; but now that the action is a little mode- 

 rated I may prove to you the nature of the gas evolved by pour- 

 ing some of it on to a lighted taper, which you see is immediately 

 extinguished; and by pouring some more of it upon this clear 

 solution of lime, which by agitation therewith is immediately 

 converted into an opaque mixture of chalk and water. Hence, 

 when uric acid is subjected to a more powerful oxidation than 

 suffices to produce oxalic acid, we obtain carbonic acid, which, 

 like the oxalic and mesoxalic acids, is also capable of colligation 

 with urea. No ureide of carbonic acid, indeed, has yet been 

 formed directly from uric acid the active treatment required to 



