142 ANIMAL CHEMISTRY LECTURE VI. 



view seems at first sight altogether discordant with the similar 

 excretion of urate of ammonia by birds and insects, whose motions 

 are so active and temperatures so high. But by having regard 

 to the following considerations, it will, I think, appear that the 

 loss, or rather non-liberation, of force resulting from the merely 

 half-burning, so to speak, of the excess of carbon excreted as uric 

 acid, is less than at first sight appears, and is, moreover, largely 

 compensated for by certain consequent advantages. 



(149.) For reasons which I cannot now discuss, the experi- 

 mental results actually obtained on the quantities of heat evolved 

 by the combustion of carbon into carbonic oxide and anhydride 

 respectively, are not applicable to the point we have under our 

 consideration, which at present therefore can only be decided 

 from analogy and general principles. Let us then imagine the 

 production of carbonic oxide and anhydride under conditions as 

 nearly as possible analogous. Let us conceive, for instance, that 

 an atom of carbon first unites with an atom of oxygen gas to form 

 solid carbonic oxide CO, which then unites with a second atom 

 of oxygen gas to form solid carb-anhydride CO 2 . Remembering, 

 as explained in my fourth lecture, that the heat produced by any 

 combination is the exact measure of the force required to sepa- 

 rate the constituents of the compound from one another, and is, 

 indeed, only a setting free of the heat which at some time or 

 other was absorbed in the act of their separation, it will fol- 

 low, provided the two atoms of oxygen in carb-anhydride are 

 retained by the carbon with an equally strong affinity, that the 

 amount of heat evolved by the combustion of carbon into solid 

 carbonic oxide will be just one half of that evolved by its com- 

 bustion into solid carb-anhydride. But we have good reason for 

 believing that the first atom of oxygen in carb-anhydride is more 

 firmly retained than the second atom, and consequently that the 

 amount of heat liberated by the combination of the first atom is 

 greater than that liberated by the combination of the second atom 

 of oxygen; or, in other words, that the heat evolved in the pro- 

 duction of solid carbonic oxide CO, is more than half of that 

 evolved in the production of solid carb-anhydride C0 2 . 



