CALORIE VALVES FROM ANALVSLS '2:i 



from its chemical lormula. The amount of heat e\ol\ ed when 

 C is oxidised to CO2 and when 2H is combined with O to form 

 water has been determined. The equations of these two reactions 

 could therefore be written : 



C + O2 = CO2 + 94-31 Cals. 

 2Ho + O2 = 2H0O + 136(5 Cals. 



(A horizontal line above the formula of a substance in a thermo-chemical 

 equation indicates that the substance is in the gaseous state, the absence of 

 any line indicates the liquid state, while a line below the formula indicates the 

 solid state. The suffix aq is intended to convey the idea that the substance 

 is in solution in such a large volume of water that the addition of more water 

 would not produce any appreciable effect — that is, the substance is so dilute 

 that its heat of dilution on the further addition of water would be negligible.) 



One must note that any alteration of gaseous volume or of 

 any other physical characteristic of any of the reacting units 

 would, by utilising some energy as positive or negative work, 

 produce an alteration in the amount of heat evolved. Welter 

 enunciated a rule whereby one might arrive at an approximate 

 value of the heat of oxidation of a compound containing oxygen 

 as well as carbon and hydrogen. According to this rule the 

 oxygen is subtracted from the molecular formula with as much 

 hydrogen as would serve to convert it completely into water; 

 the heat of oxidation of the carbon and hydrogen in the residue 

 then gives a rough value of the heat of oxidation in the whole 

 compound. For example : 



Tri-olein has the formula . . . C^^Hk^^Oq 



Deduct intramolecular water (6H2O) . H^gOg 



Leaving for oxidation .... Cg^Hgg 

 Heat of combustion .= 57 X 94-3 + 92 X 34-15 



= 53751 + 3141-8 



= 8517 Calories. 



That is, a gram molecule (884 grams) of triolein in being completely 

 oxidised to CO2 + HgO would liberate 8517 Cals. of heat, approxi- 

 mately 9-3 Calories per gram. Similarly, the energy stored in the 

 form of carbohydrate may be calculated : 



Glucose = CgHigOfi 



Intramolecular water = Hi20g 



For oxidation = 6C 



6C + 6O2 = 6CO2 + 566 Calories, 

 approximately 3-2 Calories per gram. 



