124: GENERAL PRINCIPLES OF THERMO-CHEMISTRY. 



Exothermal reactions are, as has just been said, the only ones 

 which can be effected without the aid of a foreign energy. 

 However, they often require, in order to start them, the inter- 

 vention of a certain preliminary work, analogous to ignition. 



Theorem IV. An exothermal reaction which does not take place 

 of itself at a certain temperature, can almost always take place of 

 itself at a higher temperature, that is to say, in virtue of the 

 work of heating. 



Theorem V. It can likewise take place at the ordinary tempe- 

 rature, with the aid of a suitable auxiliary work, and especially 

 with the aid of chemical work, due to a simultaneous and 

 correlative reaction. 



Theorem VI. Within the limits of temperature at which 

 exothermal reactions take place, they do so, generally speaking, more 

 rapidly the higher the temperature. 



Theorem VII. Successive transformations can only take place 

 directly without the intervention of foreign energies, if each of 

 the transformations, regarded separately, as well as their definite 

 sum, be accompanied by a liberation of heat. 



In other words, the energy proper to a system may be ex- 

 pended either all at once, or little by little, and according to 

 several distinct cycles, but there cannot be a gain of energy, due 

 to the internal actions alone, in any of the intermediate changes. 

 We shall give lastly, a theorem of the greatest importance in 

 the study of saline and many other reactions. 



Theorem VIII. Every chemical reaction capable of "being 

 accomplished without the aid of preliminary work and indepen- 

 dent of the intervention of an energy foreign to that of the bodies 

 present in the system, is of necessity produced, if it liberate heat. 



It is in virtue of the third principle that the forecast of chemical 

 phenomena is reduced to the purely physical and mechanical 

 notion of maximum work effected by the molecular actions. 



5. Numerical Tables. 



The following tables give the principal data relative to the 

 quantities of heat liberated by the formation of compounds used, 

 or capable of being used, as explosives. 



In these tables the authorities for the different determinations 

 are indicated by their initials, viz. : 



Al = Alluard Gh = Graham Pf = Pfaundler 



An = Andre* G = Grassi Rech = Rechenberg 



A = Andrews Ha = Hammerl R = Regnault 



B = Berthelot H = Hautefeuille Sab = Sabatier 



Cal = Calderon Hs = Hess Sa = Sarrau 



Ch = Chroutschoff Jo = Joannis S = Silbermann 



Ds = Desains L = Louguinine T = Thomsen 



Dv = Deville M = Mitscherlich Tr = Troost 



Dt = Ditte Og = Ogier Vie = Vieille 



D = Dulong P = Person Vi = Vielle 



F = Favre Pett = Pettersen W = Woods 



%* The authority preferred is bracketed ; F. & S. [T]. 



