262 J P. Cooke, Jr.— Berthelot’s Thermo- Chemistry. 
Principle of Molecular Work. 
I. The quantity of heat evolved is the measure of the sum 
of the chemical and physical work accomplished in any reaction. 
Principle of Conservation of Energy. 
II. When a system of bedies—simple or compound—starting 
from a given condition undergoes either physical or chemical 
changes, which bring it into a new condition without producing 
any mechanical effect on external bodies, the amount of heat 
evolved or absorbed—as the total result of these changes— 
depends solely on the initial and final states of the system, and 
is the same, whatever may be the nature or order of the inter- 
mediate states. 
Principle of Maximum Work. 
Til. In any chemical reaction between a system of bodies 
not acted on by external forces, the tendency is toward that 
condition and those products which will result in the greatest 
evolution o 
measure of chemical affinities.” When, however, we com 
his discussion of this general principle, we are disappene to 
find that the whole subject is summarily dismissed without 
giving the reader any clear conception of the distinction be- 
tween the two modes of change whose results are so inextricably 
blended in all chemical processes. ; 
Were we able to distinguish between chemical and physical 
change, the first principle would undoubtedly give us a meast 
of what we might then clearly define as chemical affinity °F . 
