522 THE THEORY OF ENERGY AND THE LIVING WORLD. 



amount of heat required to raise the temperature 1 degree of a kilogram 

 of water (large calorie) or 1 gram of water (small calorie). It has been 

 shown that whatever be the phenomena which serve in an intermediary 

 manner to accomplish the transformation, it always requires 425 kilo- 

 gram-meters to create 1 calorie, or 0.00234 calorie to create 1 kilogram- 

 meter. The number 425 is the mechanical equivalent of the calorie, or, 

 as it is inaccurately said, of heat. This fact constitutes the principle 

 of the equivalence of heat and mechanical work. 



Chemical activity has not as yet been measured directly. But it has 

 been shown that chemical activity can engender all the other kinds of 

 energy. It is, indeed, the commonest source of them all, and is prin- 

 cipally utilized to obtain heat, electricity, and mechanical energy. In 

 the steam engine, for example, the power is derived from the com- 

 bustion of carbon by oxygen of the air, which produces the heat 

 required to vaporize the water, develop the force of vapor, and finally 

 to drive the piston. The theory of the steam engine may be reduced 

 to two propositions: Chemical activity engenders heat, heat engenders 

 motion. Or to employ language to which no doubt the reader is accus- 

 tomed, chemical energy is transformed into heat energy, and the latter 

 into mechanical energy. The transformations are all governed by fixed 

 numerical rules. 



Our knowledge of chemical energy is less advanced than that of heat 

 and mechanical motion. There have been as yet no applications to its 

 transformations of processes of measurement suitable for direct numer- 

 ical verification. It can only be affirmed, not quantitatively demon- 

 strated, that chemical and heat energies are equivalent, for in the pres- 

 ent state of science it is impossible to measure chemical energy. The 

 known forms of energy may be expressed as the product of two factors. 

 Thus mechanical energy of motion is measured by the product of the 

 mass by the velocity; heat energy by the product of the temperature 

 and the specific heat; electrical energy by the product of the quantity 

 of electricity by the electro-motive force. As regards chemical energy, 

 it is suspected that it may be directly measured according to the sys- 

 tem of Berthollet as revised by the Norwegian chemists, Guldberg and 

 Waage, by the product of the mass by a force or coefficient of affinity, 

 which depends on the nature of the substance taken, the temperature, 

 and other physical conditions of the reaction. In another direction 

 the admirable researches of M. Berthelot have enabled us to make an 

 indirect evaluation in a majority of cases through the heat equivalent 

 of reactions. 



It is interesting to note that chemical energy also appears on the 

 face of things to have two states, of potential and real energy. The 

 union of carbon and oxygen in their combustion in the furnace of a 

 steam engine must first be started by a preliminary lighting, just as a 

 weight raised and left stationary at a certain height must be detached 

 from its support by a small expenditure of work. This condition of 



