CONCLUSIONS 171 



the hydrogen of this group that is capable of being replaced 

 by a metal or an organic radicle, forming a salt or ethereal salt 

 respectively. For example, acetate of sodium is CH3.C0(0Na), 

 and acetic ether is CH3.CO(OC2H5). It follows that a dibasic 

 acid must contain two CO(OH) groups, and a tribasic acid 

 three. A glance at the formulae of the organic acids given on 

 p. 154, shows that this can be the case; indeed, oxalic acid 

 is obviously composed of 2C0(0H). A study of all organic 

 compounds shows how exactly are their chemical, as well as 

 their physical properties, in accordance with their molecular 

 constitution. 



Very early in these Studies the relation was observed between 

 heat and the force of chemical attraction. A large number 

 of additional facts have now been deduced, which show that, 

 when chemical combination occurs, heat, or sometimes light 

 or electricity, are produced, and, conversely, to decompose 

 a chemical compound, heat, or sometimes light or electricity, 

 are required. Energy is never lost; there is a definite rela- 

 tion between the energy employed and the work done : the 

 heat. of combustion of two elements is a means of measuring 

 their chemical attraction; the amount of a chemical com- 

 pound decomposed by an electric current is a means of 

 measuring the quantity of electricity used. 



This conservation of energy is well illustrated in the chemical 

 processes of the animal and vegetable worlds. The chemical 

 changes in the leaves of plants are essentially processes of re- 

 duction, carbonic acid gas and water being used, and carbo- 

 hydrates and oxygen being produced. The chemical changes 

 in the animal are essentially processes of oxidation, carbo- 

 hydrate and oxygen being used, and carbonic acid gas and water 

 produced. The former is a heat-absorbing, the latter a heat- 

 producing, change. The energy derived from the sun's heat 

 and light is stored as chemical energy in the combustible con- 

 stituents of food, and the oxygen set free, until, when con- 

 sumed as animal food, recombination takes place, and heat 



