This great discovery caused a new theory of matter to be developed. Dalton had suggested, when applying the atomic theory to chemistry, that when two elements combine to form a third substance, it is probable that one atom of one element joins itself to one atom of the other, unless some exceptional condition exists. When water is formed by bringing oxygen and hydrogen together, he supposed that one atom of oxygen combined with one atom of hydrogen. Gay-Lussac subsequently proved that not only does one volume of oxygen combine with two volumes of hydrogen (not one as Dalton believed) in the production of water, but that nitric and carbonic acid gases combine with ammonia gas in the ratio of 1:1 or 1:2. He also demonstrated that one volume of nitrogen united with three of hydrogen form ammonia, and that carbonic oxide burning in a mass of oxygen consumes half its volume of oxygen. He concluded from these and other facts that gases always combine together in simple proportions by volume and that the apparent contraction of volume they show on combining bears a similar simple relationship to the volume of one or more of the gases.
Avogadro, working on Gay-Lussac's experimental data, suggested that the number of integral molecules in any gas is always the same for equal volumes, or is always proportional to the volumes. He also suggested that equal volumes of different gases at the same pressure and temperature contain the same number of molecules. Experiments on alcohol made by Williamson raised doubts as to the validity of Avogadro's hypotheses when applied to chemical combinations. These doubts were cleared in 1860, when the new chemical atomic weights and formulæ were introduced into English textbooks.
The molecular theory of matter derived from these experiments supposes that all visible forms of matter are aggregations of simpler and smaller chemical elements. Mendeléeff and Newlands showed that the physical and chemical properties of the elements are functions of their atomic weights.
Investigations of radioactivity and the observations based upon the passage of electric currents through gases have recently modified our views with respect to the atomic theory, but these points will be dealt with in the chapter dealing with radiation.
Questions regarding the eventual loss of energy in matter are best studied in gases. A considerable number of important investigations are now being carried on in Europe with the view of tracing the interchanges of molecular energies in gas molecules. Maxwell and other investigators found long ago that the motion of molecules cannot go on perpetually. The energy of motion will in time be frittered away by friction, air resistance, collisions with other molecules, vibrations set up by collisions, and other molecular movements. It has been found that the energy which is dissipated by air resistance is transformed into energy in the air. That which is lost by collisions is converted into internal vibrations within each molecule. The question now arises as to what effects are exerted on a gas. It involves the effects of the communicated internal molecular vibrations and their transference of energy to the surrounding medium. What is known as the Quantum dynamic theory has been proposed to account for this phenomena. Quantum dynamics appear to be distinct from the Newtonian.
Carnot and Clausius discovered that the motive power of heat is independent of the agents brought into play for its realization. The motive power of a waterfall depends, for example, on its height and on the quantity of water falling within a given time. Clausius stated the Carnot idea in mechanical terms by saying: That in a series of transformations, in which the final is identical with the initial stage, it is impossible for heat to pass from a colder to a warmer body unless some other accessory phenomenon occurs at the same time. A heat motor, which, after a series of transformations, returns to its initial state, can only supply work, or power, if there exist two sources of heat, and if a certain quantity of heat is given to one of the sources which can never be the hotter of the two. The output of a reversible machine working between two given temperatures is greater than that of any nonreversible engine, and it is the same for all reversible machines working between these two temperatures.
Clausius showed that this principle conduces to the definition of an absolute scale of temperature and there is another factor assisting in restoring physical equilibrium which he termed entropy. It is a variable which, like pressure or volume, serves concurrently with another variable to define the state of a body.
These discoveries of Carnot and Clausius showed the impossibility of finding a source of perpetual motion and helped to solve many of the difficulties in securing efficiency from internal combustion engines. Industrial, as well as scientific results of immense importance have developed from these principles.
Theories on the compressible fluids and elastic equilibrium were developed as the result of work done between 1875 and 1896 by J. W. Gibbs, Helmholtz, Duhem, and others on internal thermodynamic potentials. These theories have proved of incalculable value in elucidating electrical and radiation phenomena.
Another discovery of Gibbs, made in 1876, has also had brilliant results. It is known as the Phase Law. The homogeneous substances into which a material system is divided is called a phase. Carbonate of lime, lime, and carbonic acid gas are the three phases of a system which comprises Iceland spar partially dissociated into lime and carbonic acid gas. The number of phases, combined with the number of independent bodies entering into the reactions, fixes the general form of the law of equilibrium of the system. This discovery of Gibbs has resulted in greatly extending the field of physics. It is of importance in molecular and atomic investigations, in osmosis, electrolysis, and in most questions dealing with thermodynamics.