An irreversible process which permits a more complete experimental investigation is the steady flow of a fluid in a tube already referred to in section to.
Dolezalek, however, has attributed the difference to mechanical hindrances, which prevent the equalization of acid concentration in the neighbourhood of the electrodes, rather than to any essentially irreversible chemical action.
In any spontaneous irreversible change, if the system is heat-isolated, there must be an increase of entropy.
Nevertheless, the relations obtained in reversible cases such as sulphur have not yet found application in the highly interesting cases of ordinary irreversible isomerism.
The majority of thermodynamical problems may be treated without any reference to entropy, but it affords a convenient method of expression in abstract thermodynamics, especially in the consideration of irreversible processes and in reference to the conditions of equilibrium of heterogeneous systems.
A common illustration of an irreversible process is the expansion of a gas into a vacuum or against a pressure less than its own.
This inequality holds in all cases, but cannot in general be applied to an irreversible change, because Od4 is not a perfect differential, and cannot be evaluated without a knowledge of the path or process of transformation.
A very important evolutionary principle is that in such secondary returns to primary phases lost organs are never recovered, but new organs are acquired; hence the force of Dollo's dictum that evolution is irreversible from the point of view of structure, while frequently reversible, or recurrent, in point of view of the conditions of environment and adaptation.
Now the unstable movements of the needles are of a mechanically irreversible character; the energy expended in dissociating the members of a combination and placing them in unstable positions assumes the kinetic form when the needles turn over, and is ultimately frittered down into heat.
In this irreversible catena proceeding from ground to consequent, we have left far behind such things as the formal parity of genus and differentia considered as falling under the same predicable, 3 and hence justified in part Porphyry's divergence from the scheme of predicables.