Another type exists in Rhea and in the Anseriformes, greatly specialized by being spirally twisted and partly reversible like the finger of a glove.
The seats, holding two persons, are placed transversely on each side of the central passage, and have reversible backs, so that passengers can always sit facing the direction in which the train is travelling.
The existence of reactions which are reversible on slight alteration of conditions at once invalidates the principle, for if the action proceeding in one direction evolves heat, it must absorb heat when proceeding in the reverse direction.
Berthelot first accomplished the synthesis of benzene in 1870 by leading acetylene, HC: CH, through tubes heated to dull redness; at higher temperatures the action becomes reversible, the benzene yielding diphenyl, diphenylbenzene, and acetylene.
A comparison of the transformation of polymorphs leads to a twofold classification: (1) polymorphs directly convertible in a reversible manner - termed " enantiotropic " by O.
Considered thermodynamically, voltaic cells must be divided into reversible and non-reversible systems. If the slow processes of diffusion be ignored, the Daniell cell already described may be taken as a type of a reversible cell.
The cell, together with this balancing electromotive force, is thus a reversible system in true equilibrium, and the thermodynamical reasoning applicable to such systems can be used to examine its properties.
Now a well-known relation connects the available energy of a reversible system with the corresponding change in its total internal energy.
The available energy A is the amount of external work obtainable by an infinitesimal, reversible change in the system which occurs at a constant temperature T.
Any reversible cell can theoretically be employed as an accumulator, though, in practice, conditions of general convenience are more sought after than thermodynamic efficiency.
The fact that the Gibbs-Helmholtz equation is found to apply also indicates that the lead accumulator is approximately reversible in the thermodynamic sense of the term.
If secondary effects are eliminated, the deposition of metals also is a reversible process; the decomposition voltage is equal to the electromotive force which the metal itself gives when going into solution.
But his best known contribution to general chemistry is his work on the phenomena of reversible reactions, which he comprehended under a general theory of " dissociation.
There were arrangements for the brilliant illumination of the choir and its relief, which was sometimes sculptured on both sides and reversible, while the podia were intentionally more obscure.
Passed through a red-hot tube, benzene vapour yields hydrogen, diphenyl, diphenylbenzenes and acetylene; the formation of the last compound is an instance of a reversible reaction, since Berthelot found that acetylene passed through a red-hot tube gave some benzene.
The object of the present article is to illustrate the practical application of the two general principles - (I) Joule's law of the equivalence of heat and work, and (2) Carnot's principle, that the efficiency of a reversible engine depends only on the temperatures between which it works; these principles are commonly known as the first and second laws of thermodynamics.
If, starting from E, the same amount of heat h is restored at constant pressure, we should arrive at the point F on the adiabatic through B, since the substance has been transformed from B to F by a reversible path without loss or gain of heat on the whole.
In virtue of relations (2), the change of entropy of a substance between any two states depends only on the initial and final states, and may be reckoned along any reversible path, not necessarily isothermal, by dividing each small increment of heat, dH, by the temperature, 0, at which it is acquired, and taking the sum or integral of the quotients, dH/o, so obtained.
- In order that a process may be strictly reversible, it is necessary that the state of the working substance should be one of equilibrium at uniform pressure and temperature throughout.
In any small reversible change in which the substance absorbs heat, dH, from external sources, the increase of entropy, d0, must be equal to dH/9.
If the change is not reversible, but the final state is the same, the change of entropy, do, is the same, but it is no longer equal to dII/B.
In the special case of a substance isolated from external heat supply, dH=o, the change of entropy is zero in a reversible process, but must be positive if the process is not reversible.
The leaves are reversible, and provided with a notch at one end and a point at the other, so that they can be used for either forward or reverse laying.
Special reversible paddle steamers (called doubleenders) were designed for service in the inlets and estuaries, and sixty-six ironclads were built and employed during the four years.
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.
A carefully made ship's compass is usually employed, though in some cases the compass card, with its attached magnets, is made reversible, so that the inclination to the zero of the card of the magnetic axis of the system of magnets attached to the card can be eliminated by reversal.
In the absence of such a reversible card the index correction must be determined by comparison with a unifilar magnetometer, simultaneous observations being made on shore, and these observations repeated as often as occasion permits.
Artificial membranes are seldom or never perfectly semi-permeable - some leakage of solute nearly always occurs, but the imperfections of actual membranes need no more prevent our use of the ideal conception than the faults of real engines invalidate the theory of ideal thermodynamics founded on the conception of a perfect, reversible, frictionless, heat engine.
Such an arrangement may be put through a cycle of operations as in Carnot's engine (see Thermodynamics) and all the laws of reversible engines applied to it.
The available energy A is the work which may be gained from the system by a small reversible isothermal operation with an osmotic cylinder, that is Pdv.
The Hungarian peasants are very fond of their natural brown sheep coats, the leather side of which is not lined, but embellished by a very close fancy embroidery, worked upon the leather itself; these garments are reversible, the fur being worn inside when the weather is cold.
Nevertheless, the theoretical possibility, and its realization in many cases, has brought considerations to the front which have recently become of predominant interest; consequently the possible transformations of isomers and polymers will be considered later under the denomination of reversible or dynamical isomerisms.
Nevertheless, the relations obtained in reversible cases such as sulphur have not yet found application in the highly interesting cases of ordinary irreversible isomerism.
A further step in this direction has been effected by the introduction of reversibility into a non-reversible case by means of a catalytic agent.
The formation of an ester by the interaction of an acid with an alcohol is a "reversible" or "balanced" action, for as M.
Jour., 1870, 196, p. 230), in which air is drawn over a heated mixture of manganese dioxide and sodium hydroxide, the sodium manganate so formed being then heated to about 450° C. in a current of steam, the following reversible reaction taking place: 4NaOH+2Mn02+ 022Na2Mn04+2H20.
But as this reaction is reversible, we must observe the conditions necessary for directing it in the right sense.
The temperature must not be allowed to rise beyond a certain point, for the reaction NaC1+ NH 4 HC03= NaHCO 3 4-NH 4 C1 is reversible, and at a temperature of about 60° or 70° C. it is in fact practically going the wrong way, viz.
The reversible character of the principal reaction has the consequence that a considerable portion of the sodium chloride (up to 33%) is lost, being contained in the waste calcium chloride solution which issues from the ammonia stills.
A reversible level d rests on the accurately turned pivots of this axis.
- Following on the discovery in 1873 of the reversible action of the dynamo and its use as a motor, efforts began to be made to apply this knowledge to transmission of power, and S.
He has also found that this action is reversible, for when the area of the surface of contact of the acid and mercury is made to increase, an electric current passes from the mercury to the acid, the amount of electricity which passes while the surface increases by one square centimetre being sufficient to decompose.
Arrhenius, who hold that the union of toxin and antitoxin is comparatively loose, and belongs to the classof reversible actions, being comparable in fact with the union of a weak acid and base.
It may be stated that while in certain instances the union of toxin and antitoxin may be reversible, all the facts established cannot be explained on this simple hypothesis of reversible action.
We are probably safe in saying, however, that the molecules of a toxin are not identical but vary in the degree of their combining affinities, and also in their toxic action, and that, while in some cases the combination of anti-substances has been shown to be reversible, we are far from being able to say that this is a general law.
Another difficulty arose from the fact that the reaction S02+O=S03 is reversible, the opposite reaction, SO 3 = S0 2 -f 0 setting in but little above the temperature required for the synthesis of SO 3.
In water-cooled condensers it is usual to arrange that the water passes through a large number of small pipes contained in a larger one through which the gas flows, and as it constantly happened that condenser pipes became choked by naphthalene, the so-called reversible condenser, in which the stream of gas may be altered from time to time and the walls of the pipes cleaned by pumping tar over them, is a decided advance.
The coloration is due to the production of unstable compounds of the ferrous salt and nitric oxide, and it seems that in neutral solutions the compound is made up of one molecule of salt to one of gas; the reaction, however, is reversible, the composition varying with temperature, concentration and nature of the salt.