Volume 1

Watts' dictionary of chemistry / revised and entirely rewritten by H. Forster Morley and M.M. Pattison Muir ; assisted by eminent contributors.

Date:
1888-1894
Catalogue details

Licence: Public Domain Mark

Credit: Watts' dictionary of chemistry / revised and entirely rewritten by H. Forster Morley and M.M. Pattison Muir ; assisted by eminent contributors. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    778/796 (page 752)
    collisions among the moving molecules cannot be asserted. For instance, anhydrous alcohol and acetic acid, when mixed in equivalent proportions react upon each other at ordinary temperatures with extreme slowness ; in fact, it takes months to accomplish what at 100° requires only minutes, and yet it is highly probable that very many more collisions occur between the alcohol and the acid molecules than the rate of change would lead us to conclude. It may be that in these and similar cases the molecules of the two constituents of the system must be moving with a definite velocity if chemical action is to occur. But the kinetic theory of gases teaches that in a space of uniform temperature some molecules have high and others low velocities, and that the ratio between the numbers of mole- cules having high and those having low veloci- ties varies with the temperature; consequently the chemical change which occurs may be but a process of selection among the molecules according to the velocities they possess, those with velocities below a certain limit colliding, but not reacting chemically with, each other. As chemical reactions are generally formu- lated, the phenomena of change are for the most part at present viewed only in the light of the distribution of certain masses of matter of various kinds, and no cognisance is taken of the changes in the energies of the systems as these pass from the initial to the final states. In the blank that is at present occupied by the sign ' = ' lie all the real phenomena of the science of matter. Attempts have been made to fill up this blank by the investigation and measurement of the heat-disturbances that arise when a chemical system passes from the state repre- sented by one side of the equation to that repre- sented by the other side. By virtue of the inherent forces or affinities, as well as by the particular motions of the ultimate particles or atoms of matter, all substances may be looked upon as possessing a certain definite amount of energy, potential as well as kinetical, and con- sequently as capable of performing a definite amount of work. The tendency of the constitu- ents of a system is invariably towards a state the attainment of which involves a degradation of energy ; in other words the total energy of the system tends to fall from a higher to a lower level. (For the general inferences that have been drawn from the study of thermal phenomena bearing on the applications of the laws of energy to chemical change reference must be made to the section on thermal phenomena of the article Physical methods used in chemistry.) It is much to be desired that a classification of the elements, or, what seems more possible, of their compounds, should be attempted, based upon some particular dynamical properties which should include not only the conception of mass but also the conceptions of time and work; it is evident, however, that the difficulty lies in the kind of phenomena to be observed and measured. Mills (P. M. [5] 1) has propounded certain ideas relating to chemical phenomena, making motion the basis of the science; and he considers that chemical substances should be valued not for what they are conceived as being, but for what they are capable of doing. Doubt- less, however, the being as well as the doing must be considered together. The masses of various bodies necessary for the performance of unit of work Mills terms the dynamic equiva- lents, or the ' bergmannics,' of the respective bodies ; these may vary according to the sort of doing, or work, the several substances are em- ployed to effect; such as the power of various acids to invert sugar, or to decompose ethereal salts, the precipitability of salts, the coefficients of diffusion, <fcc, &c. For many valuable deter- minations of dynamical effects of substances in inducing or accelerating chemical changes, see the work of Ostwald. For a full account of this work v. the article Affinity. (In connexion with this article, v. the articles: Affinity ; Allotropy ; Chemical and physical properties of bodies, connexions between ; Combination, chemical ; Dissociation ; Equilibrium, chemi- cal ; Isomerism.) Additional References. Essai de Micanique chimique, Berthelot. Etudes de Dynamique chimique, Van 't Hoff. Etudes sur les Equilibres chimiques, Lemoine (a very full work on the subject). Modernen Theorien der Chemie, Meyer. Principles of Chemistry, Pattison Muir. Lehrbuch der allge- meinen Chemie, Ostwald. Chemical Action, Gladstone (T. 1855). Chemical Equilibrium, Gibbs (Trans. Connecticut Academy of Arts and Sciences, 1875. 1878). Chemical Change determined optically, Jellett (Trans. R. Irish Acad., vol. xxv.). Speed of Inversion of Cane Sugar, Influence of Acids, Heat, &c, Ureeh (B. 15, 2457; 16, 762, 2825 ; 17, 495, 1539) ; also Ostwald (J. pr. vols. 29 and 31) and Fleury (C. R. 1875). Influence of Pressure on Combustion, Frankland (T. 1861). Speed of Substitution of Bromine in the Fatty Acids, Hell and Urech (B. 13, 531). Speed of Absorption of Gases, Heurter (Monit. Scientifique, 1878); also Hood (P. M. 1884). Action of Oxides on Carbonates, Mallard (A. Ch. 1879); also Mills (C. J. 1879, 1881, and 1882). Chemical Changes in Gases (Mathematical Theory), J. J. Thomson (P.M. [5] xviii.). J. J- H. END OP THE FIBST VOLUME. Spottiswocde & Co. Printers, New-street Square, London.