Page images
PDF
EPUB

Concluding Remarks.

We have thus tried to gain some answers to the questions with which we started, What is the composition of compounds ? What actions are compoundscapable of performing? A complete answer to either question will be an answer to both, and that answer will include the whole of chemistry.

The atom of the chemical element has been the unit with which we have had to deal ; the properties of compounds have been regarded as conditioned on the one hand by the nature, the number, and the arrangement of the elementary atoms which together form the compound molecules, and on the other hand, by the greater or smaller quantities of energy associated with these molecules. To determine the relations between the properties of various molecules, and the nature, number, and arrangement of their constituent atoms was the first part of our task; to attempt an outline of a dynamical explanation of chemical operations between molecules was the object of the second part of the undertaking.

But inasmuch as the properties which chiefly concern us as chemists, are the properties, not of individual substances, but rather of these considered as members of changing systems, it has been impossible to consider the questions arising in the first part without to a great extent making use of methods, and conceptions, more strictly belonging to the second part of our subject.

The facts connoted by the expression chemical statics were to some extent classified by the help of the hypothesis of valency, itself an outcome of the application of the molecular and atomic theory to chemical phenomena, and by the hypothesis regarding the relations between the atomic weights of the elements, and the properties of these elements and their compounds, which is known as the periodic law. The determination of physical constants, and more particularly the quantities of heat evolved or absorbed during chemical changes, the refraction-equivalents and specific rotatory powers, and the relative volumes, of typical compounds and classes of compounds, helped somewhat towards a definite knowledge of the composition of these compounds.

The study of chemical kinetics was, we found, much advanced by the dynamical hypothesis of Guldberg and Waage, which in its primary form is nearly independent of any molecular theory of the structure of matter, but in its development and application by Ostwald forms a bridge connecting the investigation of the chemical properties of molecules with that of the actions of the forces which come into play during chemical operations. The thermodynamical methods of investigation introduced by Horstmann, Gibbs and others, and the electrical methods founded on the work of Joule and Thomson, and developed by Helmholtz and Wright, also helped us to gain some conceptions of the conditions under which chemical changes proceed, and chemical equilibrium is established, and at the same time threw a little light on the most profound parts of chemical phenomena, the nature and conditions of action of the forces concerned in the combinations and decompositions of the elementary atoms.

I have tried always to exhibit the hypotheses of chemistry as at once arising from facts, and serving as guides in the quest for facts. It is especially necessary to do this, I think, in dealing with the questions concerning structural formulæ. If these formulæ are dissociated from the chemical facts which they symbolise they become intellectual tyrants; if each formula is considered simply as a summary of facts regarding the compound formulated, they are to be classed with the other brute beasts of the intellectual domain,' and cease to have much interest for one who believes that chemistry is a branch of science.

One great difficulty in using chemical hypotheses consists in determining the limits of the class of phenomena to which cach hypothesis may be applied. Berzelius carried the hypothesis of dualism too far, and it was destroyed by the more clastic hypothesis of substitution ; in our own day the hypothesis of valency has frequently been applied to phenomena with which it has little or nothing to do.

But each failure to explain all in terms of one hypothesis makes us more hopeful for the future, and convinces us that we have to deal with a living and growing part of the study of nature.

Much work has yet to be done before a general theory of chemical change can be hoped for; a theory which shall represent every process of change as a function of the atomic weights of the elements, and the affinities of the reacting substances concerned in the operation. When such a theory is attained, will chemistry be complete ? I hope not ; for

"What's come to perfection perishes.'

6

INDEX.

The numbers refer to pages.

[ocr errors]
[ocr errors][ocr errors]

ABSORPTION-SPECTRA and molecular

structure, connection between, 331
Acetic acid, density of vapour of, 205,

363
Acids, action of metals on, 92, 102, 270

affinities, relative, of, 417, 421,

422
classification of, by help of ther.

mal data, 279
Davy's and Dulong's views re-

garding, I
electrolysis of, 93
Lavoisier's views regarding, I

Liebig's views regarding, 11 2
Affinity, a unit of, use of expression in

Affinity, thermally considered, 298, 433,

443, 448
use of term by.older chemists,

401
Affinities, relative, of acids, 417, 421, 422

tables of,

439, 441
Alchemy, the conceptions underlying, 2
Allotropy, 136

experiments by Spring bear.

ing on, 137 note

thermally considered, 273
Antimony group of haloid salts con-

sidered thermally, 276
Asymmetric atoms of carbon, 323
ATKINSON, R. W., his experiments

bearing on molecular compounds, 220
Atom, Daltonian definition of, 8

definition of, obtained by apply.

ing Avogadro's law, 36
each, has a definite replacing

value, 117
function of given, dependent on

structure of molecule, 158et seq.
of oxygen is divalent, meaning of

this expression, 123 et seq.
molecule, and equivalent, the

terms contrasted, 24
Atoms and molecules, distinction be-

tween, based on reactions, 97
arrangement of, in molecules,

133 note, 149 note
double, use of by Berzelius, 19
equivalency of (see also valency),

I

116 et seq.

formula for finding maximum

number of monovalent, in a

molecule, 139
valency of (see also valency),

121, 131
valency of, in non-gasifiable

compounds, 132, 246, 463
Atomic heat of elements, 56, 64

of oxygen in oxides, 234
refractions of elements, 316

[ocr errors]

9

theory of valency, 124, 126
attempts to measure, in terms

of electromotive force, 453
Berthollet's work on, 403
Berzelius's conception of, 109,

373
classification of methods of in.

vestigating, 405
coefficients of, 409, 449
connections between, and

changes of energy, 443, 448
connections between, and law

of maximum work, 445, note
connections between, and mole-

cular structure, 468
constants, specific, general re-

marks on, 44?
constants, specific, of acids,

429, 432
general remarks on, 458
is it connected with potential

energy of atoms? 443, 445
predisposing, 376, 427
regarded from standpoint of

vortex atom theory, 450
researches of Ostwald on, 416

9

et seq.

tables of, 401
theory of Guldberg and Waage

regarding, 407 et seq.

[ocr errors]
« PreviousContinue »