A short manual of inorganic chemistry / by A. Dupré and H. Wilson Hake.

  • August Dupré
Date:
1892
Catalogue details

Licence: Public Domain Mark

Credit: A short manual of inorganic chemistry / by A. Dupré and H. Wilson Hake. Source: Wellcome Collection.

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    supposed to be made up in almost every case of still smaller particles (called atoms*), which are to our present means indivisible, f These molecules are of course exceedingly minute, far more minute than the smallest particles visible under our microscopes, but having nevertheless a definite size and weight. The probable size, or, rather, the limits of size of these molecules has been calculated by Sir W. Thomson, who finds that their diameter ranges probably between 0-000000001 and 0-00000000005 of a millimetre, or something like from ten thousand to two hundred thousand times smaller than the smallest particle visible under our best microscopes. In order to convey some notion as to size, which the above figures entirely fail to do, Sir W. Thomson gives us the following illustration:—Suppose we could magnify an ordinary drop of water to the size of a globe equal to our earth, then the molecules of the water would become visible, and would be found to be larger than small shot, but smaller than cricket-balls. Matter, then, is made up of molecules, not in actual contact, but kept at certain distances apart. We have further every reason to believe that these molecules are in unceasing motion (see ch. vi., p. 38). Solids, Liquids, and Gases.—The special properties and conditions of any particular kind of matter depend, as we shall see more clearly later on, upon the nature of the atoms which make up the molecule, the dis- tances at which the molecules are from one another, and the character and extent of their motion. The molecules of solids and liquids are held together by a force of attraction called cohesion.X If this force is so power- ful as to keep the molecules firmly bound together, a solid substance is the result. In a solid the molecules are not free to move, but retain their relative position; the solid has a definite shape which it retains unless this * a.Tou.0}, uncut, indivisible. t The molecules in any given compound or element are identical inter se, and this identity as regards kind of matter, extends in the case of an element to the atoms, whereas, the atoms in the molecule of a compound are essentially different, being composed of dif- ferent kinds of matter. The fact may be diagrammatically expressed thus:— Element. Compound. t Coheereo, I stick together.
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