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.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

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    8 changes, the latter as chemical. Let us first select a few examples of physical changes. In winter water becomes solid, becoming liquid again on the appearance of warmer weather. All water surfaces give off vapour, and, owing to this fact, small quantities of water disappear, and things that are wet become dry on exposure to the air. This evaporation, though not so noticeable in large masses, goes on from all water surfaces without exception, the vapour thus produced descend- in o- ao-ain in the form of rain, snow, dew, &c. To take another example:— all iron structures have to be built so as to allow of a certain freedom of movement, since all such are sensibly larger in summer than in winter; the iron rails of our railways have for this reason to be laid down with small intervals between each of them. These phenomena take place without any permanent change occurring in the matter itself. Iron remains iron whether longer in summer or shorter in winter; ice or steam becomes reconverted into water with all its original properties by a mere difference of temperature. In no case has anything been added or taken away. Other examples of physical changes are the sounding of a stretched string, or of a bell when struck; the magnetisation of iron and many more will occur to all on reflection. Let us now consider some chemical changes. Iron exposed to the action of moist air becomes converted into a brown brittle material, it rusts; animal and vegetable substances so exposed gradually dis- appear; the green leaves of spring and summer become brown in the autumn, fall and rot away. In all these phenomena it will be found that the changes have gone far deeper than in the former. Substances have been produced differing widely from the substances from which they were formed, and in each case something has been added or taken away. Iron rust will be found to be heavier than the iron from which it was produced; brown leaves are lighter than the green, and so on. Just as we speak of the physical and chemical changes of any sub- stance, so also we may speak of its physical and chemical properties. For instance, a piece of sulphur is yellow; it can be scratched by a knife, but scratches apiece of chalk—that is, it has a certain hardness; when rubbed, it becomes electric—that is, it acquires the property of attracting light bodies, which it had not before. When placed in a test-tube to which heat is applied, it becomes liquid, and may even become converted into vapour; but, on removing the source of heat, the vapour condenses again to a liquid, the liquid solidifies, and assumes the ordinary form of sulphur, with which we started. All these proper- ties of sulphur are physical. During their manifestation the sulphur
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