A text-book of inorganic chemistry / by Dr. A.F. Holleman ... Issued in English in coöperation with Hermon Charles Cooper.

  • Arnold F. Holleman
Date:
1912
Catalogue details

Licence: In copyright

Credit: A text-book of inorganic chemistry / by Dr. A.F. Holleman ... Issued in English in coöperation with Hermon Charles Cooper. Source: Wellcome Collection.

    47/556 page 27
    21J COMPOSITION OF COMPOUNDS—ATOMIC THEORY. sulphur is constant and can be accurately determined; that of a mixture of tin and lead differs according to the jiroportion of the elem'uits and is in many ])ro})ortions not at all sharp, there being only a softening instead of real fusion. hi the examples cited here the distinction between a compound and a mixture is well marked. There are, however, other instances where this is i.ot the case and where it is therefore very difficult to know whether one is dealing with a compound or a mixture. We shall meet with many examples of this later. There is, however, one way whereby a compound can l)c distinguishetl from a mixture, viz., by ascertaining whether or not the substance, prepared in different ways, has a constant composition. ITIENC^.MEN.y ACCOMPANYING THE FORMATION OR DECOMPOSITION OF A COMPOUND. dlie most common phenomenon of this sort is an ele-\'ation or depression of temperature, i.e. an evolution or absorption of heat (caloric effect). Sometimes the rise of teiu{)erature is so great that light is produced. A decomposition or a combination can l)e so violent that it causes an explosion. In other instances electricity may be produced by chemical action. All these facts may be com- prised in this statement: Chemical action results in a change in the energy-supply of the reacting substances. EXPLANATION OF THE CONSTANT COMPOSITION OF COMPOUNDS.—A'rOMIC THEORY. 21. It was stated that constant composition is tlie distinctive characteristic of a chemical compound. 'Fhe proportions in which elements unite to form a certain compound are always the same. This Law of Constant Composition (definite proportions) was finally established by Proust in the beginning of the nineteenth century, and at about tlie same time Dalton offered an exjda- nation of it whicli is still accepted and may be considered as tlie foundation of theoretical chemistry. This explanation involves a hvpotliesis as to the constitution of matter. It is possible to regard matter as infinitely divisible; according to human concejition the smallest particle that can really be obtained is still capable of division into an infinite miml)ei of others. However, even the ancients were of the opinion that there
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