Man's physical universe

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THE MATERIALS OF THE UNIVERSE 557

Robert Boyle First Distinguished between Mixtures, Compounds, and

Elements.

Robert Boyle (1627-1691) early became a member of the

College, which consisted of a group of men who met together in

Invisible

England

from time to time to discuss philosophical and scientific questions.

They adopted the experimental and inductive method advocated by

Francis Bacon, "being satisfied that there was no certain way of arriving

at any competent knowledge unless they made a variety of experiments

upon natural bodies." This group of learned men was similar

to other groups which sprang up about the same time in Germany,

France, and Italy.

Later this group developed into the Royal Society,

one of the world's greatest scientific societies of today.

In 1661 Boyle published his book. The Sceptical Chymist, in which

he distinguished for the first time between mixtures, compounds, and

elements

I

mean by elements certain primitive and simple, or perfectly unmingled

bodies; which not being made of any other bodies, or of one another, are the

ingredients of which all those called perfectly mixt bodies are immediately

compounded, and into which they are ultimately resolved.

Chemical Changes Are Changes in the Composition of Matter.

Robert Boyle introduced the term analysis, which refers to the process

of determining the composition of a given sample of material.

Analysis is simply a method of separating materials so that their

individual properties may be observed. Some materials are obviously

heterogeneous in nature; different particles of material exhibit different

properties. Granite is an example of a heterogeneous substance;

crystals of feldspar are obviously different from the quartz in which

they are embedded. A mixture of sand, sugar, and iron filings is obviously

heterogeneous, for the white sugar particles can be separated by

dissolving the sugar in water and can be recovered by evaporation of

the water; and the iron filings may be removed with a magnet. All

such heterogeneous materials are called mixtures; the test of a mixture

is that its ingredients can be separated by physical means, that is, by

methods which do not change the composition of any of the components

of the mixture.

The sugar, on the other hand, is said to be homogeneous, because

every particle of it exhibits the same properties. Iron and sand are

likewise recognized as homogeneous materials. Any pure (homogeneous)

material of invariable composition is called a substance.

Mixtures are therefore composed of two or more substances which have

been intermingled in such a way that the substances have not been

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