text-book constructed along lines which have become recognized as best suited to an elementary treatment of the subject. At the same time they have made a consistent effort to make the text clear in outline, simple in style and language, conservatively modern in point of view, and thoroughly teachable. Show Excerpt these transformations all the other physical properties of a substance save weight are likely to change, the inquiry arises, Does the weight also change? Much careful experimenting has shown that it does not. The weight of the products formed in any change in matter always equals the weight of the substances undergoing change. ~Law of conservation of matter.~ The important truth just stated is frequently referred to as the law of conservation of matter, and this law may be briefly stated thus: Matter can neither be created nor destroyed, though it can be changed from one form into another. ~Classification of matter.~ At first sight there appears to be no limit to the varieties of matter of which the world is made. For convenience in study we may classify all these varieties under three heads, namely, mechanical mixtures, chemical compounds, and elements. [Illustration: Fig. 1] ~Mechanical mixtures.~ If equal bulks of common salt and iron filings

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