An introduction to the study of chemistry / by Ira Remsen.

  • Ira Remsen
Date:
1890
Catalogue details

Licence: Public Domain Mark

Credit: An introduction to the study of chemistry / by Ira Remsen. Source: Wellcome Collection.

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    those produced by fire. Take, as another example, the rusting of iron. We all know that iron when exposed to the air undergoes a serious change, becoming covered with a reddish-brown substance which we call rust. If the piece of iron is comparatively thin, and it be allowed to lie in the air long enough, it will be completely changed to the reddish-brown substance, and no iron as such will be left. If the juices from fruits, as from apples, be allowed to stand in contact with air they undergo change, becoming sour, and a somewhat similar change takes place in milk. If we bring a spark in contact with gunpowder there is a flash and the powder disappears, dense smoke appearing in its place. Think for a moment. What are the causes of these remarkable changes? Can we learn anything about them by study? If we can, surely the study is worth un- dertaking. In those changes which have been referred to, the sub- stances changed disappeared as such. After the fire the wood or the coal, or whatever may have been burned, was no longer to be found. The rusted iron is no longer iron. The gunpowder after the fiash is no .longer gunpowder. Changes of this kind in which the substances disappear and something else is formed in their place are known as chemi- cal changes, and Chemistry is the science which has to deal with changes in the composition of substances. There are many changes taking place which do not af- fect the composition of substances. Iron, for example, may be changed in many ways and still remain iron. It may become hotter or colder. There is certainly a differ- ence between a hot piece of iron and a cold piece. Its po- sition may be changed, or, as we say, it may be moved. The difference between a piece of iron moving and a piece