Now the word “element” was and is used to mean that simplest form of matter, which, with other simplest forms goes to make up the whole world of everything in it. The earth, animals, plants, the sea, the atmosphere, are all made up of one or more of some seventy substances called elements. Hence it is clear that the earth, air and water are not, as the ancients thought, elements at all. As will be seen in this little book, both air and water consist of mixtures of elements. In chemistry such mixtures are called compounds. This word occurs again and again, so its explanation should be remembered.
One great fact must be remembered, which is at the very root of chemistry. Nothing is really lost, however much its form may be changed, or however many changes it may pass through. For instance, it may seem that when a block of wood be burned that a very large amount of it is lost. If, however, the ashes, the smoke, and the carbon that is burned by the air be all weighed, the result would be exactly the same as the weight of the original block of wood.
Again take an instance of a different nature. A lump of sugar is placed in a small glass of water. Gradually the solid is dissolved, and in time disappears. It is not lost, however. By boiling the mixture until all the water has evaporated the sugar will be found adhering as crystals on the sides of the glass. If these be carefully collected, they will be found to weigh precisely as much as the original lump of sugar.
Once more, take a block of ice weighing an ounce. Having removed it into a room, the solid will in an hour or two have disappeared entirely, but the water that has replaced the block of ice will weigh neither more nor less than an ounce. If again heat be applied to the water it will all disappear, but if weighed in a jam jar, the steam, although invisible to the eye, will still weigh one ounce exactly.
From the above-given experiments it may be seen that, however matter may change its form it cannot really be destroyed. This truth will appear in every experiment that can be performed, whether those given in this little book or in the most learned treatise on chemistry.
Chemical Affinity.
This high-sounding term means that substances have a power of uniting together that can be better explained by an experiment. Allow a few drops of water to fall on a perfectly clean piece of iron. In a short time a reddish-brown substance will appear on the iron that in ordinary language is called rust. What does this mean? Water is a compound substance composed of oxygen and hydrogen, but when brought into contact with iron the oxygen prefers to unite with the iron and sets the hydrogen free. Hence, would the chemist say, oxygen has a “stronger affinity” for iron than for hydrogen. In this case the rust is composed of rust, a combination of iron and oxygen called oxide of iron. What has taken place may be shown by the following, which will be easily understood:
Oxygen
Hydrogen