WHAT CHEMISTRY IS—THE ELEMENTS—METALLIC AND NON-METALLIC—ATOMIC WEIGHT—ACIDS—ALKALIS—BASES—SALTS—CHEMICAL COMBINATION AND STUDY.

Chemistry is the science of phenomena which are attended by a change of the objects which produce them. We know that when a candle burns, or when wood is burned, or even a piece of metal becomes what we term “rusty,” that certain chemical changes take place. There is a change by what is termed chemical action. Rust on iron is not iron; it is oxide of iron. The oxygen of the air causes it. So we endeavour, by Chemistry, to find out the nature of various bodies, their changes, and the results.

In nature we have simple and compound bodies. The former are called Elements. We must not confuse these elements with the so-called elements—earth, air, fire, and water. These are really compound bodies. An element is a substance or a gas which is not composed of more than one constituent; it is itself—a compound of perfectly identical particles. Every “compound” body, therefore, must be made up of some of the elements, of which there are sixty-five. These bodies are divided into non-metallic and metallic elements, and all bodies are composed of them, or are these bodies themselves. The list is as follows. The non-metallic elements are “metalloids.” We have omitted fractions from the weights, on which chemists differ.

TABLE OF ELEMENTS WITH THEIR CHEMICAL SYMBOLS AND COMBINING WEIGHTS.

METALS.

The term “combining weight” requires a little explanation. We are aware that water, for instance, is made up of oxygen and hydrogen in certain proportions. This we will prove by-and-by. The proportions are in eighteen grains or parts of water, sixteen parts (by weight) of oxygen, and two parts (by weight) of hydrogen. These are the weights or proportions in which oxygen and hydrogen combine to form water, and such weights are always the same in these proportions. Chemical combination always occurs for certain substances in certain proportions which never vary in those compounds, and if we wish to extract oxygen from an oxide we must take the aggregate amount of the combining weights of the oxide, and we shall find the proportion of oxygen; for the compound always weighs the same as the sum of the elements that compose it. To return to the illustration of water. The molecule of water is made up of one atom of oxygen and two atoms of hydrogen. One atom of the former weighs sixteen times the atom of the latter. The weights given in the foregoing table are atomic weights, and the law of their proportions is called the Atomic Theory.

An atom in chemistry is usually considered the smallest quantity of matter that exists, and is indivisible. A molecule is supposed to contain two or more atoms, and is the smallest portion of a compound body. The standard atom is hydrogen, which is put down as 1, because we find that when one part by weight of hydrogen is put in combination, it must have many more parts by weight of others to form a compound. Two grains of hydrogen, combining with sixteen of oxygen, makes eighteen of water, as we have already seen.

Take an example so plainly given by Professor Roscoe, remembering that the numbers in our table represent the fixed weight or proportion by weight in which the simple body combines. The red oxide of mercury contains sixteen parts by weight of oxygen to two hundred parts by weight of mercury (we see the same numbers in the table); these combined make two hundred and sixteen parts of oxide. So to obtain 16 lbs. of oxygen we must get 216 lbs. of the powder. It is the same all through, and it will be found by experiment that if any more parts than these fixed proportions be taken to form a compound, some of that element used in excess will remain free. Lime is made up of calcium and oxygen. We find calcium combining weight is forty, oxygen sixteen. Lime is oxide of calcium in these proportions (by weight).

When we wish to express the number of atoms in a compound we write the number underneath when more than one; thus water is H₂O. Sulphuric acid H₂SO₄. As we proceed we will give the various formulÆ when considering the chief elements.

In chemistry we have acids, alkalis, and salts, with metallic oxides, termed bases, or bodies, that when combined with acids form salts. Alkalis are bases.

Acids are compounds which possess an acid taste, impart red colour to vegetable blues, but lose their qualities when combined with bases. Hydrogen is present in all acids. There are insoluble acids. Silicic acid, for instance, is not soluble in water, has no sour taste, and will not redden the test litmus paper. On the other hand, there are substances (not acids) which possess the characteristics of acids, and most acids have only one or two of these characteristics.

Thus it has come to pass that the term “acid” has in a measure dropped out from scientific nomenclature, and salt of hydrogen has been substituted by chemists. For popular exposition, however, the term is retained.

Alkalis are bases distinguished by an alkaline taste. The derivation is from Arabic, al-kali. They are characterized by certain properties, and they change vegetable blues to green, and will restore the blue to a substance which has been reddened by acid. They are soluble in water, and the solutions are caustic in their effects. Potash, soda, and ammonia are alkalis, or chemically, the oxides of potassium, sodium, ammonium, lithium, and cÆsium are all alkalis. Potash is sometimes called “caustic” potash. There are alkaline earths, such as oxides of barium, strontium, etc. Bases may be defined as the converse of acids.

Acids and alkalis are then evidently opposite in character, and yet they readily combine, and in chemistry we shall find that unlike bodies are very fond of combining (just as opposite electricities attract each other), and the body made by this combination differs in its properties from its constituents.

Salts are composed of acids and bases, and are considered neutral compounds, but there are other bodies not salts, which likewise come under that definition—sugar, for instance. As a rule, when acids and alkalis combine salts are found.

Chemical phenomena are divided into two groups, called inorganic and organic, comprising the simple and compound aspects of the subject, the elementary substances being in the first, and the chemistry of animals or vegetables, or organic substances, in the latter. In the inorganic section we shall become acquainted with the elements and their combinations so often seen as minerals in nature. Chemical preparations are artificially prepared. To consider these elements we must have certain appliances, and indeed a laboratory is needed. Heat, as we have already seen, plays a great part in developing substances, and by means of heat we can do a great deal in the way of chemical decomposition. It expands, and thus diminishes cohesion; it counteracts the chemical attraction. Light and electricity also decompose chemical combinations. But before proceeding it will be as well to notice a few facts showing how Nature has balanced all things.

The earth, and its surrounding envelope, the atmosphere, consist of a number of elements, which in myriad combinations give us everything we possess,—the air we breathe, the water we drink, the fire that warms us, are all made up of certain elements or gases. Water, hydrogen and oxygen; air, oxygen and nitrogen. Fire is combustion evolving light and heat. Chemical union always evolves heat, and when such union proceeds very rapidly fire is the result.

In all these combinations we shall find when we study chemistry that not a particle or atom of matter is ever lost. It may change or combine or be “given off,” but the matter in some shape or way exists still. We may burn things, and rid ourselves, as we think, of them. We do rid ourselves of the compounds, the elements remain somewhere. We only alter the condition. During combustion, as in a candle or a fire, the simple bodies assume gaseous or other forms, such as carbon, but they do not escape far. True they pass beyond our ken, but nature is so nicely balanced that there is a place for everything, and everything is in its place under certain conditions which never alter. We cannot destroy and we cannot create. We may prepare a combination, and science has even succeeded in producing a form like the diamond—a crystal of carbon which looks like that most beautiful of all crystals, but we cannot make a diamond after all. We can only separate the chemical compounds. We can turn diamonds into charcoal it is true, but we cannot create “natural” products. We can take a particle of an element and hide it, or let it pass beyond our ken, and remain incapable of detection, but the particle is there all the time, and when we retrace our steps we shall find it as it was before.

This view of chemistry carries it as a science beyond the mere holiday amusement we frequently take it to be. It is a grand study, a study for a lifetime. Nature is always willing, like a kind, good mother as she is, to render us up her secrets if we inquire respectfully and lovingly. The more we inquire the more we shall find we have to learn. In these and the following pages we can only tell you a few things, but no one need be turned away because he does not find all he wants. We never do get all we want in life, and there are many first-rate men—scientists—who would give “half their kingdom” for a certain bit of knowledge concerning some natural phenomena. There are numerous excellent treatises on chemistry, and exhaustive as they are, at present they do not tell us all. Let these popular pages lead us to the study of nature, and we shall find our labour far from onerous and full of interest, daily increasing to the end, when we shall know no more of earth, or chemistry.

As a preliminary we will put our workshop aside, and show you something of Chemistry without a Laboratory.