THE ELEMENTS
Hydrogenis the lightest of all gases, and, as we have seen, the simplest of the elements, in its constitution. Like all gases, it can be liquefied, and even frozen solid into a hard lump, like ice. On the other hand, even the densestof substances can be liquefied, and even turned into gas or vapor at a sufficiently high temperature. (Gases are rendered liquid or solid at a very low temperature.) Liquid air, for example, is so cold that when a can of it is set upon a block of ice the liquid air boils and gives off “steam”!
Oxygengas constitutes about one-fifth of our atmospheric air (the other four parts being nitrogen) and is the most essential element in supporting life. Without it, life would at once become extinct. All forms of combustion take place very rapidly in oxygen, and the combustion going on within the human body is no exception to this rule. The atmospheric nitrogen acts as a sort of dilutant, being an inert gas. If a mouse be placed under a jar of pure oxygen gas, it will often run round and round until it drops dead with exhaustion. In an atmosphere of pure oxygen, we should soon burn up, and live our lives too rapidly.
Oxygen has a great tendency to combine with various other elements, particularly metals. Thus, iron rust is due to the combination of oxygen with iron; the blackening and tarnishing of cooking pots is due to the slow oxidation of copper, etc.
In breathing, we take in oxygen from the air, which combines with the gases in the lungs, forming carbon dioxide. Curiously enough, plants thrive upon this gas, which is so poisonous to human beings, and in turn give off oxygen. Hence the value of plants and flowers in the room, or in any densely inhabited area.
Nitrogenis a very important element, entering into many chemical combinations. It forms the basis of explosives, used in war. Until relatively recently, this element had to be obtained from substances dug out of the ground, but during the late war, methods were devised for obtaining it from the air. “Nitrogen fixation” became possible. If it had not been for this discovery, Germany would have had to give up the war in 1916, at the latest.
Nitrogen combines with hydrogen, to form ammonia; with oxygen and water, to form nitric acid; with nitric acid and potash to form gunpowder, etc.
Certain oxides combine with water, to form what are known asbases. Bases can combine with acids, giving rise tosalts.
Carbonis an essential element for all living matter; it combines with oxygen, to yield carbonic acid; with hydrogen, giving rise to a great number of compounds, such as benzene, turpentine, etc. Marsh gas, illuminating gas, acetylene, etc., are compounds of carbon.
Chlorineis a very important element, combining with sodium to form common salt. As we have seen, the saltness of the sea is due to this substance. Owing to its great affinity for hydrogen, chlorine decomposes water, setting free oxygen. The result of this is that a mixture of chlorine and water has strong bleaching qualities.
Chlorine also combines with hydrogen to form hydrochloric acid. On the other hand, it shows little sympathy for oxygen, forming but few stable compounds. Chloroform, so longuseful in surgical anaesthesia, is a compound of chlorine, carbon and hydrogen.
Sulphurcan assume a variety of appearances (allotrophic variation) as we have seen. Sulphuric acid, etc., are its compounds. The latter substance is used for bleaching violets, but the flowers become violet again when put into an ammonia solution.
Sodiumis a metal, which burns when thrown into water. It is the other constituent of common salt, and enters into a great variety of combinations. Carbonate of soda is one of these.
Many of the elements—iron, nickel, gold, platinum, silver, etc.,—are too well known to necessitate more than a brief note. It is interesting to notice, however, that there are certain “family relations” among a number of the elements. Thus, sodium and potassium are “related”; and so are barium, strontium and calcium. Again, oxygen and sulphur have a number of points in common,—although one is a solid and the other a gas! Gold stands rather apart from the rest.
Two very interesting groups should be mentioned in this place. The first is the group ofrare gases—argon, neon, etc.,—most of which have been discovered only recently. They are inert, and partly on account of this, and partly on account of their rarity, their discovery was so long delayed.