Just as hydrogen burns in the air, so it burns in chlorin. The burning of hydrogen in air or oxygen is, as we have seen, simply the combination of hydrogen and oxygen, the product being water in the form of vapor, and therefore invisible. When hydrogen burns in chlorin, the action consists in the union of the two gases, the product being hydrochloric acid, HC1, which forms clouds in the air. The two gases, hydrogen and chlorin, may be mixed together and allowed to stand together indefinitely in the dark, and no action will take place. If, however, the mixture be put into a room lighted by the sun, but where the sun does not shine directly upon it, combination takes place gradually; but if the sun be allowed to shine directly upon the mixture for an instant, explosion occurs, this being the result of the combination of the two gases. The same result can be caused by applying a flame or spark to the mixture. In this case light causes chemical action. The art of photography depends upon the fact that light has the power to cause chemical changes.

Sources of chlorin.

Properties of chlorin.

Hydrogen and chlorin combined.

I will here consider hydrochloric acid somewhat in detail, because it is very important in the digestion of food, being the principal fluid composing the gastric juice of the stomach. Hydrochloric acid is always made by treating common salt (one afflicted with acid fermentation should omit the use of salt and soda), under high temperature, with sulfuric acid. This product is given off as a gas, which dissolved in water forms hydrochloric acid, sodium sulfate remaining behind as a result of this process. The chemist describes the action that takes place by writing what is called a chemical equation, as follows:

2NaCl + H2SO4 = Na2SO4 + 2HC1

Sodium chlorid Sulphuric Sodium Hydrochloric (common salt) + acid = Sulfate + acid

The reader will observe that there are as many parts of each element on the right as on the left-hand side of the = mark. Two parts of common salt yield two parts each of sodium (Na) and chlorin (Cl). The sodium appears as Na in the sodium sulfate, and the chlorin as Cl in the two parts of hydrochloric acid.

Importance and preparation of hydrochloric acid.

This method of expressing chemical action by these equations may be somewhat confusing at first to those who have not studied chemistry, but it is best to have all such become familiar with them that they may have the further benefit of understanding the general terms of chemistry.

Hydrochloric acid gives up its hydrogen when brought into contact with certain metals like iron, zinc, etc., and takes up these metallic elements in place of the hydrogen. Thus zinc and hydrochloric acid give zinc chlorid and hydrogen.

Zn +2HCL =ZnCl2 + H2

Zinc + Hydrochloric acid = Zinc chlorid + Hydrogen.