Page:International Library of Technology, Volume 93.djvu/77



TABLE I Elements Symbols Hydrogen H Oxygen

Nitrogen N Carbon C Sulphur S

The elements that will be referred to most frequently in this Section are given in Table I. In referring to an element, it is customary to use simply the symbol, which is usually the first letter of the name. Thus, H stands for hydrogen, C for carbon, etc.

4. Chemical Combination. — When two or more elements are brought in contact under favorable circumstances, they will combine and form a new substance that is unlike either of the elements. Of course, the new substance will be a compound. Thus, if carbon and oxygen are brought together at a high temperature, they will combine and form carbon dioxide. Hydrogen and oxygen combine to form water. Hydrogen, nitrogen, and oxygen, when combined in certain proportions, form nitric acid. A given volume of nitrogen and three times that volume of hydrogen combine and form ammonia, a gas that differs greatly from either nitrogen or hydrogen.

5, It is supposed by chemists that equal volumes of all gases, whether simple or compound, contain the same number of molecules. Thus, a cubic foot of hydrogen, a cubic foot of air, a cubic foot of steam, all contain the same number of molecules, when at the same pressure. Suppose that 1 cubic foot of hydrogen gas is allowed to come in contact with 1 cubic foot of chlorine gas (symbol, Cl). The mixture is exposed to heat or light, and the gases combine. The process of combination is explained as follows: There is a certain attraction or affinity between the hydrogen atoms and the chlorine atoms. Each molecule of hydrogen, as well as each molecule of chlorine, contains two atoms. Under the influence of heat or light, this attraction becomes so strong that the two atoms composing the molecule of hydrogen are torn apart. Likewise, the two atoms