Any questions in regard to photograph matters will be willingly answered by the Editor of this column, and we should be glad to hear from any of our club who can make helpful suggestions.
SIMPLE CHEMISTRY FOR AMATEUR PHOTOGRAPHERS.
In order to do good photographic work by method rather than by guess, it is necessary to understand something of the nature of the chemicals used and their effects. Even a slight knowledge of chemistry enables the amateur to work understandingly and with far better results. We are therefore going to give, for the benefit of our Camera Club, a few papers on chemistry as used in photography, and shall try to make them so plain and simple that even the youngest member will understand them.
Chemistry is that science which explains the composition of the substances which compose the crust of the earth, the atmosphere which surrounds it, and the water which occupies so much of the earth's surface. These substances are called chemical elements. A chemical element is a simple substance containing only one kind of matter, such as gold, silver, platinum, hydrogen, oxygen, etc. According to the last report of Mr. F. W. Clark, the chief chemist of the U.S. Geographical Survey, there are seventy-two known elements. About thirty of these elements are used in the different processes of photography.
Each element is represented by a symbol, this symbol being the first letter or letters of the name of the element. The symbol of hydrogen is "H"; of oxygen is "O"; of gold, "Au," the first two letters of the word "Aurum," the Latin name for gold. Each symbol also stands for the weight of one of its atoms. (An atom is supposed to be the smallest possible division of a substance.) Hydrogen is the lightest element known, and is taken as the standard of weight when comparing the weight of other atoms. The symbol "H" would therefore not only stand for the element hydrogen, but for its weight, 1, or a unit. An atom of oxygen is sixteen times as heavy as an atom of hydrogen, and an atom of gold is 196 times as heavy.
In making up chemical compounds the chemical elements are combined in different proportions, which, united, make a new substance. The way in which these elements combine is always in the same proportion. The smallest number of atoms which combine to form a new substance is called a molecule. Take water, for instance, which is composed of hydrogen and oxygen; it takes two atoms of hydrogen and one atom of oxygen to form a molecule of water. These chemical combinations are expressed or written by the symbols of the elements of which they are composed, called chemical formulas. If two or more atoms of an element are used to form a chemical compound, the number of atoms used is written directly after the symbol; thus, H_{ 2}O is the chemical formula for water.