Text-book of chemistry : inorganic and organic with toxicology for students of medicine, pharmacy, dentistry and biology / by R.A. Witthaus.

  • Witthaus, R. A. (Rudolph August), 1846-1915
Date:
1919
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Licence: Public Domain Mark

Credit: Text-book of chemistry : inorganic and organic with toxicology for students of medicine, pharmacy, dentistry and biology / by R.A. Witthaus. Source: Wellcome Collection.

    48/500 (page 32)
    atom of hydrogen; 2C1, two atoms of chlorine; C4, four atoms of carbon, etc. “What the symbol is to the element, the formula is to the com¬ pound. By it the number and kind of atoms of which the molecule of a substance is made up are indicated. The simplest kind of formulae are what are known as empirical formulae, which indicate only the kind and number of atoms which form the compound. Thus, HC1 indicates a molecule composed of one atom of hydrogen united with one atom of chlorine; 5H20, five molecules, each composed of two atoms of hydrogen and one atom of oxygen, the number of molecules being indicated by the proper numeral placed before the formula, in which place it applies to all the symbols following it. Sometimes it is desired that a numeral shall apply to a part of the symbols only, in which case they are enclosed in parentheses; thus, A12(S04)3 means twice A1 and three times S04. For other varieties of formulas, see pp. 47, 48. Equations are combinations of formulas and algebraic signs so arranged as to indicate a chemical reaction and its results. The signs used are the plus and equality signs; the former being equivalent to “and,” and the second meaning “have reacted upon each other and have produced. ’ ’ The substances entering into the reaction are placed before the equality sign, and the products of the reaction after it; thus, the equation 2K0H+H2S04=K2S04+2H20 means, when translated into ordinary language: two molecules of potassium hydroxide, each composed of one atom of potassium, one atom of hydrogen, and one atom of oxygen, and one molecule of sulphuric acid, composed of two atoms of hydrogen, one atom of sulphur, and four atoms of oxygen, have reacted upon each other and have produced one molecule of potassium sulphate, composed of two atoms of potassium, one atom of sulphur, and four atoms of oxygen, and two molecules of water, each composed of two atoms of hydrogen and one atom of oxygen. As no material is ever lost or created in a reaction, the number of each kind of atom occurring before the equality sign in an equation must always be the same as that occurring after it. In writing equations, they should always be proved by examining whether the half of the equation before the equality sign contains the same number of each kind of atom as that after the equality sign. If it does not, the equation is incorrect. The word reaction is used in chemistry with two distinct mean¬ ings: As applying to the action mentioned above, it refers to the mutual action of two substances upon each other. In the other meaning it refers to the action of substances upon certain organic pigments. Thus, the reaction of a substance is acid, when it turns