formula (for'mu-lah). 1

In chemistry, an expre ion by symbols of the elementary constitution of the molecule of a substance. It consists e entially of letters, each denoting one atom of one of the elementary substances, with figures appended denoting the number of atoms present. Collections of atoms which constitute a group by themselves (radicle) are often separated by periods or parenthesis from the rest of the f.; and in this case figures prefixed or appended to the parenthesis or placed before an expre ion contained within periods, are understood to apply to all the symbols embraced by the parenthesis or periods. In all other cases, a figure prefixed to a symbolical expre ion for a molecule is understood, like a coefficient in an algebraical f., to be a multiplier of all the symbols which follow. 2. An enumeration of the ingredients of a pharmaceutical preparation, with precise directions for making it. 3. In