Relative density
A pycnometer (from Greek: πυκνός (puknos) meaning "dense"), also called pyknometer or specific gravity bottle, is a device used to determine the density of a liquid. A pycnometer is usually made of glass, with a close-fitting ground glass stopper with a capillary tube through it, so that air bubbles may escape from the apparatus. This device enables a liquid's density to be measured accurately by reference to an appropriate working fluid, such as water or mercury, using an analytical balance.
Köhler theory
where formula_2 is the droplet water vapor pressure, formula_3 is the corresponding saturation vapor pressure over a flat surface, formula_4 is the droplet surface tension, formula_5 is the density of pure water, formula_6 is the moles of solute, formula_7 is the molecular weight of water, and formula_8 is the cloud drop diameter.