<P> The Hildebrand parameter is the square root of cohesive energy density . It can be used with nonpolar compounds, but cannot accommodate complex chemistry . </P> <P> Reichardt's dye, a solvatochromic dye that changes color in response to polarity, gives a scale of E (30) values . E is the transition energy between the ground state and the lowest excited state in kcal / mol, and (30) identifies the dye . Another, roughly correlated scale (E (33)) can be defined with Nile red . </P> <P> The polarity, dipole moment, polarizability and hydrogen bonding of a solvent determines what type of compounds it is able to dissolve and with what other solvents or liquid compounds it is miscible . Generally, polar solvents dissolve polar compounds best and non-polar solvents dissolve non-polar compounds best: "like dissolves like". Strongly polar compounds like sugars (e.g. sucrose) or ionic compounds, like inorganic salts (e.g. table salt) dissolve only in very polar solvents like water, while strongly non-polar compounds like oils or waxes dissolve only in very non-polar organic solvents like hexane . Similarly, water and hexane (or vinegar and vegetable oil) are not miscible with each other and will quickly separate into two layers even after being shaken well . </P> <P> Polarity can be separated to different contributions . For example, the Kamlet - Taft parameters are dipolarity / polarizability (π *), hydrogen - bonding acidity (α) and hydrogen - bonding basicity (β). These can be calculated from the wavelength shifts of 3--6 different solvatochromic dyes in the solvent, usually including Reichardt's dye, nitroaniline and diethylnitroaniline . Another option, Hansen's parameters, separate the cohesive energy density into dispersion, polar and hydrogen bonding contributions . </P>

In general what two classes of materials will dissolve in water