The others include butane, propylene, butadiene, butylene, isobutylene, and mixtures thereof. Manganese oxide is also used in Portland cement mixtures. Generally foods contain complex mixtures of polyphenols. Solvents, reaction mixtures, and old grease show up as transparent spots. Calcium nitrate can be used as a part of molten salt mixtures. Gallic acid is a component of some pyrotechnic whistle mixtures. Examples of mixtures are air and alloys. Many other metallic soaps are also useful, including those of aluminium, sodium, and mixtures thereof. Electron states are best represented by time-depending "mixtures" (linear combinations) of multiple orbitals. Heteroazeotropes are always minimum boiling mixtures. Separation processes are used to decrease the complexity of material mixtures. Below are some notable blended HFC mixtures. Azeotropes are useful in separating zeotropic mixtures. Consider two light sources composed of different mixtures of various wavelengths. The use of oxygen enriched mixtures is forbidden.