Solvent

Solvent, liquid substance that dissolves or breaks down another substance into a more elementary form and is usually present in greater quantity than that substance. Water, for example, is a solvent for table salt. A quantity of table salt (sodium chloride), when mixed with water, breaks down into its constituents, sodium and chlorine ions, which are evenly dispersed throughout the water. In this case, the water is the solvent, the salt is the solute, and the mixture is a solution. The solute, however, is not simply a passive or inert constituent of a solution. Both solvent and solute can be considered active. A solvent can itself have a complex composition; for example, the alcohol used in making so-called tinctures always contains 5 per cent or more of water. Solvents have a particular value commercially. They are an important component of paints, lacquers, and pharmaceuticals and are used in the production of synthetic materials.

By selecting the proper solvent, one ingredient or group of ingredients can be separated from a complex substance. This process is called solvent extraction. A solvent can, for example, remove a fragrance or flavour from a complex plant or animal substance. Once dissolved, the fragrance or flavour can be concentrated by then evaporating the solvent. In a well-designed solvent-extraction process, the solvent is recovered and used over and over again.

Solvent-extraction systems must be designed and operated with great care. The flavour of a fruit, for example, is not due to a single substance, but to a complex combination of substances. Strawberry essence has more than 80 constituents, and orange flavour has more than 90. If the proportions of these constituents are changed by the solvent extraction process, the aroma or taste may be undesirably altered.

See also Colloid; Essential Oils; Solutions.