Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Dyestuffs, any of a large group of chemicals almost exclusively organic in nature, used for the coloring of textiles, inks, food products, and other substances. Modern industrial terminology defines a dyestuff as a product containing pure organic dye and cutting agents or fillers that make the product easier to handle. Dyes are not to be confused with pigments, which are pulverized colored substances that must be mixed with adhesive binding agents before being applied to surfaces. See Dyeing.

The color properties of organic compounds depend on their structure. In general, the colored compounds used as dyes are unsaturated organic chemicals. The quality of possessing color is particularly noticeable in compounds containing certain well-defined chemically unsaturated groupings. These groups, known as chromophores (color bearers), are not all equally effective in producing color.

Dyestuffs must be capable of entering and coloring textile fibers or other substances. Chemical radicals, known as auxochromes, have the property of anchoring the desired dye effectively. They are acidic or basic and give rise to acid and basic dye salts. In the case of some compounds the addition of an auxochrome group also changes a colorless compound into a colored one.

The basic raw materials of synthetic dyes are compounds, such as benzene, that are derived from the destructive distillation of coal (see Aniline; Coal Tar). For this reason synthetic dyestuffs are often popularly known as coal-tar dyes. From the basic materials, intermediates are manufactured by a number of chemical processes that in general involve the substitution of specific elements or chemical radicals for one or more of the hydrogen atoms in the basic substance.

Dyestuffs can be classified according to their use or by their chemical structure. The chemical classification is generally made according to the nucleus of the compound. Among the more important dye groups are the azo dyes, which include butter yellow and Congo red; the triphenylmethane dyes, which include magenta and methyl violet; the phthalein dyes; the azine dyes, which include mauve; and the anthraquinone dyes, which include alizarin. Indigo is a vat dye, occurring in nature in the crystalline glucoside indican. An important new group of dyes is the phthalocyanine dyes, which are blue or green in color and resemble chlorophyll in chemical structure. Of all the groups of dyes the azo dyes are the most generally useful and widely employed.

A stain is a chemical dye or pigment used to color glass, paper, textiles, or wood. The staining substance, which uses alcohol, oil, or water as a vehicle, is transparent and thinner than paint or coating, and it penetrates into the grain of material being dyed. In microscopic and microchemical research, a dye or a chemical mixture used to distinguish between minute transparent structures is also called a stain.