powder(redirected from kept powder dry)
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powder,any mass of fine particles or dust prepared by various mechanical means, e.g., grinding of solid substances, or by chemical means, e.g., precipitation from solutions. In a special sense, the word is applied to powdered propellant explosives, e.g., gunpowder, and to powdered substances that produce a bright light when ignited. See explosiveexplosive,
substance that undergoes decomposition or combustion with great rapidity, evolving much heat and producing a large volume of gas. The reaction products fill a much greater volume than that occupied by the original material and exert an enormous pressure, which can be
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a finely ground solid, a dispersed free-flowing material.
Powder is formed by dispersion of solids and by separation of the solid dispersed phase from supersaturated solutions or vapors. The manufacture of highly dispersed powders usually involves such substances as softening solutions, dispersing agents, and stabilizers. These facilitate pulverizing and prevent the agglutination of fine particles. Particle size in powders may vary from 10-4 to 10-1 mm. Powders with particles of identical size are called monodisperse powders, and those with particles of varying size are known as polydisperse powders. Fine powders, especially hygroscopic types, are subject to lumping and caking. Highly dispersed dry powder carried off by a gas or air flow becomes dust. Powder moistened with a liquid forms a paste or dough, and when powder is rapidly agitated in a sufficiently large volume of liquid, a suspension is produced.
Many types of commercial products are manufactured and used in powder form. They include materials used in metallurgy and silicate technology; mineral binders, fillers, and pigments; ingredients for plastics, rubbers, paints, and explosives; fertilizers and pesticides; detergents; food products; and medications. Products in powder form are often granulated or compressed into tablets to ensure convenience in handling and to reduce loss and improve sanitation.
REFERENCEVoiutskii, S. S. Kurs kolloidnoi khimii. Moscow, 1964. Page 374.
L. A. SHITS
a friable solid form of medicine used internally or externally. Various synthetic preparations, antibiotics, and substances of plant and animal origin are used in powder form. The following substances are not prescribed as a powder: hygroscopic substances, such as calcium chloride and sodium bromide; mixtures of substances that are fluidized upon exposure to the air, such as phenylsalicylate and bromo-camphor or antipyrine and quinine; substances that easily decompose, such as silver nitrate mixed with organic matter; or substances that form explosive mixtures. Powders may be simple (consisting of a single substance) or compound; they can be divided or not divided into individual doses.