Apothecaries' system measure precious metals and stones. (The troy pound was already declared illegal for most other uses by the Weights and Measures Act of 1878.) In the US, the metric system replaced the apothecaries' system in the United States Pharmacopoeia of 1971. Apothecaries' system The apothecaries' system or apothecaries' weights and measures is a historical system of mass and volume units that were used by physicians and apothecaries for medical recipes, and also sometimes by scientists. The English version of the system is closely related to the English troy system of weights, the pound and grain being exactly the same in
Metal titanium and magnesium are valued for their high strength-to-weight ratios; magnesium can also provide electromagnetic shielding. These materials are ideal for situations where high strength-to-weight ratio is more important than material cost, such as in aerospace and some automotive applications. Alloys specially designed for highly demanding applications, such as jet engines, may contain more than ten elements. Metals can be categorised according to their physical or chemical properties. Categories described in the subsections below include ferrous and non-ferrous metals; brittle metals and refractory metals; heavy and light metals; and base, noble, and precious metals. The "Metallic elements" table in this