Grain - Agriculture

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A grain is a unit of measurement of mass that is based upon the mass of a single seed of a typical cereal. Historically, in Europe, the average masses of wheat and barley grain were used to define units of mass.
The grain is used to measure the mass of bullets, gunpowder, and smokeless powder; it is the measure used by the balances used in handloading; bullets are measured in increments of one grain, gunpowder in increments of 0.1 grains. Moreover, the grain is used to weigh fencing equipment, including the foil. In archery, the grain is used to weigh arrows and arrow parts.
The grain is the most common unit used to measure the hardness of water. In particular it is used to quantitively describe the abundance of calcium Ca2+ and magnesium Mg2+ minerals in water. Typically, the measure is noted in grains per gallon (gpg). Water, untreated, typically can measure up to 100 gpg. This measure is critical to setting accurately that resin cation bead regeneration cycle perodicity of both sodium chloride brine and potassium chloride brine flushed water softeners.
Grains are still used occasionally in medicine in the United States, especially in medical prescriptions, usually via the abbreviation "gr." For example, a regular tablet of aspirin is sometimes referred to as "five grain aspirin," or 325 mg. Grains are commonly used for medications that have been included in the United States Pharmacopeia for many decades, such as codeine, opium and phenobarbital combinations. For example, a prescription for tablets containing 325 mg of aspirin and 30 mg of codeine (brand name is Empirin with codeine), is written thus: "ASA gr. v c cod. gr. ss tablets," where "ASA" is short for aspirin (AcetylSalicylic Acid), "v" is the roman numeral for five, "c" is the abbreviation for "with" and "ss" stands for one-half. Likewise, a prescription for B&O Supprettes #15A, which is a compound medication containing belladonna alkaloids and opium, may be written: "Belladonna gr. 1/4 c opium gr ss", as B&O Supprettes #15A contain 16.2 mg (1/4 grain) of powdered belladonna and 30 mg (1/2 grain) of opium. Similarly, a prescription for 60 mg (1 grain) of phenobarbital is often written: "Phenobarb. gr. i". Formulations of these older medications, often use grains on the product label along with the metric equivalent. For example, Extended-Release Donnatal tablets contain 3⁄4 grain (approximately 48.6 mg) of phenobarbital. Given the potential error in mistaking the abbreviations for "grains" and "grams" (gr and g, respectively), and for consistency with other medical orders, metric units are preferred to avoirdupois or apothecary units; hence, the use of grains in the medical profession is rapidly becoming outmoded.