7. 15.556 THE METRIC SYSTEM 1. Length. The unit is the meter. It is equal to 39.37 in. 10 millimeters (mm.) = 1 centimeter (cm.) The only measures of length ordinarily used by the chemist are the millimeter and the centimeter; thus, the height of the barometer at the sea level is recorded at 76 cm. or, more commonly, as 760 mm., and not 7 dm. 6 cm. 2. Volume. The unit generally used is the cubic centimeter. 1000 cubic millimeters 1 cubic decimeter = 1 liter (1.) = 1 cubic meter The chemist uses only the cubic centimeter and the liter as measures of volume. Thus, the volume of a test tube is given as (say) 25 cc.; that of a flask as (say) 500 cc. or 0.5 liter. 3. Weight. The unit is the gram. This is the weight of 1 cc. of pure water at its temperature of greatest density (4°). It is equal to 15.43 grains. The gram is practically the only unit used by the chemist. Thus, the weight of a crucible is given as (say) 10.532 g. and not 10,532 mg. or 10 g. 5 dg. 3 cg. 2 mg. 1 pound avoirdupois = 7000 grains = 453.59 grams 1 U.S. quart = 0.95 liter Also note that 1 centimeter = nearly 3 inch 1 kilogram nearly 2 pounds (avoirdupois) 13 14 15 |