Apothecaries Weight: Dry measure. 20 grains (gr) make 1 scruple; 3 scruples make 1 drachm; 8 drachms make 1 ounce; 12 ounces make 1 pound.
Apothecaries Measure: 60 minims (m) make 1 fluid drachm; 8 fluid drachm make 1 ounce; 16 fluid ounces make 1 pint; 8 pints (O) make 1 gallon (cong.)
The metric system is based upon the meter, which is the standard unit of length of that system, and equal to 39.370432 inches, or about 10 per cent. longer than the yard.
The metric unit of fluid measure is the liter—the cube of 1/10 meter, or 1000 cubic-centimeters-equal to about 34 fluid ounces.
The metric unit of weight is the gram, which represents the weight of one cubic-centimeter of water at its maximum density. It is equal to about 15 grains.
One cubic-centimeter (cc) is equal to about 16 minims.
In writing prescriptions it is sufficiently accurate and safe to consider 1 gram as exactly equal to 15 Troy grains, and to consider 1 cubic- centimeter as equal to 15 minims. We accordingly have:
1 Gram equal to 15 troy grains.
1 troy grain equal to 1/15 Gram.
1 Cubic-centimeter equal to 1/4 fluid drachm.
1 fluid drachm equal to 4 Cubic-centimeters.
1. To convert troy grains into grams, or minims into cubic-centimeters:
a. Divide by 10, and from the quotient substract one-third; or,
b. Divide by 15; and
2. To convert apothecaries’ drachms into grams, or fluid drachms into cubic-centimeters, multiply by 4.
The Gram and the Cubic-centimeter (fluidgram) when referring to liquids, may be considered as equal quantities, except the liquids be very heavy or very light.
Measures may be discarded and weights exclusively employed, if preferred. All quantities in a prescription would then be expressed in Grams.
The average “drop” (water) may be considered equal to 0.05 c.c., or 0.05
Gm. An average teaspoon holds 5 c.c., and an average tablespoon 20 c.c.
Decimal numbers should be used as far as practicable. It is safe to prescribe 30 Gm. for one troy ounce, and 250 c.c. for eight fluid ounces.