ESSENTIALS OF PHARMACY.

INTRODUCTORY.

PHYSICS.

Metrology.

WEIGHT measures the attraction of the earth upon a body. VOLUME is the space occupied by a certain amount of

matter.

SPECIFIC WEIGHT is the relation of the weight of a body to its bulk-the relative weight of equal bulks of different bodies.

SPECIFIC VOLUME is the relation of the volume of a body to its weight-the relative volume of equal weights of different bodies.

STANDARDS OF WEIGHTS AND MEASURES.-These are dependent upon linear measure; best illustrated by the decimal system of weights and measures. In that system the meter is the standard unit of linear measure. This meter is the ten-millionth part of the distance from the equator to the poles, which is the basis of the whole system. The cube upon the one-tenth of the meter (decimeter) is the standard unit of fluid measure, the liter; the gram, which is the standard unit

of weight, is the weight of one cubic centimeter (the cube upon the one hundredth part of the meter) of pure water. (See below.)

The English and American inch (based upon the length of a pendulum vibrating seconds, in vacuum) is the basis of the Avoirdupois and Troy weight; the weight of one cubic inch of pure water (at 62° F. under the pressure of one atmosphere) is declared to be 252.458 grains. The Avoirdupois pound is equal to 7000 of such grains; and the Troy pound is equal to 5760 grains.

Systems of Weights and Measures employed in Pharmacy.

TROY OR APOTHECARIES' WEIGHT is used largely in dispensing, while the wine or Apothecaries' measure is employed for liquids (except in compounding, when the Pharmacopoeia directs, in most cases, liquids to be weighed).* The table of this system is as follows:

* The Committee of Revision of the Pharmacopoeia for 18901900 has been instructed as follows: "To direct solids to be weighed and liquids to be measured, except in such cases as they find it advisable to use weights only, and that the metric system be employed for this purpose."

WINE OR APOTHECARIES' MEASURE ("American").

THE MEASURE RECOGNIZED BY THE BRITISH PHARMACOPŒIA is known as Imperial measure; the table is as follows:

The MINIM is a variable expression of fluid measure.

The

minim of American fluid measure of water at its greatest density weighs about 0.95 grain, being the 480th part of the American fluid ounce of 455.7 grains of water. The British minim being the 480th part of the British fluid ounce of 437 grains of water, weighs about 0.91 grain.

The American fluid ounce of water weighs 455.7 grains, and is of the American pint of 7291.1 grains of water.

The British fluid ounce of water weighs 437 grains, and therefore corresponds with their weight standard (avoirdupois) ounce. It is of the British Imperial pint.

The American fluid drachm of water weighs 56.96 grains, being of the American fluid ounce of 455.7 grains of water. The British fluid drachm of water weighs 54.68 grains, being of the British fluid ounce of 437 grains of water.

The Metric System.

The units in the metric system are as follows:

THE METER (unit of length

39.37 inches).

= 15.432 grains)

The names of the subdivisions of these units are expressed by prefixing the Latin numerals, milli, centi, and deci, and

the names of the multiples by prefixing the Greek numerals, deka, hecto, and kilo, to the unit. These prefixes, arranged in numerical relation, furnish a table as follows:

If the student will supply or insert a unit (Gram, Liter or Meter) after each one of the above prefixes (milli, centi, etc.) he will have practically a complete table of the metric system. The cubic centimeter and the gram.

Fluid measure in the metric system is usually stated, in dispensing, in cubic centimeters (abbreviated c.c). The intimate connection between the cubic centimeter and gram is interesting: this connection will be seen at once, as one c.c. of distilled water (at 4° C.) weighs one gram. Hence the cubic centimeter is sometimes called a 'fluid gram" (fluigram).

Approximate equivalents in other systems.

The following are given as some of the principal equivalents for the student to commit to memory :

39.37 inches (3 ft. 3 inches and inch). two-fifths inch.

two inches.

25 Millimeters ( .025) = one inch.

II. LIQUID MEASURE.

1 Liter = 33.8 fl. oz. (2 pts., 1 fl. oz., 6 fl. dr., 30 m.).