CHAPTER II. WEIGHTS AND MEASURES.
Metrology.—Metrology (from the Greek pérpov, measure, and )é-os, a discourse) is a study of the art and science of measurements as applied to extension, volume, and weight of matter. Measure of extension may be either of length or of surface, while measure of volume or bulk applies to the cubic contents. Measure of weight is the determination of the gravitating force of bodies—that is, of their attraction by the earth toward its centre, such attraction bearing a direct relation to the quantity of matter contained in a body; hence weight is pressure exerted by a body upon a horizontal plane support- ing it; and the operation of weighing may be defined as the process of determining the number of standard masses (grammes, grains, ounces, or pounds, as the case may be) which are attracted by the earth with as much force as is the body that is being weighed. True weight can be obtained only in vacuo, where the exact measurements of the force of gravitation cannot be interfered with by atmospheric pressure; all measurements of weight in any medium, such as air or water, must therefore give low results. Ordinary operations of weigh- ing, being conducted in air, give apparent weight of the substance only.
Weighing and measuring being operations of daily occurrence in pharmacy which require care and exactness, a knowledge of the standards of weights and measures in use in this country and elsewhere is absolutely necessary. With more or less modification the standards at present in use in pharmacy in the United States and Great Britain are the same as those formerly employed by the Romans, and which in all probability were derived by them from the more ancient Greek nation. Three different systems of weights are at present employed by all English-speaking nations, namely, avoirdupois weight, apothe- caries’ weight and metric weight.
Avoirdupois Weight.—Avoirdupois weight, as its name would seem to indicate, is probably of French origin (aco'r du poids, to have weight), and was no doubt introduced into Great Britain during the reign of the Norman dynasty; it first appeared in the English statute-books in 1335 and is now designated Imperial weight throughout the British Empire. Avoirdupois weight is employed in the sale of all commodities except precious metals and precious stones; hence drugs are always bought and sold by pharmacists by this system. In 1824 the value of an avoirdupois pound was defined by law in England to be £499 of the standard troy pound. The divisions of avoirdupois weight are the
(28)
APOTHECARIES’ WEIGHT 29
pound, ounce, drachm, and grain, which are symbolized by the follow- ing characters: lb., oz., drm., gr.; each pound contains 16 ounces and each ounce 16 drachms or 437} grains. The term drachm is rarely employed, quantities less than an ounce being usually designated by common fractions, such as y's 02., } 0z., } oz., or in grains. The avoir- dupois pound containing 7000 grains (437} X 16) is the only pound used in the United States and Great Britain except at the mints; the standard pound is the equivalent in weight of 27.7274 cubic inches of distilled water at 62° Fahrenheit and normal barometric pressure.
Apothecaries’ Weight.—Apothecaries’ weight was probably derived from troy weight, which latter was introduced into Great Britain, by merchants from Lombardy, toward the close of the thirteenth century; it is employed altogether in the writing and compounding of physicians’ prescriptions, and is divided into grains, scruples, drachms, and ounces, of which 20 grains are equal to 1 scruple, 3 scruples are equal to 1 drachm, and 8 drachms are equal to 1 ounce. The apothecaries’ ounce is of the same value as the now obsolete English troy ounce. The following symbols are employed to designate the divisions of apothecaries’ weight, and always precede the number indicating the quantity intended, which is expressed in Roman numerals; thus, gr. j, for one grain; ij, for two scruples; 3iij, for three drachms; Siv, for four ounces. As far back as 1266, during the reign of Henry III, a statute was enacted in England, which provided that an English silver penny, called a sterling, round and without clipping, should equal in weight 32 wheat-grains, well dried and taken from the centre of the ear, and that of such pence 20 should make 1 ounce, and 12 ounces 1 pound. About 1497, in the time of Henry VII., the weight of the silver penny, however, was changed to the equivalent of 24 wheat- grains. These statutes clearly indicate the origin of the pennyweight and the troy system, from which the apothecaries’ weight, still in use at the present day, was subsequently derived. The choice of wheat- grains from the centre of the ear arose from a desire for uniformity in size and weight, as did likewise the directions to employ the grain well dried. The adoption of troy weight by physicians and pharmacists dates back to 1618, when the first London Pharmacopceia was compiled. In 1826 Imperial measures and standards were legalized in England, and in 1827 exact copies of these standards were furnished the minister of the United States Government at London, namely, the standard yard, a bronze bar of 36 inches length, a brass troy-pound weight of 5760 grains, and a brass avoirdupois-pound weight of 7000 grains; copies of these standards were supplied to the different States in 1836 by act of Congress. These standards remained in use until 1893, when the United States Government authorized a change so as to bring the yard and pound into direct relation to the metric standards adopted by the International Bureau of Weights and Measures at Paris, which latter was established and is maintained jointly by the principal governments of the world.
30 WEIGHTS AND MEASURES
From what has been said above it is clear that every apothecaries’ ounce is heavier than the avoirdupois ounce by 424 grains; hence to find the corresponding value in avoirdupois ounces of any given number
. 424 85 17 at Id ) of of apothecaries ounces, add to the latter 374 ~ 875 or (7 ) of that
number; thus §xxiv = 24 avoirdupois ounces plus me of 24, which is 24 + 2.33, or 26.33 ounces; or multiply the number of apothecaries’ ounces by 480 and divide the product by 437.5, the quotient represent- ing the corresponding avoirdupois weight in ounces. If, on the other hand, avoirdupois weight is to be converted into apothecaries’ weight,
. 42h 85 subtract from the number of ounces ae * 480 = (ope I i) of the number; thus 26.33 ounces = 26.33 — wot 26.33, which is equal to
26.33—2.33, or 24 apothecaries’ ounces, or multiply the number of avoirdupois ounces by 437.5 and divide the product by 480, the quotient representing the corresponding apothecaries’ weight in ounces.
While apothecaries’ weight is employed in compounding prescrip- tions both in this country and Great Britain, it is not used in either the United States or the British Pharmacopeeia, and will no doubt be entirely abolished in the course of time, when a uniform international system of weights shall have been adopted by the medical and phar- maceutical professions of both countries. The grain is the connecting link between avoirdupois, troy, apothecaries’, and Imperial weight, being the same in all.
Fluid Measure.—The fluid measure used by pharmacists of the United States is derived from the old wine measure of England (now extinct), which allowed to each wine gallon the volume of 231 cubic inches, or 58340.011 grains of distilled water at 15° C. (59° F.); the Imperial gallon of Great Britain contains 277.274 cubic inches, or 70,000 grains of dis- tilled water at 62° Fahr. In both cases the gallon is divided into 8 pints; but the pint of wine measure contains 16 fluidounces, while the Imperial pint contains 20 fluidounces. The United States fluid measure has the following units: the minim, the fluidrachm, and the fluidounce, which are represented by the following signs: mM, f3, 3; in addition, the pint and gallon are sometimes employed in commercial trans- actions, being designated by the abbreviations, 0, from Octarius, for pint, and Cong., from Congius, for gallon. The units of Imperial fluid measure bear the same names as those employed for United States fluid measure, but differ from them in value; thus, while the Imperial minim of water weighs 0.91 (0: 9114583) grain, the United States minim of water weighs 0.95 (0.9493) grain, and, since both fluidounces contain 480 minims, the Imperial fluidounce of water weighs 437.5 grains, but the United States fluidounce 455.70 grains, at 15.6° C. (60° F.). Each fluidounce is divided into 8 fluidrachms and each fluidrachm into 60 minims.
THE METRIC OR DECIMAL SYSTEM 31
It must not be overlooked that many liquids, although dispensed and sold by the apothecary by fluid measure, are purchased from the manufacturer by weight, and whenever the specific gravity of the liquid differs materially from that of water there must be also a marked difference in the relative volume; thus glycerin, syrups, chloroform, ethers, acids, essential oils, and many chemical solutions are always purchased by weight. The following list shows the number of fluid- ounces in one pound of the respective liquids, of pharmacopceial quality:
One pound of Sulphuric Acid measures about . 8} fluidounces,
Monsel’s Solution measures about | / 10 « «Chloroform res) “© «Syrup «© «et int oa «© « Ghyeerin « o@ f fate «= Goulard’s Extract“ et an « “ Ammonia Water “ & 16 oil “ Stronger Ammonia Water measures about 17° « — Spiritof Nitrous Ether 18 « « Feenciat Oil measures from. 13t0186 iat “Ether measures about . a 21h bed
The Metric or Decimal System.—The metric or decimal system of weights and measures, which is the only official system of the present United States Pharmacopeia, is supposed to have originated in the fertile mind of the French statesman, Prince de Talleyrand, toward the close of the eighteenth century, and was enforced in France by law in December, 1799. It has already become the legal standard in all civilized countries except the United States and Great Britain, and is destined to become the universal standard for commercial transactions, as it is already for strictly scientific work, the world over.
The use of metric weights and measures was legalized in the United States and Great Britain in 1866, but neither country has as yet officially adopted them, although the prospects for such desirable action are brightening. In 1878 the use of the metric system of weights and measures was made obligatory in the medical department of the United States Navy, and in 1894 in the medical department of the United States Army; in 1902 it was ordered that for all official, medical, and pharmacal purposes in the United States Public Health and Marine Hospital Service metric weights and measures only shall be employed. For some years past efforts have been made annually by the American Pharmaceutical Association to induce Congress to pass laws looking to the introduction of the metric system of weights and measures in place of those now in use, but thus far without success. Since the introduction of a new system of weights and measures must, no doubt, for a time create some confusion, a careful study of the same is required of pharmacists and physicians. The principles upon which the metric system was founded are as follows: The reduction of all weights and measures to one uniform standard of linear meaures; the use of an aliquot part of the earth's circumference as such standard; the application of the unit of linear measure to matter in its three
32 WEIGHTS AND MEASURES
modes of extension—length, breadth, and thickness—as a standard of all measures of length, surface, and solidity; the cubic contents of linear measure in distilled water at the temperature of its greatest density to furnish at once the standard measure of weight and of capacity; everything susceptible of being weighed or measured to have only one measure of weight, one measure of length, and one measure of capacity, with their multiples and subdivisions exclusively in decimal proportions; and every weight and every measure to be designated by an appropriate significant characteristic name applied exclusively to itself.
As a basis, the authors of the metric system adopted a quadrant (one-fourth) of the earth's circumference, and dividing this into ten million parts they obtained a certain measure of length, which they named METER (French métre) and adopted as a standard for all units of measurements; this meter, which was made the unit of linear measure, is equal to 39.3704 inches. One-tenth part of the meter, applied to cubic measurement, was made the unit of measure of capacity and called a Liter (French litre); it is equal to 33.8149 U. S. fluidounces or 2.1135 wine pints. The one-thousandth part of the liter (which is equal to the cube of one-hundredth part of the meter) was chosen to furnish the unit of weight; the weight of such a volume of distilled water at its greatest density, 4° C. (39.2° F.), was called a GRAMME. and is equal to 15.432: 9 grains. The multiples of these units are denoted by prefixes of the Greek numerals, deka 10, hecto 100, kilo 1000, myria 10,000; while prefixes of the Latin numerals denote the subdivisions, thus deci, one-tenth; centi, one- hundredth, and milli, one-thousandth A special subdivision of the meter has been adopted by scientists for use in microscopic measure- ments; it is the micromillimeter or micron, and represents the thous- andth part of a millimeter. It is equivalent to about y54,7 of an inch, and is expressed by the symbol »; the double symbol yu u is used to indicate the thousandth part of a micron. Although the liter is the unit of measures of capacity, the subdivisions of this unit are almost invariably spoken of as so many milliliters (or cubic centimeters), since each liter is equal to 1000 milliliters (or cubic centimeters); thus the expressions 10, 50, 100, 250, 750 milliliters (or cubic centi- meters), etc., are preferred to 1 centiliter, 5 centiliters, 1 deciliter, one-fourth of a liter, and three-fourths of a liter. In like manner the specific names of the fourth multiple of the units are rarely employed, it being customary to designate all above the third multiple as so many of that multiple; thus 10 kilometers instead of 1 myriameter, 15,000 liters instead of 1} myrialiter, and 20 kilograms instead of 2 myriagrams, etc.
The original metric standards were made of platinum by Borda, of Paris, and were designated respectively “le metre des archives” and “le kilogramme des archives.” The actual standards now in use are made of an alloy composed of platinum 90 per cent. and
THE METRIC OR DECIMAL SYSTEM . 33
iridium 10 per cent by the International Bureau of Metric Weights. and Measures; copies of these standards have been furnished to all civilized nations, those intended for the United States having been received by our Government in 1890. The theoretical units are not identical with the actual standards now in use. Thus, the theoretical meter is one ten-millionth part of the quadrant, while the actual meter is the standard meter of the International Metric Bureau; like- wise the theoretical liter is the cubic decimeter, while the actual liter is the volume at 4° C. of one actual kilogram of water, and is equivalent in volume to 1.000027 cubic decimeters or 1000.027 cubic centimeters. The theoretical kilogram is the mass or quantity of one cubic decimeter of water at 4° C., while the actual kilogram is the mass or quantity of the standard kilogram of iridio-platinum of the International Metric Bureau.
When writing the names of metric measures and weights, abbre- viations are usually employed in place of the full names, as, will be seen from the following tables, which also give the corresponding values in customary weights and measures:
Meusures of Length.
1 Myriameter, 6.2137 + miles,
1 Kilometer, 49710 + furlongs, 1 Hectometer, 19.8840 + rods. 1 Dekameter, 1 Meter, 1 Decimeter, 1 Centimeter, 1 Millimeter, Measures of Capacity. 1 Myrialiter, = 2641.7890 + gallons. 1 Kiloliter, 264.1789 « 1 Hectoliter, “ 1 Dekaliter, i “ 83.8149 + fuidounces. 3.38149 + 1 Centiliter, 0.338149 + fuidounce. 1 Milliliter, 00338149 + 1 Cubic centimeter, cc 0.0338149 + “
1 Myriagram,
} Kilogram, lectogram,
1 Dekagram,
1Gram,
1 Deci
igram, 1.543235639 1 Centigram, 0.1543235639 grain. 1 Milligram, 0.00 = 0.01543935639° “ ‘The U. S. Pharmacoperia has introduced the word “mil” to be used as a short form or contraction for milliliter, in place of the abbreviation “ml.”! The numerical expression of all weights, and measures should
‘Throughout this book the abbreviation or contraction of milliliter will be written as follows: mil. for the singular and mils. for the plural of milliliter.
3