METROLOGY.
Merrotocy is the science which treats of weights and measures. It includes measures of extension, volume, and weight. ORIGIN AND DEVELOPMENT. At the present time all systems of weights and measures are founded upon measures of extension. The standards selected are arbitrary and vary in different countries. Owing to the gradual transition now going on, more than one system is frequently used at the same time in the same country. Future generations will doubtless see a single system (the metric) of weights and measures in use throughout the civilized world. During the early centuries different nations used various arbitrary standards. The finger, thumb, hand, palm, and forearm have each served as measures of length, while handfuls and pinches were measures of bulk. Seeds were used as standards of weight and measures of length. John Quincy Adams states that the pound, ounce, foot, inch, and mile are derived from the Romans, and through them from the Greeks, as all Roman weights and measures were of Hellenic origin. The yard or girth is of Saxon origin. After the Roman conquest it lost its meaning of girth, and the length of the arm of Henry the First (1100 to 1185) was substituted as the standard yard, In 26 METROLOGY 1266 the English government declared that the sterling or English penny, round and unmutilated, should be the weight of 32 grains of wheat, dry and taken from the middle of the ear. Twenty pennyweights were to make one ounce, 12 ounces one pound, and 8 pounds a wine gallon. In 1324 the consecutive length of three round, dry barley corns were taken as the inch, 12 of these inches one foot, and three feet one yard. At the close of the fifteenth century the weight of the silver penny was changed to that of 24 grains of wheat. Hence, we have 24 grains one pennyweight, 20 pennyweights one ounce, 12 ounces one pound, which is the same as Troy weight, which had been introduced into England by the Lombardy merchants at the close of the thirteenth century. It is now confined to the weighing of gold, silver, and precious stones. Apothecaries’ weight was probably derived from Troy weight, and is used in the writing and dispensing of prescriptions. Avoirdupois weight was brought into England by merchants at the beginning of British civilization. Its origin is not definitely known. Avoir du pots, to have weight, indicates French extraction, while the earlier spelling, averdupois, suggests Roman origin from averare (middle age Latin), meaning to verify. In 1618 the London College of Physicians directed that Troy weight be used in their first Pharmacopoeia. In 1736 the Royal Society attempted to reform their standards, and in 1760, under direction of the House of Commons, prepared a standard yard and a standard Troy pound. At last, in 1816, English scientists undertook to secure an indestructible standard. It was ascertained that the length of a pendulum vibrating seconds of time in a vacuum, at sea level and in the latitude of London, is 39.13929 inches. This furnished an indestructible, unchangeable standard. Hence, the inch was to be the standard from which all measures and weights (except the metric) were to be derived. This unit inch is described as of such length that it is contained 39.13929 times in the length of the described pendulum. Weights and measures of capacity were derived from the inch as follows: A cubic inch of distilled water weighed 252.458 grains in air, at 62° F., and 30 inches barometric pressure. The Troy pound contained 5760 such grains and the avoirdupois pound contained 7000 grains. The Imperial gallon contained 10 avoirdupois pounds or 70,000 grains of distilled water at 62° F. at normal pressure, which is about 277.25 cubic inches. On January 1, 1826, the Imperial standards were legalized by Great Britain. The wine or fluid gallon used in the United States contains 231 cubic inches, or 58372.2 grains, at 62° F., and at normal pressure. In 1827 exact copies of the Imperial standards were furnished to the United States. These copies consisted of a bronze yard containing 36 inches, a brass Troy pound weighing 5760 grains, and a brass avoirdupois pound of 7000 grains. In 1836 the United States Congress furnished the different States with accurate copies of these standards. THE SYSTEM IN PRESENT USE. Although weights and measures have varied in size to correspond with the changes in standards, the denominations have remained the same for centuries. They are as follows: Apothecaries’ Weights (erroneously called Troy weight). There are: 20 grains in 1 scruple. 3 scruples, or 60 grains in 1 dram. 8 drams, or 480 grains in 1 ounce. Apothecaries’ weights are used only in writing and compounding physicians’ prescriptions. The quantities are expressed in Roman numerals and follow the symbols, thus; gr. xij equals 12 grains; Diij equals 3 scruples; Zviij, equals 8 drams; iiss, equals 24 ounces. The grain and the ounce are of the same value as those of Troy weights. Avoirdupois Weights.—There are: 437.5 grains in 1 ounce. 16 ounces, or 7000 gr., in 1 pound. This system is used in the United States for commercial purposes only. The fractions of an ounce are expressed in halves, quarters, and eighths. THE SYSTEM IN PRESENT USE 25 Wine or Fluid Measure.—There are: 60 minims in 1 fluidram. 8 fluidrams, or 480 minims, in 1 fluidounce. 16 fluidounces in 1 pint or octarius. 8 pints, or 128 fl. oz., in 1 gallon or congius, which contains 231 cubic inches. The signs used in prescription writing are m for minims, fl.3 for fluidrams, fl.3 for fluidounces, and O for pints. 1 fl. oz. of distilled water at 15.6° weighs 455.7 grains. 1 fl. oz. of distilled water at 25.0° weighs 454.6 grains. 1 minim of distilled water at 15.6° weighs 0.95 grain. 1 minim of distilled water at 25.0° weighs 0.947 grain. Imperial Measure——Used in British territory only. There are: 60 minims in 1 fluidram. 8 fluidrams, or 480 minims, in 1 fl. oz. 20 fluidounces in 1 pint. 8 pints, or 160 fl. oz., in 1 gallon, which contains 277.25 cubic inches. The names, signs, and divisions are the same as in wine measure. However, not one of the denominations is of the same value as the corresponding denomination in wine measure. 1 fl. oz. of distilled water at 15.6° weighs 437.57 grains 1 minim of distilled water at 15.6° weighs 0.9116 grains. 1 fl. oz. is equivalent to 0.96 of a wine ounce. 1 pint is equivalent to 1.2 wine pints. 1 fi. oz. of distilled water at 15.6° is equivalent to 1.0 avoirdupois ounce. In the United States three ounces, each of different size, are in use, viz., the apothecaries’ ounce of 480 gr., the ayoirdupois ounce of 437.5 gr., and the fluidounce of 455.7 gr. But in all three systems of weights and measures the grain is of the same value. The Metric System.—The metric system of weights and measures is destined to become the universal system. Centuries may be required to accomplish its acceptance, but the system is steadily gaining in favor and its universal adoption is only a question of time. It is now used in scientific work, and is the legal standard of all civilized nations except the United States and Great Britain, but in both of these countries it is permissible by law. The metric is the only system recognized in the United States Pharmacopwia. In 1790 Prince de Talleyrand submitted to the French Assembly a plan for a new system of weights and measures having a single universal standard. The standards considered were the pendulum, suggested by Huyghens, and the proportional part of the earth’s circumference, by Picard. His plan, with some modifications, was approved by the Assembly August 22, 1790. A committee from the Academy of Science was appointed to select the standard. They reported in March, 1791, in favor of one-fourth of the meridian, and recommended that a ten-millionth part of it should be taken as the standard unit of linear measure. They also recommended that a cube representing one-tenth of this be accepted as the standard of weight and volume. Committees were appointed to determine the length of the meridian’s are and the weight of a standard volume of distilled water in vacuum. They were also to construct a scale and table of weights and measures. Without waiting for these committees to complete their labors, the French Government, in 1793, passed a law adopting the system and requiring it to take immediate effect. For their standard provisional meter they used measurements made more than fifty years before. In 1799 a new meter was adopted, which was about 0.01 of an inch shorter than the old meter. The principle nations have established a new standard, which is the length between two lines drawn upon a platiniridium bar and measured at the temperature of melting ice. Its length is as nearly as possible that of the old meter, and is equal to 39.37+ inches. This standard is preserved in the International Bureau of Weights and Measures in the archives of France. The unit of volume is a cube of one-tenth of the meter, and is called a Liter. It equals 33.8149 fluidounces. The unit of weight is the weight of 0.001 part of a liter of distilled water at 4° C. It is called a Gram or Gramme, equal to 15.432 gr. Denomina- tions aboye this unit are obtained by multiplying by ten; those below are obtained by dividing by ten, using the same prefixes for measures of extensions, volume, and weight. The multiples are expressed by Greek prefixes, as, Deka, 10; Hecto, 100; Kilo, 1000; Myria, 10,000. The subdivisions are expressed by Latin prefixes, as, Deci, 0.1; Centi, 0.01; Milli, 0.001. The abbreviations of the units and multiples should begin with capital letters; those for the subdivisions with small letters. Metric Measures. METER, Myriameter, Mm.=10000.0 Kilometer, Km.= 1000.0 Hectometer,Hm.= 100.0 Dekameter, Dm.= 10.0 Meter, M. 1.0 Decimeter, dm. 0.1 Centimeter, cm. 0.01 Millimeter, mm. 0.001 Liren, Myrialiter, Ml.=10000.0 Kiloliter, KI.= 1000.0 Hectoliter,HI.= 100.0 Dekaliter, DI 10.0 Liter, L. 1.0 Deciliter, dl O14 Centiliter, cl 0.01 Milliliter, ml. 0.001 Gram. Myriagram, Mg.=10000.0 Kilogram, Kg.= 1000.0 Hectogram,Hg.= 100.0 Dekagram, Dj 10.0 Gram, Gm. 1.0 Decigram, dg== 0.1 Centigram, Milligram, mg. Many of the above terms are rarely used. Those in italics are most frequently used, and of these, the decigram and centigram are frequently expressed by an equivalent in milligrams. The milliliter is the cube of the centimeter, and is commonly called cubic centimeter, Ce. The micron or micromillimeter, mkm., or p, is one-thousandth part of a millimeter, and is used in microscopy. The cubic centimeter is usually considered as equivalent to a gram of distilled water, but this is true only when weighed in vacuo at four degrees centigrade. When weighed in air at 15.6° it weighs 0.998 Gm., and at 22° it weighs 0.9975 Gm. APPROXIMATE EQUIVALENTS. The following equivalents are not exact, but are sufficiently accurate for all practical purposes. When the equivalents of weight are given in volume it applies only to substances having the same specific gravity as water: 1 Meter equals 39.37 inches. 1 Gram equals 15.432 grains, 1 Gram equals 0,035 ayoirdupois ounce. 1 Gram equals 0.032 apothecaries’ ounce. 1 Cubic centimeter equals 16.23 apothecaries’ minims 1 Cubic centimeter equals 16.9 Imperial minims. 1 Cubic centimeter equals 0.0338 apothecaries’ fluidounce. 1 Cubic centimeter equals 0.035 Imperial fluid-ounce. 1 Grain equals 64.8 milligrams. 1 Grain equals 1.053 apothecaries’ minims. 1 Grain equals 1.097 Imperial minims. 1 Apothecaries’ ounce equals 31.1 grams. 1 Apothecaries’ ounce equals 1.097 avoirdupois ounces. 1 Apothecaries’ ounce equals 1.053 fluidounces. 1 Avoirdupois ounce equals 28.35 grams. 1 Avoirdupoisounceequals0.911 apothecaries’ ounce. 1 Avoirdupois ounce equals 0.961 fluidounce. 1 Ayoirdupois ounce equals 1 Imperial fluidounce. 1 Ayoirdupois pound equals 453.6 grams. 1 Imperial minim equals 0.9114 grain. 1 Imperial minim equals 0.059 cubic centimeter. 1 Imperial fluidounce equals 28.35 cubic centimeters. 1 Imperial fluidounce equals 0.96 apothecaries’ ounce. 1 Imperial pint equals 567.6 cubic centimeters. 1 Imperial gallon equals 4.541 liters. 1 Apothecaries’ minim equals 0.9493 grain. 1 Apothecaries’ minim equals 0.0613 cubic centimeter. 1 Apothecaries’ fluidounce equals 29.57 cubic centimeters. 1 Apothecaries ounces. 1 Apothecaries’ fluidounce equals 0.95 apothecaries’ ounce. 1 Apothecaries’ fluidounce equals 1.04 Imperial fluidounces. 1 Apothecaries’ pint equals 473 cubic centimeters. 1 Apothecaries’ gallon equals 3.496 liters. Many other equivalents might be given, but it is unnecessary, as they can be obtained by moving the decimal point. For instance, one cubic centimeter equals 0.0338 of a fluidounce; hence one liter (1000 Ce.) equals 33.8 fluidounces. As the equivalent given is that of a unit quantity, any number of times the unit quantity may be obtained by multiplying its equivalent by the given amount. For example, one ayoirdupois ounce equals 0.911 apothecaries’ ounce. Therefore, 24 avoirdupois ounces equal 24 X 0.911, or 21.864 apothecaries’ ounces. THE BALANCE. The balance, or scale, as it is commonly called, is an instrument for determining the relative weights of bodies. Scales differ in size and construction, depending upon the purpose for which they were designed. Pharmaccutically, they may be divided into two classes: First, one employing the principle of the lever resting upon one or more knife-edges. The second employs the principle of the lever resting upon tightly stretched wires or bands. Those of the first class may be subdivided into (1) single beam, and (2) compound beam. There are also two forms of the single beam balance, viz., those of equal and unequal arm. The single beam equal arm principle is used in most analytical and prescription balances (Fig. 1). The Single beam prescription balance. beam should be as light as possible and still be rigid. In the finest balances this is usually obtained by giving the beam the truss form (Figs. 1 and 2). In the centre of the beam and at right angle with it is a short shaped bar of steel or agate “knife-edge.” Its projecting ends rest upon stationary supports in such a manner that the beam may vibrate freely and also be lifted from its support when not in use, to prevent wear. The pans are suspended from similar knife-edges at the end of the beam. In all fine balances the knife-edges are of agate and vibrate on agate plains. The beam is so graduated that the smallest weights may be obtained by sliding a rider along the beam. How to Test a Balance.—Place the balance in position and so adjust it that it is level. First, see that the arms are of equal length. This is done by placing a ten gram weight oneach pan. Should either arm be longer than the other, that arm will descend, providing the weights are correct. This may be determined by reversing the weight, when, if the error is due to the weight, the opposite arm will fall. Secondly, to determine whether the knife-edges are parallel, balance the scale with weights and move the weights to different positions on the pan. The equilibrium should remain unaffected if the knife-edges are parallel. To test the sensitiveness of the balance, observe whether it responds readily to its lightest weight when either lightly or heavily loaded. THE BALANCE 33 The fulcrum or central knife-edge should be slightly above the centre of gravity. If too high, the balance vibrates rapidly and comes to rest quickly, but is not sensitive. If the point of support is too low, the equilibrium is unstable. When the support is at the centre of gravity, the pans, when equally loaded, remain wherever they may be placed without coming to a horizontal position. When using a balance do not wait for the oscillations to cease, but observe the equality of the oscillation as shown by the indicator. The life or sensitiveness of a balance is proportional to the care which it receives. Balances should be kept in closed cases, in order to protect them from dust or corrosion. Occasional cleaning with chamois skin is all that is necessary. Oil should not be used. The metallic parts should not be handled with bare hands, as the moisture from the skin is usually acid. Glass pans are preferable to metal ones, but are more easily broken. Never allow the beam of a balance to oscillate when not in use, nor add or remove weights from the pans when in motion. Never weigh corrosive or deliquescent substances on a scale pan, but use glass, tared vessels, or parchment paper. Return all weights to their proper places and clean the pans with chamois skin or soft cloth. Compound Lever or Box Balances.—This scale differs from the preceding in the fact that the pans are placed above the beam. To accomplish this and retain the pans in an upright position the multiple lever system is employed. This increases the friction and decreases the sensitiveness. 3 THE BALANCE 34 Figs. 3 and 4 illustrate different styles of the box prescription balance, and Fig. 5 a comp
Key Takeaways
- The metric system is destined to become the universal standard of weights and measures.
- Understanding historical weight and measure systems can be crucial for survival in a post-disaster scenario where modern technology may not be available.
- Balances and scales require regular maintenance and testing to ensure accuracy.
Practical Tips
- Keep a set of metric and apothecaries' weights on hand, as they are still used in some medical settings today.
- Use glass measuring devices for precision when dispensing liquids, especially in emergency situations where accuracy is critical.
- Regularly test the sensitivity and accuracy of your scale or balance to ensure reliable measurements.
Warnings & Risks
- Do not use corrosive substances on metal pans; always use appropriate containers like glass or parchment paper.
- Avoid using outdated or improperly maintained scales, as inaccurate measurements can lead to ineffective treatments.
- Be cautious when handling weights and balances; moisture from the skin can damage delicate components.
Modern Application
While historical weight and measure systems are still relevant for certain specialized applications like pharmacy, the metric system has largely replaced others in everyday use. Modern survival preparedness should include understanding both traditional and modern measurement techniques to ensure versatility and reliability.
Frequently Asked Questions
Q: What is the difference between apothecaries' weight and avoirdupois weight?
Apothecaries' weight is used in writing and dispensing prescriptions, with 20 grains in a scruple, while avoirdupois weight is used for commercial purposes, with 437.5 grains in an ounce.
Q: How can I test the accuracy of my balance?
Place it on a level surface and ensure that the arms are of equal length by using a ten-gram weight on each pan. Check if the knife-edges are parallel by moving weights to different positions without affecting equilibrium.
Q: What is the metric system, and why is it important?
The metric system uses base units like meters for length and grams for mass, with prefixes indicating multiples or fractions. It's important because it provides a universal standard that simplifies international trade and scientific communication.
Q: How do I convert between apothecaries' weight and avoirdupois weight?
1 apothecaries' ounce equals 1.097 avoirdupois ounces, or you can use the conversion factor that 24 grains in an apothecaries' scruple is equivalent to about 31.1 grams.
Q: What are some practical uses of understanding historical weight and measure systems?
Understanding these systems can help in situations where modern technology fails, such as in emergency medical care or when traveling to regions with different standards. It ensures that you can accurately measure ingredients for survival rations or medicines.