to the yard or the pound. We have several kinds of gallons and several kinds of pounds, although only two of the gallons are actually used. The original theoretical yard was of such length that the length of the seconds pendulum at Greenwich, England, expressed by 39.1393 inches, each inch being the thirty-sixth part of the standard yard; but it is not absolutely certain that either the British yard or the American yard is now identical with the value just stated, for when the original British standard yard was lost and a commission was appointed to remeasure the length of the seconds pendulum and to construct a new standard yard from the results, the task was abandoned as impracticable and an extant copy of the old standard yard was chosen and adopted as the new standard, and in our country the length of the yard is now !$£$ °f the length of the meter. The present American yard may or may not be absolutely identical with the present British yard.
Our customary capacity measures are not based upon the linear unit, but upon weight. Our bushel measures, gallon measures and their subdivisions are, in other words, constructed and verified by weight. Originally the gallon employed for the measurement of liquids (the Old English wine gallon) was 231 cubic inches, but the American gallon of today is the volume of 3785.434 grams of water at 4° 0., weighed in vacuo. Whether or not that volume is 231 cubic inches is doubtful.
The commercial pound of this country is assumed to be identical with the British imperial pound, but we also employ in America the old English Troy pound, and a copy of the old British Troy pound is kept in the custody of the United States Mint at Philadelphia for the purpose of regulating the coinage of the United States, in accordance with a resolution of Congress. The Troy weight is used also for weighing gold and silver bullion, gold and silver ware and jewelry.
The customary weights and measures of America are as follows : Linear Measure 1 league = 3 miles, or 5,280 yards 1 mile = 8 furlongs, or 1,760 yards 1 furlong = 40 poles or rods 1 pole or rod = 5 \(\frac{1}{2}\) yards 1 yard = 3 feet, or 36 inches 1 foot =12 inches
<Callout type="important" title="Standardization">It is crucial to understand the differences and equivalences between various weight and measure systems for accurate pharmaceutical calculations.</Callout>
The imperial system of Great Britain was adopted in 1824, to take effect January 1, 1825. The imperial gallon is the volume of 10 imperial pounds of pure water at 62° F., weighed in air of the same temperature. Therefore the imperial gallon is based upon weight and not upon any linear unit.
The relations between the various units of weight and measure in use by civilized nations are shown in the following tables : Long Measure 1 league = 4,828 meters 1 mile = 1,609.3 meters 1 furlong = 201.2 meters 1 rod = 5.03 meters 1 yard = 36 inches = 0.914 meters 1 foot = 30.48 centimeters 1 inch = 25.4 millimeters
<Callout type="tip" title="Conversion Shortcut">For quick conversions, remember that one meter is approximately equal to 39.37 inches.</Callout>
Measures of Capacity 1 bushel = 35.24 liters 1 peck = 8.81 liters 1 dry gallon = 4.40 liters 1 dry quart = 1.10 liters 1 American liquid gallon = 3,785.4 liters 1 American liquid quart = 0.946 liter 1 American liquid pint = 473 milliliters
Measures of Weight 1 kilogram = 2.205 avoirdupois pounds 1 gram = 15.432 grains 1 milligram = \frac{1}{64.8} grain 1 avoirdupois pound = 453.6 grams 1 avoirdupois ounce = 28.35 grams 1 grain = 64.8 milligrams
Convenient Approximate Equivalents 1 kilogram = 32 medicinal ounces 1 milligram = \frac{1}{64} grain 1 grain = 64 milligrams 480 American minims = 500 Imperial minims The weight of 96 American medicinal fluid ounces of water is 100 avoirdupois ounces.
Key Takeaways
- Understand the differences between various weight and measure systems used in pharmacy.
- Recognize that capacity measures are often based on weight rather than linear units.
- Be familiar with conversion factors between different measurement systems.
Practical Tips
- Use approximate equivalents for quick conversions, such as considering one meter to be about 39.37 inches.
- Remember that the American liquid gallon is approximately 3.785 liters.
Warnings & Risks
- Do not assume all gallons are equal; the American and British gallons differ in volume.
- Be cautious when converting between weight-based measures like pounds and volume-based measures like cubic inches.
Modern Application
While this chapter focuses on historical systems of weights and measures, understanding these foundational concepts is crucial for modern survival preparedness. Accurate measurement remains essential in pharmaceuticals, cooking, and construction, where slight errors can have significant consequences.
Frequently Asked Questions
Q: What is the difference between an American liquid gallon and a British imperial gallon?
The American liquid gallon is based on the volume of 3785.434 grams of water at 4°C, whereas the British imperial gallon is defined as the volume of 10 pounds of pure water at 62°F.
Q: How does the Troy pound differ from the commercial (avoirdupois) pound?
The Troy pound is subdivided into 12 ounces, each ounce into 20 pennyweights, and each pennyweight into 24 grains. In contrast, the avoirdupois pound consists of 16 ounces.
Q: What is the significance of the theoretical meter in relation to the metric system?
The theoretical meter was defined as one forty-millionth part of the length of the meridian from pole to equator, while the actual meter is based on a material prototype maintained by the International Metric Bureau.