Unit 27 Apothecaries’ System

Basic Principles of the Apothecaries’ System The apothecaries’ system is an old English system of measurement. –In the apothecaries’ system, the basic unit of weight is the grain. –The basic units for volume or liquid measurement are the minim, fluid dram, and fluid ounce. –These unit abbreviations are usually written in front of the number.

Basic Principles of the Apothecaries’ System Frequently Roman numerals are used in the apothecary system. Symbols are used for dram and ounce as shown on the chart in your text. Because serious medication errors can result if the wrong amount is used, these symbols are usually no longer used.

Converting Apothecary, English, and Metric Measurements To convert units in the apothecaries’ system, find equivalent measurements on the chart in your textbook and set up a proportion. To convert units between the three systems, set up a proportion. –Note that these are approximate equivalent values. Exact values are not obtained when converting between systems of measurement.

Apothecaries’ System Example: A medical laboratory technician is preparing a solution. She needs 20 grams (g) of baking soda for the solution. The only scale weighs in grains (gr). How many grains of baking soda should she use?

Apothecaries’ System –Find an apothecary-metric equivalent and set up a proportion: 1 gram : 15 grains –Multiply the extremes: 1 x X = X –Multiply the means:15 x 20 = 300 –Write as means equals extremes: 1X = 300X = 300gr –The technician needs 300 grains of baking soda for the solution.

Practical Problem A biological technician is preparing a saline solution that requires 3.5 grains (gr) of sodium chloride (NaCl). How many milligrams (mg) of NaCl does she need?

Practical Problem Find an apothecary-metric equivalent, set up a proportion, and cross-multiply: The technician needs 210 mg of NaCl.