Chapter II. 

 METROLOGY— WEIGHTS AND MEASURES 



Metrology is the science of weights and measures. 



Weight is the sum of the attraction of gravity existing be- 

 tween the earth and a body upon its surface, and in weighing we 

 simply balance a substance against another known force. 



There are several standards of weights used in the United 

 States, with which the physician, veterinarian and pharmacist 

 must become familiar. Those most used are the Troy or Apothe- 

 caries' weights and the Wine or Apothecaries' measures, besides 

 which are the Avoirdupois weights, and Metric weights and meas- 

 ures. 



Table of Avoirdupois Weights 



437.5 grains (gr.) = 1 ounce (oz.) 



16 oz. = 1 pound (lb.) = (7000gr.) 



100 IbF. = 1 hundredweight (cwt.) 



20 cwt. = 1 ton 



This table is never used in prescribing but is the one used al- 

 most exclusively in buying and selling all solid and many liquid 

 drugs. When we purchase a "pound" we get an Avoirdupois 

 pound, or 7000 grains. If we order an " oz. ' ', we receive an Avoir- 

 dupois ounce or 437.5 grains as oz. stands for Avoirdupois ounce 

 only. Many powerful drugs, like strychnine, morphine, etc., are 

 usually handled in 1/8 oz. bottles, but these do not contain 1/8 

 of an Apothecaries' ounce or 60 grains, but 1/8 of an Avoirdupois 

 ounce or about 54.7 grains. 



Table op Apothecaries' or Troy Weights 



20 grains (gr.) ^= 1 scruple (3) 



3 scruples ^ 1 drachm (5) = 60 gr. 



8 drachms ^ 1 ounce (§) = 480 gr. 



12 ounces = 1 pound (lb) = 5760 gr. 



The grain used in this system is the same as that of the Avoir- 

 dupois, but the ounces contain 480 grains against 437.5 of the 

 Avoirdupois, while the pound, lb. contains 12 ounces of 480 grains, 

 or 5760 grains instead of the Avoirdupois pound of 16 ounces of 

 437.5 each or 7000 grains. 



