All medicines are mixed by apothecaries' weight: this must be carefully borne in mind, as the apothecaries' drachm is more than double that of avoirdupois or the common weights. A set of the proper weights may be obtained at any scale-makers ; and they will be found to be marked thus: -

5 Grains 158 Medicine Weights And Measures 2 Scruples thus,

Drachms thus, 158 Medicine Weights And Measures 4 Ounces thus, apothecaries' weight. 20 grains make 1 scruple 3 scruples " 1 drachm 8 drachms " 1 ounce 12 ounces " 1 pound Medicines are always purchased wholesale by avoirdupois weight. For compounding liquids an apothecary's glass measure will be found indispensable. A two or three ounce size will be large enough for most purposes.