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—Perhaps because few physicians are in the habit of prescribing solutions of percentage strength, a difference between medical and pharmaceutical arithmetic in this respect seems to have generally escaped notice. The physician will probably suppose that in prescribing 48 grains of a soluble salt to a fluid ounce [480 minims] of a dissolving menstruum he is ordering a ten percentum mixture; but if he write simply for a fluid-ounce of a 10% solution, he (or rather his patient) will usually get but 45.6 grains of the medicament. This not inconsiderable discrepancy arises from the apparently common pharmaceutic practice of reckoning a fluid-ounce by weight, instead of by measure, as 456 grains, and computing percentages on the latter basis. For example: A well-known firm of manufacturing chemists label their tablets of cocaine muriate with the information that " each tablet contains 2¼ grains,... or the required quantity to form, with 1 fluid
Percentum Solutions in Pharmacy.. JAMA. 1892;XVIII(5):143. doi:10.1001/jama.1892.02411090023008