This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
The prescriber should be careful in deciding whether or not to use this word before the vehicle. If it had been left out in the prescription given on p. 44, the bulk of the mixture would have been nearly 10 1/2 fluid ounces; 315. c.c., and the amount of the ingredients in each dose would have been less than was intended.
The dispenser should bear the following rules in mind: (1) Read the prescription through first. (2) Next write the directions, so that they have time to dry. (3) Solution by heat should not be used if more of the salt is ordered than will dissolve in cold water. In such case it must be suspended. (4) With fluids, measure them in such an order that the measuring glass shall be finally rinsed out with the vehicle. (5) Use glass scale pans. (6) Clean and put away everything directly after use. (7) If in the slightest doubt ask the prescriber. (8) If finally the prescription contains any insoluble matter, label "Shake the bottle." (9) If the medicine is very poisonous, label it as such and use a distinctive bottle. (10) If for outward application only, label it as such. (II) In dispensing substances chemically incompatible, if there is any likelihood that the new body formed is dangerous, communicate with the prescriber before dispensing (e.g., Potassium Iodide prescribed with Spiritus AEtheris Nitrosi forms free iodine; alkaloids are precipitated by alkalies). Should there be no such reason against dispensing the prescription (e.g., Liquor Potassae and Ferrum Dialysatum), keep the incompatibles as far apart as possible by diluting each with the vehicle before mixing.