In previous laboratory exercises, the student has become familiar with weighing and measuring pharmaceutical substances, and with the limits of these weights and measures. To decide which method to use, the pharmacist must consider the time involved in each method, then physical-chemical properties of the liquid to be measured, and the type of equipment available.
Pipets deliver the most accurately measured volume of a liquid.
Unfortunately, there are several disadvantages to the use of pipets which make them unavailable in the typical pharmacy. There are many different capacities of pipets available, and the pharmacist would likely need to stock several sizes. One practical and fairly rapid way to measure volumes of less than 2 mL is to use a dropper. But it is necessary to determine the volume of a drop of the particular liquid to be measured by calibrating a dropper . This term can be very confusing.