Using Weight to Measure Liquid Volumes for Compounding
These scales typically have accuracies of 0.001% and are easy to use. Some scales that have features specifically designed to aid in compounding such as; a count down feature where the display shows the weight remaining to reach the desired cutoff point and always ends at zero for the desired weight, an analog meter display of the amount remaining to fill that aids in exact cutoff, an audible signal at cutoff, and others.
Most recipes call for fluid volumes in milliliters or liters. If the user would rather work with weights it would be wise to convert the fluid volume to its equivalent weight at the time the recipe is stored. This requires the user to enter the density of the fluid at room temperature into a very simple equation to determine the equivalent weight of the fluid volume. The equation states: The equivalent weight of the desired volume (in grams) = the density of the fluid at room temperature (expressed as grams per liter) X the volume of fluid required (expressed as liters). Please be sure that the units are consistent, in other words, grams = grams/liter X liters, or milligrams = milligrams/milliliter X milliliters. It is also wise to store the fluid volume required and the density used as notes to the recipe so that calculations can be rechecked if desired.
Cutoff at the proper quantity is usually much easier with weight (especially if the scale has cutoff aids) than with a measuring beaker. The reversal of an overfilling is also much easier with the scale.
The user must remember that using weight as the measurement device will not change the volume of fluid required (it had better not) and the user must select the proper container for holding the finished recipe and probably allowing for proper stirring (or shaking) of the final solution. The user should remember that when solids go into solution they change the density of the solution, but not the volume of the solution.
Building a compound that requires one or more fluids measured based upon weight equivalents will save some time, building the compound in its final container will save more time. Scaling a recipe up or down is much easier if everything is expressed as a weight.