A saturated solution is often ordered. The custom is subject to criticism. Many employ the term in prescribing potassium iodide, sodium phosphate, etc., when they want a solution representing a grain to the minim. The druggist usually understands what is desired and fills the prescription accordingly, but the order is open to criticism.

A saturated solution is one that contains all of the solid that will dissolve in the given solvent. Water is usually understood to be the solvent unless otherwise specified. The amount of a salt that will be dissolved depends to some extent on the temperature and other conditions. In no instance is the finished product just one grain to the minim. When such concentration is desired the inscription may be written as:

In the case of agents, as boric acid, where a concentration of a grain to the minim is not obtainable or desired, it is even more necessary to prescribe a definite amount of the salt.

The druggist usually handles orders for saturated solutions of this class by adding the salt in slight excess of the solvent, triturating and filtering. The amount of the drug that dissolves will depend very much on the patience and energy of the compounder. The prescriber should know the solubility and arrange the prescription accordingly. For example:

Boric acid is soluble in 18 parts of water. The full amount that is possible to get into solution should not be employed, as the statement"soluble in 18 parts of water"means that 1 part is the maximum amount that may be dissolved in 18 parts of water even under the most favorable conditions and by the expenditure of unlimited time and effort. These factors cannot be expected in the filling of prescriptions; so it is always better to order an amount slightly less than the quantity indicated by the given solubility.

The inscription may be arranged as follows:

The prescriber then knows what his patient will receive.