Powders which are insoluble in aqueous menstrua and which do not readily diffuse in water should be rubbed down in a mortar with some of the fluid, for if put into the bottle and shaken with the fluid, many powders of that kind float about in little balls, which are afterwards difficult to diffuse. Especially is this the case with vegetable powders, carbonate of magnesium, light calcined magnesia, calomel, and precipitated sulphur. Ipecacuanha and some other vegetable powders form a doughy mass if put into a bottle and water poured upon them.

The best plan is to triturate such powders in a mortar with syrup or glycerin, if ordered, or else with just enough water to make a thin cream (neither more nor less), and rub together until quite uniform before further dilution, e.g.:

The rhubarb and soda may with skill be diffused by the shaking-up method, but more froth is produced than the tincture will dissipate. It is preferable to begin with a mortar, powder the ammonium carbonate, add the rhubarb and soda, triturate with the syrup, dilute with water, add the tincture, and fill up.

A universal rule which no dispenser should neglect is: All potent substances which are slow of solution, such as per chloride of mercury, strychnine, and the like, should be completely dissolved before they are placed in the bottle.