Not infrequently dispensers put powders, such as bismuth and magnesia, into a bottle, and pour mucilage directly upon them, the result being that the powders are diffused in a lumpy condition. Powders ought always to be mixed with water in a mortar before adding mucilage. We remember a candidate at the Minor examination, who had a mixture containing powdered rhubarb and bicarbonate of sodium to dispense, giving in the mixture with the rhubarb floating on the surface in little balls ! Had he carefully mixed the powders with water before pouring into the bottle, this would not have happened.

When fluids are to be mixed which decompose each other, or which may form combinations, the order of mixing may have a considerable influence on the condition and appearance of the mixture. Example:

If the mucilage be added to the iron solution the two form a gelatinous mass, which will not make a clear solution with the rest of the water. But a clear yellow solution is obtained if the liquor and mucilage are each first diluted with half of the water and then mixed, or if the liquor is mixed with all the water and the mucilage added last.

When vegetable substances, wholly or partly soluble in water, especially such as contain tannin or like constituents, have to be mixed with metallic or earthy salts, the rule is that both the vegetable substance and the salt should be separately dissolved in a large portion of the water and mixed. If a precipitate is formed it is then easily diffused by shaking.