Let the dispenser know when he has done his task, and when once he has formed his emulsion let him add rapidly the remaining ingredients. Many an emulsion is ruined by over-manipulation, and the oil having been incorporated is thrown out again by continuous stirring when mechanical mixture is concerned.

[The late Mr. William Gilmour, experimenting on the theory that by always stirring an emulsion in one direction the oil is broken up in volume, minute globules resulting, but when the direction of stirring is reversed the oil tends to return to its original state, found that, although a difference in the size of the globules was observable when examined by the microscope, little difference was apparent to the naked eye, and the two emulsions were, from a practical point of view, identical. It was noticed, however, that by stirring in two directions a little longer time was required to finish the emulsion, and this was the case with several oils when operated on with different emulsifying agents. On the whole, he considered that not much importance is to be attached to the theory of stirring one way, but it is advisable not to reverse the direction towards the end of the process, because at that point the tendency to spoil seems to be particularly marked.-Ed.]

When liquids, limpid or viscous, are to be compounded, the gentlest manipulation should be employed. Increase of pressure generates heat, and heat is fatal to union. Thus, when olive oil, mucilage, and water are to be emulsified, while care must be taken to have the three entirely under the control and action of the pestle, at the same time lightness of hand cannot be too carefully studied.

On the contrary, when a solid has to be broken down and worked into a pasty saponaceous mass, an exactly opposite mode of treatment must be adopted. The object is to produce a kind of soap, which can only be extemporaneously manufactured by strong, continued muscular action, with evolution of heat to complete the change.