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 were constantly discovering some new method for accelerating the long labour of triturating, which many operators still living can remember. Venice turpentine, or oil of turpentine, various essential oils, sulphur, the saliva of a person fasting, and rancid fat were among the earlier expedients adopted and subsequently discarded. The turpentines made the ointment irritating, the sulphur formed a compound, and the rancid fat was found to be worse than the turpentines. Nitrate of potash, sulphate of potash, stearic acid, oil of almonds and balsam of Peru, the precipitation of the mercury from its solution in nitric acid, spermaceti, glycerin, and oleate of mercury have been more modern aids.

It would be outside the purpose of this sketch to deal with the questions which the numerous processes suggested have raised. Apparently it is not completely settled now whether the pill, the powder, and the ointment depend for their efficiency on any chemical action such as the oxidation of the metal in the cases of the two former, or on a solution in the fat in the case of the ointment. These theories have been held, and do not seem unlikely; but there also seems good reason to believe that mercury in a state of minute division has definite physiological effects by itself. At any rate, it is well established that the more perfectly the quicksilver is "killed" the more efficient is the resulting compound.

SILVER.

The moon was universally admitted under the theory of the macrocosm and the microcosm to rule the head, and as silver was the recognised representative of Luna among the metals the deduction was obvious that silver