it is free from the volatile oil which, as above stated, gives it its peculiar odor.  The wet method devised by Scheele is as follows:—­Make one ounce of freshly-burnt lime into a milk with from four to six ounces of hot water.  To the milk of lime, four ounces of powdered benzoin and thirty ounces of water are to be added, and the mixture boiled for half an hour, and stirred during this operation, and afterwards strained through linen.  The residue must be a second time boiled with twenty ounces of water and strained, and a third time with ten ounces; the fluid products must be mixed and evaporated to one-fourth of their volume, and sufficient hydrochloric acid added to render them slightly acid.  When quite cold, the crystals are to be separated from the fluid by means of a linen strainer, upon which they are to be washed with cold water, and pressed, and then dissolved in hot distilled water, from which the crystals separate on cooling.  When hydrochloric acid is added to a cold concentrated solution of the salts of benzoic acid, it is precipitated as a white powder.  If the solution of the salts of this acid is too dilute and warm, none or only a portion of the benzoic acid will be separated.  However, the weaker the solution is, and the more slowly it is cooled, the larger will be the crystals of this acid.  In the preparation of this acid in the wet way, lime is to be preferred to every other base, because it forms insoluble combinations with the resinous constituents of the benzoin, and because it prevents the gum-resin from conglomerating into an adhesive mass, and also because an excess of this base is but slightly soluble.

Stoltze has recommended a method by which all the acid can be removed from the benzoin:—­The resin is to be dissolved in spirit, to which is to be added a watery solution of carbonate of soda, decomposed previously by alcohol.  The spirit is to be removed by distillation, and the remaining watery solution, from which the resin has been separated by filtration, treated with dilute sulphuric acid, to precipitate the benzoic acid.  This method gives the greatest quantity of acid, but is attended with a sacrifice of time and alcohol, which renders it in an economical point of view inferior to the above process of Scheele.  It is so far valuable, that the total acid contents of the resin can be determined by it.

Dr. Gregory considers the following process for obtaining benzoic acid the most productive.  Dissolve benzoin in strong alcohol, by the aid of heat, and add to the solution, whilst hot, hydrochloric acid, in sufficient quantity to precipitate the resin.  When the mixture is distilled, the benzoic acid passes over in the form of benzoic ether.  Distillation must be continued as long as any ether passes over.  Water added towards the end of the operation will facilitate the expulsion of the ether from the retort.  When the ether ceases to pass over, the hot water in the retort is filtered, which deposits benzoic acid on cooling.  The benzoic ether and all the distilled liquids are now treated with caustic potash until the ether is decomposed, and the solution is heated to boiling, and super-saturated with hydrochloric acid, which afterwards, on cooling, deposits, in crystals, benzoic acid.