92. TO PREPARE VARIOUS KINDS OF ESSENCES.--The manner of extracting the essential oils, being attended with considerable expense of preparations, of stills, &c. a particular description of the process, would not, it is presumed, be sufficiently interesting to warrant its insertion. But the manner of reducing the oils to the state in which they are more generally sold, and is distinguished by the term "essences" is as follows. To half a pint of alcohol, add one ounce of any of the essential oils, (lemon, cinnamon, foxberry, peppermint, &c.) and shake them together; set the mixture in a warm place for a few minutes, and if then any opaque or milky appearance remains, a little more alcohol must be added. When this has become clear, it may be diluted occasionally with new rum. The essences of foxberry and cinnamon are coloured with a few drops of tincture of red saunders; and the essence of lemon, with tincture of turmeric. 93. TO PREPARE SODA WATER.--Only two articles are requisite for this preparation; one of which is super-carbonate of soda, or of potass (sal eratus,) and the other is citric or tartaric acid. The super-carbonates are formed by passing a stream of carbonic acid gas (which is produced by adding muriatic acid to pulverized marble) through a solution of soda or potass in water;--then evaporating till it crystallizes. Citric acid is prepared from the juice of lemons; and tartaric acid (which is more generally employed) is procured from super-tartrate of potass. But these being common articles of commerce, a more minute description of the process of preparing them, may not, in this place, be expedient. The compound called soda powders, consists of about ten grains of either of the super-carbonates, with an equal quantity of either of the acids, in each paper; this compound being dissolved in a glass of water, produces violent effervescence, and if drank off at the time, gives the water a smart and agreeable acid taste. The salt and acid, if mixed in powder, must be kept perfectly dry; otherwise, they would act on each other, and soon be spoiled. On this account, they are frequently prepared in separate papers, and sold by sets. Soda water is similarly prepared on the larger scale; the salts and acid being put into a cask of water, which is so confined, that the carbonic acid can have no other vent than by forcing out the water through a pipe fixed for the purpose with a tube, &c. 94. TO PRODUCE METALLIC TREES. _Process 1._--Mix one part of a saturated solution of nitrate of silver, with twenty parts of pure water, and pour the mixture upon two parts of mercury in a phial. After some time (the mercury being left standing quietly,) the branches and the figure of a tree, formed of brilliant silver, will appear to grow from the mercury in a very beautiful manner. The silver in solution being thus robbed of its oxygen by the metallic mercury, and consequently precipitated.