We find, says Dr. Hales, by the chymical analysis of vegetables, that their substance is composed of sulphur, volatile salts, water, and earth, which principles are endued with mutual attracting powers. There enters likewise in the composition, a large portion of air, which has a wonderful property of attracting in a fixed, or of repelling in an elastic state, with a power superior to vast compressing forces. It is by the infinite combinations, actions, and reactions of these principles, that all the operations in animal and vegetable bodies are effected.—Boerhaave, who is somewhat more particular with regard to the constituent parts of vegetables, says, that they contain an oil mixed with a salt in form of a sapo, and that a saponaceous juice arises from the mixture of water with the former. Thus we see, from the composition of grapes, that they have all the necessary principles to form a most exquisite liquor, capable, by a gentle heat, to be greatly attenuated. They abound with elastic air, water, oils, acid, and neutral salts, and even saponaceous juices.—The air contained in the interstices of fluids is more in quantity than is commonly apprehended. Sir Isaac Newton has proved that water has forty times more pores than solid parts; and the proportion, likely, is not very different in vegetable juices. When the fruit is in its natural entire state, the viscidity of the juices, and their being enveloped by an outward skin, prevent the expansion of the inclosed air; it lies as it were inactive. In this forced state, it causes no visible motion, nor are the principles, thus confined, either subjected to any apparent impressions of the external atmosphere, or so intimately blended as when they are expressed. A free communication of the external air, with that contained in the interstices of the liquor, is required to form a perfect mixture. By what means this is effected, what alterations it produces, or, in general, in what manner the juice of the grape becomes wines, must be the subject of our next inquiry. The process of a perfect fermentation is undoubtedly the same (where the due proportions of the constituent parts, forming the must, are exactly kept) whatever vegetable juices it is excited in. For this reason, we will observe the progress of this act in beers and ales, these being subjects we are more accustomed to, and where the characters appear more distinct, in order to apply what may be learned from thence to our chief object, the business of the brewer. SECTION VIII. _OF FERMENTATION IN GENERAL._