The saccharine fermentation, or the formation of sugar from starch, is interesting, though it does not influence such operations as are included in our Domestic Manipulations. If starch is dissolved in water, a little wheat flour added, and the whole exposed to a moderately warm temperature, it will be found that after a few days, varying in number with the degree of warmth, the starch has disappeared, and the liquid has become sweet, from the formation of sugar. The same change takes place with much greater rapidity, if starch is boiled with a solution of malt, which contains an active principle called _diastase_, capable of bringing about this fermentation in a short time. The formation of sugar from starch is an operation which constantly occurs in all growing seeds, the effect being to change an insoluble substance such as starch, into one which is capable of being dissolved in the juices of the young plant, and nourishing it during the early stages of its growth. In the operation of malting barley, the change is induced artificially, for the purpose of producing sugar in the malt, which is afterwards made to undergo the second kind of fermentation, namely, the vinous, or that in which spirit is produced. When sugar, either that which naturally exists in many plants, or as formed from starch as just mentioned, is dissolved in water, so as to form a moderately weak solution, and the whole exposed to a degree of warmth varying from seventy to eighty degrees, it rapidly undergoes a remarkable change, provided a small quantity of any vegetable ferment is present—such as yeast, or the juice of the grape or of many other fruits. The sugar wholly disappears, and is resolved into two substances—one a gas, termed carbonic acid, which escapes giving rise to a slow effervescence; and the other, a portion of spirit, which remains in the liquid. This kind of fermentation is much more difficult to prevent than to establish; in making syrups, it is found specially annoying; for if the quantity of sugar used is too small, the syrup is certain to ferment and spoil; and if too much is added, it crystallizes out in the solid form; as a general rule, however, it is found that two parts, by weight, of sugar, to one part, by weight, of water or other liquid—such as the juice of fruits, made into a syrup by boiling for a short time—neither ferments nor crystallizes. In the act of fermentation the spirit produced by the process last described is changed into acetic acid, or vinegar. Here, also, the presence of some substance capable of commencing the fermentation is requisite, for pure spirit and water will not undergo the change. The ferment employed may be the vinegar-plant—or it may be a little vinegar, which may have been previously formed.