A very common mode of aerating bread in America is by the effervescence of an acid and an alkali in the flour. The carbonic acid gas thus formed produces minute air-cells in the bread, or, as the cook says, makes it light. When this process is performed with exact attention to chemical laws, so that the acid and alkali completely neutralize each other, leaving no overplus of either, the result is often very palatable. The difficulty is, that this is a happy conjunction of circumstances which seldom occurs. The acid most commonly employed is that of sour milk, and, as milk has many degrees of sourness, the rule of a certain quantity of alkali to the pint must necessarily produce very different results at different times. As an actual fact, where this mode of making bread prevails, as we lament to say it does to a great extent in this country, one finds five cases of failure to one of success. It is a woful thing that the daughters of New England have abandoned the old respectable mode of yeast brewing and bread raising for this specious substitute, so easily made, and so seldom well made. The green, clammy, acrid substance called biscuit, which many of our worthy republicans are obliged to eat in these days, is wholly unworthy of the men and women of the Republic. Good patriots ought not to be put off in that way,--they deserve better fare. As an occasional variety, as a household convenience for obtaining bread or biscuit at a moment's notice, the process of effervescence may be retained; but we earnestly entreat American housekeepers, in Scriptural language, to stand in the way and ask for the old paths, and return to the good yeast-bread of their sainted grandmothers. If acid and alkali must be used, by all means let them be mixed in due proportions. No cook should be left to guess and judge for herself about this matter. There is an article, called "Preston's Infallible Yeast Powder," which is made by chemical rule, and produces very perfect results. The use of this obviates the worst dangers in making bread by effervescence. Of all processes of aeration in bread-making, the oldest and most time-honored is by fermentation. That this was known in the days of our Saviour is evident from the forcible simile in which he compares the silent permeating force of truth in human society to the very familiar household process of raising bread by a little yeast.