The various modes of making bread have nainly for their object the production of spon-;iness or lightness, by which a lare quantity f air is retained in it, which gives to a loaf hat lightness and uniformity of structure for vhich it is so highly prized. There are va-ious means by which this object is accom- Ushed, as by the re-action of acids upon the lkaline carbonates, which is the course gene-ally followed in the extemporaneous preparation of breed. A process sometimes fol-owed, though objectionable on some accounts, s that of thoroughly mixing bicarbonate of oda with flour, and then neutralizing it with in equivalent quantity of hydrochloric acid. The re-action that occurs in this case is best inderstood when expressed in symbols, thus: a. 0. 2C.0.H-H. Cl.=Na. Cl.+H. 0.+2C. D.s; that is, one equivalent of bicarbonate of soda and one equivalent of hydrochloric acid ire resolved, when brought together, into one iquivalent of the chloride of sodium or common salt, one equivalent of water, and two ;quivalents of carbonic acid gas. The advan-;ages ol this method are, that if proper care is ;aken, the products formed during the re-ac-;ion, are not in the least injurious to the sys-:em. The common salt is a necessary consti-;uent of the blood, and the water and carbolic acid are dissipated by the heat of baking; ;he latter being retained by the pores or vesi-:les of the bread until it is baked, by which its lightness is preserved. The objections to this process are, that the acid may contain poisonous impurities, or may not be of uniform strength, and is itself a deadly poison, ind a dangerous substance to keep about a house where there are children or careless servants. Should this substance be swallowed by accident or design, the antidote is carbon-ite of soda, or chalk—the former to be preferred in all cases. When this acid is spilled upon articles of clothing, carbonate of soda dissolved in water will remove it. Another more common process lot making bread is, by the use ol cream of tartar or bis tartrate ol potash, an ucid salt, and bicarbonate of soda. This process is based upon the fact that the tartaric acid in cream of tartar is not completely neutralized, and has the power to combine with the soda of the bicarbonate ot soda, and displace the carbonic acid of that substance. This re-action is easier comprehended when illustrated by symbols, thus : K. 0. H. 0. Trc.-f-Na. 0. 2C. 0==K. 0. Na.O. Trc.-f-2C. 0*.-f-H. 0.; that is, tartrate of Eoda and potassa or Rochelle salt, which is a biba-sic salt, is formed, and carbonic acid and water are displaced, performing the same office as in the other method. This mode of bread making is not liable to the objections urged against that where the muriatic acid is used, and according to some investigations made on this subject by my brother, Professor C. W. Wright, of this city; bread made in this way agrees better with persons laboring under certain forms of indigestion, than that made by either yeast or the muriatic acid process. The Rochelle salt, and in fact all salts containing an organic acid, are converted into carbonates oi the bases with which they are combined when they are taken into the blood of animals ; and in the present instance we have tormed the carbonates of potassa and soda. In former times pearl-ashes, or saleratus and sour milk, were more extensively used in bread making than at present. Occasionally carbonate of soda was substituted for saleratus. In this process it is the lactic acid which displaces the carbonic acid gas from the saleratus, or the carbonate of potash of chemists. The following is the re-action, expressed in symbols: K. 0. C. 0!.+Lc.=K. 0. Lc.+C. O2.; that is, the lactate of potash is formed and carbonic acid evolved. If an excess of saleratus be used, the bread is of a yellow color and disagreeable alkaline taste ; if deficient, it is watery, heavy, and very indigestible. Saleratus, by itself, is a poison when taken in a large dose; several persons having lost their lives by swallowing it. The antidote is vinegar, or any oily or fatty substance, as sweet oil or butter. Carbonate of ammonia is occasionally used in the preparation of bread, and being a very volatile body, rises as a gas, and diffuses ii self through the dough during the operation of baking, by which the same object is accomplished as in other processes. The soapy taste which is perceived in the various kinds ot pound-cakes, & c, in which butter or lard is a constituent, is due to the formation of a soap, and where the carbonate of ammonia or sal volatile is used, volatile liniment is generated, which is a species of soap. The carbonates of the alkalies should, however, never be employed in the preparation of these substances, as they are very apt to produce derangement of the system of persons in delicate health. The so-called " quick yeast," and all similar preparations, consist of the carbonate of soda and cream of tartar or tartaric acid, which, when dissolved in water, causes the evolution of carbonic-acid, and which, by rising through the dough, is the cause of its lightness. The foregoing substances are more frequently used in the preparation of biscuit, rolls; & c than other lorms of bread. The very ancient process of rising bread by means of leaven or yeast, depends also upon the developement of carbonic acid; but in this case the carbonic acid is formed from the sugar that exists in the dough, and which undergoes the vinous fermentation, whereby alcohol and carbonic acid are generated. The alcohol is expelled by the operation of baking, but by proper care can be collected and examined. The sugar is formed by the transformation of starch into that substance. Bread, when first baked, is always lighter than it is after it has cooled, from the expanded state of the gases in its pores by the high temperature to which it has been subjected ; but the contraction which it suffers after it has become cold is due to the loss of water by evaporation. In the operation of baking, the starch is in part rendered soluble in water, being converted into a species of gum, at the same time sugar is tormed, and the bread rendered much more nutritive and digestible than flour that has not been subjected to this operation. Good bread generally contains about SO jwr cent, of water. Common salt prevents the rapid drying of bread, and the same effect is produced by the admixture of potato meal. Various substances are used to improve the quality of inferior or damaged flour. Thus alum is used to whiten bread made of bad flour and make it rise better, and a small quantity is not injurious but decidedly advantageous. Sulphate of copper or blue vitriol, which is sometimes used, is a very poisonous adulteration, and should never be employed. The latter substance is used with the view of whitening the flour, which, when damaged, is generally of a yellow color, and by the admixture of a blue substance it is changed to white, on the same principle that indigo is used to whiten linen articles in washing. There are establishments in this city where the flour is worked up with soap-suds, made from common yellow soap, instead of water. On several occasions I have seen distinct particles of soap in bread purchased from these bakeries, and it is frequently perceptible to the taste. What their object is in employing this nauseating substance, I cannot conjecture, unless it is to neutralize the acid formed during the fermentation ot the dough, and by which acetic acid or vinegar is formed, from a partial oxydation of the alcohol, which is always generated in these cases. MRS. JULIA A. COOK. Cincinnati, June, 1853.