These ingredients are now considered indispensable by the London bakers in the manufacturing of second or household bread, that is, the bread in daily use in the metropolis. The effects of alum upon bread are not well understood: but it is generally said to bleach and act as an astringent. Accum says, that " the theory of the bleaching property of alum, as manifested in the panification (making into bread) of an inferior kind of flour, is by no means well understood; and indeed it is really surprising, that the effect should be produced by so small a quantity of that substance, two or three ounces of alum being sufficient for a sack of flour. From experiments in which I have been employed, with the assistance of skilful bakers, I am authorized to state, that without the addition of alum, it does not appear possible to make white, light, and porous bread, such as is used in this metropolis, unless the flour be of the very best quality."

Mr. A. Booth, the lecturer on Chemistry, asserts, that "alum bleaches from the attraction of alumina, one of its constituent parts, to the colouring matter of the flour, and also acts as an astringent on the bread."

If these opinions are to be relied upon, of course the question is settled, as to the indispensability of alum in making London bread. Accum asserts, that he, in conjunction with skilful bakers, has tested the thing by experiments, which prove that alum cannot be dispensed with. For our part, we are inclined to think, that the whiteness of the London bread is owing, in some degree, to the process of baking, a process widely differing from that followed by women in making home-baked bread; which, as we have elsewhere asserted, is never so white or so porous, though made of the same flour, as bakers' bread. Accum, whatever talent he might possess as a chemist, was a fraudulent writer, and therefore his assertions are not to be relied on, as to the experiments which he alleges he had made. We agree with him, however, in his observation, that "the theory of the bleachinn-property of alum, etc, is by no means well understood."

The quantity of alum used in baking is much less than the public generally imagine, even by the most fraudulent of cheap-bread bakers, and indeed much smaller than many of the bakers themselves imagine. This may appear a strange assertion, and it is probably one never made before in print; but a little explanation will make the point quite clear. It is well known that the bakers are liable to a heavy fine if alum is found on their premises. To avoid this liability as much as possible, they have long been in the habit of buying the alum ready powdered at the drug-gists, under the appellation of stuff', The druggists keep this stuff, which the bakers imagine is unadulterated ground or powdered alum, but which is, in fact, a compound, consisting of one part alum, and three parts of muriate of soda, that is, common table salt. This compound is made by pounding the salt with the alum in a mortar, and is kept by the druggists in pound packages, which they sell at twopence each. For this statement we have the authority of several druggists, and the evidence of our own eyes. It may appear extraordinary that the bakers should suffer themselves to be so cheated; but be this as it may, we believe it to be the fact. It should be recollected, that few bakers are readers, particularly of scientific or medical works. In the fourth edition of Gray's supplement to the Pharmacopoeia and Treatise on Pharmacology, under the head of stuff, this term is thus defined: - "Alum, in small crystals, one pound, common salt three pounds, to mix with flour for baking." We have the evidence of our own senses for know-ing, that the respectable bakers of home or household bread do not put more than half a pound or eight ounces of stuff to a sack of flour; and this stuff, as we have shown on the authority of Gray, only contains one-fourth part, or two ounces, of alum, the remainder being common salt. Some persons, however, will ask for powdered alum, but the druggist, knowing from the quantity required and the appearance of his customer that it is wanted for baking, uniformly serves him with the before-described mixture of salt and alum. This we have frequently seen done. The object of the druggist is profit. It would be scarcely worth his while to sell powdered alum for twopence a pound. Gray, in his book, puts it down at one shilling and sixpence a pound. This is ridiculously too high to sell by the pound, but it is generally charged a penny an ounce. The writer, giving this information to his baker, he exclaimed, "You don't say sol - the infamous rogues - why the rascally druggists cheat us before we can cheat our customers!!"

Such being the case, it seems almost inconceivable, that so small a quantity as two ounces of alum in two hundred and eighty pounds of flour, the weight of a sack, should have any effect in bleaching it; especially when we consider that one hundred parts of alum contain but a fraction more than ten parts of alumina, the only constituent in alum, as we are informed, that possesses the property of bleaching. Nevertheless, there can be no doubt that alum, though perhaps not by itself, yet in conjunction with other ingredients, has the effect of whitening the bread. A circumstance occurred, which we have from indisputable authority, of a baker leaving out of his dough, by accident, his usual quantity of stuff, containing not more than two ounces of alum. The consequence was a batch of brown bread, which he was obliged to sell at half price.

Alum, it is true, is used in small quantities - for the most part in quantities too small to affect the health, perhaps, materially; but still, as it only whitens the bread, and makes it otherwise more pleasing to the eye, while it deteriorates its wholesomeness, and injures its flavour, one would suppose that the great majority of people would prefer home-baked bread, as it is called, or bread without alum. This, however, they do not do; and there is little probability that they ever will. The Londoners in particular do not like home-baked bread. There have been many instances of persons being induced for the sake of their health to eat it for a time, but they always return to the alumed bread; and we question whether there is a single baker in the metropolis who sells sufficient home-baked bread to support himself and his family.