"Mr. Davy made a great number of comparative experiments with other substances, mixed in different proportions with new bread flour. The fixed alkalies, both in their pure and carbonated state, when used in small quantity, to a certain extent were found to improve the bread made from new flour; but no substance was so efficacious in this respect as carbonate of magnesia.
"The greater number of his experiments were performed on the worst new seconds flour Mr. Davy could procure. He also made some trials on seconds and firsts of different quality. In some cases the results were more striking and satisfactory than in others; but in every instance the improvement of the bread, by carbonate of magnesia, was obvious.
"Mr. Davy observes, that a pound of carbonate of magnesia would be sufficient to mix with two hundred and fifty-six pounds of new flour, or at the rate of thirty grains to the pound. And supposing a pound of carbonate of magnesia to cost half-a-crown, the additional expense would be only half a farthing in the pound of flour.
"Mr. Davy conceives that not the slightest danger can be apprehended from the use of such an innocent substance, as the carbonate of magnesia, in such small proportion as is necessary to improve bread from new flour."
METHOD OF DETECTING THE PRESENCE OF ALUM IN BREAD.
Pour upon two ounces of the suspected bread, half a pint of boiling distilled water; boil the mixture for a few minutes, and filter it through unsized paper. Evaporate the fluid, to about one fourth of its original bulk, and let gradually fall into the clear fluid a solution of muriate of barytes. If a copious white precipitate ensues, which does not disappear by the addition of pure nitric acid, the presence of alum may be suspected. Bread, made without alum, produces, when assayed in this manner, merely a very slight precipitate, which originates from a minute portion of sulphate of magnesia contained in all common salt of commerce; and bread made with salt freed from sulphate of magnesia, produces an infusion with water, which does not become disturbed by the barytic test.
Other means of detecting all the constituent parts of alum, namely, the alumine, sulphuric acid, and potash, so as to render the presence of the alum unequivocal, will readily suggest itself to those who are familiar with analytical chemistry; namely: one of the readiest means is, to decompose the vegetable matter of the bread, by the action of chlorate of potash, in a platina crucible, at a red heat, and then to assay the residuary mass—by means of muriate of barytes, for sulphuric acid; by ammonia, for alumine; and by muriate of platina, for potash[46]. The above method of detecting the presence of alum, must therefore be taken with some limitation.
There is no unequivocal test for detecting in a ready manner the presence of alum in bread, on account of the impurity of the common salt used in the making of bread. If we could, in the ordinary way of bread making, employ common salt, absolutely free from foreign saline substances, the mode of detecting the presence of alum, or at least one of its constituent parts, namely, the sulphuric acid, would be very easy. Some conjecture may, nevertheless, be formed of the presence, or absence, of alum, by assaying the infusion of bread in the manner stated, p. [109], and comparing the assay with the results afforded by an infusion of home-made or household bread, known to be genuine, and actually assayed in a similar manner.
EASY METHOD OF JUDGING OF THE GOODNESS OF BREAD CORN, AND BREAD-FLOUR.
Millers judge of the goodness of bread corn by the quantity of bran which the grain produces.