Another method, which is a modification of that of Dupré, is as follows:--The ash obtained by the calcination of the flour (or bread), is fused, together with four times its weight of pure mixed sodium and potassium carbonates, the fused mass treated with hydrochloric acid, the solution evaporated to dryness and the separated silica collected and weighed. A few drops of sodium phosphate solution are added to the filtrate from the silica, then ammonium hydroxide in excess, by which the calcium, magnesium, ferric and aluminium phosphates are precipitated. The two latter are next separated by boiling the liquid with an excess of acetic acid (in which they are insoluble), and brought upon a filter, washed, dried, and weighed. The iron sometimes accompanying the precipitate of aluminium phosphate, can be determined by reduction with zinc and titration with potassium permanganate. If the presence of alum is indicated by the logwood test, and it is quantitatively determined by either of the preceding methods, it has been suggested that an allowance be made for the small proportion of aluminium silicate occasionally found in unadulterated flour or bread, and a deduction from the total alum present of one part of alum for every part of silica obtained is considered proper. The weight of aluminium phosphate found, multiplied by 3·873, or by 3·702, gives respectively the corresponding amounts of potash-alum or ammonia-alum contained in the sample examined. BREAD. Bread is usually prepared by mixing flour with water, kneading it into a uniform dough, submitting it to a process of “raising,” either by means of a ferment or by the direct incorporation of carbonic acid gas, and finally baking the resulting mass. Unleavened bread, however, is made by simply kneading flour with water, with the addition of a little salt, and baking. The oatcake of the Scotch, the passover bread of the Israelites, and the corncakes of the Southern States are the best known varieties of unleavened bread. The porosity peculiar to raised bread is caused by the generation of a gas, either previous to, or during the process of baking. In former times (and to some extent at present, notably in Paris), fermented bread was made by the use of _leaven_, which is dough in a state of incipient decomposition; but in this country, the common agent employed in raising bread is yeast, which consists of minute vegetable cells (_Torula cerevisiæ_) forming either the froth or deposit of fermenting worts. By the action of these ferments, the gluten of the flour first undergoes a modification and enters into a peculiar combination with the starch-granules, which become more or less ruptured; the soluble albumen is rendered insoluble, and the starch is transformed, first into sugar, then into carbonic acid and alcohol. These changes are perfectly analogous to those which occur in the fermentation of the wort in the preparation of fermented liquors.