=Harmfulness of Baking Powder Residues.=--The question of the harmfulness of the residues left by the various forms of baking powder is one which has been of much interest to the hygienist and physician. It is not claimed in any case that these residues are beneficial. The principal question which has been discussed is which of them is the least harmful. This is a question which it is not proper to enter into in this manual. It might, however, not be out of place to say that the use of chemical reagents for leavening bread is not as advisable as the use of the ordinary fermentation. It would be better, evidently, if all people used more yeast bread and less baking powder rolls. At the same time the utility and convenience of baking powder cannot be denied, and this is a factor which must be taken into consideration in the general discussion and final resolution of the question. =Character of Alum Residues.=--Every one is agreed that the substance known as alum, namely, the sulfate of alumina in conjunction with another mineral or base, such as soda, potash, or ammonia, is not a desirable constituent of food products. In the manufacture of baking powders containing alum an effort is made to so balance the constituents that when the reaction is completed no undecomposed alum remains. If this condition is secured in every instance the materials which remain in the bread are not alum but the residues above mentioned, consisting of aluminium hydrate, and sulfates of soda, potash, or ammonia.