to act on baking soda, and is
a convenient and safe ingredient for baking powder. When soda and
cream of tartar are mixed dry, they do not react on each other,
neither do they combine rapidly in _cold_ moist dough, but as soon as
the heat of the oven penetrates the doughy mass, the cream of tartar
combines with the soda and sets free the gas needed to raise the
dough. The gas expands with the heat of the oven, raising the dough
still more. Meanwhile, the dough itself is influenced by the heat and
is stiffened to such an extent that it retains its inflated shape and
spongy nature.

Many housewives look askance at ready-made baking powders and prefer
to bake with soda and sour milk, soda and buttermilk, or soda and
cream of tartar. Sour milk and buttermilk are quite as good as cream
of tartar, because the lactic acid which they contain combines with
the soda and liberates carbon dioxide, and forms a harmless residue in
the dough.

The desire of manufacturers to produce cheap baking powders led to the
use of cheap acids and alkalies, regardless of the character of the
resulting salt. Alum and soda were popular for some time; but careful
examination proved that the particular salt produced by this
combination was not readily absorbed by the stomach, and that its
retention there was injurious to health. For this reason, many states
have prohibited the use of alum in baking powders.

It is not only important to choose the ingredients carefully; it is
also necessary to calculate the respective quantities of each,
otherwise there will be an excess of acid or alkali for the stomach to
take care of. A standard powder contains twice as much cream of tartar
as of bicarbonate of soda, and the thrifty housewife who wishes to
economize, can make for herself, at small cost, as good a baking
powder as any on the market, by mixing tartar and soda in the above
proportions and adding a little corn starch to keep the mixture dry.

The self-raising flour, so widely advertised by grocers, is flour in
which these ingredients or their equivalent have been mixed by the
manufacturer.

212. Soda Mints. Bicarbonate of soda is practically the sole
ingredient of the soda mints popularly sold for indigestion. These
correct a tendency to sour stomach because they counteract the surplus
acid in the stomach, and form with it a safe neutral substance.

Seidlitz powder is a simple remedy consisting of two powders, one
containing bicarbonate of sod