y, is
"mildly purgative in doses of from 1 to 2 ounces." The claim is made by
the makers of phosphate baking powders that the phosphates of sodium and
calcium, products left after the baking, restore the phosphates which
have been lost from the flour in the bran. This baking powder residue
does not restore the phosphates in the same form in which they are
present in grains and it does furnish them in larger amounts--nearly
tenfold. However, the residue from these powders is probably less
objectionable than that from alum powders. The chief drawback to the
phosphate powders is their poor keeping qualities.

198. Alum Baking Powders.--Sulphuric acid is the acid constituent of
these powders. The alums are double sulphates of aluminium and an
alkali metal, and have the general formula _x_Al(SO_{4})_{2} in which
_x_ may be K, Na, or NH_{4}, producing respectively a potash, soda, or
ammonia alum. Potash alum is most commonly used, soda and ammonia alums
to a less extent. The reaction takes place as follows:

475 504 157
2 NH_{4}Al(SO_{4})_{2} + 6 NaHCO_{3} = Al_{2}(OH)_{6}

426 132 264
+ 3 Na_{2}SO_{4} + (NH_{4})_{2}SO_{4} + 6 CO_{2}.

If it is a potash or soda alum, simply substitute K or Na for NH_{4}
throughout the equation. The best authorities regard alum baking powders
as the most objectionable. Ammonia alum is without doubt the worst form,
since all of the ammonium compounds have an extremely irritating effect
on animal tissue. Sulphates of sodium and potassium are also
objectionable. Aluminium hydroxide is soluble in the slightly acid
gastric juice and has an astringent action on animal tissue, hindering
digestion in a way similar to the alum itself. Many of the alum powders
contain also mono-calcium phosphate; the reaction is as follows:

475 234 336
2 NH_{4}Al(SO_{4})_{2} + CaH_{4}(PO_{4})_{2} + 4 NaHCO_{3}

245 136 132
= Al_{2}(PO_{4})_{2} + CaSO_{4} + (NH_{4})_{2}SO_{4}

284 176 72
+ 2 Na_{2}SO_{4} + 4 CO_{2} + 4 H_{2}O.

These are probably less injurious than the straight alum powders,
although the residues are, in general, open to the same objection.

199. Inspection of Baking Powders.--Many of the states have enacted
laws seeking to regulate the sale of alum baking powders. Some of these
laws simply