Several students have sent me recipes they like to use for making baking powder. The claim is made that these cost rather less than the kinds that can be bought, and also that they are much more effective. Here is one:
1/2 lb. cream of tartar.
1/4 lb. cooking soda (bicarbonate of soda).
1/8 lb. corn starch.
The best quality of each must be bought. Sift them together at least a dozen times, the last time into baking powder boxes. Be careful to seal up all cracks by pasting over them paper strips. About one half as much of this is required as for the average powder sold.
These proportions would probably give a slight excess of acid. We might combine 21/4 parts of the acid salt with one part of soda if our salts are chemically pure. The corn starch is added to keep the soda and acid salt from forming quite such an intimate mixture. The two salts in contact would very slowly combine, and the baking powder thus lose its strength.