Baking powder is composed of bicarbonate of sodium, NaHC02, which has in its composi-tion carbon dioxide and some acid. When the mixture is wet, the acid serves to liberate the carbon dioxide from the sodium bicarbonate. In order to keep those materials dry and to prevent chemical action from taking place before they are used, starch is added and is called a "filler" In cheap baking powders the starch is added in very large amounts. The value of a baking powder depends upon the amount of gas it gives off. Its healthfulness depends upon its freedom from injurious residue left in the food.

There are three classes of baking powder upon the market:

1. Cream of Tartar.

2. Phosphate.

3. Alum.

Cream of tartar is potassium acid tartrate, KHC4H406. It is prepared from the argols which collect on the inside of wine casks. These are then refined and purified and known as cream of tartar.

The chemical reaction of cream of tartar baking powder is as follows: potassium acid + bicarbonate = Rochelle + carbon + water tartrate of sodium salt dioxide

HKH4C4O6 +NaHC03 = KNaC4H406 + C02 + H20

There is left as a residue in a loaf of bread made from baking powder more Rochelle salt than is found in a Seidlitz powder; but the amount eaten at any one time is so small as to have very little physiological effect.

Cream of tartar is expensive, so cheaper forms of acid are often used in baking powders.

Phosphate Baking Powders

The acid used is phosphoric acid, which is obtained by the action of sulphuric acid on ground bone. The phosphate probably has little power to furnish phosphate to the body, not being in a form in which the body can assimilate it.

Alum Baking Powders

These are the most objection-able forms of baking powders, as their residue has an irri-tating effect upon the mucous membranes of the digestive organs. They are very cheap powders, so, unfortunately, they are extensively used.

Bicarbonate of sodium is obtained from common salt, is a very cheap product, and, therefore, is not adulterated.

Proportions of acid and alkalies to be used in cooking:

1 ts. soda and 2 slightly rounding ts. of cream of tartar for 1 qt.

flour.

2 ts. baking powder for each c. flour. 1 ts. soda for 1 pt. thick sour milk.

1 ts. soda to 1 c. molasses for batters.

1/2 ts. soda to 1 c. molasses for a stiff dough.

Baking powder may be substituted for cream of tartar and soda, in the proportion of 2 level ts. for each c. flour or meal.

Reduce the amount of baking powder by 1/2 ts. for each egg added to the mixture.