150 BAKING POWDERS AND SODA 



done by mixing a little soda in the flour, because the heat of the 

 oven causes the soda to give off bubbles of gas, and these in 

 expanding make the heavy mass slightly porous. Bread is 

 never lightened with soda because the amount of gas thus given 

 off is too small to convert heavy compact bread dough into a 

 spongy mass ; but biscuit and cake, being less compact and 

 heavy, are sufficiently lightened by the gas given off from soda. 



There is one great objection, however, to the use of soda alone 

 as a leavening agent. After baking soda has lost its carbon 

 dioxide gas, it is no longer baking soda, but is transformed 

 into washing soda. Sodium carbonate has a disagreeable taste 

 and is by no means desirable for the stomach. But man's 

 knowledge of chemicals and their effect on each other has 

 enabled him to overcome this difficulty and, at the same 

 time, to retain the leavening effect of the baking soda. 



Baking powders. If some cooking soda is put into lemon 

 juice, vinegar, or other acid, bubbles of gas form and escape 

 from the liquid. After the effervescence has ceased, a taste of 

 the liquid will show you that the lemon juice has lost its 

 acid nature, and has acquired in exchange a salty taste. Baking 

 soda, when treated with an acid, is transformed into carbon 

 dioxide and a salt. The various baking powders on the 

 market to-day consist of baking soda and some acid substance, 

 which acts upon the soda, forces it to give up its gas, and at 

 the same time unites with the residue to form a harmless salt. 



Cream of tartar contains sufficient acid to act on baking 

 soda, and is a convenient and safe ingredient for baking pow- 

 der. 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 pene- 

 trates 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 





