46 The Bulletin. 



The efficiency of a baking powder as a leavening agent depends 

 on the amount of gas it sets free in the dough, and must be considered 

 apart from the wholesomeness of the residue it leaves. 



CLASSIFICATION OF BAKING POWDERS. 



Baking powders are classified according to the acid constituents 

 they contain, as follows : 



Tartrate Powders, in which the acid is tartaric acid in some form. 



Phosphate Powders, in which the acid is phosphoric acid, as an 

 acid phosphate. 



Alum Powders, in which the acid is sulphuric acid, contained in 

 some form of an alum salt. 



Alum-phosphate Powders, in which the acids are both sulphuric 

 and phosphoric acids. 



TARTARIC ACID BAKING POWDERS. 



Tartaric acid is the principal acid in grapes, and is contained in 

 all grape wines. 



The residue left in bread prepared with tartaric acid powders is 

 sodium tartrate. 



CREAM OF TARTAR BAKING POWDERS. 



Cream of tartar is the name by which bitartrate of potash or acid 

 tartrate of potash is known in commerce. 



The residue left in bread made with cream of tartar baking powders 

 is sodium-potassium tartrate or Rochelle salts. 



PHOSPHATE BAKING POWDERS. 



The acid constituent of these powders is a purified acid phos- 

 phate of lime. 



The residue left in bread by a phosphate powder is phosphate of 

 lime, phosphate of soda and calcium sulphate, the latter being an 

 impurity in the calcium phosphate used in making the powder. 



ALUM BAKING POWDER. 



The acid material in an alum powder is some one of the class of 

 salts known as alums, which are double sulphates of aluminium 

 and an alkali. The acid in these is sulphuric acid and the carbon- 

 dioxide is set free from the bicarbonate of soda by the substitution 

 of sulphuric acid for the carbonic acid, the aluminium being left as a 

 hydroxid. 



