FOOD INSPECTION. 137 



There are practically three classes of baking powders on the 

 market, differing chiefly in the source of the acid. 



Tartrate powders, in which the acid is either cream of tartar 

 (bi-tartrate of soda) or tartaric acid. 



Phosphate powders, in which calcium or sodium acid phos- 

 phate is the acid constituent. 



Alum powders, in which the acid constituent is the sulphate 

 of aluminum as it occurs in the various alums. 



There are of course many complex baking powders on the 

 market which are made up of mixtures of two or more of the 

 three classes above named. Of these mixtures, phosphate-alum 

 powders are the most common. Indeed, phosphate-alum pow- 

 ders are far more common than straight alum powders. 



Whether the acid principle be tartaric acid, calcium phosphate 

 or aluminum sulphate, there is always a residual product which 

 is undesirable as a food.* Cream of tartar powders leave a 

 residue of Rochelle salt, the active principle of Seidlitz powders ; 

 tartaric acid powders leave a residue of sodium tartrate; phos- 

 phate powders leave a residue of sodium and calcium phosphates ; 

 and alum powders leave a residue of ammonium, potassium 

 or sodium sulphate, in accordance with the kind of alum used. 

 The residues of the phosphate-alum powders differ somewhat 

 from those of either alum or phosphate powders and vary with 

 the proportion of the different acid constituents used. When 

 the ingredients are properly proportioned in the baking powder, 

 neither alum or alum phosphate powders leave any considerable 

 amount of alum in the resulting bread or cake. 



The per cent of available carbonic acid gas furnished by the 

 different classes of baking powders is, according to Wiley,f as 

 follows : 



Cream of tartar baking powder, 12 per cent available carbonic 

 acid gas. 



Phosphate baking powder, 13.0 per cent available carbonic 

 acid gas. 



Alum baking powder, 8.1 per cent available carbonic acid 

 gas. 



* Many people seem to believe that the chemicals used in baking pow(le^^^ com] 

 pletely or nearly completely disappear. Cream of tartar baking powders belong 

 to one of the best classes and yet, according to Wiley, the amount of Rochelle 

 salt formed as a residue from a teaspoonful and a half of a cream of tartar baking 

 powder equals that of one Seidlitz powder. 



tThe figures are quoted from Bui. 1? of Div. of Chemistry, U. S. Dept. of Agr. 



