BAKING POWDERS. 565 



substances', which, though not of themselves articles of food, enter into 

 the composition of food preparations. Considerable space is devoted 

 in such works, however, to the adulteration of bakers' chemicals. If a 

 substance is sold as cream of tartar, for instance, which either is not 

 cream of tartar, or is sophisticated with some cheaper substance, the 

 seller could be convicted under food-adulteration laws, but if such a 

 fraudulent cream of tartar were incorporated into a mixture with other 

 chemicals and the whole sold as baking-powder, BO conviction could be 

 secured. In the famous "Norfolk baking-powder case" iu England, 

 which will be alluded to further on, the powder in question contained 

 alum, which substance bakers are not allowed by law to use in bread. 

 Yet the prosecution was not successful because it was directed against 

 the sale of the powder, not against the bread made from it, there being 

 no legal standard for substances sold as baking-powder in England. 



CLASSIFICATION OF BAKING-POWDERS. 



Baking-powders maybe conveniently classified according to the na- 

 ture of the acid constituent they contain. Three principal kinds may 

 be recognized as follows : 



(1) Tartrate powders, in which the acid constituent is tartaric acid 

 in some form. 



(2) Phosphate powders, in which the acid constituent is phosphoric 

 acid. 



(3) Alum powders, in which the acid constituent is furnished by the 

 sulphuric acid contained in some form of alum salt. 



All powders sold at present will come under some one of these heads, 

 although there are many powders which are mixtures of at least two 

 different classes. 



TARTRATE POWDERS. 



The form in which tartaric acid is usually furnished in this class is 

 bitartrate of potassium, or " cream of tartar." Sometimes free tartaric 

 acid is used, but not often. Bitartrate, or acid tartrate of potassium 

 is made from crude argol obtained from grape juice. It contains one 

 atom of replaceable hydrogen, which gives it the acidity that acts upon 

 the carbonate. The reaction takes place according to the following 

 equation : 



188 84 210 44 18 



KHC 4 H 4 O 6 + NaHCO 3 = KTaC 4 H 4 O fi + CO 2 + H 2 O 



Potassium Sodium Potasaium-sodium Carbonic Water, 



bitartrate. bicarbonate. tartrate. dioxide. 



It will be seen that the products of the reaction are carbonic acid and 

 double tartrate of potassium and sodium, the latter constituting the 

 residue which remains in the bread. This salt is generally known as 

 Rochelle salt, and is one of the component parts of seidlitz powders. 





