28 The Bulletin. 



tabtabic acid baking powders. 



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

 all gTape 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 Avhich bitartrate of potash or acid 

 tartrate of potash is known in commerce. 



The residue left in bread made with cream of tartar baking pow- 

 ders is sodium-potassium tartrate or Rochelle salts. 



PHOSPHATE BAKING POWDERS. 



The acid constituent of these powders is a purified acid phosphate 

 of lime, sometimes called super-phosphate. 



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 POWDERS. 



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 sul- 

 phuric acid for the carbonic acid, the aluminium being left as a 

 hydroxide. 



The residue left in bread from an alum powder is more complex 

 than the residue from any of the other classes previously mentioned, 

 and depends on the kind of alum used. Sodium sulphate and alu- 

 minium hydroxide are necessarily present, and if potash and am- 

 monium alum are used their respective sulphates would be present 

 also. 



There is a class of powders that contain two, and sometimes even 

 more, acid-furnishing materials ; of these the alum-phosphate pow- 

 ders are the most important. They arc mixtures of alum and phos- 

 ])hate powders, and the residue left in the bread by them would bo a 

 mixture of the residues already referred to under alum and phos- 

 phate powders, with a small amount of aluminium phosphate in addi- 

 tion. 



All baking powders, without exception, leave in the bread certain 

 salts, above mentioned, which arc foreign to flour and objectionable, 

 and most of which are used in medicine, though some of them not 

 internally. 



