BAKING POWDERS. 567 



haps be more difficult also to prevent action of the free acid upon the 

 alkali, so that the powder would be more likely to deteriorate in keep- 

 ing. Only one sample among those I examined was found to have been 

 made with the free acid. 



One obstacle formerly encountered in the manufacture of bitartrate 

 powders was the difficulty of obtaining the bitartrate pure. It con- 

 tained from 5 to 15 per cent, of tartrate of lime incident to the method 

 of manufacture. This brought a large quantity of inert material into 

 the powder and lowered its efficiency. Bitartrate can now be had 98 

 per cent, pure, quoted and guaranteed as such in the markets, so that 

 there is no excuse for manufacturers to use the impure salt, which can 

 properly be considered adulterated. 



PHOSPHATE POWDERS. 



The salt commonly used to furnish the phosphoric acid in this class 

 is acid phosphate of lime, sometimes called superphosphate. The pure 

 salt is monocalcic phosphate, CaH 4 (PO 4 ) 2 . It is made by the action of 

 sulphuric acid upon ground bone, the result being an impure monocalcic 

 phosphate with calcium sulphate. This mixture is sold as a fertilizer, 

 as superphosphate. The salt is, of course, more or less purified for use 

 in baking-powders, but the sulphate of lime is very difficult to get rid 

 of entirely, and most phosphate powders contain considerable amounts 

 of this impurity. The reaction which occurs when a phosphate powder 

 is dissolved, that is the action of bicarbonate of soda upon monocalcic 

 phosphate, is not well established, and perhaps varies somewhat with 

 conditions. The following equation probably represents it fairly well: 



234 168 136 142 88 36 



CaH 4 (PO 4 ) 2 + 2tfaHC0 3 = CaHPO 4 + Na 2 HPO 4 + 2CO2- + 2H 2 O 



Monocalcic Bicarbonate of Mpnohydrogen Disodic Carbonic Water, 



phospha'e. soda. calcic phosphate. phosphate. dioxide. 



Two hundred and thirty-four grains of monocalcic phosphate com- 

 bined with 168 grains of bicarbonate of soda give 136 grains of mono- 

 hydrogen calcic phosphate, and 142 grams of disodic phosphate. But 

 crystallized sodic phosphate contains twelve molecules of water, and 

 has a molecular weight of 358. So the total amount of residue from 402 

 grains of the powder would be 494 grains, of which 136 grains is phos- 

 phate of lime, and the rest phosphate of soda. So we see that here 

 also the quantity of chemicals introduced into the dough is fully equal 

 to the amount of the baking-powder used, including filling. As to the 

 nature of this residue in phosphate powders, it would seem to be about 

 as unobjectionable as in the tartrates. Phosphate of soda is " mildly 

 purgative in doses of from 1 to 2 ounces" (480-960 grains), according 

 to the United States Dispensatory. Phosphates of calcium have the 

 general physiological effect which is ascribed to all forms of phosphoric 

 acid, but which does not seem to be well understood. 



Phosphates are administered therapeutically in some cases of defec- 



