394 ORGANIC CHEMISTRY. 



subsequently added in proper proportion, the weaker 

 carbonic acid is expelled. A light sponge is produced 

 by its escape, without the loss of the starch and sugar 

 which are consumed in the process of fermentation. 

 Soda and tartaric acid prepared for this purpose are 

 known under the name of yeast powders. Carbonate 

 of ammonia being entirely volatile by heat, may be 

 employed alone for the same purpose. A portion of 

 the salt probably remains in the bread, and is more or 

 less injurious, on account of its alkaline character. 



987. TEST FOR YEAST POWDERS. The 



What is the . . f , 



objection to great objection to the use of these pow- 



*fa U inlfreadf ^ GYS * u the P re P aration f bread, consists 

 in their liability to contain soda or acid in 

 undue proportion. Whether this is the case, may be 

 ascertained by dissolving the powders in water, and 

 mixing the solutions. If the product is neutral to the 

 taste and does not effervesce on the addition of 

 either soda or acid, this fact will be evidence of their 

 proper preparation. If otherwise, more or less injury 

 is to be anticipated from their use. Excess of the al- 

 kalies especially interferes with the process of diges- 

 tion, by neutralizing the acids which accomplish it. 

 The use of soda and saleratus with sour milk is liable 

 to the same objections. 



What is said, ^88. THEIR EFFECT ON HEALTH. It 



Ihe^rfffe^'on ma ^ wel1 be <l liestioned whether bread 

 the health ? prepared by this process, is ever as healthy 

 as that made with yeast. For even the neutral tar- 

 trate, formed when the materials are used in proper pro- 

 portion, will tend to neutralize certain stronger acids, 



