386 CHEMISTRY. 



converts some of the starch of the dough into sugar, and 

 then makes from this sugar alcohol and carbonic anhydride. 

 It is the expansion of the gas thus produced in every part 

 of the mass that makes the numberless cells in it, and thus 

 causes the "raising;" the volatile alcohol escapes at the 

 same time. In the baking of bread part of the starch of 

 the flour is converted by the heat into dextrin. A shining 

 coat is given to the loaf by dissolving some of this gum on 

 the surface by moistening the loaf after it is baked, and 

 then subjecting it for a few minutes to heat again, which 

 quickly dries and hardens the gum. Bread is often raised 

 by other means than fermentation. Tartaric acid and hy- 

 dro-sodium carbonate are used for this purpose. If the bi- 

 carbonate, as it is commonly called, be thoroughly mixed 

 with the dough, and the tartaric acid be then added, it will 

 seize the soda, and the released carbonic anhydride, as it ex- 

 pands into its gaseous state, raises the bread, as it does 

 when generated by yeast. Bakers sometimes use ammonium 

 carbonate to raise their light, spongy cakes. There is no 

 need of any acid in this case, for the heat volatilizes the 

 carbonate, and as it escapes it makes the cakes porous. 

 Hum and alcohol have sometimes been employed, the vapor 

 produced by the heat answering the purpose. There is 

 considerable water in bread. In every 100 pounds of flour 

 there are 16 of water. Then in the making of the flour into 

 bread there are added 50 pounds more of water, so that 

 there are 66 pounds of water in 150 pounds of bread. When 

 bread becomes "stale," its dryness is not owing to an es- 

 cape of water, but to a more thorough incorporation of the 

 water with the bread. 



547. Ether. This singular fluid, so different from alcohol 

 in its properties, is prepared from alcohol, and differs from 

 it but little in its composition having the same ingredi- 

 ents, though not in the same proportions. Alcohol being 



