178 PRACTICAL LESSONS IN SCIENCE. 



wood. Vinegar is a dilute acetic acid which is prepared in various 

 ways. It is made from alcohol treated with yeast. It is made 

 from wine or cider by adding a ferment called the mother of 

 vinegar, and is prepared from dilute solutions of sugar. Acetate 

 of lead, or sugar of lead, is used in medicine, and aluminum ace- 

 tate is used in dyeing. 



The process of fermentation is intimately related to bread- 

 making. Flour is composed of starch, an albuminoid substance 

 called gluten, with some mineral substances. The flour is mixed 

 up into a dough with water, yeast and salt, and allowed to stand 

 for some hours at a temperature of between 70 and 75 F., 

 during which time some of the starch has been broken up by 

 fermentation into alcohol and carbon dioxide, which causes the 

 dough to swell up and become porous. The bread is then baked 

 at a temperature of about 500 F. The dioxide expanded some- 

 what by the heat increases the lightness of the bread, finally 

 escaping with the alcohol and some of the water. The internal 

 portions of the bread do not rise above the temperature of 

 boiling water, but the outside becomes much hotter and is 

 hardened into a crust, and some of the sugar is converted into 

 a caramel-like substance which gives the crust a sweetish taste. 

 Sometimes the fermentation is caused by leaven, being dough in 

 which fermentation has already commenced, and sometimes the 

 gas for making the bread light is formed from soda bicarbonate 

 and hydrochloric acid. 



The various fats and oils, whether of vegetable or animal 

 origin, are mixtures of three well-defined bodies, stearin and 

 palmatin solids and olein, a liquid. Tallow is mainly stearin, 

 olive oil mainly olein, lard a mixture of olein and palmatin. They 

 are composed of carbon, hydrogen and oxygen of a complicated 

 formula, but are in effect salts of glyceryl. When stearin is boiled 

 with milk of lime, calcium stearate and glycerin are formed, and 

 when olein is boiled with litharge (PbO) lead oleate and glycerin 

 are formed. Glycerin (C 3 H 8 3 ) is a sweet, colorless, sirupy 

 liquid which dissolves in water or alcohol, but not in ether. It 

 is used in medicine and ag a preservative fluid. 



