THE ALCOHOLS: FERMENTATION 149 



has the properties of spirits of wine ; for, if a glass rod be dipped 

 in the liquid, the adhering alcohol is inflammable and burns 

 with a pale blue flame. 



In order to separate from water, distil the weak alcohol 

 from a smaller flask. Shake the first portion of the distillate 

 with anhydrous carbonate of potassium, a useful drying agent, 

 then mix the alcohol with quicklime, and allow to stand for a 

 few hours ; finally distil from a flask fitted with a ther- 

 mometer. Note that the nearly anhydrous alcohol begins to 

 distil at 78° or a little over, but that the boiling point gradually 

 rises as the distillation proceeds, this being due to other pro- 

 ducts of fermentation of higher boiling point. The alcohol 

 may be "rectified" by fractional distillation from these im- 

 purities, which constitute, when thus separated, "fusel oil." 



Yeast consists of a mass of minute organisms termed the "yeast plant," 

 together with a chemical compound called invertase. The invertase first 

 converts the cane sugar into grape and fruit sugar, 



C12H22O11 + HgO = CgHigOg + CgHjaOg, 



which are then converted by the yeast plant into alcohol and carbonic acid 

 gas, 



CgHiaOs = aCgHgO + 2CO2. 



Both changes are said to be "fermentative," being brought about by organic 

 substances of animal and vegetable origin, which remain the same before 

 and after the reaction. The yeast plant is an "organised ferment," the 

 invertase a "soluble ferment." 



Bread. — This consists of dough which has been "raised" by aeration 

 with carbonic acid gas and then baked. The aeration is usually effected 

 by mixing the dough with yeast. A portion of the starch in the dough is con- 

 verted into maltose, and the maltose into alcohol and carbonic acid gas, which 

 renders the dough spongy. On baking, the air-spaces are further distended 

 by the rise in temperature, while on the outside a crust is formed in which 

 a part of the starch has been converted into dextrin by heat. Instead of 

 yeast a baking powder is sometimes employed ; for instance, a mixture of 

 bicarbonate of sodium and tartaric acid, which react with each other when 

 moistened with water, carbonic acid gas being given off and tartrate of 



