~Laboratory preparation of alcohol.~ The formation of alcohol and carbon dioxide from glucose may be shown as follows: About 100 g. of glucose are dissolved in a liter of water in flask A (Fig. 90). This flask is connected with the bottle B, which is partially filled with limewater. The tube C contains solid sodium hydroxide. A little baker's yeast is now added to the solution in flask A, and the apparatus is connected, as shown in the figure. If the temperature is maintained at about 30 deg., the reaction soon begins. The bubbles of gas escape through the limewater in B. A precipitate of calcium carbonate soon forms in the limewater, showing the presence of carbon dioxide. The sodium hydroxide in tube C prevents the carbon dioxide in the air from acting on the limewater. The alcohol remains in the flask A and may be separated by fractional distillation. [Illustration: Fig. 90] 2. _Properties._ Ethyl alcohol is a colorless liquid with a pleasant odor. It has a density of 0.78 and boils at 78 deg.. It resembles methyl alcohol in its general properties. It is sometimes used as a source of heat, since its flame is very hot and does not deposit carbon, as the flame from oil does. When taken into the system in small quantities it causes intoxication; in larger quantities it acts as a poison. The intoxicating properties of such liquors as beer, wine, and whisky are due to the alcohol present. Beer contains from 2 to 5% of alcohol, wine from 5 to 20%, and whisky about 50%. The ordinary alcohol of the druggist contains 94% of alcohol and 6% of water. When this is boiled with lime and then distilled nearly all the water is removed, the distillate being called _absolute alcohol_. ~Commercial preparation of alcohol.~ Alcohol is prepared commercially from starch obtained from corn or potatoes. The starch is first converted into a sugar known as maltose, by the action of _malt_, a substance prepared by moistening barley with water, allowing it to germinate, and then drying it. There is present in the malt a substance known as diastase, which has the property of changing starch into maltose. This sugar, like glucose, breaks down into alcohol and carbon dioxide in the presence of yeast. The resulting alcohol is separated by fractional distillation.