Alcohol is really made in this way, only it is already mixed in the water in which the grains fermented and from which people then distil it. Gasoline and kerosene are distilled from petroleum; there is a whole series of substances that come from the crude oil, one after the other, according to their boiling points, and what is left is the foundation for a number of products, including paraffine and vaseline.
Experiment 40. Put some dry, fused calcium chlorid on a saucer and set it on the plate of the air pump. This is to absorb the moisture when you do the experiment. (This calcium chlorid is not the same as the chlorid of lime which you buy for bleaching or disinfecting.) Fill a flask or beaker half full of water and bring it to a boil over a Bunsen burner. Quickly set the flask on the plate of the air pump. The water will stop boiling, of course. Cover the flask and the saucer of calcium chlorid with the bell jar immediately, and pump the air out of the jar. Watch the water.
The water begins to boil again because water will boil at a lower temperature when there is less air pressure on its surface. So although the water is too cool to boil in the open air, it is still hot enough to boil when the air pressure is partially removed. It is because of this that milk is evaporated in a vacuum for canning; it is not necessary to make it so hot that it will be greatly changed by the heat, if the boiling is done in a vacuum. On a high mountain the slight air pressure lets the water boil at so low a temperature that it never becomes hot enough to cook food.
Application 30. Two college students were short of money and had to economize greatly. They got an alcohol lamp to use in cooking their own breakfasts. They planned to boil their eggs.
"Let's boil the water gently, using a low flame," one said; "we'll save alcohol."
"It would be better to boil the eggs fast and get them done quickly, so that we could put the stove out altogether," the other replied.
Which was right?
Application 31. Two girls were making candy. They put a little too much water into it.
"Let us boil the candy hard so that it will candy more quickly," said one.
"Why, you wasteful girl," said the other. "It cannot get any hotter than the boiling point anyhow, so you can't cook it any faster. Why waste gas?"
Which girl was right?
Inference Exercise
Explain the following:
161. Warm air rises.
162. The lid of a teakettle rattles.
163. Heating water makes a steam engine go.
164. When an automobile with good springs and without shock absorbers goes over a rut, the passengers do not get a jolt, but immediately afterward bounce up into the air.
165. Comets swing around close to the sun, then off again into space; how do they get away from the sun?
166. When you wish to pour canned milk out, you need two holes in the can to make it flow evenly.
167. Liquid air changes to ordinary air when it becomes even as warm as a cake of ice.
168. Skid chains tend to keep automobiles from skidding on wet pavement.
169. A warm iron and a blotter will take candle grease out of your clothes.
170. Candies like fudge and nougat become hard and dry when left standing several days open to the air.
Section 20. Conduction of heat and convection.
Why does a feather comforter keep you so warm?
When you heat one end of a nail, how does the heat get through to the other end?
How does a stove make the whole room warm?
Here is a way to make heat run a race. See whether the heat that goes through an iron rod will beat the heat that goes through a glass rod, or the other way round:
