Man's physical universe

xanabras

244 PHYSICAL LIMITATIONS HAVE BKEN OVERCOME

sure has been released, thus allowing the extra gas to escape from

solution.

In making alcoholic liquors by fermentation, in

which the liquor is

bottled before fermentation is complete, the amount of carbon dioxide

formed by the fermentation after bottling frequently becomes so great

that all

of the liquor shoots out of the bottle along with the gas when

the cap is removed. This effect would be decreased by cooling the

bottle before opening it,

because gases become more soluble at lower

temperatures. The solubility of gases decreases as the temperature

is raised, until, when the boiling-point of the solvent is reached, most

gases become completely insoluble.

All of the gases dissolved in water could thus be removed by boiling

the water, unless they form compounds with the water or constantboiling

solutions. It is the gases dissolved in ordinary water that give

it

the palatable properties to which we are accustomed and which we

therefore prefer. Freshly boiled water has an objectionable flat taste

which is removed by simply pouring it from one vessel to another

through the air a few times to dissolve some air.

When water is heated, bubbles of gas are observed to form on the

side of the heating vessel long before the boiling-point is reached.

These bubbles form, of course, because the solubility of the gas is

reduced as the temperature is raised.

Although the solubility of oxygen in water is very small, it is very

important. Most fish have gills with which to remove the dissolved

oxygen from the water. The water of small aquariums should be

changed or agitated regularly in order to dissolve more oxygen in the

water to replace that taken out by the fish.

The Properties of Liquid Solvents Are Changed to the Same Extent by

Equivalent Amounts of Liquid or Solid Solutes.

1. The Vapor Pressure Is Lowered. Equivalent amounts of solutes

(that is,

weights that contain the same number of molecules or other

lower the vapor pressure of solvents to the same

particles of solute)

degree. Thus a little glycerine or sugar might be added to a skin lotion

to keep the skin from getting dry because these substances would

lower the tendency of the moisture of the perspiration to evaporate and

would thus tend to retain the moisture of the skin.

Some substances, such as calcium chloride, sodium or potassium

hydroxide, and sulfuric acid, are so soluble in

water that they lower

the vapor pressure of the film of moisture that condenses on their

surface to the extent that it is below that of the water vapor in the air.

In such cases moisture continues to collect on the surface of such sub-