Handbook of Meteorology/Forms and Properties of Matter

by Jacques Wardlaw Redway

CHAPTER II

FORMS AND PROPERTIES OF MATTER IN ITS
RELATION TO METEOROLOGY

Ether and Matter.—It is not necessary to assume that the universe and space are one and the same; nor that the universe is boundless; nor that space is without limits. So far as that part of the universe with which human knowledge comes in contact is concerned, the existence of two factors is assumed. Matter is perceptible to the human senses. It is visible, tangible, and transformable. It can be measured and compared; some, at least, of its properties are known. Its ultimate constitution, however, is not known. It is usually described in terms of atoms, molecules and masses.

In certain respects, more is known about ether than about matter: for although the existence of ether is merely assumed, ^[1] the magnitudes attributed to it are real values that have been fully established. That the universe is pervaded by an invisible, intangible, but measureable something is conceded. It is assumed that the manifestations to the senses known as heat, light, magnetism, electricity, and radiant energy traverse the known part of the universe by the means of the ether. It is not improbable that these manifestations are undulations of the ether itself.

The telescope and the spectroscope have shown that the matter entering into the composition of other visible bodies in the universe does not differ from that which composes the earth. Many of the chemical elements that compose the earth have been discovered in the sun and other heavenly bodies, and no chemical element has been discovered in any heavenly body that does not occur in the earth. Air and water vapor occur on the planet Mars, and it is not unreasonable to assume that the meteorology of this planet has much in common with the meteorology of the earth. The occasional occurrence of dust storms on Mars adds weight to the reasonableness of such an assumption.

Forms of Matter.—For practical purposes it may be assumed that matter exists in three forms—solid, liquid and gaseous.^[2] Most of the metals and some of the non-metals may be changed easily from one form to another. Thus, iron is a solid at ordinary temperatures; it “melts” or liquefies at a temperature somewhat above 2100° F (1150° C); at a still higher temperature it gives off a reddish-brown vapor. Mercury is ordinarily a liquid; it “boils” or becomes a vapor at 675 F (375° C) and “freezes” or solidifies at −38° F (−39° C). Water is the most common illustration of all; it solidifies at 32° F (0° C) and gradually becomes a vapor at ordinary temperatures; but at 212° F (100° C) the vapor pressure is that of the air at sea level. Practically all the ordinary gases have been liquefied and solidified. Liquid air and carbon dioxide are articles of commerce.

The conditions which surround the liquefaction of ice and snow, the evaporation of water, and the condensation of the water vapor of the air are fundamental factors in the science of weather. The distribution of precipitation—that is, rain, snow, hail, and the floating forms of fog and cloud—affect the habitability of the earth and human activities to a very great degree.

Matter may be changed in physical form, but it cannot be annihilated. Thus, the coal in the fire-box is changed to carbon dioxide, a gas, instead of a solid; but the chemist may separate the carbon from the oxygen. Nothing, not even the energy, is lost; to nature nothing can be added, and from nature nothing can be taken away.

Properties of Matter.—All forms of matter have certain properties—volume, density, weight, etc., in common. Other properties, such as malleability and ductility, affect groups or classes of matter—chiefly the metals.

Cohesion is a somewhat archaic term denoting molecular attraction. In solids, the cohesion is usually strong, so that more or less force is required to sunder the mass—that is, to separate the molecules. The resistance of cohesion is usually expressed in such terms as tension, torsion, shearing, etc. In the liquefaction of a solid, or the vaporization of a liquid, the force employed to overcome cohesion is measured in terms of heat. For instance, in the liquefaction of ice, about 147 times as much heat is required to change ice at 32° to water at 32° as will raise the temperature of the same weight of water one degree Fahrenheit in temperature. In the case of liquids, the cohesion seems to be slight, inasmuch as the molecules possess a considerable mobility. Nevertheless, they are held together by a powerful force. Thus, the heat used in converting one pound of water at 212° F to a vapor at 212° F would raise 967 pounds of water one degree in temperature. Measured thus, in terms of heat units, great power is required to overcome molecular attraction. In the case of gases, not only is the molecular attraction negligible, but the molecules apparently repel one another.^[3] Perhaps it is more nearly correct to say that they diffuse themselves throughout the space which contains them. In other words they apparently cease to possess molecular attraction.

Crystallization is a form of molecular attraction which indicates that the molecules possess a certain kind of polarity, usually assuming regular geometric forms. Frost and snowflakes frequently exhibit marvelous forms, infinite in variety but regular and similar in construction. The study of these forms is one of increasing importance in weather science.

Expansion-contraction is a property of matter true in its ordinary forms. The volume of a substance increases when it is heated and contracts with cooling. Thus, iron will increase 0.00000648 of its length for each degree F of increase in temperature, this being its “coefficient of linear expansion.” The coefficient of expansion of air is 0.00367; of ethyl alcohol, 0.0005; of mercury, 0.0002.^[4] In meteorology the principles of this property are fundamental. The expansion of mercury and of alcohol are used to determine the intensity of heat; and to the unequal heating of the air in different localities are due the movements of the air—that is, the winds.

Magnetism is a property pertaining chiefly to iron and steel, but possessed to a lesser degree by other metals. When in the condition known as magnetized, a piece of iron or of steel attracts and holds other pieces of iron and steel. Steel retains its magnetism permanently; iron is sensibly magnetic only when within magnetic influence—that is, a “magnetic field.” Nickel, cobalt, certain manganese alloys and tungsten alloys exhibit magnetism very sensibly. A bar of magnetized steel, suspended by a thread attached at its center of gravity, comes to rest pointing nearly or quite north and south, the negative or marked end pointing in a general way to the earth’s north magnetic pole. A few substances, chiefly bismuth, similarly suspended come to rest across the magnetic field when between the poles of a horseshoe magnet. The investigations concerning the earth’s magnetic properties are carried on in the United States by the Coast and Geodetic Survey.

Properties of Gases.—Gases are perfectly elastic. A gas fills any space within which it is confined. A cubic inch of a gas whose density has been measured, if set free in a space whose dimensions are a cubic foot, or a cubic yard, will fill the space.^[5] Manifestly its density and tension will be lessened in proportion. It is the custom to say, therefore, that a gas has no specific volume of its own; its volume is that of the container.

Equal volumes of a gas, temperature and density remaining the same, contain an equal number of molecules. If hydrogen, the lightest known gas, be taken as the unit of measurement, the molecular weight of any gas may be determined by comparing its weight with that of an equal volume of hydrogen. This is known as Avogadro’s law.

If a volume of gas be heated from 32° to 459° F^[6] (0° to 273° C) its volume will be doubled.^[6] That is, equal volumes of gases expand equally with the same increase of temperature.

If a given volume of gas—say 1 cubic foot of oxygen—be introduced within a container, its pressure or tension noted, the same volume of another gas having the same tension may be introduced without an increase of tension of the mixture. Thus 1 volume of oxygen added to I volume of nitrogen will make but 1 volume of the mixture, having the same tension as each of the two gases. That is, one gas is practically a vacuum for another. This property has its limitations; when several other gases are introduced within the container a noticeable increase of the tension of the mixture takes place.

Inasmuch as the science of meteorology is chiefly a study of the air, a mixture of gases differing in their specific properties, a clear exposition of these general properties is necessary to an understanding thereof—more especially to the solving of the problems of weather, climate, and habitability.

Gravity is a property of matter that exists apparently throughout the known universe. The apparent fact that matter in masses attracts all other matter in masses is practically all that is known of the essence of it. The whirling of the sun and the planets about a common center of gravity balances the attraction that otherwise would bring them together. More exactly stated, planetary bodies tend to move in straight lines; gravity tends to draw them to a common center; the result is orbital movement. These complex movements and forces have a great and very measureable influence on the movements of the sea and the air.

It is convenient to note the density—practically the “weight” —of various kinds of matter, comparing them volume for volume, under standard conditions, with the density of a given substance. This ratio of weight is the specific gravity of the substance. Distilled water at its maximum density, 39.1° F (3.94° C) is usually taken for the comparison. Thus, a given volume of mercury weighs 13.6 times as much as an equal volume of water, and an equal volume of alcohol 0.81 times as much as an equal volume of water.

For gases, air and hydrogen are both used as units of comparison. The specific gravity of hydrogen, in terms of air, is 0.069; of air in terms of hydrogen, 14.4; of coal gas, commonly used for inflating balloons, about 0.061; of water vapor, 0.62. When metric units are employed, the weight of a cubic decimeter is the specific gravity of the given substance,^[7] a cubic decimeter of water under standard conditions, weighing in theory, but not in fact, 1 kilogram.

1. “In recent years, doubt as to the necessity for assuming the existence of an ether has been expressed by some who claim that it is sufficient to attribute the power of transmitting radiation to space itself. It may be doubted whether this is more than a dispute about terms. One cannot discuss the question, here; but, pending the settlement of the controversy, it seems wise to continue the use of the word ‘ether’ as at least denoting the power of space, vacant or occupied by matter, to transmit radiation.”—Duff, A Textbook of Physics.
2. In meteorology the discussion of the radiant form of matter may be omitted.
3. In mechanics the repellent force of the water vapor, usually called steam, is termed “pressure” and is rated in “pounds per square inch,” or in “atmospheres” of 14.7 pounds per square inch. In meteorology the repellent force is expressed sometimes as tension, but more commonly as pressure.
4. Different values are given by different authorities; the foregoing are on the authority of H. Whiting.
5. This property of gases is not quite true at temperatures near to their condensation, but it holds good at temperatures which are materially higher than the temperature approaching condensation.
6. This may be expressed by the formula

   $V'=V[i+k(t'-t)]$,

   where $V$ is the given volume; $V'$ the volume sought; $t$ the given temperature; $t'$ the temperature of the volume sought; and $k$, 0.00367. This is known as Boyle’s law, and also as Mariotte’s law. It is true at high temperatures, but not exact at ordinary temperatures.

7. The following formulas are useful: Sp. gr. $={\frac {wt.}{vol.}}$; weight $=vol.\times sp.gr.$; volume $={\frac {wt.}{sp.gr.}}$.