(a) Upon Substances

Upon some substances oxygen acts at ordinary temperature. Iron becomes covered with rust when exposed to air and moisture. Wood and other vegetable and animal substances undergo slow decomposition when exposed to the air. This is partly due to the action of oxygen at ordinary temperature.

Properties of oxygen.

A splinter of wood will burn brilliantly in a jar of pure oxygen, and much more rapidly than in common air. Pure oxygen gas will cause many substances to burn which will not burn in air. Iron can be burned in pure oxygen, leaving only a reddish powder.

When iron rusts the carbon dioxid and water vapor combine chemically with the iron, and form what is known as a basic hydroxid or carbonate of iron. The process is somewhat complex. When iron burns in oxygen a red powder is formed - ferric oxid, Fe2O3. Iron dissolves in water, or moisture from the air containing carbonic acid, forming acid ferrous carbonate -

Effect of air upon iron and wood.

Pure oxygen aids combustion.

Formation of iron-rust.

Fe + 2H2CO3 = FeH2(CO3)2 + H2

Iron + Carbonic acid = Acid ferrous carbonate + Hydrogen

This acid ferrous carbonate, on drying or further oxidation, is converted into iron-rust. If we represent iron-rust by the formula Fe2O3. 2Fe(OH)3, the equation is as follows:

4FeH2(CO3)2+ O2 =Fe2O3. 2Fe(OH)3+H2O +8CO2 Acid ferrous Carbon carbonate + Oxygen = Iron-rust +Water+ dioxid.

(b) In Living Bodies

The most interesting action of oxygen at ordinary temperature, however, is that which takes place in our bodies and the bodies of all other animals.

By the constant action or beating of the heart all the blood in the body is brought to the lungs every two or three minutes. The actual time has not been determined in man. In large arteries the blood flows ten times as fast as in very small ones. The usual time through a capillary is one second. The time has been determined, however, in lower animals. In a horse the blood travels one foot a second in the largest artery. At present the accepted theory is that in the circuit the blood makes throughout the body, it picks up the waste matter from tissue that has been torn down by work or effort, and brings it to the lungs, where it meets with the oxygen we breathe and is oxidized or burned.

If the body undergoes excessive effort or exercise, it tears down an excessive amount of tissue, and there is created, therefore, an excessive amount of waste or carbon dioxid. Nature very wisely provides for this contingency by increasing the heart action, thereby sending the blood through the body at greater velocity, forcing more blood to the lungs, thus increasing the demand for oxygen, which is expressed by deep and rapid breathing. When a substance burns it gives off heat, and generally light. The heat is the result of chemical change or combination, and the light is the result of heat. Whenever oxidation takes place, no matter in what form, heat is produced.

Rate of blood circulation.

Oxidation of waste matter.

The amount of heat given off by the combination of a given amount of oxygen with some other substance is always the same. If it takes place at a very high temperature, as in explosives, the heat is all given off at once, but if it takes place more slowly, the heat passes away, and we may not observe it, but careful experiments prove that heat is always present in oxidation, and the amount of heat is always measured by the amount of oxygen.

Generation of heat and light.

Amount of heat determined by amount of oxygen.

That the combination of oxygen with other substances always produces a certain amount of heat is a very important fact to the food scientist, as this law enables him to determine in the laboratory the exact amount of heat that is produced in the oxidation of a pound, or of any given quantity of food; this food will also produce exactly the same amount of heat if oxidized in the human body.

We know that by means of heat we can produce motion. The steam-engine is the best example of this law. We build a fire under the boiler; the oxygen of the air unites with the carbon in the coal; the combustion converts the water into steam; the steam is conveyed to a cylinder; the pressure pushes a piston; the motion of the piston causes motion in the engine, and the train or ship moves.

Law governing oxidal on of given quantity of food.

Heat and motion.

From such facts we know that not only the amount of heat, but the amount of work or energy that food or fuel will yield can be determined with reasonable accuracy. Many conditions obtain in the body, however, that do not occur in the laboratory, hence we must study these conditions before we can fully understand the natural laws that govern the production of heat, and energy or work, by oxidation in the living body.

Determination of body-heat and energy.