Oxygen is much more than a breath of fresh air

Posted in Biology, Discoveries, Historical articles, History, Medicine, Plants, Science on Friday, 10 February 2012

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This edited article about science originally appeared in Look and Learn issue number 636 published on 23 March 1974.

Antoine Lavoisier, picture, image, illustration

Antoine Lavoisier experimented with a gas which he was to call oxygen, by Gerry Wood

All the paraphernalia of scientific investigation were at hand . . . a rather sleepy mouse in a box and a candle. Joseph Priestley, an English clergyman whose hobby was chemistry, had put some mercuric oxide in a glass jar shaped like a bell and heated it.

A silvery film formed on the glass, and Priestley recognised this as mercury. In 1774, when this experiment was being conducted, the action which causes a metal to oxidise was not known. And so, Priestley did not know what kind of gas was escaping from his jar.

When he lit the candle and put it into the jar, the flame flared brightly. And when he popped the mouse in, the little creature became the friskiest little mouse Priestley had ever seen.

To carry his experiment to its ultimate conclusion. Priestley breathed the gas himself and found that it was very exhilarating. He concluded that the gas he had discovered was not common air but a substance of much greater perfection.

Some years earlier, a Swedish chemist, Karl Wilhelm Scheele, had made something he called “fire air” from various oxides and other substances. However, the results of his experiments were not published until 1777 and were unknown to Priestley.

Nevertheless, both men had stumbled, quite independently upon one of the greatest scientific discoveries of the 18th century. They had discovered the gas upon which the very existence of life depends. They did not call it oxygen, although that is what it was. The coining of that name was performed by Antoine Lavoisier, a French chemist.

When Lavoisier burned carbon and sulphur in the new gas, he found that the ash which resulted released an acid upon being shaken up with water. It was, therefore, a substance that was acid-making, and the Greek words for that have given us the name of oxygen.

Only a few people understood the importance of this discovery, for the mysterious work of the chemists was regarded by the ordinary folk of the time as something akin to witchcraft.

Lavoisier was beheaded on the guillotine in 1794 after the French Revolution by a citizens’ court whose chairman declared. “France needs no more scientists.” And in Britain, Priestley’s house was ransacked by a mob in 1791. They destroyed his records and instruments. As a result, Priestley went to America, where he died in 1804.

But the work of these men lives on in the knowledge they have given us of the nature of oxygen which forms one-fifth of the air we breathe. Carried in cylinders, it has helped men to climb the highest mountains, to walk upon the moon, to explore the depths of the oceans and to recover from serious illnesses.

Oxygen, in short, is the breath of life. Not only do we breathe it, but nearly half of the Earth’s crust is made up of it in combination with other substances like calcium and silicon. Eight-ninths of water is oxygen (the other ninth is hydrogen) which is absorbed from the water by the fishes through their gills.

This colourless and odourless gas is the most abundant of all the Earth’s elements and is known by the symbol O. It is obtained from air for commercial uses, for air is mainly a mixture of oxygen and nitrogen. The air is cooled until it is liquid. When the temperature is raised, the liquid nitrogen boils off first leaving behind almost pure liquid oxygen. This is either kept as a liquid or compressed as a gas in steel cylinders.

In this form, it plays a vital role in surgery, particularly in a machine which takes over the job of the heart and lungs so that these can be operated upon.

This is a complicated and truly wonderful piece of apparatus and it consists of two sections – a pump that drives the blood through the patient’s body and the oxygenator that circulates oxygen through the blood so that it can be absorbed.

In the oxygenator, the blood flows over plastic cylinders perforated with holes. As these revolve, a precise amount of oxygen – calculated according to the age, weight and blood-content of the patient – passes from them and into the blood.

The blood is then ready to be returned to the patient’s body so that he can remain alive until his own heart and lungs are ready to take over this job. Clearly, without such an oxygenator and pump, heart and lung surgery would be virtually impossible and many lives would be lost.

In fact, before it was invented, one eminent surgeon said that any doctor who contemplated operating upon a wounded heart deserved to be turned out of the medical profession.

However, many problems had to be solved before the heart and lung machine reached a state of perfection. That they were solved is due to a series of experiments by a man named John H. Gibbon, who built a number of machines while he was still a young surgeon. But it was not until he had been perfecting these machines for 22 years that he dared to try one out on a person. The success of this led other surgeons to use them.

This illustrates the use of oxygen for humanitarian purposes. But it has also had deadly uses such as when, near the end of the Second World War, it was used in the manufacture of fuel for the German V-2 rocket.

For this use it took the form of hydrogen peroxide, which is a compound of hydrogen and oxygen which readily splits up into water and oxygen. When the Germans used it in their rockets, a jet of steam and oxygen was produced and gave the missile its thrust.

Nowadays, liquid oxygen is used in the motors of space craft to hasten the burning of other fuels and to give the vehicle its tremendous impetus.

However, all of these uses of oxygen are small compared to the tremendous quantities used in the steel industry. For instance, it is used in the smelting of ore in a blast furnace where it enables amazingly high temperatures to be attained. And it is used, too, in the refining of steel, such as when high-pressure oxygen is injected into newly formed molten steel to force out the impurities.

Before it can be used by industry, however, the oxygen has to be converted into a suitable form for transportation by the manufacturer. This is done by converting it into a liquid. The value of this is shown when you realise that 32 grams of liquid oxygen will only occupy about 28 cubic centimetres. But, as a gas, this same amount of oxygen would need 800 times as much space.

A gas may be liquefied if it is compressed so tightly that its molecules stick together. But oxygen must be cooled as well as compressed before it will become a liquid.

In one of the processes for obtaining oxygen, air is drawn in through a filter, compressed and cooled. After the carbon dioxide has been removed, the air is cooled by making it work an expansion engine. It then goes as a liquid to a separator where the nitrogen and the oxygen are separated. The liquid oxygen is stored in cylinders and the nitrogen is allowed to become a gas for use in the cooling system.

In case this has puzzled you a little, perhaps we should say that a gas can be cooled if it is compressed and then allowed to expand rapidly.

Just as oxygen can be used to maintain life and in the creation of such things as steel, it can also be a destroyer. The name of the process which brings this about is oxidation – and one of the visible signs of it is rust on iron and steel.

This is caused by the action of the oxygen, in the air, and water on the iron which causes a loss of electrons in the iron and changes its character. In short, it changes from iron to hydrated ferric oxide, the scourge of all motorists.

However, oxidation is not always a menace. When zinc and aluminium oxidise, a thin film of oxide is formed which protects the metal from further oxidation. Sometimes this effect is produced commercially and the oxide is dyed so that the metal is attractive as well as protected.

And the complexities of this gas which destroys one metal and protects another do not end here. It sustains life, mixed with the other gases found in air. But it can also destroy, for if you breathed pure oxygen for any length of time it would poison you. Clearly, it is a substance to be treated with respect, even reverence.

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