Читать книгу Marvels of Scientific Invention - Thomas W. Corbin - Страница 11

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We now enter for a while the realm of organic chemistry, a branch of knowledge which is of supreme interest, since it covers the matters of which our own bodies are constructed, the foods which we eat and the beverages which we drink, besides a host of other things of great value to us.

Although the old division of chemistry into inorganic and organic is still kept up as a matter of convenience, the old boundaries between the two have become largely obliterated. The distinction arose from the fact that there used to be (and are still to a very great extent) a number of highly complex substances the composition of which is known, for they can be analysed, or taken to pieces, but which the wit of man has failed to put together. Consequently these substances could only be obtained from organic bodies. The living trees, or animals, could in some mysterious way bring these combinations about, but man could not. The molecules of these substances are much more complicated than those with which the inorganic chemist deals. The important ingredient in them all is carbon, which with hydrogen, nitrogen and oxygen almost completes the list of the simple elements of which these marvellous substances are compounded. In some cases there appear to be hundreds of atoms in the molecule.

If one takes a glance at a text-book on organic chemistry the pages are seen to be sprinkled all over with C's and O's, N's and H's, with but an occasional symbol for some other element.

Another feature of this branch which cannot fail to strike the casual observer is the queer names which many of the substances possess. Trimethylaniline, triphenylmethane and mononitrophenol are a few examples which happen to occur to the memory, and they are by no means the longest or queerest-sounding.

Another peculiarity about these organic substances is that a number of them, each quite different from the others, can be formed of the same atoms. Certain atoms of hydrogen, sulphur and oxygen form sulphuric acid, and under whatever conditions they combine they never form anything else. On the other hand, there are sixty-six different substances all formed of eight of carbon, twelve of hydrogen and four of oxygen. This can only mean that in such cases as the latter the atoms have different groupings and that when grouped in one way they form one thing, in another way some other thing, and so on. This explains the extreme difficulty which the chemist finds in building up some of these organic substances.

Every now and again we are startled by some eminent man stating that the time will come when we shall be able to make living things, when the laboratory will turn out living cows and sheep, birds and insects, even man with a mind and soul of his own. Yet one cannot but feel that such men, no matter how great their authority, are simply "pulling the public's leg," to use a colloquial expression. For they hopelessly fail to make many of the commonest things. In many cases where they wish to produce an organic substance they have to call in the aid of some living thing to do it for them, even if it be but a humble microbe. For the microbes perform wonderful feats in chemistry, far surpassing those of the most eminent men. Hence the latter very sensibly use the microbe, employ it to work for them, just set things in order and then stand by while the microbe does the work.

Thus most things can be analysed—that is to say, taken to pieces—while many things can now be synthesised—that is to say, built up from their constituent atoms—but still a great many remain, and among them the most important, the synthesis of which completely baffles man. One of the most useful and widespread substances, for example, cellulose, is, at present at least, utterly beyond us. We do not even know how many atoms there are in the cellulose molecule. The molecules may, for all we know, contain thousands of atoms. Indeed many of these organic matters have very large molecules.

And even if the chemist were able to make all kinds of organic matter, he would still be as far off as ever from making living matter. Indigo used to be derived entirely from plants of that name. One of the greatest triumphs of the organic chemist was when he produced artificial or synthetic indigo. But he is as far off as ever from making the indigo plant. It is claimed that "synthetic" rubber is exactly the same as natural rubber, although some users say it is not quite the same. Still, if it be so, it is dead rubber, not the living part of the plant. The time, then, is infinitely far distant when the chemist will be able to make anything with the characteristics of life—namely, to grow by accretion from within and to reproduce its kind. The most wonderful product of the laboratory is dead. At most it simply resembles something which once was alive.

But that is somewhat of a digression. This dissertation on organic chemistry was simply intended to lead up to the question of liquid fuels, all of which are organic.

In the life of to-day one of the most important things is petroleum. This is a kind of liquid coal. Just how it was formed down in the depths of the earth is not clear. One idea is that it is due to the decomposition of animal and vegetable matter. Another is that certain volcanic rocks which are known to contain carbide of iron might, under the influence of steam, have in bygone ages given off petroleum, or paraffin, to use the other name for the same thing.

In many parts of the world these deposits of oil are obtained by sinking wells and pumping up the oil. In others the liquid gushes out without the necessity of pumping at all. This is believed to be due to the fact that water pressure is at work. Artesian wells, from which the water rushes of its own accord, are quite familiar, and are due to the fact that some underground reservoir tapped by the well is fed through natural pipes, really fissures in the rock, from some point higher than the mouth of the well. Now supposing that a reservoir of oil were also in communication with the upper world in the same way, the descending water would go to the bottom, underneath the lighter oil, and would thus lift it up, so that on being tapped the oil would rush out.

Another source of mineral oil is shale, such as is to be found in vast deposits in the south-east of Scotland. This shale is mined much as coal is: it is then heated in retorts as coal is heated at the gas-works: and the vapour which is given off, on being condensed, forms a liquid like crude petroleum.

In all these cases the original oil is a mixture of a great number of grades differing from each other in various ways. They are all "hydro-carbons," which means compounds of carbon and hydrogen, and they extend from cymogene (the molecules of which contain four atoms of carbon and ten of hydrogen) to paraffin wax, which has somewhere about thirty-two of carbon to sixty-six of hydrogen. For practical purposes their most important difference is the temperature at which they boil, or turn quickly into vapour.

This forms the means by which they are sorted out. In a huge still, like a steam-boiler, the crude or mixed oil is gradually heated, and the gas given off is led to a cooling vessel where it is chilled back into liquid. The lightest of all, cymogene, is given off even at the freezing-point of water. That is led into one chamber and condensed there. Then, as the temperature rises to 18° C., rhigolene is given off: that is collected and condensed in another vessel. Between 70° and 120° petroleum ether and petroleum naphtha are produced, and they together constitute what is commonly called petrol. Between 120° and 150° petroleum benzine arises. All the foregoing taken together constitute about 8 to 10 per cent. of the whole crude oil. Then between 150° and 300° there comes off the great bulk of the oil, nearly 80 per cent., the kerosene or paraffin which we burn in lamps. Above 300° there is obtained another oil, which is used for lubrication, also the invaluable vaseline, and finally, when the still is allowed to cool, there remains a solid residuum known as paraffin wax. This process is known as fractional distillation, and it will be noticed that it consists essentially in collecting and liquefying separately those vapours which are given off at different ranges of temperature. For our purpose in this chapter we are mainly concerned with the petrol and the kerosene.

Many efforts have been made in times gone by to use kerosene for firing the boilers of steam-engines. In naval vessels a great deal is so used at the present time. But the chief method of employing oil for generating power is to use it in an internal combustion-engine. These machines have been dealt with at length in Engineering of To-day and Mechanical Inventions of To-day and so must be simply mentioned here. They consist of two types. In one, which is exemplified by the ordinary car or bicycle motor, the oil is gasified in a vessel called a carburetter or vaporiser and then led into the cylinder of the engine, together with the necessary air to enable it to burn. At the right moment a spark ignites the mixture, which burns suddenly, causing a sudden expansion, in other words, an explosion. Thus the power of the engine is derived from a succession of explosions. If the fuel be petrol it vaporises at the ordinary temperature of the engine and needs no added heat. With kerosene, however, heat has to be employed in the vaporiser to make it turn readily into a gas.

The other method is employed in engines of the new "Diesel" type, in which the cylinder of the engine, being already filled with hot air, has a jet of oil sprayed into it. The heat of the air causes it to burst into flame, causing an expansion which drives the engine.

An important feature in the latter type of engine is that the oil is very completely burnt, so that very heavy oils can be used, oils which, if employed in an engine of the other kind, would choke up the cylinder with soot. In other words, the range of oils which can be used in this new kind of engine is much wider than is possible in the others. The latter may be likened to a fastidious man who is very particular about his food, while the former resembles the man of hearty appetite who can eat anything. And just as a man of the latter sort is more easily provided for by the domestic authorities, so the Diesel engine makes the problem of the provision of liquid fuel much simpler.

For it must never be forgotten that the provision of liquid fuel for the world is by no means a simple matter, since the supply is by no means adequate. The output runs into thousands of millions of gallons, and the whole world is being searched for new fields of oil, and yet it is all swallowed up as fast as it can be produced, while the coal mines do not feel the competition. A year or so ago the United States and Russia between them (and they are the greatest producers) obtained 5,000,000,000 gallons of oil, seemingly an enormous quantity. But, on the other hand, Great Britain alone produces over 250,000,000 tons of coal per annum. If, therefore, liquid fuel is to displace coal, as some people lightly think it is going to do, the supply will have to be multiplied many times. In the amount of heat which it is capable of giving the coal of Great Britain alone beats the oil produced by the whole world.

And another thing to be borne in mind is that as the coal miner goes down to the seam and sees for himself what is there, while the oil producer simply stays at the surface and draws it up with a pump, the coal man knows far more as to how much there is still left than the oil man does. We know that the coal deposits will last for many years to come, even if the production go on increasing, whereas the oil supply may fall off in the near future instead of increasing.

And in both cases we are using up capital. Coal is not being made on the earth now, at any rate in any appreciable quantity. The stage of the earth's history favourable to the formation of coal measures has long gone by. And the same probably applies to oil.