Читать книгу Meteorology: The Science of the Atmosphere - Charles Fitzhugh Talman - Страница 6

Exploring the Upper Air. Left: Beginning of a pilot-balloon flight. Right: Sending up a sounding-balloon. Note the parachute, which wafts the basket of instruments gently to the ground after the balloon bursts. (Photographs from U. S. Weather Bureau.)

Although, when air is liquefied, the oxygen and nitrogen are condensed simultaneously, the latter has a lower boiling point than the former and therefore passes off more rapidly when the liquid is allowed to evaporate. This fact makes it possible to separate the two substances, by the process known as “fractional distillation,” and hence liquid air plants have been established for the special purpose of manufacturing oxygen and nitrogen, for both of which there is a large and growing commercial demand. Scores of millions of cubic feet of oxygen are used every year in the wonderfully efficient process of welding metals with the oxyacetylene blowpipe, the flame of which has a temperature of about 6,000° Fahrenheit. Most of the supply now comes from liquid air. An equally large amount is used in a recently introduced method of cutting metal. The object to be cut is first heated to incandescence, after which a jet of oxygen is played upon it. The metal actually burns away in the stream, and a clean cut is made like that of a saw. It is interesting to reflect, when we fill our lungs with oxygen in order to keep our bodily machinery in operation, that the same atmospheric gas is applied to the building of motor cars, bicycles, safes, boilers, and battleships. Cartridges made of lampblack, dipped for a few moments in liquid oxygen and then primed with a fulminate cap, constitute an explosive as powerful as dynamite and much cheaper to produce. A small percentage of oxygen added to the air supplied to blast furnaces has been found to effect a great saving of fuel used in the furnace.

Meteorograph for use with Sounding Balloon. (Fergusson pattern. U. S. Weather Bureau, 1919.) The aluminum case, surrounded by hoops of rattan to protect the apparatus when it falls to the ground at the end of the flight, contains a set of very light self-registering meteorological instruments. (Photograph from U. S. Weather Bureau.)

Kite Meteorograph. (U. S. Weather Bureau Pattern.) The four pens record the barometric pressure, temperature, humidity, and wind-force on a sheet of paper wound around the large cylinder, which is turned by clockwork. Note the fan wheel inside the tube, for measuring the force of the wind. The apparatus is made chiefly of aluminum and is inclosed in an outer case of aluminum when sent aloft attached to the kite. (Photograph from U. S. Weather Bureau.)

The most important industrial demand for nitrogen is for use in “fixation” processes—i.e., for making nitrogen compounds to be used as fertilizers, explosives, etc. Before describing these processes, it may be of interest to mention that some of the “rare” gases of the atmosphere are now obtained on a commercial scale as by-products of the manufacture of oxygen and nitrogen from liquid air. Thus neon, on account of its exceedingly small resistance to the passage of electric discharges, is a promising substance for filling glow lamps; especially as means have been found of correcting the glaring red color of the light which characterized the original neon lamps. Argon is likewise used for filling electric lamps.

The idea of using the unlimited store of atmospheric nitrogen for the benefit of agriculture and the manufacturing industries has been very prominently before the public in recent years, and gained special notoriety during the late war, when great efforts were being made to increase the supply of nitrogenous materials suitable for use in explosives. Nitrogenous matters in the soil are indispensable to the growth of plants, and as long ago as 1898 Sir William Crookes, in an address before the British Association for the Advancement of Science, alarmed the world by pointing out the possibility of a general famine owing to the prospective exhaustion of Chilean nitrates and other sources of nitrogenous fertilizers. Nitrogen also enters on an immense scale into the composition of many industrial products besides explosives. No wonder popular writers have dwelt upon the fact that the atmosphere contains far more nitrogen than mankind needs for every possible purpose—actually something like 20,000,000 tons over every square mile of the earth’s surface.

A widespread misunderstanding, however, prevails as to the problem involved in utilizing this supply of nitrogen. Free (i.e., uncombined) nitrogen is of no use as a fertilizer, and it cannot be readily used in the arts. The process of extracting it from the atmosphere is an easy one, thanks to the liquid air industry. The real difficulty is to make this inert gas enter into chemical combination with other substances, forming useful compounds such as ammonia and nitrates; in other words, to “fix” it.

As we have stated on another page, lightning discharges cause nitrogen and oxygen to combine in the atmosphere, and perhaps also combine nitrogen and hydrogen to form ammonia. There is one other natural process by which atmospheric nitrogen is fixed. Certain species of bacteria are able to extract this gas from the atmosphere and combine it with other materials. Some of these bacteria are independent organisms, while others form colonies of parasites growing on the roots of higher plants, chiefly members of the pea family. In the latter case the bacteria use the nitrogen of the air and carbohydrates drawn from the roots on which they grow to form nitrogenous compounds, which are, in part, transmitted to the host plant.

Unfortunately these natural processes do not suffice to maintain agricultural soils in a high state of fertility. Mineral deposits of combined nitrogen are practically limited to the nitrate fields of Chile, from which more than two million tons of nitrate of soda are exported annually; but this supply cannot last more than a few decades. Combined nitrogen in the form of ammonia is supplied on a large and rapidly growing scale from by-product coke ovens, and another perennial source of nitrogenous matter is found in animal and vegetable refuse of all kinds, including fish scrap and slaughter-house refuse, garbage, sewage, manure, etc. Since, however, the demands of agriculture and the manufacturing industries greatly exceed the total amount of combined nitrogen obtainable from all these sources, the ingenuity of inventors has been spurred to the task of fixing atmospheric nitrogen by artificial methods, and several such methods have now been put in operation commercially. Their combined product at present constitutes nearly one-third of the total nitrogen supply of the world.

It is not proposed here to describe these methods in detail, but it may be mentioned that one of them, known as the “arc process,” imitates the action of lightning in combining the nitrogen and oxygen that occur naturally in the air, while the others utilize nitrogen that has been previously separated from the air by the liquid air process. The arc process requires, for commercial success, a large supply of cheap electrical power, and it is at present almost confined to Norway and Sweden, where electricity is obtained from waterfalls. In this process air is blown through a huge electric flame, spread out by a powerful electromagnet. The air yields nitric oxide, which is combined with water to form nitric and nitrous acids, and these substances are combined with others to form marketable products. The most widely used fixation process, and the one which the United States Government proposed to employ in the large plants that were in course of construction in this country at the close of the war, is known as the “cyanamide process.” This process requires, as a part of its raw materials, large supplies of limestone and coke, from which calcium carbide is made in an electrical furnace. The calcium carbide, at red heat, absorbs nitrogen, forming an intermediate product from which, by further processes, are made ammonia and nitric acid. A third method of fixing atmospheric nitrogen, which has been applied on a vast scale in Germany and is now coming into use in other countries, is commonly called the “Haber process.” In this process nitrogen is combined with hydrogen, obtained from water, to form ammonia, the combination being facilitated by the presence of what chemists call a “catalyzer,” i.e., a substance that enables other substances to combine without itself undergoing any change. Several different catalyzers have been used in the Haber process.

Two or three other methods of nitrogen fixation are beginning to assume commercial importance.

While the power of the wind holds an important place among the resources of the atmosphere, it cannot be said that the utilization of this resource has undergone developments in modern times at all comparable with the striking inventions and discoveries we have just been recording, if we except the use of the wind in aeronautics. Atmospheric resources used by aeronauts will be discussed in subsequent chapters.

The chief use made of the wind to-day, as in ages past, is to propel sailing ships, and its use for this purpose is, of course, of less importance, in a relative sense, than it was before the introduction of steam. The importance of windmills has also greatly declined. This fact was strikingly brought out some years ago when the United States Bureau of Statistics collected, through American consuls abroad, detailed information concerning the use of the windmills in foreign countries. In most parts of Europe windmills are rapidly disappearing. In Holland, for example, the traditional home of the windmill, the perpetual task of draining the polders is now performed by steam pumps, and the total number of windmills is estimated to be only about one-tenth what it was centuries ago. Our own country is probably the only one in which the use of windmills is increasing. The modern American windmill, with its disklike assemblage of numerous light sails, and ingenious contrivances for veering, reefing, etc., is a much more efficient contrivance than the old-fashioned windmill; but its utility, like that of other windmills, is limited by the irregular force of the winds.

For years the hope has been entertained that the windmill would eventually become a common means of generating electricity, but this hope has not yet been realized, though isolated installations of this character are in successful use.