CHEMICAL WIZARDRY

New Zealand Herald, Volume LXXI, Issue 21972, 1 December 1934, Page 5 (Supplement)

CHEMICAL WIZARDRY

nitrates from the air BY A.M.I.M.E. The title of-this talk sounds rather mysterious, doesn't it? Industrial chemists use the more ponderous term "The fixation of atmospheric nitrogen" which,* however, means very much the same thing. This is a big subject, of -course, but its history is one of those fascinating stories of how modern science has made possible the manufacture of many important substances and compounds which we use in everyday life. Some of you will have noticed references to this subject in the Herald during the last few months, dealing with proposals to generate large supplies of hvdro-electric power in the West Coast Sounds locality, in the South Island-. ' You have probably wondered what electric power has to do with getting : "nitrates" out of the air, and what < '-'nitrates" ar?, anyway. It all sounds! very puzzling, to be sure] Now, l t would like to tell you something about j this commodity: what it is, why it is I sucn great importance, and also i - give you a general idea of bow it i s ! manufactured.. Well then, let us start at tlie beginning and take the subject ■ step by step ana I don't think you will i find any real .difficulty in gaining an \ idea of what it all means. We shall i deal with some wonderful and very in- ! xeresting things, such as the way in j wiiich certain chemical compounds are j formed, the kinds of food that plants I need, and liquid air, a fluid that is so ' '"amazingly cold that it will boil furiously on a block of ice, and can make various substances so brittle that a rubber ball, for instance, will shatter like glass if dropped on the floor! But to get back to nitrates and what they are. These- compounds are formed bv the chemical union of nitric acid with various substances, generally metals, which are termed "bases." In silver nitrate, for instance, silver is the base. Nitrate, of soda has for its base j the metal sodium. Nitric acid is com- ' posed of the three gases, hydrogen, j nitrogen and oxygen, but only'the two latter elements enter into combination with the base to form a nitrate, the hydrogen being given off during the formation of the compound. Now, before going any further, let us just take note of the very important difference between a compound, and a simple mixture of several different substances. When two or more elements combine they form what is known as a compound. A very 7 curious and interesting fact about such chemical combinations is that they are generally entirely different in appearance I and properties from the elements composing them. A good example is found in the commonest of all compounds, water, which is formed by the union of two gases, oxygen and hydrogen. Air, on the other hand, is a mixture of ! oxygen and nitrogen. It possesses the ! vitalising properties of oxygen, which Bre "toned down" by the presence of i the inert gas, nitrogen. But if you t dissolve sugar or salt in water the ' solution thus formed is really a mix- . t-ure, even though the substance dissolved disappears' in each case. Nitric acid was known to the alchemists of centuries ago and was highly valued by them on account of its property of dissolving metals, being •called "aqua fortis" (strong water). Nowadays, it is a very important commodity in industry, being used in the manufacture of- dyes, drugs, leather and silk substitutes, photographic films, explosives and fertilisers. The nitrogen fixation industry, now one of the greatest in the world, produces nitrogenous compounds indispensable not only in our daily lives, but for the deadly purposes of warfare, also. About one-eighth of the world's total anmial production of nitrogen is used for industrial purposes, the remainder, reaching the enormous figure of roughly 1£ million tons, being used for agriculture. What a marvellous . achievement that this vast weight of gas, is extracted from the air, which doesn't seem to us to have any weight at all! But air. although a symbol of lightness, is surprisingly heavy, as yon will see from the fact that the amount contained in an ordinary room weighs roundabout one hundred -pounds! You may think that if the extraction of nitrogen goes on at this rate, there must surely come a time when there will be a shortage of it in the atmosphere. But there is no danger of this happening for on every square mile of the earth's surface there rests something like twenty million tons of nitrogen! Of course, this vast and almost incredible figure is beyond one's i grasp, but you can form , some idea of the immensity of the weight from the fact that it is, roughly, equal to that of a layer of solid rock ten feet . thick covering the earth. ' " Until about twenty years ago, the saltpetre (sodium nitrate) deposits of Chile were the source of the world s supply of nitric acid and nitrogenous fertilisers. There is still a large export of saltpetre, and there is no doubt that these natural deposits will, in time, be exhausted. But for the artificial production of nitrates, the world would some day be faced with the problem of avoiding starvation due to the lack of fertilisers for essential crops. The question arises why is nitrogen such a vitally important element for agricultural purposes? To understand this, we must first know something about the food substances needed by plants. The three principal ones which | the plant obtains from the soil are nitrogen, phosphorous and potassium. ; Calcium (in the form of lime) is also , necessary, but it is not used directly j as a food, its function being to set j free the other elements and to correct acidity in the soil. As vegetation derives its nutriment from the soil, 'the necessary foods must be present in a form that is soluble in the root liquids. The plant cannot use them in their sim ple, elementary con-j dition. They need to be present as nitrates, phosphates and potash. X should mention, however, that there is one large family of plants which makes use of "the nitrogen in the atmosphere through the agency of "nitrogen fix-, ing" bacteria, minute organisms which j are able to convert the nitrogen into nitrate. These bacteria live in little Modules, or wart. l ;, which are to be, foiind on the, roots of peas, beans, i lupins, _ and all other plants of the j Leguininosae family. Now, let us see what uses the plant makes of the trio of essential foods' just mentioned. It is an interesting fact that each one produces certain j definite results. Nitrogen is" especially active in producing leaves and in buildJSg up new growth. That is why nitrate of scia is so good for lettuces, cabbages etc. Phosphorus helps in the pro- 1

duction of flowers and fruit and also ! promotes root-growth and early ripenI ing. Potash produces vigorous growth and the early maturing of plants. It is essentia) to fruit trees. In addition, phosphates and potash both act as a check on the excessive absorption of nitrate, which causes plants to make rank growth. The general fertility of soil depends largely upon the amount of lime it contains Next week we will deal with the different methods used for extracting nitrogen from the atmosphere.