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and nitric acids. Cryolite, the double fluoride of sodium and aluminum, is also a source from which is made the bicarbonate of soda, and the nitrate of soda is the refined nitrate deposit of South America. From these commercial products the C. P. grades are prepared by recrystallization. C. P. sodium acetate is prepared by recrystallization of commercial acetate of soda. C. P. carbonate of soda is prepared from the bicarbonate. C. P. caustic soda is made from the chloride of electrolysis. C. P. sodium phosphate is prepared by recrystallizing commercial phosphate which is derived from phosphate rock. All other C. P. sodium salts are prepared from the carbonate or hydrate by combination with the different acids. All C. P. strontium salts are made from commercial carbonate of strontium. As noted above, all the salts of tin and zinc are made direct from the metal and purified by recrystallization.
THE UTILIZATION OF ATMOSPHERIC NITROGEN, PARTICULARLY FOR THE MANUFACTURE OF AIR-SALTPETRE.‘ BY HOPRATPROF.DR. A. BERNTHSEN
Ludwigshafen a/Rh., Director of the Badlsche Anilin- u Soda-Fabrik.
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Of the two chief constituents of the atmosphere, n e have hitherto been accustomed to look upon oxygen as the fundamentally important element. \&’e are compelled to breathe i t in order to support life; i t is indispensable to almost every process of heating and combustion, and in the form of oxides, salts and the like, i t constitutes nearly one-half of the earth’s crust. Nitrogen, on the other hand, we regard as a gas which will not support combustion. IVe breathe i t in and out without i t benefitting us in any way, in fact, unless mixed with oxygen, we are unable to exist in it, and i t is generally characterized by a great disinclination to enter into chemical reaction, In spite of this, however, compounds of nitrogen play such a n important part in the nutrition of all living organisms, that the task of finding out and opening up new sources of nitrogen compounds, has become one of the most interesting and pressing problems of the day. Schulz-Lupitz, one of the first of Liebig’s pupils in the domain of agricultural chemistry, has written: “Nitrogen is, after water, the greatest factor in the creation, growth, and working of nature; to bind i t and be its master, that is the problem, to make use of it, therein lies real agriculture, t o bring its sources, which are inexhaustible, into service, that i t is which creates wealth.” I propose, therefore, to occupy your attention for a short time, with the problem of the utilization of atmospheric nitrogen, a problem on which, a few decades ago, scarcely any one would seriously have thought of lecturing. The supply of nitrogen conipounds has become of particular importance t o the department of agriculture, and this is a branch of national economy on which the prosperity of nations to a great extent depends, for even if a country, owing t o special circumstances, develops into a n industrial state, i t is nevertheless dependent on progress in agriculture, if not within its own shores, then in other countries. This progress is, however, by no means such a matter of course, as was often assumed in former times. 1 An address delivered at the Seventh International Congress of Applied Chemistry, London 1909.
I t used to be generally believed that the carbonic acid contained in the air, and continually supplied thereto from processes of combustion and putrefaction, and also from the breathing of men and animals, formed sufficient food for the plant, and for the production of starch, sugar, fats and cell walls, but Liebig investigated the ashes of plants and showed that mineral substances, in particular, potassium and phosphoric acid, also play a n important part in the builiding up of plant organisms. H e taught us further, that plants also derived nitrogen from the earth, in order to be able to build up the nitrogenous part of their organisms, in particular, for the synthesis of albumen, which in its turn is used a s nourishment for the human and animal organism, just as much as are the carbohydrates and fats. Consequently, the necessity arises, not only of returning to the earth in the shape of manure all the products of decomposition and other changes of living matter (this had been carried out empirically for a long time, and in China was even enforced by law), but also of adding a n extra supply of potassium and phosphoric acid salts, and of nitrogen compounds to the ground. I t is true that the soil can yield crops for many years in succession, even when no such additions be made. This is especially the case if the cultivation be not forced too much, and if a suitable rotation of crops be followed, but if greater demands are made on the earth, sooner or later the fertility diminishes, and the soil finally becomes exhausted. Liebig, who is the founder of modern agricultural chemistry, ascribes the decline of civilized nations from the height of their prosperity, to the robbery of the soil, and to the ignorant and unscrupulous using up of its treasures, without any regard to the possibility of exhausting them. He says: “Both the rise and decline of nations are governed by the same law of nature. The deprivation of the soil of its conditions of fruitfulness brings about their decline, while the maintenance of such conditions leads to their permanence, prosperity and power.” H e goes on to say: “The nation is not fed by peace, nor destroyed by war, these conditions only exercise a temporary influence on it. I t is the soil on which man builds his home, which is instrumental in holding human society together, or dispersing it, and in causing nations and empires to disappear, or to become powerful The absolute fruitfulness of the ground is independent of mankind, but he possesses the power of diminishing or prolonging such fruitfulness.” I n Liebig’s treatise on the relation of organic chemistry to agriculture and physiology, which appeared about seventy years ago, he protested most strongly against the way in . which the English wasted manure through their method of sewage canalization. This treatise, however, although i t created a tremendous sensation throughout the whole civilized world, was not a t all well received by the landowners of that period. We, who long ago absorbed Liebig’s precepts into our very flesh and blood, find it difficult t o understand how great the opposition was, which was then raised against them. I n his excellent biography of Liebig, which has recently been published, Volhard describes, in a very interesting manner, the battle waged, and the reason of its failure at the commencement. H e mentions, as a symptom of the feeling then prevalent, that a n English agricultural paper even refused to print a correction sent them by J,iebig himself. Since the end of the fifties, however, Liebig’s teach-
ADDRESSES. ings rapidly acquired a band of enthusiastic followers. Liebig foresaw that, just a s in his time “chemical preparations were used for healing fever and goitre,” so, in the future, manure for the fields would be manufactured in chemical factories. This prophecy has been amply fulfilled. The potassium salts used are obtained from the deposits of the valuable German potash works in and around Stassfurt. The phosphoric acid, although used to some extent in the form of guano, is applied also as bone ash, or superphosphate, and in the form of the basic Bessemer slag which is particularly rich in phosphorus, and a s the mineral phosphorite. Finally, in order to supply nitrogen to the soil, we use both ammonium sulphate froni the gas and coke factories, and also saltpetre which is imported froni Chili. The iniportance of these different artificial manures is shown by the fact that in the year 1906 Germany used AIj,ooo,ooo worth. Of this sum nearly ~sj,ooo,ooowere spent on ammonium sulphate, ~ 6 , 0 0 0 , 0 0 0on Chili saltpetre, while the remainder went on basic slag and superphosphate, potassium salts, guano, and the like. The supply of the nitrogen compounds which I have mentioned, is much more important than is the supply of the potassium and phosphoric ,acid compounds. The ground may be well treated with other plant foods, but i t is all to no purpose if the necessary nitrogen compounds are missing. These latter have a special importance of their own, since, as Lawes and Gilbert showed, not only do they act as fertilizers, but they also play a part in assisting the plant t o take up other kinds of food. The enormous influence of nitrogenous manure is shown by the following figures. According t o bvagner’s experiments carried out in Hessen, the yield of oats went back 17 per cent. when phosphorus was omitted from the manure, 19 per cent. when potassium was omitted, but when nitrogen was left out the yield fell by no less than 89 per cent. The average of all his experiments, carried out over a period of several years, showed that the profit per year and per hectar amounted to iM96 when complete manure was employed, 3162 when potassium mas omitted from the coniplete manure, 3448 when phosphoric acid was omitted, and only M j when the nitrogenous compounds were left out. Such lacts a s these prove the necessity of supplying special nitrogenous matter to the soil, and this appears all the more surprising, when we consider that theoretically a plant should be able to absorb nitrogen from the unlimited quantity a t its disposal in the air, just as easily a s it is able, under the inlluence of light, to assimilate the carbonic acid contained in the air. I t has been known, however, for a long time, that plants, in general, have not this power; on the other liand, i t is true t h a t plants do profit indirectly by atmospheric nitrogen, even if only to a very slight extent. I n the first place, the electrical discharges, which take place in the air, cause the nitrogen and oxygen to combine and lead to the formation of nitrates and nitrites, which are thus continually being supplied to the soil. It has been estimated that, in this manner, u p to I 2 . j kg. of combined nitrogen are supplied yearly to each hectar of land in this latitude ( = I X Ibs. per acre). I n those parts of the tropics where thunder storms are frequent, the quantity is greater. -4nd then again, although the actual plants themselves are unable to assimilate
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nitrogen directly from the air, we know from the celebrated researches of Hellriegel and Willfahrt, carried out in 1886, that leguminar plants, such a s peas, beans, vetch, clover, and lupines, are able to absorb nitrogen directly from the air. The peculiar nodules on their roots, which were known even to Malphigi in the year 1687, contain colonies of bacteria, such as Bacillus radicicola and others, which have the property, otherwise seldom niet with, of fixing atmospheric nitrogen, and conveying it to the plant. Several recent attempts to supply combined nitrogen to the soil have been based upon this property, and i t has been suggested to supply cultures of the bacteria to the soil. Of course the oldfashioned custom known a s “rotation of crops” is also founded on this property, although i t had not been discovered a t the time the custom came into existence, and the same remark applies to the alternative custom of raising some leguminar crop every few years, on ground which is otherwise used for raising corn crops, and eventually ploughing such leguminar crop into the ground as green manure. I n this way, a rotation of crops tends to enrich the soil again with nitrogen, and such sources of nitrogen may suffice to support vegetation for a long time on virgin soil, for instance, in the tropics. If however, as is generally the case, the soil be more intensively cultivated, even supposing all the animal and vegetable refuse be used up as manure, it has been calculated that only from about 30-40 per cent. of the total amount of nitrogen required is thus supplied, so t h a t considerable quantities of artificial nitrogenous manure are still necessary. The amount required, however, is rendered still greater, since b y no means all of the combined nitrogen contained in the body of the plant returns to the soil. Quite apart from the enormous loss brought about by the present system of sewage disposal, huge quantities of combined nitrogen, which have been stored up during countless ages in our coal deposits, are set free during the processes of combustion and putrefaction, and are thus lost to the soil. Then again, large quantities of combined nitrogen are used up in the form of nitrates, in the production of gunpowder and other explosives, and when these are fired off, the nitrogen is set free in the elementary state. It was this wagte of combined nitrogen, that led Bunge to arrive a t the paradox, “every shot destroys life, even if the bullet does not hit the target.” The absolute necessity and the fundamental importance of supplying combined nitrogen to the soil, either in the shape of ammonia salts, or as saltpetre, becomes consequently all the greater. According to Bertrand, the assinlilation of ammonia by the soil is dependent on several conditions, which d o not come into consideration in the case of saltpetre. It is generally assumed that, before ammonia can be taken up by the plant, i t is converted into nitrates, by the action of the bacteria in the soil, or is in a n y case assimilated only with great difficulty, while the conversion into nitrate appears to be not quite complete, some of the nitrogen being set free. Moreover, ammonium sulphate is retained longer in the soil, and, in its action, is slower and less uniform than saltpetre. In order to obtain the best results, it should be applied to the soil before the seed is sown, whereas saltpetre should be strewed on the ground during germination. I t is pretty generally agreed that the nitrogen contained in ammonia is only nine-tenths as valuable a s
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the nitrogen in saltpetre, and Wagner states that, when used
the soil was hitherto considered inexhaustible, or the chemical industries of which are developing rapidly, are now comquantity of saltpetre used per year is more than three times mencing to use saltpetre in larger quantities. AS a n inas large as that of ammonium sulphate. stance, I mention the United States of America, where the We will now consider the future possibilities of producing quantity imported has risen during the last ten years, from 100,ooo tons to 400,000 tons. these two sources of combined nitrogen, namely ammonia and nitrates. IJntortunately, nature has only provided us with a comPractically all the ammonium salts in commerce are obparatively restricted supply to meet this great demand. tained as by-products, during the conversion of coal, and Limited quantities, arising from the action of bacteria on animal excrement, have always been found in various places, siniilar substances, into gas and coke, whereby, however, only a small percentage of the nitrogen contained in the coal such as India; further, some has been found near the Death is recovered as ammonia. At the present time, the 26,- Valley in California, and deposits are also reported to have ooo,ooo tons of coal employed annually for this purpose in been found in the Sahara desert, close to the Tuat Oasis, Germany yield only about 260,000 tons of ammonium sul- b u t the only deposits which i t pays to work are those in phate, valued a t ,&3,~50,000. I n 1906, the quantity pro- Chili, which up to 1879were in possession of Peru and Bolivia, duced was 235,000 tons, and of this 197,000tons came from The saltpetre district (Pampa Salitrera) stretches from the the coke-ovens, and the rest from the gas works. Five times 19th to the 26th degree of latitude, and in particular covers this quantity could be produced in Germany alone, if all the the eastern parts of the hill country, reaching towards the coal consumed there (amounting in 1907 to 143,000,ooo Pampa de Tamarugal and the Atacama deserts. I t is from tons) were converted into coke, and this quantity could be 35-45 miles from the coast and from 3,000-5,ooo feet above again trebled or quadrupled, if rational methods were used the sea-level. The saltpetre is not found in a pure state, to convert the nitrogen into ammonia, for instance, by using but is contained in the mineral caliche, and this is covered by a crust or “costra,” varying in thickness from I 1/2-9 Moxid’s process for converting coal into water-gas by means of steam. Such a n increase, however, is not likely to take feet. The caliche has to be extracted with water, and the solution is then evaporated till the saltpetre crystallizes out. place, because the production of ammonia will probably never be the main object, b u t will always be dependent on These operations are simple enough in themselves, but the the increase in the production of coke and gas. The same scarcity of water, labor and fuel in those regions rather reasoning applies to the calculations, which have recently complicate matters. been made, as t o the quantities of nitrogen obtainable from Up to 1905,about 62 companies had been formed for the the refuse yielded by washing coal, and from peat, although purpose of working the saltpetre deposits in Chili, and they the possibility has been advanced of obtaining a profit, by had a total capital of about ~23,000,000.The State has working up the large quantities of peat found in North Gerimposed a n export duty on saltpetre, and this brings in over many, and elsewhere, and producing nitrogen compounds, ,&,25o,ooo annually. This is considerably more than onein addition to gas for power purposes. Frank has obtained half of its total income from all sources. The cost, f. 0. b., is 40 kg. of ammoniuni sulphate from I ton of peat, so t h a t the from ,&7: 5s to ~$3: 10s per ton, and the average profit is German peat bogs should yield theoretically 360,000,000 estimated a t about A I: 2s. tons of sulphate of ammonia. Some of the deposits, in particular those in Tarapaca, are The second and most important source of combined more favorably situated and are richer in saltpetre than the nitrogen is Chili saltpetre, or sodium nitrate. To-day i t others, and consequently yield a bigger profit, but i t is just these rich deposits, which are rapidly approaching exhaussounds incredible, but i t is a fact that the first ship-load tion. Those of Tarapaca will be worked out in about nine which arrived at Hamburg in 1825 was thrown into the sea, because no one knew what t o do with it. The export from years’ time. Several estimates have been made of the total quantity of Chili for agricultural purposes only began to assume consaltpetre still in Chili, but of course these are only approxisiderable proportions at the beginning of the sixties, but since then it has grown so rapidly that a t present nearly mate, and they also vary according to whether or not deposits are taken into consideration, which, by reason of the paucity 2,000,000 tons are used annually. The actual quantity in of their nitrate, and their relative inaccessibility, could not 1908 was 1,730,oootons, possessing a value of more than ~17,goo,ooo and of this, Germany alone took one-third, be worked a t a profit, unless the price of saltpetre were conthat is, about 600,000 tons, and employed three-quarters siderably increased. It is interesting to compare the differof i t for agricultural purposes, while the remaining quarter ent estimates. The most reliable figures vary from 120,was used up in the chemical industry, for making nitric acid, ooo,ooo tons down to 65,000,000 or even 50,000,000tons, explosives, aniline dyes, azo dyes, indigo, celluloid, and so whereas the estimate of the Delegacion Fiscal in 1908 ran up to 223,000,000tons. Now if the consumption of salton. The yearly increase in the world‘s consumption petre continue to increase annually by a t least 50,000 tons averages at least 50,000 tons, and last year amounted to 72,000 tons. (and we must assume t h a t this will be the case), 90,000,000 Considerably more than this, however, is required. It has tons will be used up in 33 years, i. e., by the year 1942,while been estimated, that, if Germany doubled the amount of 120,000,000would last for 42 years, and 50,000,000 tons nitrogenous manure applied to its soil, i t would not only only for 2 1 years. The price of saltpetre has been tending t o rise for several be able t o raise all the corn and potatoes i t required for consumption, but would also be able to export large quan- years. I n 1900 i t cost A;8: 7s per ton, in 1902 A9: 3% in 1904 ,&IO: 3s, and in 1908 610: 7s. I n 1906,the price even tities. 11s per tan. Since 1908 i t rose for a short period to LII: A further point to be considered is that countries of which
on a large scale, this proportion sinks to 7 5 per cent. The
ADDRESSES. has fallen a little. Owing t o the lack of labor, wages have risen 2 j per cent. since 1892, and there seems no possibility, a t any rate for t h e near future, of the cost of production and t h e selling price in Europe becoming cheaper, even should the method of transport be improved. Sir n l l l i a m Crookes, i n his treatise entitled “ T h e Wheat Problem ” published in 1899, taking into consideration these facts, and also the continually increasing population of the world, prophesied t h a t the supply of saltpetre would be exhausted before very many years had passed, and he described the situation a s of far greater importance, than the possibility of t h e British coal-fields becoming exhausted. H e even calls i t a n impending catastrophe, and points out, that, although details perhaps cannot be foretold, yet some of t h e immediate consequences are sufficiently apparent. I n the year 1935 there will be such a demand for wheat, that, even if all the ground now available be planted, the yield per acre must be increased from 12.7-20 bushels, i n order to supply it. To obtain this result, however, 12,ooo,ooo tons of saltpetre will be required annually, over and above t h e 1,750,000 nom being used. I n other words, even if we could assume t h a t i n 1935 Chili would still possess 50,000,000 tons of saltpetre t o dispose of, this quantity would be used u p in four years. We can consequently appreciate Crookes when he says: “ T h e fixation of atmospheric nitrogen is one of t h e greatest discoveries awaiting the ingenuity of chemists. It is certainly deeply important i n its practical bearings o n the future welfare and happiness of the civilized races of mankind.” We will now consider t o what extent this problem has been, and is a t present being solved. Quite a number of celebrated chemists have been working for some time past, on the fixation of atmospheric nitrogen, all of their experiments being instigated by the fact t h a t the air can supply us with such enormous quantities of nitrogen. % \e’ know t h a t the quantity of air which rests upon I square inch of the earth weighs 15 lbs. and t h a t four-fifths of this are nitrogen, consequently the total nitrogen of the atmosphere amounts in round figures to four thousand billion tons, On the other hand, about 300,000 tons of nitrogen are a t present used up annually i n the shape of saltpetre. Consequently, reckoning on the basis of the present annual consumption, even if none of the nitrogen were replaced, there is sufficient i n the air for the production of fourteen thousand million years’ supply of saltpetre. The different methods employed in the fixation of atmospheric nitrogen can be divided into three groups: First, the direct formation of ammonia from its elements, nitrogen a n d hydrogen, both of which have t o be isolated for the purpose. The second group covers those processes in which the nitrogen is first isolated, and then converted into metallic nitrides and cyanogen compounds, which, in their turn, can be subjected t o chemical reaction, a n d lead to the production of ammonia. The methods of the third group aim a t t h e direct oxidation of atmospheric nitrogen, and the conversion thereof into nitrates and the like. I n this case the air itself is used directly, and a previous isolation of t h e nitrogen is unnecessary. It is n o t difficult nowadays to obtain nitrogen from the air; several methods can be employed on a large scale. One method consists in passing the air over red-hot copper,
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which retains the oxygen forming copper oxide This latter has of course to be reduced again, and the reduction can be carried o u t by passing generator gas over it, and i t is then able t o absorb a fresh quantity of oxygen from the air. An alternative method consists i n liquefying air according t o Linde’s process, and then separating the nitrogen from the oxygen by fractional distillation. Such processes however, always increase the cost of the total operation to a greater or less extent. Hydrogen can also be obtained without great difficulty, since i t results a s a by-product, for instance, during the electrolysis of potassium and sodium chloride, b u t here again its cost depends upon the price which can be obtained for the other products of the electrolysis, namely chlorine and the alkali. Turning now to the direct combination of nitrogen and hydrogen, we are a t once met by great difficulties, since, a t the high temperature a t which the combination takes place, the reverse reaction also sets in, and the ammonia formed is t o a great extent decomposed back again into its elements. Consequently only a small fraction of the gases can be converted into ammonia, while t h e rest remains unchanged. The problem certainly presents many interesting features. The second group of methods of fixing atmospheric nitrogen depends on the property of nitrogen of combining with certain metals, t o form nitrides, or with metals and carbon to form cyanogen compounds, either simple or complicated. These nitrides and cyanogen compounds are then made t o undergo a further chemical reaction, and give rise, on the one hand to ammonia, a n d on the other hand t o metallic oxides and carbonic acid or other carbon derivatives. These methods consequently bring about a n indirect synthesis of ammonia from its elements. The intermediate products formed during t h e reaction are sometimes of such importance, t h a t they are manufactured in this manner, without being finally worked up for ammonia. I refer i n particular t o the cyanides, especially potassium cyanide, which is used i n great quantities i n the extraction of gold from its ores. Bunsen discovered, nearly seventy years ago, t h a t potassium cyanide occurs in blast furnace gases, and further, t h a t i t could be synthesized from atmospheric nitrogen, carbon and potassium compounds, and even a t t h a t time, he caused experiments t o be made a t Grenelle, and later a t Newcastle, t o determine if this reaction could be developed on a large scale. It was found to be unprofitable, a t any rate under the conditions then existing. Marguerite and Sourdeval found in 1863, t h a t if barium compounds be used instead of potassium compounds, analogous results are obtained, b u t the reaction proceeds more easily, so t h a t if nitrogen be passed over a mixture of carbon and barium carbonate a t red heat, large quantities of barium cyanide are obtained, a n d this on suitable treatment yields ammonia, while at the same time barium hydroxide is generated, and can be used over again instead of the carbonate. Another metal, which has the power of fixing gaseous nitrogen, is titanium, as was first pointed o u t by St. ClaireDeville and Wohler in 18j7. Either titanium nitride is formed, or, if carbon also be present, titanium cyanonitride, and these compounds resemble the cyanides of the alkaline earths in being easily convertible into ammonia, while a t t h e same time titanium compounds are regenerated, and can be used for the absorption of fresh quantities of nitro-
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gen from the atmosphere. Both these processes have recently been investigated a t the Badische Anilin- u. SodaFabrik. Frank, in Berlin, and Nikodenius Caro, in Lodz, working in collaboration with Rothe, in Hamburg, noticed t h a t when nitrogen was made to react with carbon and barium carbonate, or with barium carbide, some barium cyanide was formed, b u t a t the same time large quantities of another body were obtained, which differed from barium cyanide in containing a smaller proportion of carbon. This body is barium cyanamide. The matter was then taken up by the Cyanid-Gesellschaft, which was formed for this purpose by Siemens & Halske, the Deutsche Gold- und Silber-ScheideAnstalt and Dr. Frank. Pfleger had suggested t h a t the barium carbide be replaced by calcium carbide, which can be so easily obtained b y heating lime and charcoal i n a n electric furnace. On carrying out this suggestion, however, t h e investigators were surprised to find t h a t the product contained no calcium cyanide a t all, b u t t h a t i t consisted chiefly of calcium cyanamide, mixed with graphitic carbon. T h e raw product contained lime and carbon a s impurities; i t was black i n appearance a n d had a n unpleasant odor, b u t the chief point was t h a t i t contained 20 per cent. of fixed nitrogen. The preliminary production of calcium carbide was subsequently found to be unnecessary, since similar results could be obtained by starting directly with a mixture of lime and carbon. The product is now generally known by the name “ Kalkstickstoff ” or nitrolime. A similar product, the so-called “Stickstoffkalk,” was obtained by Polszenius b y carrying out the process in the presence of small quantities of calcium chloride, which had t h e effect of causing the reaction t o take place a t a lower temperature. Certain other salts possess a similar influence. T h e cyanamides, on being treated with superheated steam, are split u p with t h e formation of ammonia, and so this constitutes another process for the indirect synthesis of this compound. Kalkstickstoff or nitrolime has a n additional interest, since other compounds such a s the alkali cyanides, urea, a n d dicyandiamide can be prepared from i t , and i t can further be employed for case-hardening steel as well as being used itself a s a manure. I n the latter case, after being applied t o the ground, it is acted upon by bacteria and the like, giving rise t o ammonia, and consequently, like the ammoniacal manures, it must be applied to the soil before the seed is sown, otherwise serious damage can be done t o the crops. According t o published researches i t can only be used on special kinds of soil, such a s heavy absorbent soils. It is not suitable for vegetable soils and high moorlands. It also produces different effects on the various classes of plants. T h e figures as t o the quantitative results produced by cyanamides vary to a considerable extent. Wagner has come to the conclusion t h a t the farmer should not pay for the nitrogen contained therein, more than 80 per cent. of the price paid for an equal weight of nitrogen i n the shape of Chili saltpetre, or i n the saltpetre obtained from the air. I n making these calculations he has taken into consideration that saltpetre is much easier t o use and control. Great hopes have been laid on the further development of these processes, and a n industrious agitation has led to quite a number of companies being floated; most of the
factories though are still in the state of construction, and a t present i t is too early to prophesy what success this industry will meet with. It will also still have to be decided whether the nitrolime is entirely suitable for application t o the soil a s such, or whether i t will be advisable to convert i t first into ammonium sulphate, and i n this case how much of t h e profit will disappear in carrying out this further step. It is interesting to learn t h a t at Piano d’Orta, a t the first nitrolime factory erected, a plant has already been p u t down for converting i t into ammonium sulphate, instead of using i t as manure, and, according t o recent reports, other works are following this example. The third method of bringing nitrogen into a state of combination, suitable for use on a practical scale, consists in converting i t by direct oxidation into oxides of nitrogen, which are then transformed into nitric acid and nitrates. Although, as I mentioned before, nitrogen shows little tendency to enter into chemical reaction, i t can, under certain conditions, be made to combine with oxygen. The first compound formed is nitric oxide, KO, a colorless gas containing equal atomic proportions of nitrogen and oxygen. On mixing i t with oxygen or air, it assumes a yellowish red color, owing t o the formation of a higher oxide of nitrogen, which is termed nitrogen tetroxide, or nitrogen peroxide, and which possesses a constitution corresponding to the formulae NO, or N,O,. This is then converted into nitric acid, or into some other form suitable for practical purposes. The direct combination of nitrogen and oxygen is brought about by means of high temperatures, b u t the degree of combination is limited by the fact, t h a t the same temperature which brings about the formation of nitric oxide also tends t o decompose i t back again into its components. For every temperature, there exists a definite state of equilibrium between the oxide of nitrogen formed, and the unaltered mixture of nitrogen and oxygen, and the quantity of nitric oxide, produced a t a n y given temperature, cannot exceed t h a t corresponding to the state of equilibrium for this temperature. Only a t a temperature under I Z O O O C. is nitric oxide stable against t h e action of heat, but, at this temperature, the amount formed is exceedingly small. Even at 1500~ C., only one-tenth per cent. of the nitrogen in the air is converted into nitric oxide, and a very much higher temperature is necessary t o bring about a reasonable degree of oxidation, Muthmann and Hofer, and especially Nernst and his pupils have closely studied the course of the reaction, and from their results i t appears t h a t a t a temperature of zzooo C. the gases contain I per cent. of nitric oxide, ~ they contain z per cent., a t 2854O C. they cona t 2 5 7 1 C. tain 3 per cent., and a t 3 3 2 7 O C. they contain 5 per cent. The equilibrium constant is given by the equation
From the figures I have just quoted, i t is apparent that, in order t o be able t o work profitably, the air must be heated t o as high a temperature as possible, and then cooled down again with the utmost rapidity, so t h a t a s little opportunity as possible is given, for t h e nitric oxide, formed a t the high temperature, t o decompose back again into its elements. Many methods have been, and are still being proposed, i n which the air is raised t o a sufficiently high temperature by t h e combustion of suitable materials, and Pawlikowsky,
ADDRESSES. Hauser, Brunler, Ketteler and others have paid special attention t o experiments in this direction. All the methods proposed, however, suffer, on the one hand from the difficulty of obtaining a really high temperature, and on the other hand from the fact t h a t the oxides of nitrogen formed are mixed with enormous quantities of the other products of combustion, especially water vapor, and consequently, the concentration of the nitric oxide is disadvantageously affected, and the difficulty of cooling the gases with sufficient rapidity is greatly increased. Haber’s process, which consists in burning carbon monoxide with air under pressure, and thus attaining a high temperature, belongs t o this class of reaction, b u t appears t o be a n improvement, since the formation of water is avoided. The second method of bringing about the combination of nitrogen and oxygen is by the use of electricity. As long ago as 1781, Cavendish noted t h a t when hydrogen was burned in a n excess of air, the watfr produced was not pure, b u t contained nitric acid. H e first made this discovery public, however, three years later, about the same time as Priestley discovered i t and made i t known. In 1785 Cavendish showed that all the nitrogen contained in a given supply of air could be transformed into oxides of nitrogen, by adding the necessary quantity of oxygen to it, and supplying sufficient energy in the shape of electric spark discharges. The combination of the gases can be easily shown experimentally in a eudiometer tube, over a liquid containing blue litmus; on passing electric sparks through the air enclosed in this tube, the liquid rapidly turns red, owing t o the formation of nitric acid. It is generally accepted t h a t electricity brings about the reaction by means of the high temperature produced, but on the other hand, it is possible that i t exercises also a specific electrical action on the gases, for we know that nitric oxide is produced from its elements by the action of silent discharges, a s well a s by the action of spark discharges and electric arcs. I have already referred t o the part played in nature by atmospheric electricity, and will now turn more particularly to the results obtained by artificial means. All efforts in this field have been applied to the production of series of sparks or of electric arcs, and during the last decade, a n intense activity has been developed, both in the laboratory and also on the practical scale. I should like to refer here to the labors of Crookes and Lord Rayleigh, both published in 1897, then Lepel, Guye and Naville, MacDougal and Howles, Kowalsky and Moscicki, Brode, Pauling, L e Blanc and Niirenen, Birkeland and Eyde, and Schonherr. The different companies which have taken up work in this direction include the Genfer and Freiburger Studien-Gesellschaft, the Atmospheric Products Company a t the Niagara Falls, the Norsk Hydroelektrisk Kvaelstof-Cie, the Badische Anilin- u. Soda-Fabrik, the Salpetersaure-Industrie-Gesellschaft of Gelsenkirchen, and others. I propose only to take the most important of them, dealing particularly with the steps which led up to the processes now in use. One class of scientists started by assuming t h a t in order to use up the electrical energy to the best advantage, it should be distributed over a large number of small sparks or arcs. Bradley and Lovejoy founded their process on this assumption, and the Atmospheric Products Company was floated towards the end of last century, with a capital of one million dollars, and carried out their process at Niagara,
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making use of power obtained from the Falls. They employed iron cylinders about 4 1 / 2 feet high and 4 feet in diameter. I n the axis of each of these a steel shaft rotated, containing, mounted one above the other, twenty-three zones of electrode arms, each zone containing six arms, and each a r m being provided with a platinum sparking terminal. The wall of the iron cylinder formed the other electrode, and was provided with a similar number of platinum terminals or poles, situated opposite to the terminals of the rotatable electrode. When the shaft was p u t into motion, the electrode poles, attached to the ends of the arms, came within sparking distance of the poles on the cylinder, and sparks sprang across from one pole to the other. As the motion of the shaft continued, the electrode poles were separated irom one another, and the arc was drawn out and finally snapped, only to be formed again as soon as the next pair of poles came within sparking distance of each other. A direct current of 10,000 volts was employed and no fewer than 414,000 arcs or sparks were formed and extinguished every minute, Air was passed through the cylinder, and so came into contact with a great number of arcs, each characterized by great length and extreme thinness, and consequently the air was enabled to attain rapidly t h e high ternperature which is so necessary for the reaction, and was also cooled down again with great rapidity. According t o Muthmann, the yield amounted to 430 kg. saltpetre per kilowatt-year; this yield, however, was somewhat small, and, coupled with the complexity of the apparatus as well as its initial expense and the expense of keeping i t i n order, sufficed to prevent the process being worked a t a profit. The plant was closed down in the summer of 1904. The first practical success in this direction was obtained, in 1903, by Professor Kristian Birkeland in Christiania, who worked in collaboration with the Korwegian engineer, Samuel Eyde. The details of their method were first published by Edstrom, i n a lecture held in 1904, before the International Congress of Electricians a t St. Louis. Otto N. Witt also described the process in a lecture given at the opening of the new Industrial-Chemical Institute of the Technical High School a t Charlottenburg, and Birkeland himself lectured on i t before the Faraday Society in London in 1906. It was already known t h a t if a n electric arc, fed with a n alternating current, be made to burn between the poles of a n ordinary magnet, or of a n electro-magnet which is excited by a direct current, the arc assumes the form of a disc. More correctly s’peaking, the arc is blown into a half-disc a t every half-period, b u t the impression on the eye is t h a t of a quietly burning disc, like the sun. Birkeland and Eyde enclosed this in a flat iron-clad furnace of fire-proof clay, and passed a strong current of air through it, and they thus obtained considerable yields of oxides of nitrogen, so t h a t the prospects of being able to work their process on the technical scale appeared very bright. Since their first experiments, the furnaces have gradually been increased in size, until those now used are so large, t h a t each of them is fed with 700 kilowatts a t a tension of 5,000 volts, and the disc of flame is over two yards in diameter. Each furnace uses up nearly 1,000 h. p., t h a t is, one hundred times as much a s those of the Atmospheric Products Company. The utilization of this large quantity of electricity in a single discharge constitutes the great difference between Birkeland and Eyde’s process, and those of earlier experimenters,
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who all attempted to make use of a very small current for each separate discharge, while employing an extraordinarily large number of flames, and consequently meeting with great difficulties in effecting a n even distribution of the current. The great importance attaching to the possibility of fixation of atmospheric nitrogen, had, several years before t h a t time, been recognized in the Badische Anilin- u. SodaFabrik, and after the task of manufacturing indigo on a commercial scale had been brought to a successful conclusion in 1Sg7, special attention v a s paid to this new problem, a t the instigation of their head director, Heinrich von Brunck. As the result of these labors, Otto Schonherr succeeded, in 1905, in discovering, and with the assistance of the engineer Hessberger, working out a process of producing a n electric arc, and was thus enabled to solve the problem in a surprisingly simple manner, presenting considerable advantages over the method of Birkeland and Eyde. It is not a mere modification of their process, as has sometimes been falsely assumed, but differs fundamentally from it, for while Birkeland and Eyde cause the electric discharge to burn in a strong magnetic field, and thus spread i t out in the shape of a flat, more or less circular, disc, Schonherr dispenses entirely with magnets and magnetic fields, and produces his arc inside a n iron tube of comparatively small diameter, a t the same time passing the air through the tube, and thus bringing it into contact with the arc. H e has described his process a t a lecture in Berlin, of which a full report has just appeared in the Electro-technisclte Zeatscltrift for 1909, Vols. 16 and 1 7 . The manner in which the arc is developed is in itself very peculiar and interesting. The iron tube, or arc tube as I will designate it, contains an insulated electrode a t one end, and can itself serve as the second electrode. The arc, a t its formation, springs from the insulated electrode to a n adjacent part of the arc tube which is only a few millimeters away, b u t the air, which is passing through the tube, being preferably introduced with a tangential or rotary motion, immediately carries the end of the arc along the wall of the tube, so t h a t i t either enters the tube at a considerable distance from the electrode, or i t ends on a special electrode placed for the purpose, say, a t the other end of the arc tube. A slight modification consists in using a n arc tube of non-conducting material, and inserting i n i t a wire-spiral along which the end of the arc can travel, or providing other means for bringing about the initial formation of the arc. I n each case, a column of flame is obtained, burning quietly in the axis of the tube, and surrounded by the air which is being passed through the tube. The arc, as seen through a mica-covered opening, emits a n intense light, and is quite stable, as opposed to arcs which are formed in the open air, since these latter are easily extinguishable. The air passing through the tube comes into contact with the arc, becomes partially converted into nitric oxide, and is then rapidly cooled dovvn by contact with the outside layers of air, and consequently a decomposition back again to nitrogen and oxygen is avoided. The cooling action is still further increased by surrounding the upper end of the arc tube with running water, after the manner of the Liebig condenser. The gases leaving the tube contain about 2 per cent. of nitric oxide, t h a t is, from one and a half times to nearly twice as concentrated a s the gases which Birkeland and Eyde produce. The method of introducing the air can be subjected t o
many variations. For instance, instead of the air being passed in its entirety into the space between the electrode and the mall of the tube as shown here, i t can be introduced partly or wholly into the tube at other points above or below the electrode, and i t can be made to enter the tube either through one or more openings or through a number of openings which are distributed over a part or the whole of the tube. The opening may be in the form of a ring extending all round the tube, or several such ring-shaped openings can be employed, or instead of these, long slits, either parallel or at a n angle to the axis of the tube, can be provided. The openings may be situated so t h a t the air enters a t right angles or a t any other angle to the axis of the tube. In the latter case, the gases generally pass through the tube with a rotary motion. IVith the aid of Schonherr’s invention, i t is possible to send extraordinarily large quantities of electrical energy through a single tube ; even the small experimental apparatus which you see before you uses about 5 . j h. p. of electrical energy, and works with a tension of 5,000 volts. The experimental furnaces a t Christianssand are fed with about 600 h. p. a t 4,200 volts, and although i t appears possible to build furnaces which could consume 2,000 h. p., those regularly used will probably be built for 1,000 h. p. These furnaces require about 40,000 cu. ft. of air every hour, and the arcs produced are nearly eight yards long. T o u will probably have noticed t h a t this process departs from the principle, hitherto followed, of bringing the air only for a s short a time as possible into contact with the electric flame, for, as is evident, the air requires a not inconsiderable space of time to travel from the one end of the arc tube to the other. The slide now shown illustrates a construction of the furnace on the large scale. The air passes into the arc tube through a number of tangentially-bored holes in the p a r t of the tube surrounding the electrode, and over these holes is a n iron ring or cylinder, which can be moved from the outside by means of a lever, so that any desired number of the holes can be closed, and consequently, the strength of the rotary motion of the air regulated, and this in turn assists in regulating the length of the arc. The insulated electrode can be cobled by means of water or air, and i t is also provided with a central hollow space through which passes a n iron rod The arc actually springs from this iron rod, and a s i t burns or volatilizes away, i t can be pushed forward by a simple arrangement; the rate of burning, however, is very slow. An ignition lever, or other simple arrangement, is provided so that the arc can be started afresh; should it from any cause become extinguished, this, however, is very rarely the case. The furnace itself is connected electrically to earth, so t h a t any part of the apparatus, with the exception of the insulated electrode, can be handled with impunity. The gases which leave the arc tube pass down a channel lined with brick, and concentrically surrounding the inner parts of the furnace. They are thus made to give up a portion of their heat to the air which is entering the furnace, and which is subsequently passed through the arc tube, thereby raising i t to a fairly high temperature. As you see, the apparatus is extremely simple, and a t the same time very durable; ordinary iron tubes are employed; there are no movable parts and no expensive electro-
ADDRESSES. magnets, and the manufacture runs smoothly without interruptions. Though in this process there is very little loss of electrical energy in producing the arc, yet only a few per cent. of the energy serve to bring about chemical reaction; t h e rest is converted into heat. This latter, however, is not by a n y means wasted, 30 per cent. of i t is employed producing hot water, 40 per cent, heats the boilers, I O per cent. has t o be removed by cooling, and only 1 7 per cent. is lost by radiation. T h e evaporation of t h e calcium nitrate solutions obtained is carried o u t solely by the heat generated in the arc. Interesting results have been obtained by studying the chemical activity of this kind of arc. Brode showed t h a t the inner zone of t h e a r c was t h e hottest part, and i n i t , the formation of the nitric oxide was effected, while the decomposition back again into nitrogen and oxygen took place in the outer zone. Following u p this line, Grau and Russ proposed t o draw off the reaction gases from the hottest zone through very narrow cooled tubes. Haber and Konig found that, a t a low pressure, say one-eighth of a n atmosphere, and on using a tube of such diameter, t h a t i t was filled by the electric arc, and, a t the same time cooling the tube from the outside, they could obtain a gas mixture with I O per cent. of nitric oxide. T h e arc produced possesses a comparatively low temperature, and t h e experimentists believe t h a t the combination is brought about, a t a n y rate to a certain extent, b y some electrical phenomenon, such as ionic impulses. T h e process is certainly very interesting from a theoretical point of view, b u t i t is too early to give an opinion on its practical utility. In accordance with the theory, the yield of nitric oxide increases if, instead of atmospheric air, a mixture thereof with oxygen, up to equal volumes of nitrogen and oxygen, be employed. Haber and Konig were able, in this manner, to obtain gases with 14 per cent. of nitric oxide. The advantages, however, a r e only apparent, since the production of the oxygen required is comparatively costly, and also because a very large proportion of the gases pass through the system unchanged, and are subsequently lost. T h e various suggestions of enriching the gases coming from the absorbers with fresh nitrogen and oxygen in combining proportions, and then feeding them into the arc tube again, and also t h a t p u t forward on the one hand by Siemens & Halske, and on the other hand by Sir William Ramsay, of separating the air into its constituents, and using the nitrogen in the production of nitrolime, and the oxygen in the manufacture of air-saltpetre, do not a t present appear likely t o be successful. I t is interesting to note, in passing, t h a t the arcs produced by Schonherr’s process send o u t electrical waves, and, founded on this observation, a method has been worked o u t and patented by the Badische Anilin- u. Soda-Fabrik, for producing electrical oscillations of great frequency and regularity, suitable for use in wireless telegraphy. Another procsss of producing electrical discharges for the purpose of obtaining nitric acid from the air has recently been described by Dr. Franz Russ a t a meeting of the Society of Austrian chemists a t Vienna. This is the process worked out by Pauling and utilized near Innsbruck by the Salpetersiiure-Industrie-Gesellschaft of Gelsenkirchen. I t depends on the use of divergent electrodes. From the d a t a given
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by the author the process is inferior to the Badische process. After the nitrogen has been converted into nitric oxide, according to a n y of the processes I have referred to, the actual “combustion” of the nitrogen is completed, b u t on cooling t h e reaction gases, as soon as the temperature reaches a certain point lying a t about 600’ C., the nitric oxide begins to combine with the excess of oxygen, forming nitrogen tetroxide. The oxidation does not go past this stage of its own accord. T h e next task is t o bring these oxides of nitrogen i n t o a marketable state, t h a t is, either into the form of nitric acid, nitrates, or nitrites; also nitrogen tetroxide as such will be capable of isolation. Up to the present time both nitric acid and nitrites have been manufactured from saltpetre by chemical reaction, nitric acid, which is largely used in making explosives of various kinds, a s well a s celluloid, artificial silk, and coal t a r dyes, being produced by heating saltpetre with concentrated sulphuric acid, while nitrites, also of great importance in the coal tar dye industry, result on heating sodium nitrate with metallic lead, which extracts one atom of oxygen, and is itself converted into lead oxide. Both nitric acid and nitrites are consequently more expensive than saltpetre. Kitrogen in concentrated nitric acid is two and a half times, and t h a t in nitrites is one and a half times a s valuable as nitrate-ni trogen. It would, therefore, be more profitable to make nitric acid and nitrites, provided the consumption of these compounds were sufficiently great, b u t since the demand is limited, the chief aim of every large factory is t o convert the supply of nitrogen into the form of saltpetre, for which, a s we have seen, there is a n unlimited market. Before the nitrogen tetroxide contained i n the furnace gases, after they have been cooled, is capable of yielding nitric acid, i t requires to be combined with a further atom of oxygen, and this combination is generally brought about by the action of water. The gases are passed through a n absorption tower down which water is trickling, and during the reaction which takes place, two-thirds of the nitrogen is converted into nitric acid, while one-third is regenerated a s nitric oxide, which combines again with the excess of oxygen present in the gases forming nitrogen tetroxide, and this goes through the same course of reactions again. This constitutes the so-called “acid” absorption process. T h e absorbing liquid can be run down the tower several times, each time becoming richer in nitric acid, until a 40 per cent. acid is obtained. On neutralizing this with soda, a concentrated solution of sodium nitrate is obtained, and can be evaporated until the solid salt crystallizes out. On a practical scale, however, ordinary limestone is employed instead of soda, and calcium nitrate is obtained. This is a t least as valuable as sodium nitrate for manuring purposes, and is consequently isolated as such, and brought on the market under the name of “Korwegian saltpetre” or “airsaltpetre.” If i t be desired t o obtain marketable nitric acid, the 40 per cent. acid obtained by absorption must be concentrated, and there are several methods available for this purpose. Most of them depend on the removal of water b y means of sulphuric acid or certain anhydrous salts, and another process has been proposed, in which the water is removed indirectly by means of electrolysis.
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Nitrites can be obtained directly from the furnace gases, by employing sodium carbonate or milk of lime as the absorbing agent, and at the same time maintaining the temperature and other conditions, such that, during the absorption, the gases contain equal quantities of nitrogen tetroxide and unaltered nitric oxide. According to this process, the Badische Anilin- u. Soda-Fabrik manufacture, at Christianssand, the sodium nitrite they require in their dye factory a t Ludwigshafen. Finally, if t h e reaction gases be cooled down t o a temperature considerably below zero, nitrogen tetroxide separates o u t as a liquid, or, if the temperature be sufficiently low, i t can even be obtained in the solid state, like ice or snow. Should the gases contain moisture, more or less dilute nitric acid is produced, the quantity depending on t h e amount of water present. A further method of working u p the furnace gases consists in passing them over quicklime. Halvorsen carried out this process at ordinary temperature, while Schloesing obtained better results by working a t a raised temperature. The latter employs special briquettes of quicklime, prepared b y moulding slaked lime into the required shape, and then reheating it, and he places these briquettes in iron vessels, and heats them on the counter current principle, by means of the furnace gases, to from 300-350° C. The final product of absorption contains dry calcium nitrate in admixture with free lime, and some calcium nitrite. T h e absorption a t Notodden is a t present carried out according to the “acid” process; the first product is dilute nitric acid, which is subsequently converted into calcium nitrate. The apparatus necessary is very extensive, on account, both of the small contents of nitric oxide in the gases, and also of the very large volume of the gases treated. The hot gases, on leaving the electric furnace, are first made t o pass through boilers, thereby giving up some of their heat, and creating the supply of steam used for heating the vacuum pans, in which the solutions of calcium nitrate are evaporated. These vacuum pans can be heated directly by the furnace gases if desired, or by the intermediate agency of steam. T h e gases are then still further cooled and afterwards passed into a large empty tower or other receiver, in which time and opportunity are given for the nitric oxide to be oxidized t o nitrogen tetroxide. If the gases contain z per cent. of nitric oxide, 12 seconds are required for the oxidation of 50 per cent. of it, while the oxidation of go per cent. requires IOO seconds. The gases are then passed into very large granite towers about 65 f t . high, and filled with lumps of quartz, and, i n these towers, t h e acid absorption is effected by means of water, or of the dilute nitric acid which is collected a t the bottom of the tower. I n order to recover the oxides of nitrogen which remain unabsorbed, t h e gases a r e finally treated with milk of lime or soda, and give rise either to a mixture of nitrite and nitrate, or t o pure nitrite. The more dilute the gases are, the more difficult is the absorption, and consequently the greater concentration of the gases obtained by the process of the Badische Anilin- u. Soda-Fabrik constitutes a not unimportant advantage over Birkeland and Eyde’s process. More recent experiments a t the Badische Anilin- u. SodaFabrik have shown the possibility of effecting the absorption directly with milk of lime, and, in this case, the “acid”
absorption could be dispensed with, and the absorbing towers and the initial outlay on plant considerably reduced The calcium nitrate, obtained by means of the operations described, can, without further treatment, replace Chili saltpetre for the purposes of agriculture. Even a certain quantity of free lime, say 20 per cent., appears to have no deleterious action on vegetable life, and the same remark applies t o a n y calcium nitrite mixed with the nitrate. I n fact, experiments carried out by Wagner at Darmstadt last summer, corroborate the results obtained by Schloesing and show t h a t no difference can be noticed between the crops obtained, whether the soil be treated with Chili saltpetre, or with pure calcium nitrate, or with a mixture of this latter with 10-20 per cent. of calcium nitrite, or even with pure calcium nitrite. It is b y no means inconceivable, t h a t calcium nitrite will become the artificial manure of the future, especially a s its manufacture is so simple, and i t is richer i n nitrogen than calcium nitrate (it contains 2 1 . 2 per cent. of nitrogen). I t possesses the further advantage of being less hygroscopic than calcium nitrate. Both the process of the Badische Anilin- u. Soda-Fabrik and of Birkeland and Eyde require cheap water power, before they can be carried out profitably. The waterfalls i n Norway, which, owing to the climate, have a fairly cons t a n t supply throughout the year, are particularly suitable. The Badische Anilin- u. Soda-Fabrik secured the right of using several falls there, and commenced by putting down a n experimental plant a t Fiskaa near Christianssand. A few thousand h. p. were available, and manufacture was started in the autumn of 1907. In the meantime the Norsk Hydro Elektrisk KvaelstofAktieselskab, t h a t is, the Norwegian-French Company founded by Birkeland and Eyde, had commenced building a factory a t Notodden t o use u p 30,000 h . p . The interests of the two companies lay in the same direction, and negotiations were opened, and, towards the end of 1906, resulted in a n agreement, according t o which the Badische Anilin- u. Soda-Fabrik and its two allied firms, the Farbenfabriken vorm. Friedr. Bayer & Co. of Elberfeld and the Actiengesellschaft fur Anilinfabrikation i n Berlin on the one side, and t h e Norwegian-French concern on the other side, combined forces and floated two new Norwegian companies. These were: ( I ) A power company with a capital of 16,000,000Kronen, whose d u t y i t is to develop and bring into harness further Norwegian waterfalls, and ( 2 ) The Norsk Salpeterverker with a capital of 18,000,ooo Kronen, which is concerned in building and running Norwegian saltpetre factories, making use of the power supplied by the first company. The two parties have come to a n arrangement as to the exploitation of their patents outside Norway, and the granting of licenses lies in t h e hands of the Badische Anilin- u. Soda-Fabrik. The works a t Christianssand and biotodden remain the special property of the original owners. The first large factory erected by the new Norwegian companies will be situated i n t h e interior of Telemarken on the Rjukan, one of those immense waterfalls in Norway. The total fall of 1820 f t . is divided into two steps, and, with a flow of about eleven thousand gallons of water per second, is capable of yielding a quarter of a million horse-power. The upper fall is now being developed, and with ten turbines
NOTES A N D CORRESPONDENCE. will provide about 140,000 h. p. I t is expected t h a t the factory will s t a r t running in about two years’ time. The saltpetre will be carried along z g miles of new normal-gauged railway, and by a ferry along Lake Tin, which is z j miles in length, until i t reaches Notodden, from here i t will be transported via Skien to the sea. At present, the Norsk Hydro Kvaelstof-Aktieselskab is using up 30,000 h. p. a t its factory a t Notodden, where 35 of Birkeland’s furnaces have been erected, and, a t the present time, a n experimental plant on the system of the Badische Anilin- u. Soda-Fabrik is being constructed there, in order t o determine which type and size of furnace is most suitable for erection at Rjukan. Water power on the Matre and on the T y n in West Norway have been acquired, and will be held in reserve for future use. I n Germany, the water power suitable for the production of saltpetre is very limited. I n South Bavaria, the Alz is able t o supply sufficient power for a moderately large factory, and negotiations have already taken place with the Bavarian Government, with regard to a scheme for the production of j 0 , o O O h. p , , and the erection of a factory near Burghausen. Kegotiations have also been going on for some time ITith a view to the introduction of the manufacture into this country, but here also suitable water power is hard to find. Considerable quantities of air-saltpetre will shortly be put on the market, and probably, within a few years, the annual output will reach IOO,OOO tons. This quantity, however, is none too large, when we remember t h a t the world’s demand increases by a t least t h a t much every two years, and we need not expect a n y demoralization of the saltpetre market. On the other hand, i t is not likely that Chili saltpetre will unfavorably influence the development of the factories already started, especially as air-saltpetre has decided advantages over Chili saltpetre, since i t is free from injurious admixtures of perchlorate and other compounds, which are contained in the natural saltpetre : then again air-saltpetre is able to supply the lime, which is indispensable if the plant is to flourish, whereas the soda of Chili saltpetre is very often directly harmful. Experiments have been made a t Grandeau, Sjolemma, and others, showing the great advantage of using air-saltpetre on soils which are poor in lime. It has recently been asserted by Caro, t h a t i t is more rational to manufacture nitrolime than air-saltpetre, because the former requires only one-third of the amount of electricity to fix the same quantity of nitrogen, and the economy of both processes depends on the quantity of power used. Such a comparison can easily lead t o confusion. The production of air-saltpetre requires, in addition t o electrical power, only the very cheapest materials, namely water and limestone, whereas, in order to produce nitrolime, coal has to be employed, and, in addition, the nitrogen used in the process cannot be taken in the form of air, b u t first must be separated from the oxygen. These points have to be taken into consideration; it is not sufficient merely to compare the electrical energy used in each case, Moreover, there are other points in favor of the production of air-saltpetre. 9 o t only has the nitrogen contained i n i t a higher value than t h a t in ammonium sulphate, or in nitrolime, but, by the oxidation of nitrogen, the nitric acid, nitrates and nitrites which are so indispensable in the cheniical industry are obtained. These compounds have a higher
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value than air-saltpetre, the nitrogen in nitric acid being worth more than twice a s much as t h a t in ammonia. The prospects of a profitable conversion into nitric acid, of the ammonia obtained from nitrolime, appear very doubtful. As a matter of fact, however, our previous considerations have shown us t h a t the world’s demand for combined nitrogen is growing so enormously, t h a t there is room and to spare for these two processes and others a s well to develop side by side. I t has in recent times been suggested t h a t the large waterfalls in Germany should be taken over by the State, for the purpose of electrifying the railways, for lighting purposes, and for supplying power to small manufacturers. It is, however, difficult t o find a purpose to which the waterpower could be better applied in the interests of the State, than in the production of combined nitrogen, and further, there is, a t the present time, no other industry which would be in a position to take up such large quantities of cheap power. l y e have a classical illustration of this in the case of Korway, 11 here, although small quantities of water power are sought after, up to the present, i t has been difficult to find a use for the large waterfalls. This is probably due to the fact, t h a t the distribution of electricity, in those parts of the country in which the population is scattered, and the houses and small villages lie far apart, would require so high a n outlay for installation, t h a t a general adaptation for lighting purposes, and for supplying power on a small scale, is out of the question. The reverse, however, applies to the utilization of the large falls for the production of air-saltpetre ; such production would be coupled with remarkable advantages, for i t would open u p large industries, just in those parts of the country which from natural causes have hitherto been most neglected. Another factor which must not be underestimated when considering the advantages of the new air-saltpetre industry, is its non-participation in the destruction of the valuable coal deposits, which have been stored up for us during such countless ages. I t obtains the power i t requires from water, or as i t has been fancifully termed “white coal,” which can be employed over and over again without being exhausted, since a s soon as i t has been used, i t is raised up again into the sky by the agency of the sun, and this circulation has gone on through countless ages, and will continue as long as we have a n y need of saltpetre. \Ve have consequently every reason, from such different points of view as those of the agriculturist, the industrial chemist, and the whole of mankind, to hope t h a t the new process for the combustion of nitrogen will continue to develop and flourish.
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NOTES AND CORRESPONDENCE.. A USEFUL FORM OF PYCNOMETER FOR DETERMINING THE SPECIFIC GRAVITY O F SEMI-SOLID BITUMENS. The inconvenience and difficulty of employing the ordinary narrow-neck pycnometer when determining the specific gravity of dense residual oils and soft tar pitches has led the writer to devise a modified form suitable for use in this connection. 4 description of this apparatus is therefore given for the benefit of those who have occasion to determine the specific gravity of such materials. Except in cases
