FERTILIZER FROM THE AIR. A PROJECT FOR CHEMISTRY STUDENTS AT THE SECONDARY-SCHOOL LEVEL HOWARD R. WILLIAMS,WESTERNRESERVE ACADEMY,HUDSON, OHIO
Nitrogen and oxygen from the air were caused to unite to form nitrogen dioxide under the infEuence of a n electric arc between copper points in a phs:er of Paris combustion chamber. The spark was obtained from a model " T Ford spark coil energized by storage batteries. The resulting gases were drawn through distilled water which formed nitric acid by reaction with the nitrogen dioxide. 3NOs H1O -+ 2HNOa NO.
+
+
The acid was then neutralized with calcium c a r b m t e to form calcium nitrate .fertilizer. The fertilizer thus made was fed to growing corn i n a pot in the school laboratory, beside which another pot of corn without fertilizer was g r m . The growth difference in one month was quite marked and prowed the efficacy of the fertilizer made.
. . . . . .
The youths of pragmatic America are becoming pragmatists. They are rapidly developing the questioning mind. Very probably, this attitude is noticed a t its greatest intensity and a t its best by the teaching profession of America. Time and again the teacher is confronted by the question, expressed by word or attitude, "Of what practical importance is all this to me?" This is as i t should be. The curriculum content, be i t chemistry, English, mathematics, or whatnot, has very little if any justification unless i t contributes to the happiness and welfare of the student either a t the present time or in the fairly immediate future. The ingenuity of the teacher is sometimes taxed to the limit to find practical and worthwhile applications for the subject matter of the curriculum. A few years of chemistry teaching is enough to impress any one that the theory of chemistry needs illumination by numerous examples of practical uses. This is usually done in a didactic way and by a field trip or two to some chemical manufactory when possible. It seems, to the writer, that while this is all good, i t is not quite adequate. Therefore, for the past several years, we have been developing a practical laboratory method for vivifying elementary chemistry a t Western Reserve Academy. The procedure used in this work has been outlined rather fully in two previous articles in this journal ( 1 ) . I t is sufficient to state here that the procedure is an adaptation of the project method of teaching in which actual industrial processes are duplicated in miniature in the school laboratory; the work being done by the student with a minimum of assistance and advice from the instructor. The manufacture of atmospheric nitrogen into nitrates by the Birkeland-Eyde process furnishes a project that is a t once intensely interesting, 462
VOL. 8. No. 3
FERTILIZER FROM THE AIR
483
instructive, and important. The importance of the process is growing as the natural deposits of nitrates disappear, so that the appeal of the project to the student is enhanced by the feeling that he is working upon a problem that is some day going to be the means of keeping human life from perishing from the earth. Upon first thought i t might seem that the project would be much beyond the possibilities of the equipment on hand or obtainable in a high-school laboratory. However, we believe we have simplified the apparatus so that the project is well within the reach of any high-school chemical laboratory. At least just a little borrowing from the physics department or from friends will make it possible to obtain all the necessary apparatus. The requisite parts of the apparatus are as follows: (1) a combustion chamber in which the nitrogen and oxygen of the air are burned to oxides of nitrogen, (2) a source of electrical energy of from six to twelve volts, (3) an induction coil for transforming the original low-voltage current into a current of high enough potential to form a fairly generous continuous spark or arc, (4) an absorption chamber where the nitrogen oxides may be converted into nitric acid, and (5) a suction apparatus that will keep the air and gases moving in a continuous stream through the apparatus. The first thing we constructed was the combustion chamber or furnace. BULB Our first furnace was made of glass, so SIDE Tuess that we might closely observe everything that took place. The glass blowing required in the construction of the furnace was done by the instructor. All the rest of the project was carried on by the student. A glass bulb with four side tubes was blown as shown in Figure 1. Two opposite side arms were larger in diameter to receive the copper electrodes or arc points. The other pair of opposite side arms were smaller in diameter as they carried the air current into and out of the combustion chamber. The main body of the furnace was a bulb about one and one-half inches in length and about one and onequarter inches in diameter. The side arms were about two and onequarter inches in length, giving the entire assembly a diameter of about six inches. It is not a t all necessary to follow these dimensions in reproducing the work, but we found the furnace of this size to give excellent results.
464
JOURNAL OF CHEMICAL EDUCATION
MARCH.1931
While we found the glass chamber exc&ent for clear vision, the high temperature to which i t was subjected caused it to crack. If pyrex glass were used it would, of course, obviate this difficulty. However, lacking the pyrex glass, we made an exactly similar furnace from molded plaster of Paris with side arms of glass tubing set into the nlaster and a elass window on the top of the furnace for purposes of observation. The mold for the plaster of Paris furnace was made from a block of white pine about four inches square and one and one-half inches thick. In the center of this block we gouged a hemispherical hollow two inches in diameter and one 2.-MOLD FOR FURNACE inch deep. Next semi-cylindricalgrooves FIGURE were cut for the glass tubing inserts for the electrodes and air inlet and outlet as described above. The construction of the mold is shown in Figure 2. The mold was then thoroughly greased with vaseline to keep the plaster of Paris from adhering as it set. Enough thin plaster was then mixed and poured into the mold to fill it about two-thirds full. It was then squeezed out with the thumb to fill the mold and side grooves and leave a hollow depression in the center which was to be the inside of the furnace. While the plaster was yet soft, the glass tubes to be used as side arms were pressed into the grooves to about half their diameters so as to leave their imprints. After the plaster had thoroughly hardened the cast was shaken out of the mold and the same process used to make a second cast for the other half of the furnace. Before assembling the furnace, a square hole was cut in the upper half as shown in Figure 3. A piece of window glass was set into this hole and plastered around the edges. wi-aor This was the window through which the spark could be watched in adjusting the electrodes and spark coil points. The furnace was then ready for assembling. The glass
-
-
tubes were cemented into FIGURE~.-SIDEVIEW OF FURNACE SHOWING place and the two halves of OPENINGCUTFOR WINDOW the furnace were cemented together (Figure 4). Thin plaster of Paris was used as the cement. The copper electrodes or arc points were made from two pieces of heavy copper wire, about one-eighth inch in diameter, and four inches long. The inside or arc ends of these electrodes were bound so as to be roughly hemi-
VOL.8,No. 3
spherical in shape. A groove was filed in the outer ends to facilitate the attachment of the wires from t h e spark coil. A piece of small rubber tubing about threequarters of aninch long was slipped over the ends of the glass side tubes of the furnace and the copper electrodes passed through them. T h e r u b b e r tubing kept air from entering the chamber through t h e t u b e s carrying t h e electrodes, and a t the same time gave enough friction on the comer .. electrodes t o hold them steadily a t the right spark distance and to allow of easy adjustment. A continuous spark or arc was used inside the furnace to cause the nitrogen and oxygen of the air to unite. This spark was ohtained from an ordinary model "T" Ford spark coil. Any other induction coil of like c a p a c i t y would d o fully as well. The difficulty of attaching wires to the terminals of the Ford spark coil was overcome by mak-
FERTILIZER FROM THE AIR
I1
466
JOURNAL OF CHEMICAL EDUCATION
MARCH, 1931
ing a wooden frame in which to set the coil and placing binding posts and spring brass strips in this frame so that they would make contact with the coil terminals as shown in Figure 5. Ordinary stove bolts and nuts were used as binding posts. The source of electric energy for the spark coil may be governed by available supply. It just so happened that we have a small motor-generator set which delivers A. c. to D. c. a t a potential of twelve volts. We have also operated this acid plant on two six-volt storage batteries with complete success. A six-volt current such as is obtained from one storage batterv or from a model "T" Ford generator will also furnish energy enough to make the apparatus successful. T h e twelve-volt source, making the spark larger and more efficient, cuts down the time of operation for obtaining an acid of given strength. We next assembled the apparatus as shown in Figures 6 and 7. Air was drawn through the apparatus by means of an aspirator or filter pump placed a t the end. The air was drawn first through a calcium chloride tube to remove water vapor and dust. Next it entered the combusFIcune ~.-SHOWING METHODOF ATTACHINO tion chamber where i t came WIRESTO THE TERMINALS OF THE FORD SPARK into contact with the spark. COIL Here a part of the nitrogen was caused to combine with oxygen under the intense heat of the spark. The following reactions (2) represent what probably takes place:
As the nitrogen monoxide is drawn away from the spark, and as it cools, it unites with more oxygen,
The nitrogen dioxide thus formed was drawn through about ten cubic centimeters of distilled water in the test tube absorption chamber as shown in Figure 6. Here the nitrogen dioxide united with the water to form nitric acid and nitrogen monoxide,
3N02
+ HnO+2HN03 4-NO.
The nitric acid remained in the water in the absorber and the nitrogen monoxide byproduct was probably drawn on through the apparatus and lost. During the operation of the apparatus, with the glass combustion chamber described above, the brown color of nitrogen dioxide was plainly visible in this chamber, clearly showing the course of the reaction in that part of the plant. We placed a trap bottle, as shown, between the absorber and the aspirator. During the operation of the plant, a small but perceptible vacuum is maintained throughout the apparatus. When it became necessary to shut the plant down, to clean or adjust the spark coil points or for any other reason, t h e vacuum caused water to be suddenly sucked from the aspirator back into the apparatus. The trap bottle caught such water on the back-kick and prevented it from entering and fouling the acid in the absorbing chamber. We occasionally stopped the process to test the acid in the absorber. After a run of onehalf hour the acid in the absorber was of sufficient concentration to change blue litmus to red. After a few hours of rnnning the acid was so strong that a drop of it on
2
2 n 5
E "7
2
m
FT 1.
'D
m
$
E
408
JOURNAL OF CHEMICAL EDUCATION
MARCH.1931
the tongue tasted quite sour and set the teeth "on edge." All told we operated the plant for twelve hours. The acid taken from the apparatus was next neutralized by the addition of a slight excess of finely precipitated calcium carbonate. We prepared this by treating a strong solution of calcium chloride with a solution of sodium carbonate. Some finely ground limestone would do just as well. We next evaporated the calcium nitrate to dryness and weighed it. The twelve hours run gave us 0.4732 gram of calcium nitrate. This was equivalent to 0.3058 gram of nitric acid or very close to a three per cent solution. Although the commercial Birkeland-Eyde plant yields nearly a 50 per cent solution, we were quite pleased with our modest results. Our pleasure was further heightened by the whiteness of our finished product which indicated high purity. The calcium nitrate thus formed was the fertilizer which we had started out to make. We wished, however, t o go one step farther and test the usefulness and efficacy of the fertilizer we had made. Accordingly, we obtained two small tins cans which we transformed into flower pots by punching holes in their bottoms. We filled the cans with some rather mediocre soil, of which we have a great abundance in our immediate neighborhood. We next ran a test for acidity on the soil we were using. We placed about five cubic centimeters of the soil in a test tube and then filled it about
V ~ L8.. NO. 3
FERTILIZER FROM THE AIR
469
two-thirds full of freshly prepared blue litmus solution. Upon thorough shaking and subsequent settling, we found the litmus solution to have turned pink. We therefore added about one-quarter teaspoonful of dry calcium hydroxide (lime) to the soil in each can to correct the soil acidity shown by this test. In the soil in each can, we then planted three grains of corn (maize) obtained gratis from a local feed store. Pot No. 1 we kept watered with pure distilled water, to make sure that the young FIGURE X EFFECT OF CALCIUM N ~ ~ K AUTP OEN CORN plants received nothing exThe seed had been planted just four weeks the cept what they got from the day this photograph was taken. soil. Pot No. 2 we watered with distilled water into which we put our calcium nitrate. We placed our entire output of 0.4732 gram of calcium nitrate into twenty-five cubic centimeters of water. This we fed t o the plants in pot No. 2 at the rate of fifteen drops a day, five to each plant. This was not so. much fertilizer as is usually given by a farmer to his field corn, but wasmfficient to make the growth difference shown in the photograph in Figure 8. Calculations from data gathered showed that the average farm application is equivalent t o about twenty grams of nitrate per hill of four or five stalks, or about five grams per stalk. After the completion of the project, we recapitulated by analyzing the project for educational objectives. We found that the project went into the fields of biology and physics as well as chemistry and likewise into the field of English when the project was written up and orally reported to the class. However, confining ourselves to the field of science, we found the project to require a knowledge of a t least the following objectives: To transform a low-voltage direct current into a high-voltage current. To learn about combustion a t high temperatures. To write chemical reactions. To absorb a gas in water. To build chemical apparatus. To make a salt from an acid and a carbonate (making calcium nitrate from nitric acid and calcium carbonate).
470
JOURNAL OF CHEMICAL EDUCATION
MARCH.1931
TO-use calcium chloride as a drying agent. To use plaster of Paris and learn why i t "sets." To attach batteries in series so as to get the sum of their voltages and the amperage of one, rather than the sum of their amperages. T o use a nitrate fertilizer. To calculate the amount of fertilizer to use on a given amount of seed. T o learn how the growth of a plant depends upon fixed nitrogen. To make an acid from a non-metallic oxide and water. To calculate the equivalent amount of nitric acid formed from the weight of calcium nitrate obtained. T o make a carbonate by metathesis (making the calcium carbonate from calcium chloride and sodium carbonate). Literature Cited (1)
12)
WILLIAMS, "A Working Model By-Product Coke Plant. A Chemistry Project for a Student at the Secondary Level," J. CHEM. EDUC., 6, 745-52 (Apr., 1929); "From Corn to Karo," ibid., 7, 1147-53 (May. 1930). The readions given are taken from MCPHERSON and HENDERSON, "A Course in General Chemistry," Ginn & Co.. Boston. Mass.. 1915.
