Phosphoric acid 8.17 "
Potash 13.06 "
Lime 12.60 "
Magnesia 4.75 "
-----
Total 59.29 "
The weight of the whole crop from which these figures were taken was
eight hundred and forty-seven pounds, so that cotton exhausts land
less than any staple crop, if the roots, stems, leaves, etc., be
turned under and only the lint and seed be removed. Of these the lint
(one hundred pounds) takes 1.17 pound from the soil, and the seed
13.89 pounds, making 15.06 pounds net loss.[47] But ignoring returns
that may be made in the shape of cotton-seed meal, etc., and lime,
with which our soils are abundantly supplied, we see that nitrogen,
phosphoric acid, and potash have been removed. Suppose the owner puts
bone meal on his exhausted land: the phosphoric acid in the bone will
supply one need, and an improvement results. On the strength of this,
bone meal will be loaded into the soil again, and let us suppose the
deficit not yet made up, the crop again shows improvement. Now,
phosphoric acid abounds in the soil, though the deficiency in nitrogen
and potash has become steadily greater; so, when the customary bone
meal is applied, the crop falls back, because the plants are starving
for potash and nitrogen. They are like scurvy-smitten sailors, but
many thoughtless farmers would attribute the decline to the maker of
the bone meal, and say that its quality was not so high as
formerly--an opinion similar to that of a sea captain who would
ascribe to the poor quality of salt beef an outbreak of scurvy on his
vessel.
As crops of any description extract potash, nitrogen, and phosphoric
acid from soils, the question how they are to be replaced is an
important matter, and its answer may be most readily found by studying
Nature's methods. In parts of the Old World there are fields that are
fertile in the extreme after thousands of years of tillage, and it is
apparent that mere cultivation does not prove injurious. The tropical
forests have something growing wherever a plant can find foothold--a
population in which the struggle for food is secondary to that for
light and air, and yet the soil supporting this vegetation is
marvelously rich. Every leaf that falls remains where it fell until in
the warm, moist, half-lighted forest it becomes a little heap of mold.
The bacteria of decomposition require warmth and moisture for their
life; light is deleterious to them, but they thrive in the dense shade
of the jungle. The tangled web of roots, weeds, and vines retains the
rainfall, retarding evaporation, and preventing both droughts and
freshets. Receiving dead and broken leaves, boughs, and other
vegetable products, and spared the washing of violent torrents, the
forest is inestimably fertile.
On a smaller scale this goes on universally. The annual weeds,
deciduous leaves, and such matter, fall prey to molds and bacteria, by
which they are made soluble. Snows and rains bear the products into
the soil, and there other bacteria, clustering around the roots, form
the acids needed to complete solution. Every one knows that
"well-rotted" manure is better than that which is fresh, and many
wonder at this, but the reason is apparent. In feeding delicate
patients, physicians often prescribe predigested foods or the
digestive ferments to aid enfeebled assimilation; and similarly the
manures that have been thoroughly acted on by bacteria, or containing
those capable of producing the matters that plants need, are of most
value for nourishing vegetation.
In producing an article of any sort, the cheapness and ease with which
it can be made is largely dependent on the shape in which the raw
material reaches the factory. If a foundry can procure iron that needs
only to be melted and cast, the owner can fill his orders more
readily than would be possible if he had to reduce the metal from the
ore; and Nature uses this principle over and over again. The
importance of nitrogen to plants and its abundance in Nature have been
mentioned, but it has also been said that plants can not use it
directly, as most animals do with oxygen. The tiny bacteria intervene,
and this they do in two ways: first, by causing decay of animal or
vegetable matter containing nitrogen, and by this decay producing
substances that plants can absorb; and, secondly, by producing little
nodules or "tubercles" on the rootlets, through which the plant can
take up nitrogen.[48] Now, when a plant is sated with nitrogen, it
ceases to form these tubercles, and their formation is a sure sign
that the plant is craving this article of food. When it is supplied,
and its own life is ended, these form reservoirs from which other
plants may be supplied, as new castings may be made from broken
wheels. The great value of "green manuring" depends on the store of
available nitrogen so laid up, but it is open to failure in one
direction. The liability of fermentation to go to the acid stage from
contamination with acid-forming ferments has been mentioned, an
accident the possibility of which is impressed on us from time to time
by sour bread; and similarly the organic matter turned under may
undergo acid fermentation, rendering the ground "sour" and unfit for
cultivation.
The limits of this paper forbid the consideration of special
fertilizers, but from the general principles laid down the rules for
any special case may be deduced. A soil should contain a sufficient
amount of potash, soda, lime, iron, and a few other minerals;
phosphoric acid, nitrogen, organic matter, and, for some special
crops, some other ingredients may be needed. When the soil needs
renewing, there are two ways of accomplishing it. One way is to guess
at what is needed; to buy fertilizers at high prices, without
inquiring whether the soil needs the substances in that particular
brand or not. Though very common, this is not a good plan. It is as
though a physician were to give a patient any drug that was
convenient, without inquiring into the disorder or the needs of the
system, and it is followed by much the same result. That acid
phosphate gave Farmer A a good crop, is no reason that Farmer B's land
is also deficient in phosphorus. The same reasoning would teach that a
heart stimulant that rouses a patient from shock would benefit one in
danger of apoplexy, where the least increase in heart force might be
fatal. A physician using such reasoning as the basis of his practice
would not be considered a master of his art; and were he to attribute
the fatal outcome of his logic to the poor quality of his stimulant,
he would display criminal ignorance of drugs as well as disease; yet
it is very common to see farmers put guano on a soil begging for
potash, and then heap execration on the head of the dealer who sold
the guano when the crop failed. To revert to a simile used above, a
captain must not blame the salt pork for scurvy.
The other way to buy and use fertilizers is to ascertain what a
certain crop needs; then find out whether these be in the soil, and to
what extent. With these data the deficiency may be made good without
the wasteful cost of the former method. State and Federal Departments
of Agriculture furnish their aid freely and gladly, and already the
signs are seen of the day when agriculture will take its place among
the semiexact sciences, and the present haphazard methods will become
obsolete.
FOOTNOTES:
[46] An address delivered before the Richmond County (Georgia)
Agricultural Society, on February 19, 1898.
[47] United States Department of Agriculture. Farmers' Bulletin, No.
48.
[48] Leguminous Plants for Green Manuring and for Feeding. E. W.
Allen, Ph. D. United States Department of Agriculture. Farmers'
Bulletin, No. 16.
SKETCH OF AUGUST KEKULÉ.
"This news," said Herr H. Landrelt, president, announcing Kekulé's
death in the German Chemical Society at Berlin, "will be received with
sorrow not only by our society but by the whole chemical world.
Science has again lost one of its greatest representatives, one of
those extremely rare spirits who were called upon to found a new epoch
in it and push it mightily forward."
FRIEDRICH AUGUST KEKULÉ was born at Darmstadt, September 7, 1829, and
died, after a long illness, at Bonn, July 13, 1896. He was originally
destined by his father for the profession of an architect; and some
houses, he told his students in a festival address, still existed (in
1892) in Darmstadt of which he drew the plans when, a youth, he was
attending the gymnasium. The leading events of his life were very
tersely told by himself in an address responding to an ovation from
the students of the University of Bonn on the twenty-fifth anniversary
of his professorship there; a translation of which, from the
_Kölnische Zeitung_, was published by Mr. J. E. Martin in Nature, June
30, 1892.
At Giessen, he said, where he went to study architecture, he attended
Liebig's lectures, and was thereby attracted to chemistry. But his
relatives would not at first hear of his changing his profession, and
he was given a half-year's grace to think over it. He spent his time
in the Polytechnicum at Darmstadt. His first teacher in chemistry at
Darmstadt was Moldenhauer, the inventor of lucifer matches. His
leisure time was spent in modeling in plaster and at the lathe. He was
then permitted to return to Giessen. "I attended," he said, "the
lectures, first of Will and then of Liebig. Liebig was at work on a
new edition of his letters on Chemistry, for which many experiments
had to be carried out. I had to make estimations of ash, of albumen,
to investigate gluten in plants, etc. The names of the young chemists
who helped Liebig were mentioned in the book, among them mine. The
proposal was then made to me, just at the time Liebig intended to make
me his assistant, that I should go for a year abroad, either to
Berlin, which was at that time to Giessen a foreign land, or to Paris.
'Go,' said Liebig, 'to Paris; there your views will be widened; you
will learn a new language; you will get acquainted with the life of a
great city; but you will not learn chemistry there.' In that, however,
Liebig was wrong. I attended lectures by Frémy, Wurtz, Pouillet,
Regnault; by Marchandis on physiology, and by Payen on technology. One
day, as I was sauntering along the streets, my eyes encountered a
large poster with the words _Leçons de philosophie chimique par
Charles Gerhardt, ex-professeur de Montpellier_. Gerhardt had resigned
his professorship at Montpellier, and was teaching philosophy and
chemistry as _privat docent_ in Paris. That attracted me, and I
entered my name on the list. Some days later I received a card from
Gerhardt; he had seen my name in Liebig's Letters on Chemistry. On my
calling upon him he received me with great kindness, and made me the
offer, which I could not accept, that I should become his assistant.
My visit took place at noon, and I did not leave his house till
midnight, after a long talk on chemistry. These discussions continued
between us at least twice a week for over a year. Then I received the
offer of the post of assistant to von Plauter, at the Castle of
Reichenau, near Chur, which I accepted, contrary to Liebig's wish, who
recommended me as assistant to Fehling, at Stuttgart. So I went to
Switzerland, where I had leisure to digest what I had learned in Paris
during my intercourse with Gerhardt. Then I received an invitation
from Stenhouse, in London, to become his assistant, an invitation I
was loath to accept, since I regarded him, if I may be allowed the
expression, as a _Schmierchemiker_. By chance, however, Bunsen came to
Chur on a visit to his brother-in-law, at whose house I first met him.
I consulted Bunsen as to Stenhouse's offer, and he advised me by all
means to accept it. I should learn a new language, but I should not
learn chemistry. So I came to London, where as Stenhouse's assistant I
did not learn much. By means of a friend, however, I became acquainted
with Williamson. The latter had just published his ether theory, and
was at work on the polybasic acids (in particular on the action of
PCl_{5} on H_{2}SO_{4}). Chemistry was at one of its turning points.
The theory of polybasic radicals was being evolved. With Williamson
was also associated Odling. Williamson insisted on plain, simple
formulæ, without commas, without the buckles of Kolbe or the brackets
of Gerhardt. It was a capital school to encourage independent
thought. The wish was expressed that I should stay in England and
become a technologist, but I was too much attached to home. I wished
to teach in a German university. But where? In order to get acquainted
with the circumstances at several universities, I became a traveling
student. In this capacity I came, among other universities, to Bonn.
Here there was no chemist of eminence, and hence there were no
prospects. Nowhere did there seem so much promise and so great a
future as at Heidelberg. I could ask no help of Bunsen. 'I can do
nothing for you,' he said, 'at least not openly. I will not stand in
your way, but more I can not promise.' I fitted up a small private
laboratory in the principal street of Heidelberg at the house of a
corn merchant--Gross, by name--a single room with an adjoining
kitchen. I took a few pupils, among whom was Baeyer. In our little
kitchen I finished my work on fulminate of silver, while Baeyer
carried out the researches, which subsequently became famous, on
cacodyl. That the walls were coated thick with arsenious acid, and
that silver fulminate is explosive, we took no thought about. After
two years and a half I received a call to Ghent as ordinary professor.
There I stayed nine years, and had to lecture in French. With me to
Ghent came Baeyer. Through the kindness of the then Prime Minister of
Belgium, Rogier, I obtained the means to establish a small laboratory.
I had there with me a number of students, among whom I may name
Baeyer, Hübner, Ladenburg, Wichelhaus, Linnemann, Radzizewski. There
was not so much a systematic course of instruction as a free and
pleasant academic intercourse. After nine years' work I received the
call to Bonn." Professor Kekulé concluded his address with some
account of his work at Bonn, and of the great attention he had always
received from his pupils. For a full account of Kekulé's scientific
career and achievements, we are indebted to the memorial address made
by President Landelt to the German Chemical Society on the occasion of
his death, of which we translate the more important passages from the
_Berichte_:
"The works which Kekulé has left behind him belong, as we all know, to
the bases of all chemistry. His teachings have so passed into our
flesh and blood that it seems almost superfluous to remind a circle of
professional chemists of them. I shall be able to present only in the
most general outlines this evening the immense influence which the
dead master has exercised upon science; a complete view of all his
labors is a subject for a biography, which we must wait for.
"Kekulé's scientific work began in 1854, with the discovery of
thiacetic acid, by which he at once separated from the old school of
chemistry that was still prevailing, and, founding a new one,
revealed himself as an adherent of the new doctrine of types. After
his habilitation at Heidelberg, which followed in 1856, came the essay
on fulminating mercury, in which the view so important for the future
was expressed, that to the three typical combinations of
chlorhydrogen, water, and ammonia, hitherto recognized, might be added
a fourth, marsh gas. In the next essay, on binary combinations and the
theory of polyatomic radicals, he put forward the conception of mixed
types, and first reached the knowledge of various atomicity or valency
of the radicals. These researches were continued, and there appeared
shortly afterward, in the spring of 1858, the two great treatises
which have since exercised so powerful an influence on chemistry--that
on the constitution and metamorphoses of chemical combinations, and
that on the chemical nature of carbon. In these theses Kekulé passed
from the valency of the radicals to that of the elements themselves,
and showed that the composition of all those compounds that contain
one atom of carbon lead to the conclusion that that element is
quadrivalent; and that, further, the relations of combination of a
complex of carbon atoms are explainable if we suppose that the latter
are mutually bound by a certain number of their four unities of
attraction. This idea was suggested very carefully, and the words
which the author added at the end of his essay read very curiously
to-day: 'Finally, I think I ought still to insist that I attach only
little value to speculations of this sort. Since one delving in
chemistry must once in a while, in the lack of exact scientific
principles, content himself with probabilities and temporary
hypotheses, it seems proper to communicate these conceptions, because,
as it appears to me, they furnish a simple and fairly general
expression for the newest discoveries, and because, therefore, the use
of them may assist in the discovery of new facts.' How diffident the
words sound, and how far have the expectations been exceeded! We all
know that the theory of valency is to-day the leading guide through
all our science; and, although another investigator had a share in its
origination, no one disputes that its main foundation and its eminent
value in organic chemistry are primarily due to Kekulé's idea of the
quadrivalency of carbon.
"After he was called to the University of Ghent, in 1858, Kekulé
exhibited an indefatigable activity. He began the great series of
investigations of the organic acids which, beginning with succinic
acid, malic acid, and tartaric acid, and extending afterward to many
others, have given complete conclusions as to the nature of these
bodies. Contemporaneously, in 1860, appeared the first number of the
_Lehrbuch der organischen Chemie_, which was soon followed by other
numbers, so that the whole first volume was completed in 1861. All his
fellow-chemists who are acquainted with the events of that period
will remember the enthusiasm with which the work was received. For the
first time, in place of the former system of organic chemistry based
on the old radicals of Berzelius, a system of treatment appeared which
in the dress of the theory of types had the doctrine of valency as its
foundation, and exposed the construction as well as the isomeric
relations of the numerous carbon compounds with wonderful clearness.
The work, the first two published volumes of which contained the
substances designated by Kekulé as the fatty compounds, is still
recognized as the prototype of many text-books that followed it.
"In 1855 Kekulé put forth the second of his great theories. First in
the Bulletin of the Chemical Society of Paris, and afterward in fuller
form in Liebig's _Annalen_, appeared the essay, Researches among the
Aromatic Compounds, in which he showed that the substances so
designated all contain six or more atoms of carbon, and that they
could be described as derivatives of the simplest of them, benzene. He
proposed two hypotheses to explain the constitution of this substance,
one of which, the only one afterward pursued, supposed that the six
carbon atoms are associated in a ring, and alternately linked by one
and two valencies. By replacing the hydrogen atoms corresponding to
each carbon atom by other elements or radicals one could arrive at the
knowledge of the constitution of a large number of aromatic bodies
which now figure as benzol derivatives. These considerations led,
however, to another question--namely, whether or not the supplied
places of the six hydrogen atoms are chemically equivalent. The
question of space relations in chemistry first came up in connection
with this investigation, and Kekulé at once endeavored to solve it.
All these ideas were, however, expressed at first with reserve, and
this essay closes with the words, 'I place no more value on these
views than they are worth, and I believe that much labor must still be
applied before such speculations can be regarded as anything else than
more or less elegant hypotheses; but I believe, too, that at least
experimental speculations of this kind must be used in chemistry.'
"In this case, again, Kekulé's modest expectations have been
surpassed. The wonderful results that have accrued from the benzol
theory are patent to all of us. We know that it was the instigation to
the carrying out of an innumerable multitude of researches which are
still pursued with undiminished industry. Rarely has a thought
exercised so fructifying and forwarding an influence on chemistry, and
so redounded to the advantage of both pure science and art.
Thankfulness for this gift, as you know, prompted our society to honor
the author of the benzol theory and the twenty-fifth year of the
announcement of it by a public festival; and the Kekulé celebration,
which took place in this house on the 11th of March, 1890, is
memorable to all for the brilliant and witty speech with which the
master responded to the many addresses made to him. It is preserved in
our reports (_Berichte_ 23, 1892), and the repeated reading of it
always affords rich enjoyment."
Kekulé assumed his last position, as professor at the University of
Bonn, in the fall of 1867. He there devoted his attention for a period
to the erection of a new institute building, but it was not long
before numerous works began again to appear--some of them by himself
alone, like the important investigation of the condensation products
of aldehyde; and others in co-operation with his many students. The
continuation of his _Lehrbuch_ was taken in hand at the same time. In
1867 he gratified his fellow-chemists by the publication of the first
volume of his Chemistry of the Benzol Derivatives. This was followed
from 1880 to 1887 by single numbers, prepared with the help of
co-workers, of the second and third volumes.