But what Lavoisier was seeking to
understand after 1791 was the general cycle of living matter.Prior
to his work, it was thought that the living world consisted of
only two kingdoms: the vegetable, destined to develop nutriments,
and the animal,which drew its required energy from the nourishment
provided by the former."I consider nature a vast chemical
laboratory in which all kinds of compositions and decompositions
are formed.Vegetation is the basic instrument the Creator uses to
set all of nature in motion. Vegetables are organized bodies that
grow on the dry areas of the globe and within its waters.Their
function is to combine immediately the four elements (water,
earth, air and fire) and to serve as food for animals.Nature uses
both kingdoms to form all existing combustible matter."(A.
Baumé, Chymie expérimentale et raisonnée,
Paris, Didot, 1774, vol. I, p. xi.)
Later, Bernard would criticize this way of dividing up Nature's
kingdoms: "In living beings, the phenomena of destruction or vital
combustion were absolutely separated from the phenomena of
reduction or organic synthesis.The role of vital creation had been
assigned to the vegetable kingdom, whereas organic destruction had
been reserved for the animal one.The animal organism was incapable
of forming any of the principles of which it is made up - fat,
albumin, fibrin, starch, sugar; they were all provided by the
vegetable kingdom and animal nutrition was hardly more than the
placing inthem of materials uniquely developed by plants."(C.
Bernard, Leçons sur les phénomènes de la vie
communs aux animaux et aux végétaux, Paris,
Baillière, 1878, vol. I, p. 136.)
But Lavoisier's vision was much more modern.In the Traité
élémentaire de chimie in 1789, he explained how he
had been led to invent the technique for analyzing organic bodies
by combustion as early as 1774.
The chemical analysis of organic matter by fire allowed him to
show that oak, for example, was a combination of water, acids and
oils of which the residue was charcoal, itself decomposable into
earth and fixed alkali.But Lavoisier felt that the analysis needed
to be pushed further: "We still do not know," he wrote in his
third laboratorynotebook, "1) what is the quality of that immense
amount of air that is released during distillation: it is probably
a combination of fixed and inflammable air; 2) the nature of oil:
it appears that it can be reduced to air and water by combustion,
but we know nothing more; 3) what charcoal is; we know, of course,
that when it burns, it converts the surrounding air into fixed
air; but we do not know if it itself gives fixed air; nor do we
know what is released during combustion orthe relationship of what
remains with the original weight of charcoal." (Quoted byM.
Berthelot in Larévolution chimique Lavoisier, Paris,
Félix Alcan, 1902, p. 260.)
But the inconvenience ofthetechnique of anlysis by fire was that
instead of separating the components into vegetable matter, it
destroyed them completely.In July 1777, learning that Torbern
Bergman (1735-1784) had obtained a saccharic acid (oxalic)
throughdistillation, by having nitric acid react on
sugar,Lavoisierhadtried to repeat the experiment.Butinstead of
oxalic, he had obtained nitric acid, water anda charcoal-like
residue.In February 1799, heating sugar more slowly, he had been
able to synthesize oxalic acid.He understood that in the previous
experiment the intense heat had decomposed the sugar into hydrogen
and carbon.In combining with the oxygen of the nitric acid, the
carbon formedcarbonic gas and hydrogen formed water.That meant
that by measuring the quantities of carbonic gas and water
produced by the decompositon of sugar, one could deduce the
quantities of carbon and hydrogen contained in the sugar.
This success had allowed Lavoisier to apply to organic acids his
general theory on the formation of acids.But , above all, it had
revealed the principle oforganic chemical analysis : it was
possible to determine the quantity of carbon and hydrogen
contained in any organic matter by measuring the quantities of
carbonic gas and water produced by its combustion. Using this
method to analyze spirits of wine, olive oil and wax, he had seen
that vegetable as well as animal matter results from the
combination of oxygen, hydrogen and carbon.(Lavoisier, Oeuvres,
vol. II, p. 588.)"The least degree of heat, as long as it is
slightly higher than boiling water, suffices for uniting oxygen
and hydrogen, and hydrogen and carbon, and for forming oil and
water.But also the phenomena become more complicated, because
there exists, as M. Berthollet has shown, a fourth principle in
animal matter, nitrogen, which, with hydrogen, forms volatile
alkali or ammonia." (Lavoisier, Oeuvres, vol. II, pp. 664-66.)
Lavoisier had established the essential relationships.From the
point of view of interest, the theoretical approach prevailed over
the experimental part, and when he sought to demonstrate the
equation that linked these diverse elements by calculating their
weight, all the figures were inaccurate, but his general
conclusion was correct.He had understood that no separation exists
between the chemistry of minerals, vegetables and animals.He had
undertaken the exploration of life by the analysis of its
physio-chemical mechanisms, thus opening the way to modern
biochemistry.He would have neither the time nor the means to go
further; ambition, his responsibility for State finances and, very
soon, his personal concerns were going to distance him from
research.