It was a little late to search for the philosophers' stone in 1669, yet
it was in such a search that phosphorus was discovered. Wilhelm Homberg
(1652-1715) described it in the following manner: Brand, "a man little
known, of low birth, with a bizarre and mysterious nature in all he
did, found this luminous matter while searching for something else. He
was a glassmaker by profession, but he had abandoned it in order to be
free for the pursuit of the philosophical stone with which he was
engrossed. Having put it into his mind that the secret of the
philosophical stone consisted in the preparation of urine, this man
worked in all kinds of manners and for a very long time without finding
anything. Finally, in the year 1669, after a strong distillation of
urine, he found in the recipient a luminant matter that has since been
called phosphorus. He showed it to some of his friends, among them
Mister Kunkel [sic]."[1]
Neither the name nor the phenomenon were really new. Organic
phosphorescent materials were known to Aristotle, and a lithophosphorus
was the subject of a book published in 1640, based on a discovery made
by a shoemaker, Vicenzo Casciarolo, on a mountain-side near Bologna in
1630.[2] Was the substance new which Brand showed to his friends? Johann
Gottfried Leonhardi quotes a book of 1689 in which the author, Kletwich,
claims that this phosphorus had already been known to Fernelius, the
court physician of King Henri II of France (1154-1189).[3] To the same
period belongs the "Ordinatio Alchid Bechil Saraceni philosophi," in
which Ferdinand Hoefer found a distillation of urine with clay and
carbonaceous material described, and the resulting product named
escarbuncle.[4] It would be worth looking for this source; although
Bechil would still remain an entirely unsuccessful predecessor, it does
seem strange that in all the distillations of arbitrary mixtures, the
conditions should never before 1669 have been right for the formation
and the observation of phosphorus.
[Illustration: Figure 1.--THE ALCHEMIST DISCOVERS PHOSPHORUS. A painting
by Joseph Wright (1734-1779) of Derby, England.]
For Brand's contemporaries at least, the discovery was new and exciting.
The philosopher Gottfried Wilhelm von Leibniz (1646-1716) considered it
important enough to devote some of his time (between his work as
librarian in Hanover and Wolfenbüttel, his efforts to reunite the
Protestant and the Catholic churches, and his duties as Privy Councellor
in what we would call a Department of Justice) to a history of
phosphorus. This friend of Huygens and Boyle tried to prove that Kunckel
was not justified in claiming the discovery for himself.[5] Since then,
it has been shown that Johann Kunckel (1630-1703) actually worked out
the method which neither Brand nor his friend Kraft wanted to disclose.
Boyle also developed a method independently, published it, and
instructed Gottfried Hankwitz in the technique. Later on, Jean Hellot
(1685-1765) gave a meticulous description of the details and a long
survey of the literature.[6]
[Illustration: Figure 2.--GALLEY-OVEN, 1869. The picture is a cross
section through the front of the oven showing one of the 36 retorts, the
receivers for the distillate, and the space in the upper story used for
evaporating the mixture of acid solution of calcium phosphate and coal.
(According to ANSELME PAYEN, _Précis de Chimie industrielle_, Paris,
1849; reproduced from HUGO FLECK, _Die Fabrikation chemischer Produkte
aus thierischen Abfällen_, Vieweg, Braunschweig, 1862, page 80 of volume
2, 2nd group, of P. BOLLEY'S _Handbuch der chemischen Technologie_.)]
To obtain phosphorus, a good proportion of coal (regarded as a type of
phlogiston) was added to urine, previously thickened by evaporation and
preferably after putrefaction, and the mixture was heated to the highest
attainable temperature. It was obvious that phlogiston entered into the
composition of the distillation product. The question remained whether
this product was generated _de novo_. In his research of 1743 to 1746,
Andreas Sigismund Marggraf (1709-1782) provided the answer. He found the
new substance in edible plant seeds, and he concluded that it enters the
human system through the plant food, to be excreted later in the urine.
He did not convince all the chemists with his reasoning. In 1789,
Macquer wrote: "There are some who, even at this time, hold that the
phosphorical ('phosphorische') acid generates itself in the animals and
who consider this to be the 'animalistic acid.'"[7]
Although Marggraf was more advanced in his arguments than these
chemists, yet he was a child of his time. The luminescent and
combustible, almost wax-like substance impressed him greatly. "My
thoughts about the unexpected generation of light and fire out of water,
fine earth, and phlogiston I reserve to describe at a later time." These
thoughts went so far as to connect the new marvel with alchemical wonder
tales. When Marggraf used the "essential salt of urine," also called
_sal microcosmicum_, and admixed silver chloride ("horny silver") to it
for the distillation of phosphorus, he expected "a partial conversion of
silver by phlogiston and the added fine vitrifiable earth, but no trace
of a more noble metal appeared."[8]
Robert Boyle had already found that the burning of phosphorus produced
an acid. He identified it by taste and by its influence on colored plant
extracts serving as "indicators." Hankwitz[9] described methods for
obtaining this acid, and Marggraf showed its chemical peculiarities.
They did not necessarily establish phosphorus as a new element. To do
that was not as important, at that time, as to conjecture on analogies
with known substances. Underlying all its unique characteristics was the
analogy of phosphorus with sulfur. Like sulfur, phosphorus can burn in
two different ways, either slowly or more violently, and form two
different acids. The analogy can, therefore, be extended to explain the
results in both groups in the same way. In the process of burning, the
combustible component is removed, and the acid originally combined with
the combustible is set free. Whether the analogy should be pursued even
further remained doubtful, although some suspicion lingered on for a
while that phosphoric acid might actually be a modified sulfuric acid.
Analogies and suspicions like these were needed to formulate new
questions and stimulate new experiments. They are cited here for their
important positive value in the historical development, and not for the
purpose of showing how wrong these chemists were from our point of
view, a point of view which they helped to create.
The widespread interest in the burning of sulfur and of phosphorus,
naturally, caught Lavoisier's attention. In his first volume of
_Opuscules Physiques et Chimiques_ (1774), he devoted 20 pages to his
experiments on phosphorus. He amplified them a few years later[10] when
he attributed the combustion to a combination of phosphorus with the
"eminently respirable" part of air. In the _Méthode de Nomenclature
Chimique_ of 1787, the column of "undecomposed substances" lists sulfur
as the "radical sulfurique," and phosphorus, correspondingly, as the
"radical phosphorique." The acids are now shown to be compounds of the
"undecomposed" radicals, the complete reversion of the previous concept
of this relationship. A part of the old analogy remained as far as the
acids are concerned: sulfuric acid corresponds to phosphoric; sulfurous
acid to phosphorous acid with less oxygen than in the former.[11]