t 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, [Pg 179]“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.
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[Pg 180] 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]
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[Pg 181] 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]
The most exciting early use, however, was in medicine. It is not
surprising that such a use was sought at that time. Any new material
immediately became the hope of ailing mankind—and of striving
inventors.[16] Phosphorus was prescribed, in liniments with fatty oils
or as solution in alcohol and ether, for external and internal
application. A certain Dr. Kramer found it efficient against epilepsy
and melancholia (1730). A Professor Hartmann recommended it against
cramps.[17] However, in the growing[Pg 182] production of phosphorus for
matches, the workers experienced the poisonous effects. In the plant of
Black and Bell at Stratford, this was prevented by inhaling turpentine.
Experiments on dogs were carried out to show that poisoning by
phosphorus could be remedied through oil of turpentine.[18]
In the years after 1770, phosphorus was discovered in bones and many other parts of various animals. Treatment with sulfuric acid decomposed these materials into a solid residue and dissolved phosphoric acid. Many salts of this acid were produced in crystalline form. Heat resistance had been considered one of the outstanding characteristics of phosphoric acid. Now, however, in the processes of drying and heating certain phosphates, it became clear that three kinds of phosphoric acids could be produced: ortho, pyro, and meta.
Berzelius cited these acids as examples of compounds which are ISOMERIC. This word was intended to designate compounds which contain the same number of atoms of the same elements but combined in different manners, thereby explaining their different chemical properties and crystal forms. It was in 1830 that Berzelius propounded this companion of the concept, ISOMORPHISM, which was to collect all cases of equal crystal form in compounds in which equal numbers of atoms of different elements are put together in the same manner. Together, the two concepts of isomerism and isomorphism seemed to cover all the known exceptions from the simplest assumption as to specificity and chemical composition.
However, only a few years later Thomas Graham (1805-1869) proved that the three phosphoric acids are not isomeric. He used the proportion of 2 P to 5 O in the oxide which Berzelius had thought justified at least until “an example of the contrary could be sufficiently established.”[21] Refining the techniques of Gay-Lussac (1816) and several other investigators, Graham characterized the three phosphoric acids as “a terphosphate, a biphosphate, and phosphate of water.” Actually, this was the wrong terminology for what he meant and formulated as trihydrate, bihydrate, and monohydrate of phosphorus oxide. In[Pg 183] his manner of writing the formulas, each dot over the symbol for the element was to indicate an atom of oxygen; thus, he wrote:
This result has later been confirmed, but the analogy by means of which it had been obtained was very weak, in certain parts quite wrong.
The acids from the two lower oxides of phosphorus were also considered as three-basic. Adolphe Wurtz (1817-1884) formulated them in 1846, according to the theory of chemical types:
Among the analogies and generalizations by which the research on phosphoric acid was supported, and to the results of which it contributed a full share, was the new theory of acids. Not oxygen, Lavoisier’s general acidifier, but reactive hydrogen determines the character of acids. In this brief survey, it seems sufficient just to mention this connection without describing it in detail.
The study of phosphoric acids led to important new concepts in theoretical chemistry. The finding of polybasicity was extended to other acids and formed the model that helped to recognize the polyfunctionality in other compounds, like alcohols and amines. The hydrogen theory of acids was fundamental for further advance. In another dimension, it is particularly interesting to see that large-scale applications followed almost immediately and directly from the new theoretical insight. The first and foremost of these applications was in agriculture.
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.
Figure 1.—The alchemist discovers phosphorus. A painting
by Joseph Wright (1734-1779) of Derby, England.
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.)
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[Pg 181] 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]
Early Uses
In the 18th century, phosphorus was a costly material. It was produced mostly for display and to satisfy curiosity. Guillaume François Rouelle (1703-1770) demonstrated the process in his lectures, and, as Macquer reports, he “very often” succeeded in making it.[12] Robert Boyle had the idea of using phosphorus as a light for underwater divers.[13] A century later, “instant lights” were sold, with molten phosphorus as the “igniter,” but they proved cumbersome and unreliable.[14] Because white phosphorus is highly poisonous, an active development of the use in matches occurred only after the conversion of the white modification into the red had been studied by Émile Kopp (1844), by Wilhelm Hittorf (1824-1914) and, in its practical application, by Anton Schrötter (1802-1875).[15]
Figure 3.—Distillation apparatus (1849) for refining
crude phosphorus. The crude phosphorus is mixed with sand under hot
water, cooled, drained, and filled into the retort. The outlet of the
retort, at least 6 cm. in diameter, is partially immersed in the water
contained in the bucket. A small dish, made from lead, with an iron
handle, receives the distilled phosphorus. (From Hugo Fleck, Die
Fabrikation chemischer Produkte ... page 90.)
Figure 4.—Apparatus for converting white phosphorus into
the red allotropic form, 1851. Redistilled phosphorus is heated in the
glass or porcelain vessel (g) which is surrounded by a sandbath (e) and
a metal bath (b). Vessel (j) is filled with mercury and water; together
with valve (k), it serves as a safety device. The alcohol lamp (l) keeps
the tube warm against clogging by solidified vapors. Because of hydrogen
phosphides, the operation, carried out at 260° C., had to be watched
very carefully. (According to Arthur Albright, 1851; reproduced from
Hugo Fleck, Die Fabrikation chemischer Produkte ..., page 112.)
Chemical Constitution of Phosphoric Acids
In a long article on phosphorus, Edmond Willm wrote in 1876: “For a century, urine was the only source from which phosphorus was obtained. After Gahn, in 1769, recognized the presence of phosphoric acid in bones, Scheele indicated the procedure for making phosphorus from them.”[19] Actually, Gahn used at first hartshorn (Cornu cervi ustum), and Scheele doubted, until he checked it himself, that his esteemed friend was right. A few years later, Scheele corrected Gahn’s assumption that the sal microcosmicum was an ammonia salt; instead, it is “a tertiary neutral salt, consisting of alkali minerali fixo (i.e., sodium), alkali volatili, and acido phosphori.”[20]In the years after 1770, phosphorus was discovered in bones and many other parts of various animals. Treatment with sulfuric acid decomposed these materials into a solid residue and dissolved phosphoric acid. Many salts of this acid were produced in crystalline form. Heat resistance had been considered one of the outstanding characteristics of phosphoric acid. Now, however, in the processes of drying and heating certain phosphates, it became clear that three kinds of phosphoric acids could be produced: ortho, pyro, and meta.
Berzelius cited these acids as examples of compounds which are ISOMERIC. This word was intended to designate compounds which contain the same number of atoms of the same elements but combined in different manners, thereby explaining their different chemical properties and crystal forms. It was in 1830 that Berzelius propounded this companion of the concept, ISOMORPHISM, which was to collect all cases of equal crystal form in compounds in which equal numbers of atoms of different elements are put together in the same manner. Together, the two concepts of isomerism and isomorphism seemed to cover all the known exceptions from the simplest assumption as to specificity and chemical composition.
However, only a few years later Thomas Graham (1805-1869) proved that the three phosphoric acids are not isomeric. He used the proportion of 2 P to 5 O in the oxide which Berzelius had thought justified at least until “an example of the contrary could be sufficiently established.”[21] Refining the techniques of Gay-Lussac (1816) and several other investigators, Graham characterized the three phosphoric acids as “a terphosphate, a biphosphate, and phosphate of water.” Actually, this was the wrong terminology for what he meant and formulated as trihydrate, bihydrate, and monohydrate of phosphorus oxide. In[Pg 183] his manner of writing the formulas, each dot over the symbol for the element was to indicate an atom of oxygen; thus, he wrote:
... :: .. ... . .
Figure 5.—Oven for the calcination of bones, about 1870.
“The operation is carried out in a rather high oven, such as shown....
The fresh bones are thrown in at the top of the oven, B. First, fuel in
chamber F is lighted, and a certain quantity of bones is burnt on the
grid D. When these bones are burning well, the oven is gradually filled
with bones, and the combustion maintains itself without addition of
other fuel. A circular gallery, C, surrounds the bottom of the oven and
carries the products of combustion into the chimney, H. The calcined
bones are taken out at the lower opening, G, by removing the bars of
grid B.” (Translation of the description from Figuier, Merveilles de
l’industrie, volume 3, 1874, page 537.)
Figure 6.—An advertisement with view of plant for
manufacturing superphosphate about 1867. (From E. T. Freedley,
Philadelphia and its Manufacturers in 1867, page 288.)
[Pg 184]
Graham had come to this understanding of the phosphoric acids through
his previous studies of “Alcoates, definite compounds of Salts and
Alcohol analogous to the Hydrates” (1831). Liebig started from analogies
he saw with certain organic acids when he formulated the phosphoric
acids with a constant proportion of water (aq.) and varying proportions
of “phosphoric acid” (P) as follows:
Figure 7.—Florida hard-rock phosphate mining. (From
Carroll D. Wright, The Phosphate Industry of the United States, sixth
special report of the Commissioner of Labor, Government Printing Office,
Washington, 1893, plate facing page 43.)
[Pg 185]2 P 3 aq. phosphoric acid
3 P 3 aq. pyrophosphoric acid
6 P 3 aq. metaphosphoric acid.
Salts are formed when a “basis,” i.e., a metal oxide, replaces water.
When potassium-acid sulfate is neutralized by sodium base, the acid-salt
divides into Glauber’s salt and potassium sulfate, which proves the
acid-salt to be a mixture of the neutral salt with its acid. Sodium-acid
phosphate behaves quite differently. After neutralization by a potassium
“base” (hydroxide), the salt does not split up; a uniform
sodium-potassium phosphate is obtained. Therefore, phosphoric acid is
truly three-basic![23]
This result has later been confirmed, but the analogy by means of which it had been obtained was very weak, in certain parts quite wrong.
The acids from the two lower oxides of phosphorus were also considered as three-basic. Adolphe Wurtz (1817-1884) formulated them in 1846, according to the theory of chemical types:
(PO) · · ·
O3 phosphoric acid
H3
O3 phosphoric acid
H3
(PHO) · ·
O2 phosphorus acid
H2
Further proof for these constitutions was sought in the study of the
esters formed when the acids react with alcohols.O2 phosphorus acid
H2
Among the analogies and generalizations by which the research on phosphoric acid was supported, and to the results of which it contributed a full share, was the new theory of acids. Not oxygen, Lavoisier’s general acidifier, but reactive hydrogen determines the character of acids. In this brief survey, it seems sufficient just to mention this connection without describing it in detail.
The study of phosphoric acids led to important new concepts in theoretical chemistry. The finding of polybasicity was extended to other acids and formed the model that helped to recognize the polyfunctionality in other compounds, like alcohols and amines. The hydrogen theory of acids was fundamental for further advance. In another dimension, it is particularly interesting to see that large-scale applications followed almost immediately and directly from the new theoretical insight. The first and foremost of these applications was in agriculture.