up, 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