he acids react with alcohols.

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.

Phosphates as Plant Nutrients

One hundred years after the discovery of "cold light," the presence of
phosphorus in plants and animals was ascertained, and its form was
established as a compound of phosphoric acid. This knowledge had little
practical effect until the "nature" of the acid, in its various forms,
was explained through the work of Thomas Graham. From it, there started
a considerable technical development.

At about that time (1833), the Duke of Richmond proved that the
fertilizing value of bones resided not in the gelatin, nor in the
calcium, but in the phosphoric acid. Thus, he confirmed what Theodore de
Saussure had said in 1804, that "we have no reason to believe" that
plants can exist without phosphorus. Unknowingly at first, the farmer
had supplied this element by means of the organic fertilizers he used:
manure, excrements, bones, and horns. Now, with the value of phosphorus
known, a search began for mineral phosphates to be applied as
fertilizers. Jean Baptiste Boussingault (1802-1887), an agricultural
chemist in Lyons, traveled to Peru to see the guano deposits. Garcilaso
de la Vega (ca. 1540 to ca. 1616) noted in his history of Peru (1604)
that guano was used by the Incas as a fertilizer. Two hundred years
later, Alexander von Humboldt revived this knowledge, and Humphry Davy
wrote about the benefits of guano to the soil. Yet, the application of
this fertilizer developed only slowly, until Justus Liebig sang its
praise. Imports i