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 into England rose and far exceeded those into France where, between 1857 and 1867, about 50,000 tons were annually received. The other great advance in the use of phosphatic plant nutrients started with Liebig's recommendation (1840) to treat bones with sulfuric acid for solubilization. This idea was not entirely new; since 1832, a production of a "superphosphate" from bones and sulfuric acid had been in progress at Prague. At Rothamsted in 1842, John Bennet Lawes obtained a patent on the manufacture of superphosphate. Other manufactures in England followed and were successful, although James Muspratt (1793-1886) at Newton lost much time and "some thousands of pounds" on Liebig's idea of a "mineral manure." [Illustration: Figure 8.--FLORIDA LAND-PEBBLE PHOSPHATE MINING. (From Carroll D. Wright, _The Phosphate Industry of the United States ..._, plate facing page 58.)] It was difficult enough to establish the efficacy of bones and artificially produced phosphates in promoting the growth of plants under special conditions of soils and climate; therefore, the question as to the action of phosphates in the growing plant was not even seriously formulated at that time. The beneficial effects were obvious enough to increase the use of phosphates as plant nutrients and to call for new sources of supply. Active developments of phosphate mining and treating started in South Carolina in 1867, and in Florida in 1888.[25]