In 1857 he pointed out that phosphate rock could be treated in a similar manner. In 1840, Leibig suggested dissolving bones with sulfuric acid to render the contained phosphorus soluble and available to crops. In 1769 Gahn, a Swedish chemist, reported that phosphorus was an essential constituent of bones, but the untreated natural materials continued to be the main sources of fertilizer until about the middle of the 19th century. Although the composition of such phosphate materials was unknown, their function in increasing crop yields was generally recognized. The Incas of Peru and the American Indians applied fish and guano to the soil long before America was discovered by Europeans. The dung of birds was employed by the Carthaginians before 200 B.C., and the early agricultural writers recommended applications of natural phosphate materials to increase crop yields. The earliest use of phosphatic materials was for fertilizer purposes, but fur many years these materials were applied in a raw or natural state. The various intermediate and end products derived from phosphate rock and their more important industrial applications are shown in figure 1. Phosphorus and phosphoric acid have certain direct industrial applications, but they are more commonly used as intermediates in manufacturing the products included in the other three groups. The products derived from phosphate rock by these treatment methods may be divided into the following live broad groups: Calcination or fusion with silica, sodium salts, magnesium minerals, or small quantities of phosphoric acid.Reduction by carbon at high temperature.Three fundamental methods are employed in decomposing phosphate rock:

Phosphorite oxygen not included