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)... O^{3} phosphoric acid H^{3} (PHO).. O^{2} phosphorus acid H^{2} (PH^{2}O). O hypophosphorous acid.[24] H Further proof for these constitutions was sought in the study of the esters formed when the 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.