2 P 3 aq. phosphoric acid 



3 P 3 aq. pyrophosphoric acid 

 6 P I aq. metaphosphoric acid. 



Sails arc formed when a "basis," i.e., .i metal oxide. 

 replaces water. When potassium-acid sulfate is neu- 

 tralized by sodium base, the acid-salt divides into 

 ( Hauber's salt and potassium sulfate, which proves the 

 acid-salt to be a mixture of the neutral sail with ib 

 acid. Sodium-acid phosphate behaves quite differ- 

 ently. After neutralization 1>\ a potassium "base" 

 (hydroxide), the salt does not split up; a uniform 

 sodium-potassium phosphate is obtained. Therefore, 

 phosphoric acid is truly three-basic! 23 



This result has later been confirmed, but the an 

 1>\ 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 lS4b, according to 

 the theory of chemical types: 



(PO) • • 

 II 



l'lloi ■ 



II 

 (I'll «0) 

 II 



phosphoric acn 



phosphorus a 



< * h\ pophosphorous acid. 14 



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 studv of phosphoric acids led to important new 



"JUSTUS LiEBJo's Annalen dcr Pharniu, vol. 26, 



p. 1 1 1 IT. 



11 A. WuRTZ, Annates de Chimic el de Physique, series I, vol. 16 

 (1846), p. 190 



concepts in theoretical chemistry. The finding ol 

 polybasicity was extended to othei acids and fi 



the model that helped to recognize the pol\ function- 

 ality in othei ds, lik' alcohols and amines. 

 The hydrogen theory ol acids was fundamental foi 

 furthei advance. In am ision, it is partic- 

 ularly interesting to see that large-scale applications 

 followed almost immediately ami directly from the 

 new theoretical insight. The Inst ami foremost of 



tin se applications was m agl icnlturc. 



Phosphates as Plant Nutrients 



One hundred years aftei the discovery of "cold 

 light," the presence ol phosphorus in plants and 

 animals was asi 1 1 tained, 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 tune (1833), the Duke of Richmond 

 proved that the fertilizing value of bones resided not 

 in the gelatin, nor in the calcium, but in the phos- 

 phoric acid. Thus, he confirmed what Theodore de 

 Saussure had said in 1804, that "we have no reason 

 to beli<ve" 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 agricul- 

 tural chemist in Lyons, traveled to Peru to see the 

 guano deposits. ( i.ucilaso de la Vega (ca. 1540 to ca. 

 1616) noted in his history of Peru (1604) that guano 

 was used bv 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 ol 

 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 ions were annually 

 received. 



The othei great advance in the use of phosphatic 

 plant nutrients started with I.icbig's recommendation 

 (1840) to treat bones with sulfuric acid for solubili- 

 zation. This idea was not entirely new: since 1832, 

 a production of a "superphosphate" from bones and 

 sulfuric acid had been in progress at Prague. \i 



PAPER 4<): HISTORY OF PHOSPHORUS 



185 



