On Tribasic Phosphoric Acid. L59 



laws of nature, but it lias been a bearer of fruitful ideas, 

 which have arisen from the reflections of the most pene- 

 trating and ingenious chemists of all countries, who for 

 one hundred and fifty years have labored to remove the dif- 

 ficulties, to explain the anomalies, and to reduce to a fun- 

 damental law the enigmatic phenomena which surronnd the 

 knowledge of this acid and of its salts. The spirit of tin- 

 present century has not yet succeeded in finding this; and 

 whenever the tacts become too complicated, we have recourse 

 to the assumption of modifications, which, however, leave 

 the causes unexplained. The defectiveness of Buch interpre- 

 tations we see all the more glaringly in the case of phosphoric 

 acid, as in this acid we have to assume many modifications, 

 and are obliged to express them with almost arbitrary consti- 

 tutional signs in order to make them comparable with each 

 other. I will, however, not dwell on the differenl phosphoric 

 acids, which in part seem to bear a semi-organic character, 

 but will o;ive a brief historical review of the so-called tribasic 

 modification, and then enter upon the criticism of the modes 

 of separating it from bases. 



Before doing this, however, I will tabulate the forty-two 

 phosphatic minerals according to the year of their discovery, 

 giving in the second number the time when the phosphoric 

 acid in them was first determined quantitatively. 



77-1834. Tusquois, Pliny (xxxvii., :;:: ; Oallais, Oallaina). 

 Zellner (Isis 637). 



M. John made, in 1811, the first analysis, in which 1 \ 



looked phosphoric acid (Al a 0,=73 p. c.) I 1 



the same time mentioned the presence of a Little PO (Ai Q. d. 



M. II. iii. 231). 



Al, 0,2, I'" • 5 BO. 



77-1864. CallamiU, I 'liny (XXXVII., 83; Callais, I 

 laina). 



Damour (C. R. LIX. 936). 



Damour made the first and only analysi to the 



