1 68 ARRANGEMENT OF THE ELEMENTS IN COMPOUNDS. 



and racemates which have long been known to chemists, are 

 also bibasic salts. It is the character of a bibasic acid to unite 

 at once with two different bases, which accounts for the for- 

 mation of Rochelle salt, the tartrate of potash and soda, of 

 which the formula is KO, Na O + C 8 H 4 O 10 . Liebig has also 

 lately shown that gallic acid is bibasic,* the gallate of lead 

 being thus composed 2Pb O + C 7 H O 3 . Now if we attempt to 

 make this a monobasic salt by dividing the atoms both in base 

 and acid by two, an atom of gallic acid would come to contain 

 half an equivalent of hydrogen, which Liebig considers as con- 

 clusive against the division of its atomic weight. Lactic 

 acid also is likely to prove bibasic. 



3. Tribasic Salts. The tribasic phosphates have proved to 

 be the type of a class of salts. One atom of arsenic acid neu- 

 tralizes three atoms of base ; so, it is probable, does one atom 

 of phosphorous acid. Tannic acid also saturates three atoms 

 of base, the formula of the tannate of lead being 3PbQ + C 18 

 H 5 O 9 (Liebig). There is the same necessity to admit that 

 citric acid is tribasic, and the formula of a citrate 3MO-{-C 12 

 H 5 O n , (in which M represents an atom of metal or of hy- 

 drogen) as there is to allow that gallic acid is bibasic. Most 

 of the citrates contain two atoms of fixed base, and one of water, 

 but the citrate of silver contains three atoms of oxide of silver. 

 Cyanic, cyanuric and fulminic acids are isomeric, and all tribasic 

 according to Liebig. The same chemist has also lately ascertained 

 that the related acids, meconic, metameconic and pyromeconic, 

 are respectively tribasic, bibasic and monobasic.f 



Two of the three atoms of base in this class of salts may be 

 different as is observed in certain citrates, cyanurates and 

 phosphates, or the whole three may be different as in the 

 phosphate called microcosmic salt^ which contains at once soda, 

 oxide of ammonium and water as bases.J Two or more of the 

 bases may likewise be isomorphous, or at least belong to the 

 same natural family as soda and oxide of ammonium, water 

 and magnesia. This class and the last will probably be rapidly 

 augmented by the addition of organic acids. Dumas considers 

 it probable that the organic acids which are not volatile, like 



* L'Institut, May 1838, page 141. 

 t Letter from M. Liebig, dated April 2, 1838. 



% Inquiries respecting the constitution of salts ; of oxalates, nitrates, phosphates, 

 sulphates and chlorides. Phil. Trans. 1837, page 47. 



