llti Van Name and Huff- — Hydrolysis and Electrical 



Molecular Conductivity and Molecular Formula. — In 

 support of the smaller molecular formula for hypophos- 

 phoric acid, Rosenheim and Pinsker emphasize the fact 

 that the molecular conductivity referred to the formula 

 BLPO3 (see Table V, lower section, column 4) is of the 

 same order of magnitude as the molecular conductivities 

 of H 3 P0 3 and H 3 P0 4 (Table VII) and seems to tend with 

 dilution toward the same limit. This tendency would be 

 expected, as they point out, if the normal molecule were 

 H 2 P0 3 , since the anions HP0 3 ', H 2 P0 3 ', and H 2 PO/, on 

 account of their similarity in composition would probably 

 have nearly the same velocities. 



This argument is not a strong one, for the facts can 

 be equally well explained upon the other hypothesis. 

 Owing to the high velocity of the hydrogen ion the con- 

 ductivity of 1/2 (H+ + H+ + H 2 P,0 6 ") would be nearly 

 the same as that of (H+ + HP0 3 ') which would account 

 for the tendency above mentioned. That two and only 

 two of the equivalents of hydrogen in the molecule 

 H 4 P 2 6 are extensively ionized is indicated by the fact 

 that two of these equivalents of hydrogen, but not the 

 third, can be titrated in the presence of methyl orange. 



It is interesting to note that ionization relations of this 

 kind have been proved to exist in the case of pyrophos- 

 phoric acid by Abbott and Bray, 11 who determined the 

 ionization constant for each of its four equivalents of 

 hydrogen. This is important, because, if the formula 

 of hypophosphoric acid is H 4 P 2 6 , we should expect a 

 rather close analogy with pyrophosphoric acid H 4 P 2 7 , 

 both in conductivity and in other properties. Such an 

 analogy unquestionably exists. If we calculate the con- 

 ductivity of pyrophosphoric acid at 25° from the results 

 of Abbott and Bray for 18°, allowing for a temperature 

 coefficient of 1% per degree in round numbers, we find 

 that within the range of dilution covered by their experi- 

 ments (20 to 800 liters) the molecular conductivities of 

 H 4 P 2 6 and H 4 P,0 7 show a maximum difference of less 

 than 10%, and approach one another at higher dilutions. 

 Abbott and Bray have also showed that with reference 

 to the ionization of the first equivalent of hydrogen, 

 pyrophosphoric acid is not far below the strongest acids 

 in strength; with reference to the second equivalent, it 



« J. Am. Chem. Soc, 31, 729, 1909. 



