532 Scientific Intelligence. 



the case of a hydrogen cell while this addition decreases it in the 

 case of a cell containing oxygen. His results show the potential 

 difference to be independent of the density of the gas and of its 

 temperature up to 70°. With carbon electrodes, however, the 

 phenomena obtained were quite different. — Am. Phys. Cheni. II, 

 xliv, 45*7; J. Chem. Soc, lxii, 393, April, 1892. g. f. b. 



2. On the Basicity of Phosphoric Acid. — D. Berthblot has 

 studied the relative conductivities of the monobasic aud dibasic 

 phosphates and has shown that while the conductivity is the same 

 for the monobasic ammonium and potassium phosphates, the con- 

 ductivity of the dibasic ammonium salt is about six per cent less 

 than that of the potassium salt. Moreover, in the case of the 

 tribasic phosphates the conductivities are. widely different, that of 

 the potassium salt being much the greater. It is well known that 

 when potassium, sodium or ammonium hydroxide is continuously 

 added to a dilute solution of phosphoric acid, the decrease in the 

 electrical conductivity of the solution is represented by a straight 

 line up to the point at which one of the basicities of the acid is 

 neutralized. So that, as it would appear, these three monobasic 

 phosphates are not dissociated even in dilute solutions. At this 

 point the conductivity-curve shows a well-marked angular deflec- 

 tion, and on continuing to add the base, the resulting increase in 

 conductivity is again represented by a straight line up to the 

 point corresponding to the formation of a dibasic phosphate. 

 Consequently, these dibasic phosphates must also be stable even 

 in dilute solutions. If more base be added, another change 

 occurs in the direction of the curve, but now the change in con- 

 ductivity is no longer represented by a straight line. Moreover 

 there is no further change in direction at the point corresj)onding to 

 the formation of tribasic phosphate. Hence the tribasic alkali phos- 

 phates are almost completely dissociated in dilute solutions. If 

 the solution be made stronger, a distinct although small angular 

 deflection may be observed at the point corresponding to the form- 

 ation of tribasic phosphate. It would seem, therefore, that phos- 

 phoric acid differs materially from the true tribasic acids, such 

 as citric, aconitic and tricarballylic, in the fact that in the case of 

 these acids the monobasic and dibasic salts are partially disso- 

 ciated in solution, while the tribasic salt is stable. Since accord- 

 ing to Lenz the ammonium and potassium salts of strong acids 

 show the same conductivity in dilute solution, while according to 

 the author's experiments the conductivities of these two salts with 

 feeble acids are distinctly different, though approximately the 

 same, and the conductivities in the case of phenol are entirely 

 different, he concludes that the first acid function of phosphoric 

 acid is analogous to that of strong acids, the second to that of 

 feeble acids and the third to that of phenols. In fact therefore 

 phosphoric acid is not a true tribasic acid, but a monobasic acid 

 with a complex function. Simular conclusions follow from thermo- 

 chemical data. — C. P.. cxiii, 851, J. Chem. Soc, lxii, 394, April, 

 1892. G. F. B. 



