RECENT PROGEESS IN PHYSICS. 383 



evolved at the positive, hydrogen at the negative pole. The current 

 was interrupted alter 48 cubic inches of hydrogen had been obtained. 

 The fluid in the cell at the positive pole, carefully saturated with 

 nitrid acid, gave with nitrate of silver a copious yelloio precipitate, c 

 phosphoric acid had, therefore, evidently been carried to the positive 

 cell. 



A like result was obtained, when instead of the salt 2 N^OHO, PO^ 

 a solution of 3 N^O, PO5 was put into the negative cell ; in this case, 

 too, after the termination of the electrolysis tri-basic phosphoric acid 

 "was found in the negative cells. But when, on the otlier hand, a 

 solution of the bi-basic phosphate of soda 2 N^O, PO., was used on the 

 side of the negative pole, after the termination of the electrolysis it 

 was found that b phosphoric acid had been transferred to the solution 

 of soda of the positive cell, for the fluid, when neutralized with nitric 

 acid, gave, on the addition of nitrate of silver, a white precipitate. 



Finally, a solution of the mono-basic phosphate of soda N^O, PO5 

 was electrolized under the same circumstances, and the fluid of the 

 positive pole yielded with nitrate of silver, after the termination of 

 the electrolysis, a white gelatinous precipitate, thereby proving that 

 a j)hosphoric acid had been transferred to the positive cell. 



Here we have the remarkable phenomenon that the same body PO5 

 with equal composition occurs in different modifications, conditions 

 usually ascribed to an allotropic state ; PO5 saturates, according to 

 circumstances, one or two or three equivalents of base. In the elec- 

 trolysis of phosphates the phosphoric acid always appears at the posi- 

 tive electrode in the same modification in which it was present in the 

 salt of the negative cell. From a tri-basic salt c phosphoric acid is 

 transferred to the positive electrode, from a bi-basic salt c phosphoric 

 acid, and from a mono-basic salt a phosphoric acid. 



The view of the constitution of the salts to which Daniell was led 

 by his experiments on electrolysis, and which has been explained in 

 § 171, is in perfect agreement with the electrolytic relations of the 

 phosphates when considered in connexion with the above described pe- 

 culiariiies of these salts. 



According to this theory we must consider 



3 Na 0, P O3 as Na.+P 0^„ Tritoxyphosphion of Sodium, 



2 Na O, P O5 as Na2-}-P Oj, Deutoxyphosphion of Sodium, 



Na 0, P 0^ as Na+P 0^, Protoxyphosphion of Sodium. 



In the electrolysis of Tritoxyphosphion of Sodium, Na3 is liberated 

 at the negative pole, while P 63 passes to the positive. Q^ the oxy- 

 dati(m of the three e([uivalents of Na, three equivalents of H are 

 evolved at the negative pole, while at the other pole three equivalents 

 PI combine with P 0, to form H3-f-P 0^, that is the Ter- or Trito-hy- 

 drate, so that three equivalents of oxygen must necessarily escape at 

 the positive pole. 



In the electrolysis of the Deutoxyphosphion of Sodium, P 0^ passes 

 to the positive pole and evolves two equivalents of oxygen, by com- 

 bining with H. to form Ho+P O7, that is Deutohydrate, while at the 

 other pole two equivalents of Sodium are formed and two equivalents 

 of hydrogen evolved. 



