



382 Dr. J. Shields on Hydrolysis 



If the equation 



Na 3 P0 4 + HOH = Na 2 HP0 4 + NaOH 



represented accurately the amount of hydrolysis, then fi at 

 the commencement should be TOO. A glance at the last 

 column of the table shows that the equation must be nearly 

 true. In order to find approximately the initial value of /-t, 

 a curve (fig. 2) has been drawn by plotting the values of fi as 

 ordinates against the times t as abscissse. 



Fio:. 2. 



Time, in minutes. 



By referring to the curve it will be found that the initial 

 value of fju is 0*98 at least ; that is to say, at least 98 per cent, 

 of one of the sodium atoms in Na 3 P0 4 exists as free caustic 

 soda in a ^molecular normal solution of the salt at 24°"2 C. 

 In other words, although trisodium phosphate exists in the 

 solid state, yet in dilute solution it is for the most part 

 decomposed into hydrogen disodium phosphate and sodium 

 hydrate. This result is in entire agreement with Berthelot's 

 recent researches. 



