380 



Dr. J. Shields on Hydrolysis 



this substance in pretty dilute solution was almost entirely 

 decomposed into acid and base ; but the preceding experi- 

 ments go to prove that in a ^ molecular normal solution 

 rather less than one per cent, is decomposed by the water. 

 If the statement that the amount of free alkali in the solution 

 is proportional to the square root of the concentration holds 

 good for borax, then a solution in which the borax was com- 

 pletely hydrolysed would be almost infinitely dilute. 



Rose has described a very interesting experiment which is 

 intended to show the decomposition of borax by water. A 

 tincture of litmus reddened with acetic acid is added to a 

 concentrated solution of borax until the red colour has almost 

 but not quite disappeared ; the whole is then diluted with 

 water, when the red colour changes to blue. I have repeated 

 this experiment, and find that a solution prepared in the way 

 Rose has indicated becomes distinctly blue on dilution. Joulin 

 (Bull Soc. Chim. de Paris [2] vol. xix. p. 344, 1873), how- 

 ever, could not observe this change of colour, and moreover 

 has attempted to show r that water exercises no decomposing 

 influence at all on salts ; but there is little doubt that he has 

 been too hasty in coming to this conclusion, and that Rose, 

 at least qualitatively speaking, was right. 



Trisodium Phosphate. 

 A preliminary experiment with a ^ solution of this salt 

 showed that the velocity of reaction, on saponifying ethyl 

 acetate, was singularly great when compared with what had 

 been observed in the case of the other salt-solutions, and in 

 fact closely approached that for a -^ normal solution of 

 caustic soda itself. This seemed to indicate that the solution 

 under examination was almost entirely hydrolysed in the 

 sense of the equation 



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



The formulae which have hitherto been employed are of no 

 use in this case, for they depend on the condition that A 

 should be very small compared with x. Here A can in no 

 case be neglected ; consequently the equation (3) 



A= K(C-g ) 

 is inapplicable. os 



The general equation 



~=.h{G l -x){C- x ) 



becomes 



dt 



=K(C s -ff)(C-*), 



(8) 



