in Aqueous Salt-Solutions, 379 



that is to say, the amount of free potash is proportional to the 

 square . root of the concentration of the potassium-cyanide 

 solution. 



It has long been known that water decomposed certain salts, 

 with formation of free acid and free base, but the amount of 

 such decomposition has up to the present time only been 

 measured in a few cases. It is true some guesses at it have 

 occasionally been made, but they have proved rather unsatis- 

 factory. For example, it has been supposed (see Ostwald's 

 Lehrbucli der allgem. Chemie, vol. ii. p. 187, 2nd edit.), from 

 measurements of the heat of neutralization of hydrocyanic 

 acid by caustic soda, that a solution of sodium cyanide con- 

 tains only one fifth of the salt as such, whilst the other four 

 fifths are decomposed into free acid and free base. 



The experiments which I have made on the velocity of 

 reaction show that in a tenth-normal solution of potassium 

 cyanide only about one per cent, of the salt is decomposed in 

 the way indicated. The results which J. Thomsen (Thermo- 

 chemische Untersuchungen, vol. i. p. 161) obtained on neutra- 

 lizing one molecule of sodium hydrate with n molecules of 

 hydrogen cyanide are as follows : — 



n. NaOHAq, wHONAq. 



J . . . . 13*68 heat units. 



1 . . . . 27*66 „ 



2 . . . . 27-92 



These numbers indicate that the amount of heat which is 

 developed increases in the same proportion as the quantity of 

 hydrogen cyanide added, until there are equivalent quantities 

 of acid and base present. An excess of acid, then, produces 

 only a very slight alteration in the value of the heat of 

 neutralization. 



Now manifestly this small increase in the heat of neutrali- 

 zation means that the first equivalent of hydrogen cyanide 

 has almost all combined with the sodium hydrate. The cause 

 of the incomplete combination is due of course to the mass 

 action of the water. In short, it would seem that only a small 

 fraction, presumably about one per cent., of the potassium 

 cyanide is decomposed by the water into free acid and free 

 base. 



This corroborates the result which I have obtained by a 

 totally different method. 



A guess which H. Rose (Jahresbericht, 1852, p. 311) 

 hazarded as to the amount of hydrolysis in an aqueous solu- 

 tion of borax is just as unsatisfactory. Rose supposed that 



