xix BALANCED ACTIONS 503 



partially decomposed by the potash, and that the sulphuric 

 acid was divided between the two bases " (pp. 8-9). 



" Equal weights of potash and of carbonate of lime, finely 

 pulverised, were boiled in a small quantity of water, which, 

 after being filtered and rendered transparent, effervesced 

 strongly with acids; and the residue, after evaporation, 

 having been treated with alcohol, in order to dissolve the 

 alkali, furnished a substance that had all the qualities or 

 characters of the carbonate of potash" (pp. 10-11). 



Balanced actions. All the cases quoted by Berthollet 

 are examples of BALANCED ACTIONS, i.e. reversible actions in 

 which chemical change proceeds in both directions at the same 

 time and under the same conditions. Such actions may be 

 represented by equations in which the opposing actions are 

 shown by two arrows, but without any signs to suggest that 

 different conditions are required to produce reversal. The 

 cases quoted above are shown thus : 



Ba(OH) 2 + K 2 S0 4 ^ 2 KOH + BaS<V 

 Ca(OH) 2 + K 2 CO 3 ^ 2KOH + CaCO 8 . 



In the first case, it had been supposed that baryta and 

 potassium sulphate interacted to form caustic potash and 

 barium sulphate by an interaction that was non-reversible 

 and complete. Berthollet showed that the action could be 

 reversed, and was, in fact, incomplete, the acid being shared 

 to some extent between the two bases. In the second case 

 it had been supposed that carbonate of potash was deprived 

 of all its carbonic acid and rendered completeiy caustic by 

 the action of lime ; Berthollet proved that the converse 

 change could be brought about, and that the action was 

 " balanced " and incomplete. He concludes : 



"It is evident, from the preceding experiments, that the 

 bases which are supposed to form the strongest combinations 

 with the acids, may be separated from them by others, whose 

 affinities are supposed to be weaker, and that the acid 



1 It is probable that carbonic anhydride was absorbed from the air, and 

 that the balanced action was really BaCO 3 + K 2 SO 4 ^ K 2 CO 3 + BaSO 4 . 



