1871.] 



Law in Chemical Dynamics. 



499 



is shown in the 5th and 6th columns. The law then breaks down, and 

 after about 7 per cent, the increased action is almost in direct ratio with the 

 increased strength. 



The position of the plate in the solution was found to make no difference 

 to this 2-3 law. 



Similar series of experiments were made with zinc and chloride of copper, 

 zinc and sulphate of copper, zinc and nitrate of lead, iron and sulphate of 

 copper, and other combinations ; and in every instance where the solution 

 was weak and the action simple, the law of three times the chemical change 

 for twice the strength was found to hold good. 



It was proved that the breaking down of the law at about 3*5 per cent, 

 of salt in solution was irrespective of the quantity of the liquid, or of the 

 time for which the plate was exposed. With 72 cub. centims. of a 1*41 

 per cent, solution of nitrate of silver the rate of action remained sensibly 

 the same for as long as twenty-five minutes, notwithstanding the constant 

 deposition of silver. This apparently paradoxical result is due to fresh 

 relays of the original solution being brought up to the plate by the cur- 

 rents produced, and that period of time elapsing before any of the products 

 of decomposition are brought back again in their circuit. 



When it was perceived that within easily ascertainable limits the che- 

 mical action is the same for similar consecutive periods of time, experiments 

 were made in far weaker solutions. It was only necessary to lengthen the 

 time of exposure. It was thus found that the law of three times the che- 

 mical action for twice the strength of solution holds good through at least 

 eleven terms of the powers of 2 ; in fact, from a solution that could dissolve 

 one gramme of copper during the hour, to a solution that dissolved only 

 1 000001 gramme, a million times less. 



The manner in which the silver is deposited on a copper plate was exa- 

 mined, and the currents produced were studied. At first a light blue cur- 

 rent is perceived flowing upwards from the surface of the plate, presently a 

 deep blue current pours downwards, and these two currents in opposite di- 

 rections continue to form simultaneously. A similar phenomenon was 

 observed in every case where a metallic salt attacked a plate of anotner 

 metal. The downward current was found to be a solution of almost pure 

 nitrate of copper, containing about three times as much N0 3 as the original 

 silver solution, while the upward current was a diluted solution of the 

 mixed nitrates. Moreover the heavy current took its rise in the entangled 

 mass of crystals right against the plate, while the light current flowed from 

 the tops of the crystalline branches. It was evident that when the fresh 

 silver was deposited on these branches, and the fresh copper taken up from 

 the plate, there was not merely a transference of the nitric element from 

 one combination to another, but an actual molecular movement of it 

 towards the copper plate, producing an accumulation of nitrate of copper 

 there, and a corresponding loss of salt in the liquid that is drawn within the 

 influence of the branching crystals. Hence the opposite currents. 



2 r 2 



