Dr. Gladstone and Mr. Tribe on a Law in Chemical Dynamics. 227 



In the earlier terms of this series, twice the percentage of silver- 

 salt gives three times the chemical action. The mathematical expres- 



log_3 



sion of this law is c=C^ lo s 2 , c being the chemical action, C the 

 constant, and p the proportionate quantity of salt. The close 

 agreement of the observed numbers with those calculated on this 

 supposition as far as the 9th term is shown in the 5th and 6th 

 columns. The law then breaks clown, 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 held 

 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 l*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 currents 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 

 chemical action is the same for similar consecutive periods of time, 

 experiments were made in far weaker solutions. It was only neces- 

 sary to lengthen the time of exposure. It was thus found that the 

 law of three times the chemical action for twice the strength of so- 

 lution 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 0*000001 gramme, 

 a million times less. 



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

 examined, and the currents produced were studied. At first a light- 

 blue current is perceived flowing upwards from the surface of the 

 plate; presently a deep-blue current pours downwards; and these 

 two currents in opposite directions continue to form simultaneously. 

 A similar phenomenon was observed in every case where a metallic salt 

 attacked a plate of another 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 



Q2 



