Double Cyanides by an Electric Current. 38 1 



Another question suggested itself in connection with the 

 decomposition of cyanide of potassium and silver, namely, 

 does the cyanide of potassium which is in union with the 

 cyanide of silver take any part in these decompositions? To 

 determine this, the experiment just detailed was repeated, 

 taking care to reduce the power of the current of electricity 

 when any indication of gas was perceived at the cathode; 

 when the experiment was completed, the solution containing 

 the negative electrode was tested for the quantity of cyanide of 

 potassium by nitrate of silver ; it indicated 67*4 grains, which 

 is more than an equivalent, independent of loss by decomposi- 

 tion. The reason of the cyanide of potassium being more 

 than the equivalent, is from that invariable endosmose which 

 takes place when a current of electricity is passing which is 

 in the direction of the negative division. From this experiment 

 it appears that the cyanide of potassium which is combined 

 with the cyanide of silver undergoes no change by the electric 

 current, if it be properly regulated to the condition of the 

 solution, so long as cyanide of silver is present: this exhibits 

 beautifully the different conducting power of the two salts, 

 and so long as there is not more electricity than the best con- 

 ductor can transmit, it will pass through it in preference to 

 any other salt mixed with it, although such other may be also 

 an excellent conductor. But when the current is more than 

 the best conductor will transmit, it passes through the next 

 best present, which accordingly suffers decomposition ; so 

 that in the case of cyanide of potassium and silver, when the 

 current is more than the cyanide of silver will transmit, the 

 cyanide of potassium is also decomposed, so that two propor- 

 tionals of cyanogen pass to the positive electrode, which 

 being dissolved increases the quantity of silver in the solution, 

 while potassium is liberated at the negative electrode, decom- 

 posing water with the escape of hydrogen gas. 



If platinum electrodes be used there is no necessity for add- 

 ing free cyanide of potassium, the pure solution being decom- 

 posed by a weak current, and the cyanogen liberated at the 

 anode is absorbed by the solution, turning it dark brown and 

 leaving a slight blackish precipitate, probably paracyanogen ; 

 this has been already observed by Professor Faraday in cya- 

 nide of potassium alone; but if the current be increased to 7 

 or 8 pairs of plates, oxygen gas is evolved from the anode, and 

 cyanide of silver is precipitated upon its surface, the cyanogen 

 being decomposed forming ammonia and probably formic 

 acid, which latter decomposes the cyanide of potassium com- 

 bined with the cyanide of silver, forming hydrocyanic acid 

 and formiate of potash, the cyanide of silver being precipi- 

 tated. Several other reactions take place, but my experiments 



