94: Scientific Intelligence. 



iron through the external circuit. If two iron plates he used in 

 a solution of common salt, a little ferric chloride heing placed 

 near the lower one, the change produced illustrates the equation 

 Fe fl +++ 4- Fe = Fe a M . In the case of the reversible reaction 

 Fe ++ -f I = Fe ++ + -f I - , the electrical exchanges were shown by 

 means of two platinum electrodes standing in small crystallizing 

 dishes placed within a larger dish, the latter being tilled with 

 a solution of potassium chloride. In one of the small dishes 

 is contained some iodine and in the other ferrous chloride 

 solution. Under these conditions the current in the exter- 

 nal circuit flows from the iodine to the strong ferrous 

 solution ; but by increasing the concentration of the iodine ions 

 or of the ferric ions, the reaction is reversed and with it the 

 direction of the current. In a similar way the exchange I - -(- 

 Br = Br + -(-I was shown. When electrodes of iron and 

 platinum are immersed in a potassium chloride solution and a 

 little iodine is added near the platinum, the current developed 

 corresponds to the reaction Fe + I 2 = Fe ++ = I~. Again a 

 saturated solution of hydrogen chloride in toluene does not con- 

 duct electricity even under a pressure of 72 volts ; nor does such 

 a solution act on calcium carbonate. But the addition of a little 

 water enables it to accomplish both these results. A saturated 

 solution (0*1 normal) of carbonic acid colors methyl orange less 

 intensely red than a 001 normal solution of acetic acid, owing to 

 their dissociation difference. By adding a trace of hydrogen 

 sodium carbonate to the carbonic acid, the diminution of dissocia- 

 tion produced by increasing the concentration of one ion is 

 shown by the disappearance of the red color. The same result 

 follows the addition of sodium acetate to the acetic acid solution; 

 though no change of color is produced when sodium chloride is 

 added to a weak solution of hydrogen chloride colored by 

 methyl orange. A similar phenomenon is the precipitation of lead 

 chloride from its saturated solution by adding a solution of 

 common salt. In the next place, if copper be present in the form 

 of cation in a solution of copper suphate, or in that of a complex 

 anion in Fehling's solution, this fact may be proved by passing a 

 current through two U-tubes, in one of which is a solution of 

 copper sulphate having one of sodium sulphate floating upon it, 

 while in the other is the Fehling's solution and on it an alkaline 

 solution of Rochelle salt. In the one tube the blue zone moves 

 in the same direction as, and in the other in the opposite direction 

 to, that of the current. The absence of cupric ions from Feh- 

 ling's solution was further shown by means of a galvanic cell 

 containing lead and copper immersed respectively in solutions 

 of lead acetate and copper sulphate. Under these conditions, 

 lead dissolves and copper is thrown down ; but both the reaction 

 and the direction of the current are reversed if an alkaline solu- 

 tion of Rocbelle salt is added to the cupric sulphate solution. — 

 Zeitschr. Electrochem, iv, 105-113, August, 1897. g. f. b. 



4. On the Photoelectric Properties of Certain Colored 



