140 Prof. Buff on Galvanic Circuits in which 



with sufficient rapidity, no hydrogen is visible, and the negative 

 polar surface is not polarized. 



Supported by these experiments, from four to five per cent, of 

 hydrochloric acid was added to the perchloride of iron, and the cir- 

 cuit established as before. A small quantity only of H CI is required, 

 as it is always renewed during the progress of the experiment. 



The circuit thus composed showed a satisfactory constancy as 

 long as the deviation did not exceed 14°. Currents of 18° 

 showed, a short time after the circuit had been closed, a slight 

 decrease. The inconstancy of the current increased slowly but 

 gradually with a deviation of 30° or 40°. The time was mani- 

 festly too short to allow the hydrogen separated on the charcoal 

 to be changed again into hydrochloric acid ; for when the circuit 

 was opened a short time, the original strength of the current 

 was regularly established. The deviation of 14° remained un- 

 changed even when the circuit was kept closed longer than two 

 hours. A current which deviated the needle 45° would, accord- 

 ing to experiment, have separated in 31 seconds 1 millegramme 

 of hydrogen. By a deviation of 14° the same quantity requires 

 accordingly 124 seconds. The constancy of this electromotive 

 couple extends therefore only to those currents whose chemically 

 decomposing power does not exceed 1 millegramme hydrogen in 

 124 seconds. 



Manifestly this only holds good for an element of the dimen- 

 sions employed. They were the usual ones ; a charcoal cylinder 

 of 5-7 centimetres interior width by 13*5 centimetres high, of 

 which, however, only 8*5 centimetres were in contact with the 

 solution; the zinc cylinder, 9 centimetres high and 4 centi- 

 metres wide, clipped in sulphuric acid of 1*25 spec, grav., con- 

 tained in a porous cell which almost filled the cylindrical exca- 

 vation of the charcoal. Of course with a greater extent of the 

 electromotor, particularly when a greater surface of the charcoal 

 was placed in contact with the liquid, constant streams of greater 

 strength would be obtained. 



A still more favourable result presented itself when the sul- 

 phuric acid in the porous cell was changed for a concentrated 

 solution of common salt. 



The constancy extended now to a deviation of 22° (one mille- 

 gramme of hydrogen in 77 seconds), and the retrograde motion of 

 the needle by higher deviations was smaller than in the preceding 

 case. There was, further, neither deposition of iron, nor evolu- 

 tion of gas at the charcoal cylinder ; not even when the circuit 

 was directly closed by a short, thick, copper wire. A fine pla- 

 tinum wire was kept in a state of incandescence. 



Compared with other galvanic elements, the perchloride of 

 iron element, as far as power and constancy is concerned, is 



