376 RECORD OF SCIENCE FOR 1886. 



action of a film of condensed vapor or gas on their surfaces. Sacli a 

 pair of plates is thus similar to a voltaic cell with its electrotype divided 

 by a diaphragm of air of other gas ; and it is the difference of potential 

 of the films that is measured in "contact" experiments, the metals 

 themselves being at one potential. His experiments were made with an 

 electrometer having quadrants of the metals under consideration. A 

 reversal of the electro- motive force takes place with pairs of copper-iron 

 when hydrogen sulphide or ammonia is added to the air surrounding 

 them; with silver-iron when hydrogen sulphide is added; and with 

 copper-nickel when either ammonia or hydrogen chloride is added. 

 Neutral or inert gases have little or no effect. By placing the (appar- 

 ently) dry plates of copper and zinc in close proximity, so that their 

 films were in contact, a permanent current was produced, which ceased 

 when the metals touched or were separated to a certain distance. This 

 "film-cell" could be polarized by sending a current through it from 

 another battery. When the zinc plate of a Volta condenser was joined 

 to the zinc quadrant of the electrometer and the copper of the con- 

 denser to the copper of the electrometer, on altering the capacity of 

 the condenser an alteration of the difference of potential near the quad- 

 rants was produced. (ISTature, December, 1886, xxv, 142.) 



Knott has examined the resistance and thermo-electric properties of 

 hydrogenized palladium. He finds that the electro-motive force in a 

 circuit of pure and of hydrogenized palladium, the temperature of the 

 junctions being 0° and lOOo, is 20 x 10^ 0. G. S. units, or 0.002 volt. If 

 a palladium wire be hydrogenized for half its length by immersing that 

 half in an electrolytic cell, and the ends of the apparently uniform wire 

 be connected to a galvanometer, then on allowing a flame to play gently 

 on the central portion of the wire a strong current is obtained, which 

 increases to a maximum and then decreases to zero. (Nature, Septem- 

 ber, 1886, XXXIV, 462.) 



Bidwell has exhibited to the Physical Society of London a cell with a 

 solid electrotype thus constructed : Upon a plate of copper a layer of 

 quite dry precipitated copper sulphide is spread. On this is placed a 

 clean plate of silver, covered with a slight film of silver sulphide by 

 pouring on it a solution of sulphur in carbon disulphide and evaporat- 

 ing the free sulphur by heat. On connecting the cell with a galva- 

 nometer a considerable deflection is obtained ; far greater than, and in 

 the opposite direction to, the deflection obtained with a silver plate not 

 thus treated. The resistance of the cell was very great— 6,500 ohms— 

 but was greatly reduced by compression. The electro-motive force was 

 0.07 volt. (Nature, July, 1886, xxxiv, 211 ; Phil. Mag., V, xx, 328; J. 

 Phys., July, 1886, II, v, 339.) 



Toscani has demonstrated experimentally: First, that if in a battery 

 cell both surfaces of the zinc are active, the contribution made by each 

 of them to the general useful effect is in the inverse ratio of the square 

 of their distance from the center of the inactive electrode ; and, second, 



