1835.] Scientific Intelligence. 233 



placed on the zinc, and was pressed upon by the ends of the platinum 

 wire. When under these circumstances, the plates were dipped into 

 the acid of the vessel described, there was an immediate effect at the 

 bibulous paper, the iodide being decomposed, and iodine appearing at 

 the anode, i. e., against the end of the platinum wire. As long as 

 the lower ends of the plates remained in the acid, the electric current 

 continued, and the decomposition of the iodide proceeded. On re- 

 moving the end of the wire from place to place on the paper, the 

 effect was evidently very powerful, and on placing a piece of turmeric 

 paper between the white paper and zinc, both papers being moistened 

 with the solution of iodide of potassium, alkali was evolved at the 

 cathode, against the zinc, in proportion to the evolution of iodine at 

 the anode. Hence, the decomposition was perfectly polar, and 

 decidedly dependent upon a current of electricity passing from the 

 zinc through the acid to the platinum in the vessel, and back from 

 the platinum, through the solution to the zinc at the bibulous paper. 

 The fact of the decomposition being produced by the electrical cur- 

 rent, was proved by the circumstance of the decomposition ceasing 

 when the acid and its vessel were removed from the plates, and being 

 again removed when the contact was repeated. The same position 

 was deduced by varying the experiment, amalgamating pieces of 

 zinc over the whole surface, and employing dilute sulphuric acid in 

 the vessel. The same effects resulted when caustic potash was used 

 instead of acid, and also when brine was substituted. The inferences 

 which the author draws are, 1st., That metallic contact is not neces- 

 sary for the production of the voltaic current; 2d., That a most 

 extraordinary mutual relation of chemical affinities of the fluid exists 

 which excites the current and the fluid which is decomposed by it. 



The use of metallic contact in a single pair of plates appears evi- 

 dent from the experiments. For when an amalgamated zinc plate 

 is dipped into dilute sulphuric acid, the force of chemical affinity 

 exerted between the metal and the fluid is not sufficiently powerful 

 to cause sensible action at the surfaces of contact, and occasion the 

 decomposition of water by the oxidation of the metal, although it is 

 sufficient to produce such a condition of the electricity as would 

 produce a current if there was a path open for it. 



Now, the presence of a piece of platinum touching both the zinc 

 and the fluid to be decomposed opens the path required for the elec- 

 tricity, because only one set of opposing affinities are to be overcome ; 

 whereas, when metallic contact is not allowed, two sets of opposing 

 affinities must be conquered. Some have considered it impossible to 

 decompose bodies by Hare's calorimeter, or Wollaston's powerful 

 single pair of plates, but this was owing to their considering the 

 decomposition of water a test of the passage of an electric current. 

 But the author observed that bodies would differ in facility of decom- 

 position by a given electric current, according to the condition and 

 intensity of their ordinary chemical affinities, and he has corroborated 

 the fact by new experiments. In employing different fluids to excite 

 the action, he procured currents of electricity varying in intensity 

 and by consequence in their effects. Dilute sulphuric acid acting 

 upon the zinc and platinum plates decomposed iodide of potassium. 



