143 



Art. XV. PROGRESS OF FOREIGN SCIENCE. 



I. Chemical Science. 



I. Principles of Combination. In Sir H. Davy's researches 

 " on some chemical agencies of electricity," published in the 

 Phil. Trans, for 1807, we find it stated, that " when oxalic, 

 succinic, benzoic, or boracic acid, perfectly dry, either in 

 powder or crystals, was touched upon an extended surface, 

 with a plate of copper insulated with a glass handle, the copper 

 was found positive, the acid negative. In favourable weather, 

 and when the electrometer was in perfect condition, one con- 

 tact of the metal was sufficient to produce a sensible charge ; 

 but seldom more than five or six were required. Other metals, 

 zinc and tin, for instance, were tried with the same effect. 

 And the metal received the positive charge, apparently to the 

 same extent, whether the acid was insulated upon glass, or con- 

 nected with the ground. The solid acid of phosphorus, which 

 had been strongly ignited, and most carefully excluded from the 

 contact of air, rendered the insulated plate of zinc positive by 

 four contacts, but after exposure to the atmosphere for a few 

 minutes, it wholly lost this power. When metallic plates were 

 made to touch dry lime, strontites, or magnesia, the metal be- 

 came negative : the effect was exceedingly distinct, a single 

 contact upon a large surface being suflScient to communicate a 

 considerable charge. For these experiments the earths were 

 carefully prepared ; they were in powder, and had been kept for 

 several days in glass bottles before they were used. It is essen- 

 tial to the siiccess of the process, that they be of the temperature 

 of the atmosphere. In some experiments which I made upon 

 them, when cooling after having been ignited, they appeared 

 strongly electrical, and rendered the conductors brought in con- 

 tact with them positive." — " Supposing two bodies, the par- 

 ticles of which are in different electrical states, and those states 

 sufficiently exalted to give them an attractive force superior to 

 the power of aggregation, a combination would take place, 

 which would be more or less intense, according as the energies 

 are more or less perfectly balanced ; and the change of pro- 

 perties would be correspondingly proportional. This would be 

 the simplest case of chemical union. But different substances 

 have different degrees of the same electrical energy in relation 

 to the same body ; thus the different acids and alkalis are pos- 

 sessed of different energies with regard to the same metal," ^c. 



These experiments, and views relative to electro-chemical 

 action, have met with universal admiration and general ac- 

 quiescence from the chemical world. The electroscope was 

 that of Bennet, furnished with small condensing plates. 



