Chemical Science. 397 



raised. By means of a torsion-balance, and a press for compressing 

 bodies, the author has arrived at some curious results. He found 

 that the excess of electricity acquired by each body was proportional 

 to the degree of pressure to which it was submitted. If, for ex- 

 ample, a thin plate of mica and a thin disc of cork be pressed 

 together with a certain force, and then separated, and the electric 

 tension ascertained, and if the experiment be repeated with a double 

 pressure, the electric tension will also be double. The author found, 

 by submitting the discs, first to a great pressure, and without 

 separating them, to a smaller, that the effects of the great pressure 

 remained for some time ; and when the discs were separated, they 

 were found to possess a higher electric tension than that which 

 belonged to the least pressure. These remarks only apply to bad 

 conductors of electricity. 



The author has demonstrated that heat has no effect on free elec- 

 tricity, but has a considerable effect on the neutral fluid naturally be- 

 longing to metallic bodies. If one end of a metallic rod is heated, that 

 extremity manifests positive electricity, whilst the other end exhibits 

 the negative state. The author compares the series o. decomposi- 

 tions and recompositions of the two elements of the neutral fluid 

 along the metallic rod, to the transmission of heat from one mole- 

 cule to another by conduction. He then shows how the electricity 

 thus developed by heat may be removed, and the opposite state 

 rendered evident. Having rolled the end of a platina wire in a spiral 

 form, and placed it on the cap of a gold cup electrometer, (metallic 

 contact being prevented,) he applied the flame of a spirit lamp to the 

 spiral which projected over the cap of the instrument, till it was 

 raised to a red heat. The lamp being removed, and the spiral 

 touched with a piece of moist paper on a heated rod of glass, the 

 positive electricity was removed, and the gold leaves diverged with 

 negative electricity. M. Dessaignes discovered long ago, that if the 

 end of a plate of silver be heated, and the two ends brought in con- 

 tact with the nerves and muscles of a frog, that contractions were 

 produced. Mr. Ritchie has shown, in the Philosophical Transactions, 

 that a powerful electro-magnetic effect could be produced by two 

 pieces of the same metal, having one of the ends raised to a high 

 temperature ; but this experiment of the author is the only one in 

 which electric tension, capable of causing divergence in conductors 

 by heat alone, has been observed. The author tried experiments 

 with the more oxidable metals, and found them to possess the same 

 property, though in a less degree, and that in bismuth, tin, and an- 

 timony, the effects were scarcely sensible. The second part of this 

 memoir contains theoretical views of the electric and chemcial theory, 

 which the curious in such matters can examine in the original. 



4. CRYSTALLIZATION OF PERCHLORIC ACID. (Serullas.) 

 Solution of perchloric acid was concentrated by evaporation until 



