into the Cause of Voltaic Electricity. 281 



there will therefore only be a very feeble positive tension, often 

 scarcely any. But if the diluted acid be replaced by concen- 

 trated sulphuric acid, though the chemical action will be less 

 lively, the electric tension will be much stronger, this acid being 

 a very bad conductor; and the passage of the electricity from the 

 liquid to the metal immersed in it being extremely difficult, the 

 two electricities uniting immediately upon the surface attacked 

 in a much smaller proportion : if, instead of a piece of metal, a 

 piece of wood rather moist be immersed in the concentrated sul- 

 phuric acid, the positive tension acquired by the acid is still 

 stronger. If a capsule made of an oxidable metal be employed, 

 and, after heating it, a few drops of a liquid capable of attack- 

 ing it at that high temperature in ever so small a degree (pure 

 water is sufficient), be poured into it, a quantity of negative 

 electricity is developed, which is sufficiently strong to be sen- 

 sible without the assistance of the condenser, and even to give 

 sparks. In this case the drop of liquid injected into the heated 

 capsule is converted into vapour while it is attacking the metal, 

 and carries off with it the positive electricity, which cannot then 

 combine immediately with the negative electricity left in the 

 metal ; but if even the smallest quantity of the liquid remains 

 in the capsule unvaporized the immediate recomposition takes 

 place, and only very feeble traces of negative electricity can be 

 obtained. If the electricity developed by the action of a gas, 

 or by that exerted by a humid body, such as the hand or a piece 

 of wood, upon the metal with which it is in contact, is often 

 much stronger than the electricity resulting from the much live- 

 lier action of a liquid, the reason is, that in the former case the 

 immediate recomposition of the two electrical principles is al- 

 most null, in consequence of the imperfect conductibility of the 

 exciting bodies, and that the electricity produced is almost en- 

 tirely perceived. There is, however, a slight recomposition, 

 for the negative tension of an insulated metal is sensibly aug- 

 mented by giving a translatory motion to the gas which attacks 

 its surface; the consequence of which is, that the positive 

 electricity accumulated in the gas being removed with it, can- 

 not unite with the negative left in the metal*. 



The principle of immediate recomposition of the two elec- 



• The most successful method of performing experiments of this kind is, 

 to take tubes of zinc, copper, or any other metal susceptible of attack, to 

 suspend them to an insulating handle, and cause a current of very dry air 

 mixed with a little chlorine to pass interiorly. If a communication be esta- 

 blished between the metallic tube and an electroscope, it will be found 

 charged with strong positive electricity. The positive electricity carried 

 off by the current of gas may also be collected by causing the current to 

 pass through a tube of platina after it has passed through the metallic tube 

 which it has attacked. 



Third Series. Vol. 11. No. 07. Sept. 1837. 2 O 



