Page:Text-book of Electrochemistry.djvu/132

 Faraday's Laws. — The relationship just mentioned was known to Davy. Faraday (i), working on this fact, in- vestigated the behaviour of one and the same quantity of electricity when it passed through several water-decomposi- tion apparatus which differed in having their poles unequal in size, divided into two, or consisting of different metals, such as platinum, zinc, or copper. These decomposition apparatus were connected in series in a circuit, an arrange- ment which ensures that the same quantity of electricity shall pass through all. By such experiments Faraday found that, no matter how the apparatus was arranged, the same quantity of explosive mixture (hydrogen and oxygen) was obtained in each of them. It was further observed that the same current passing through the apparatus in one case twice as long as in another gave twice as much of the explosive mixture. In other words, a given quantity of electricity corresponds with a certain definite quantity of explosive mixture. The quantity of electricity in coulombs is generally measured by its action on a magnetic needle. Kohlrausch (-5) and Lord Bayleigh (6) have determined that coulombs are required. From this and other determinations (with silver nitrate, etc.) it can be calculated that the charge for 1 gram-equivalent is 96,500 coulombs.

Faraday then sent the same current through several " voltameters " arranged in series, in one of which hydrogen was evolved, in another silver was deposited, in a third copper, etc. As a result of the experiment, he found that equal quantities of electricity decomposed chemically equiva- lent quantities of different substances.

This important result is known as Faraday's (second) law.

Faraday's first law, that the quantities of electricity are proportional to the quantity of decomposed substance, had already been sug gested by Berzelius, but he had not been able to definitely ^prove. it/ (compare pp. 7 and 18).

The simplest conception which can be derived from this

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