Page:Outlines of Physical Chemistry - 1899.djvu/202

 184 OUTLINES OF PHYSICAL CHEMISTRY

electromotive force of one volt. When the current- strength is one ampSre the unit of quantity passes in one second, and this unit is called one coulomb.

When one coulomb experiences a fall of potential of ergs is transformed into some other form of energy (heat, light, motion, chemical energy, &c).

A small calorie is equivalent to about 427 gram-metres, or better (according to Bowland, at the temperature 18°) to 41,880,000 ergs.

Volt x coulomb, that is, the unit of electrical energy, is equal to 10 7 ergs, and equivalent to 10,210 gram-centi- metres or 0*24 calorie.

Faraday's Law. — Bodies which allow electricity to pass through them may be divided into two classes. Con- ductors of the first class, such as the metals and certain varieties of carbon, &c, transmit the electric current without suffering any chemical change. As a rule their conductivity diminishes as the temperature rises.

Conductors of the second class, or electrolytes, only transmit the current through the intervention of a chemical decomposition. Their conductivity, on the contrary, increases with the temperature. To this group fused or dissolved salts belong as well as bases and acids in aqueous solution. The effect of the passage of the current is to decompose these substances into their ions. The cathion which is of an electropositive nature moves with the current and separates at the negative electrode or cathode. The anion moves in the opposite direction and is separated at the anode. The following are some examples of electrolytic decomposition :

Oathion Anion . K 4 FeCy s . K, FeCy,

The ions separated by electrolysis do not always remain free, but frequently react with the electrode or with the solvent.

�� �Cathion

�Anion

� �KC1.

�. K

�CI

�K 4 FeCy a.

�K,S0 4.

�K^eCy,.

�KGjHA

�. K

�CsHgOj

� �� �