By grouping the simple circles forming a voltaic battery in various numerical relations, the _quantity_ and _intensity_ effects are modified. Thus, if a series of thirty pairs of Grove's battery are all connected together in consecutive order, the smallest _quantity_ and the largest _intensity_ effect is produced. If changed to two groups of fifteen each, the quantity is doubled--that is to say, it will produce double the quantity of the mixed gases from the voltameter with half the intensity. If arranged in three groups of ten each, it is trebled with a proportional loss of intensity, until the grouping reaches six series of five each, when a maximum supply of the mixed gases is obtained from the voltameter. In arranging the groups, all the zinc ends of each series are connected, and all the platinum ends are likewise joined by proper wires. _Sixth Experiment._ A plate-glass trough, containing a few grains of iodide of potassium dissolved in water with some starch, is quickly decomposed into its elements by placing in two platinum plates and connecting them with the wires of the voltaic battery. If the glass trough is divided in the centre with a bit of cardboard, the purple colour of the iodine and starch is shown very beautifully on one side, but not on the other, as iodine is liberated at one pole and the alkali at the other. (Fig. 185.) [Illustration: Fig. 185. A A. A glass trough containing the salt dissolved in water, and divided temporarily with a bit of cardboard, B. C C are the two platinum plates connected with the battery, and the shaded side is supposed to represent the liberation of the iodine.] _Seventh Experiment._ Some solution of common salt coloured with sulphate of indigo and placed in the trough is decomposed into chlorine, which bleaches one side of the indigo solution, and the alkali liberated on the other does not affect it. _Eighth Experiment._ Some nitrate of potash dissolved in water and coloured with litmus placed in the glass trough, changes red on one side of the cardboard by the liberation of acid, and is not affected on the other. In these experiments the oxygen, iodine, chlorine, and nitric acid are liberated at the electro-positive pole, and are hence termed electro-negative bodies, whilst hydrogen and the alkalies are set free at the electro-negative pole, and are therefore called electro-positive bodies. [Page 200] Faraday has modified these terms, and calls the two classes "_anions_" and "_cathions_," and the two poles "anodes" and "cathodes."