In order to obtain a resistance of 0.0001 of an ohm, it is necessary to sensibly satisfy the equation 20,000 l/s = 1/10,000 _l_ expressing the thickness of the voltameter expressed in meters, and _s_ being the section in square millimeters. For example: For l = 1/10, s = 20,000,000, say 20 square meters. It will be seen from this example what should be the proportions of apparatus designed for a production on a large scale. The new principles that permit of the construction of such voltameters are as follows: (1) the substitution of an alkaline for the acid solution, thus affording a possibility of employing iron electrodes; (2) the introduction of a porous partition between the electrodes, for the purpose of separating the gases. _Electrolytic Liquid._--Commandant Renard's experiments were made with 15 per cent, solution of caustic soda and water containing 27 per cent. of acid. These are the proportions that give the maximum of conductivity. Experiments made with a voltameter having platinum electrodes separated by an interval of 3 or 4 centimeters showed that for a determinate E.M.F. the alkaline solution allows of the passage of a slighter intenser current than the acidulated water, that is to say, it is less resistant and more advantageous from the standpoint of the consumption of energy. _Porous Partition._--Let us suppose that the two parts of the trough are separated by a partition containing small channels at right angles with its direction. It is these channels alone that must conduct the electricity. Their conductivity (inverse of resistance) is proportional to their total section, and inversely proportional to their common length, whatever be their individual section. It is, therefore, advantageous to employ partitions that contain as many openings as possible.