The different porcelains and earths behave, from this point of view, in a very unequal manner. For example, an earthen vessel from the Pillivayt establishment supports some decimeters of water, while the porcelain of Boulanger, at Choisy-le-Roi, allows of the passage of the gas only at pressures greater than one atmosphere, which is much more than is necessary. Wire gauze, canvas, and asbestos cloth resist a few centimeters of water. It might be feared, however, that the gases, violently projected against these partitions, would not pass, owing to the velocity acquired. Upon this point experiment is very reassuring. After filling with water a canvas bag fixed to the extremity of a rubber tube, it is possible to produce in the interior a tumultuous disengagement of gas without any bubbles passing through.

FIG. 2. - ARRANGEMENT FOR THE STUDY OF CAPILLARY REACTION IN POROUS VESSELS.

From an electrical point of view, partitions are of very unequal quality. Various partitions having been placed between electrodes spaced three centimeters apart, currents were obtained which indicated that, with the best of porcelains, the rendering of the apparatus is diminished by one-half. Asbestos cloth introduces but an insignificant resistance.

To this inconvenience of porous vessels is added their fragility, their high price, and the impossibility of obtaining them of the dimensions that large apparatus would call for. The selection of asbestos cloth is therefore clearly indicated; but, as it does not entirely separate the gases, except at a pressure that does not exceed a few centimeters of water, it was always necessary to bring back the variation of the level to these narrow limits by a special arrangement. We cannot, in fact, expect that the entire piping shall be always in such conditions that no difference in pressure can occur. The levels are brought back to equality within the effective limits by interposing between the voltameter and the piping an apparatus called a compensator, which consists of two vessels that communicate in the interior part through a large tube. The gases enter each vessel through a pipe that debouches beneath the level of the water. If a momentary stoppage occurs in one of the conduits, the water changes level in the compensator, but the pressure remains constant at the orifice of the tubes. The compensator is, as may be seen, nothing more than a double Mariotte flask.

When it is desired to obtain pure gases, there is introduced into the compensator a solution of tartaric acid, which retains the traces of alkalies carried along by the current of gas. The alkaline solution, moreover, destroys the ozone at the moment of its formation.

It will be seen that laboratory studies have furnished all the elements of a problem which is now capable of entering the domain of practice. The cheapness of the raw materials permits of constructing apparatus whose dimensions will no longer be limited except by reasons of another nature. The electrodes may be placed in proximity at will, owing to the use of the porous partition. It may be seen, then, that the apparatus will have a considerable useful effect without its being necessary to waste the electric energy beyond measure.

Industrial Apparatus

We have shown how the very concise researches of Commandant Renard have fixed the best conditions for the construction of an industrial voltameter. It remains for us to describe this voltameter itself, and to show the rendering of it.

FIG. 3. - PLANT FOR THE INDUSTRIAL ELECTROLYSIS OF WATER.

The industrial voltameter consists of a large iron cylinder. A battery of such voltameters is shown to the left of Fig. 3, and one of the apparatus, isolated, is represented in Fig. 4. The interior electrode is placed in an asbestos cloth bag, which is closed below and tied at its upper part. It is provided with apertures which permit of the ascent of the gases in the interior of the cylinder. The apparatus is hermetically sealed at the top, the two electrodes being naturally insulated with rubber. Above the level of the liquid the interior electrode is continuous and forms a channel for the gas. The hydrogen and oxygen, escaping through the upper orifices, flow to the compensator. The apparatus is provided with an emptying cock or a cock for filling with distilled water, coming from a reservoir situated above the apparatus.

FIG. 4. - DETAILS OF AN INDUSTRIAL VOLTAMETER.

The constants of the voltameter established by Commandant Renard are as follows:

The iron plate employed is 2 millimeters in thickness. The electric resistance is about 0.0075 ohm. The apparatus gives 365 amperes under 2.7 volts, and consequently nearly 1 kilowatt. Its production in hydrogen is 158 liters per hour.

It is clear that, in an industrial exploitation, a dynamo working under 3 volts is never employed. In order to properly utilize the power of the dynamo, several voltameters will be put in series - a dozen, for example, if the generating machine is in proximity to the apparatus, or a larger number if the voltameters are actuated by a dynamo situated at a distance, say in the vicinity of a waterfall. Fig. 3 will give an idea of a plant for the electrolysis of water.

It remains for us to say a few words as to the net cost of the hydrogen and oxygen gases produced by the process that we have just described. We may estimate the value of a voltameter at a hundred francs. If the apparatus operates without appreciable wear, the amortizement should be calculated at a very low figure, say 10 per cent., which is large. In continuous operation it would produce more than 1,500 cubic meters of gas a year, say a little less than one centime per cubic meter. The caustic soda is constantly recuperated and is never destroyed. The sole product that disappears is the distilled water. Now one cubic meter of water produces more than 2,000 cubic meters of gas. The expense in water, then, does not amount to a centime per cubic meter. The great factor of the expense resides in the electric energy. The cost of surveillance will be minimum and the general expenses ad libitum.

Let us take the case in which the energy has to be borrowed from a steam engine. Supposing very small losses in the dynamo and piping, we may count upon a production of one cubic meter of hydrogen and 500 cubic decimeters of oxygen for 10 horse-power taken upon the main shaft, say an expenditure of 10 kilogrammes of coal or of about 25 centimes - a little more in Paris, and less in coal districts. If, consequently, we fix the price of the cubic meter of gas at 50 centimes, we shall preserve a sufficient margin. In localities where a natural motive power is at our disposal, this estimate will have to be greatly reduced. We may, therefore, expect to see hydrogen and oxygen take an important place in ordinary usages. From the standpoint alone of preservation of fuel, that is to say, of potential energy upon the earth, this new conquest of electricity is very pleasing. Waterfalls furnish utilizable energy in every locality, and, in the future, will perhaps console our great-grandchildren for the unsparing waste that we are making of coal. - La Nature.

[Continued from SUPPLEMENT, No. 818, page 13066.]