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Scientific American Supplement, No. 819, September 12, 1891试读：
THE PRODUCTION OF HYDROGEN AND OXYGEN THROUGH THE ELECTROLYSIS OF WATER.
All attempts to prepare gaseous fluids industrially were premature as long as there were no means of carrying them under a sufficiently diminished volume. For a few years past, the trade has been delivering steel cylinders that permit of storing, without the least danger, a gas under a pressure of from 120 to 200 atmospheres. The problem of delivery without pipe laying having been sufficiently solved, that of the industrial production of gases could be confronted in its turn. Liquefied sulphurous acid, chloride of methyl, and carbonic acid have been successively delivered, to commerce. The carbonic acid is now being used right along in laboratories for the production of an intense coldness, through its expansion. Oxygen and nitrogen, prepared by chemical processes, soon followed, and now the industrial electrolysis of water is about to permit of the delivery, in the same manner, of very pure oxygen and hydrogen at a price within one's reach.
Before describing the processes employed in this preparation, we must answer a question that many of our readers might be led to ask us, and that is, what can these gases be used for? We shall try to explain. A prime and important application of pure hydrogen is that of inflating balloons. Illuminating gas, which is usually employed for want of something better, is sensibly denser than hydrogen and possesses less ascensional force, whence the necessity of lightening the balloon or of increasing its volume. Such inconveniences become serious with dirigible balloons, whose surface, on the contrary, it is necessary to diminish as much as possible. When the increasing interest taken in aerostation at Paris was observed, an assured annual output of some hundreds of cubic meters of eras for the sole use of balloons was foreseen, the adoption of pure hydrogen being only a question of the net cost.
Pure or slightly carbureted hydrogen is capable of being substituted to advantage for coal gas for heating or lighting. Such an application is doubtless somewhat premature, but we shall see that it has already got out of the domain of Utopia. Finally the oxyhydrogen blowpipe, which is indispensable for the treatment of very refractory metals, consumes large quantities of hydrogen and oxygen.
For a few years past, oxygen has been employed in therapeutics; it is found in commerce either in a gaseous state or in solution in water (in siphons); it notably relieves persons afflicted with asthma or depression; and the use of it is recommended in the treatment of albumenuria. Does it cure, or at least does it contribute to cure, anæmia, that terrible affection of large cities, and the prime source of so many other troubles? Here the opinions of physicians and physiologists are divided, and we limit ourselves to a mention of the question without discussing it.
Only fifteen years ago it would have been folly to desire to obtain remunerative results through the electrolysis of water. Such research was subordinated to the industrial production of electric energy.
We shall not endeavor to establish the priority of the experiments and discoveries. The question was in the air, and was taken up almost simultaneously by three able experimenters—a Russian physicist, Prof. Latchinof, of St. Petersburg, Dr. D'Arsonval, the learned professor of the College of France, and Commandant Renard, director of the military establishment of aerostation at Chalais. Mr. D'Arsonval collected oxygen for experiments in physiology, while Commandant Renard naturally directed his attention to the production of pure hydrogen. The solutions of the question are, in fact, alike in principle, and yet they have been developed in a very different manner, and we believe that Commandant Renard's process is the completest from an industrial standpoint. We shall give an account of it from a communication made by this eminent military engineer, some time ago, to the French Society of Physics.
Transformations of the Voltameter.—In a laboratory, it is of no consequence whether a liter of hydrogen costs a centime or a franc. So long as it is a question of a few liters, one may, at his ease, waste his energy and employ costly substances.
The internal resistance of a voltameter and the cost of platinum electrodes of a few grammes should not arrest the physicist in an experiment; but, in a production on a large scale, it is necessary to decrease the resistance of the liquid column to as great a degree as possible—that is to say, to increase its section and diminish its thickness. The first condition leads to a suppression of the platinum, and the second necessitates the use of new principles in the construction of the voltameter. A laboratory voltameter consists either of a U-shaped tube or of a trough in which the electrodes are covered by bell glasses (Fig. 1, A and B). In either case, the electric current must follow a tortuous and narrow path, in order to pass from one electrode to the other, while, if the electrodes be left entirely free in the bath, the gases, rising in a spreading form, will mix at a certain height. It is necessary to separate them by a partition (Fig. 1, C). If this is isolating and impermeable, there will be no interest in raising the electrodes sensibly above its lower edge. Now, the nearer together the electrodes are, the more it is necessary to lower the partition. The extension of the electrodes and the bringing of them together is the knotty part of the question. This will be shown by a very simple calculation.FIG. 1.—A, B, COMMONEST FORMS OF LABORATORY VOLTAMETERS. C, DIAGRAM SHOWING ASCENT OF BUBBLES IN A VOLTAMETER.
The visible electrolysis of water begins at an E.M.F. of about 1.7 V. Below this there is no disengagement of bubbles. If the E.M.F. be increased at the terminals of the voltameter, the current (and consequently the production of gas) will become proportional to the excess of the value over 1.7 V; but, at the same time, the current will heat the circuit—that is to say, will produce a superfluous work, and there will be waste. At 1.7 V the rendering is at its maximum, but the useful effect is nil. In order to make an advantageous use of the instruments, it is necessary to admit a certain loss of energy, so much the less, moreover, in proportion as the voltameters cost less; and as the saving is to be effected in the current, rather than in the apparatus, we may admit the use of three volts as a good proportion—that is to say, a loss of about half the disposable energy. Under such conditions, a voltameter having an internal resistance of 1 ohm produces 0.65 liter of hydrogen per hour, while it will disengage 6.500 liters if its resistance be but 0.0001 of an ohm. It is true that, in this case, the current would be in the neighborhood of 15,000 amperes. Laboratory voltameters frequently have a resistance of a hundred ohms; it would require a million in derivation to produce the same effect. The specific resistance of the solutions that can be employed in the production of gases by electrolysis is, in round numbers, twenty thousand times greater than that of mercury. 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.
The separating effect of these partitions for the gas is wholly due to capillary phenomena. We know, in fact, that water tends to expel gas from a narrow tube with a pressure inversely proportional to the tube's radius. In order to traverse the tube, the gaseous mass will have to exert a counter-pressure greater than this capillary pressure. As long as the pressure of one part and another of the wet wall differs to a degree less than the capillary pressure of the largest channel, the gases disengaged in the two parts of the trough will remain entirely separate. In order that the mixing may not take place through the partition above the level of the liquid (dry partition), the latter will have to be impenetrable in every part that emerges. The study of the partitions should be directed to their separating effect on the gases, and to their electric resistance. In order to study the first of these properties, the porous partition, fixed by a hermetical joint to a glass tube, is immersed in the water (Fig. 2). An increasing pressure is exerted from the interior until the passage of bubbles is observed. The pressure read at this moment on the manometer indicates (transformed above the electrolytic solution) the changes of level that the bath may undergo. 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:Height ofexternalelectrode3.405 m."internal"3.290 m.Diameter ofexternal"0.300 m."internal"0.174 m.
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.]
MUSICAL INSTRUMENTS: THEIR CONSTRUCTION AND CAPABILITIES.
By A.J. HIPKINS, F.S.A.LECTURE II.
I will now invite your attention to the wind instruments, which, in Handel's time, were chiefly used to double in unison the parts of stringed instruments. Their modern independent use dates from Haydn; it was extended and perfected by Mozart, Beethoven, and Weber; and the extraordinary changes and improvements which have been effected during the present century have given wind instruments an importance that is hardly exceeded by that of the stringed, in the formation of the modern orchestra. The military band, as it now exists, is a creation of the present century.
The so-called wood wind instruments are the flute, oboe, bassoon, and clarinet. It is as well to say at once that their particular qualities of tone do not absolutely depend upon the materials of which they are made. The form is the most important factor in determining the distinction of tone quality, so long as the sides of the tube are equally elastic, as has been submitted to proof by instruments made of various materials, including paper. I consider this has been sufficiently demonstrated by the independent experiments of Mr. Blaikley, of London, and Mr. Victor Mahillon, of Brussels. But we must still allow Mr. Richard Shepherd Rockstro's plea, clearly set forth in a recently published treatise on the flute, that the nature and the substance of the tube, by reciprocity of vibration, exercise some influence, although not so great as might have been expected, on the quality of the tone. But I consider this influence is already acknowledged in my reference to equality of elasticity in the sides of the tube.
The flute is an instrument of embouchure—that is to say, one in which a stream of air is driven from the player's lips against an edge of the blow hole to produce the sound. The oboe and bassoon have double reeds, and the clarinet a single reed, made of a species of cane, as intermediate agents of sound production. There are other flutes than that of embouchure—those with flageolet or whistle heads, which, having become obsolete, shall be reserved for later notice. There are no real tenor or bass flutes now, those in use being restricted to the upper part of the scale. The present flute dates from 1832, when Theobald Boehm, a Bavarian flute player, produced the instrument which is known by his name. He entirely remodeled the flute, being impelled to do so by suggestions from the performance of the English flautist, Charles Nicholson, who had increased the diameter of the lateral holes, and by some improvements that had been attempted in the flute by a Captain Gordon, of Charles the Tenth's Swiss Guard. Boehm has been sufficiently vindicated from having unfairly appropriated Gordon's ideas. The Boehm flute, since 1846, is a cylindrical tube for about three-fourths of its length from the lower end, after which it is continued in a curved conical prolongation to the cork stopper. The finger holes are disposed in a geometrical division, and the mechanism and position of the keys are entirely different from what had been before. The full compass of the Boehm flute is chromatic, from middle C to C, two octaves above the treble clef C, a range of three octaves, which is common to all concert flutes, and is not peculiar to the Boehm model. Of course this compass is partly produced by altering the pressure of blowing. Columns of air inclosed in pipes vibrate like strings in sections, but, unlike strings, the vibrations progress in the direction of length, not across the direction of length. In the flute, all notes below D, in the treble clef, are produced by the normal pressure of wind; by an increasing pressure of overblowing the harmonics, D in the treble clef, and A and B above it, are successively attained. The fingerholes and keys, by shortening the tube, fill up the required intervals of the scale. There are higher harmonics still, but flautists generally prefer to do without them when they can get the note required by a lower harmonic. In Boehm's flute, his ingenious mechanism allows the production of the eleven chromatic semitones intermediate between the fundamental note of the flute and its first harmonic, by holes so disposed that, in opening them successively, they shorten the column of air in exact proportion. It is, therefore, ideally, an equal temperament instrument and not a D major one, as the conical flute was considered to be. Perhaps the most important thing Boehm did for the flute was to enunciate the principle that, to insure purity of tone and correct intonation, the holes must be put in their correct theoretical positions; and at least the hole below the one giving he sound must be open, to insure perfect venting. Boehm's flute, however, has not remained as he left it. Improvements, applied by Clinton, Pratten, and Carte, have introduced certain modifications in the fingering, while retaining the best features of Boehm's system. But it seems to me that the reedy quality obtained from the adoption of the cylindrical bore which now prevails does away with the sweet and characteristic tone quality of the old conical German flute, and gives us in its place one that is not sufficiently distinct from that of the clarinet.
The flute is the most facile of all orchestral wind instruments; and the device of double tonguing, the quick repetition of notes by taking a staccato T-stop in blowing, is well known. The flute generally goes with the violins in the orchestra, or sustains long notes with the other wood wind instruments, or is used in those conversational passages with other instruments that lend such a charm to orchestral music. The
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