The performance of automobiles and of most other powered machines could be upgraded to this level of efficiency by a single technological advance: the development of a device for transforming the energy of chemical bonds directly into electric current. Most devices now used for harnessing the energy of fuel, such as internal-combustion engines, employ a process that involves three or more wasteful steps. Fuel is first burned, a reaction in which electrostatic energy is liberated in the form of heat. The heat is then converted into mechanical energy by the moving parts of the engine. In many installations the mechanical energy is finally transformed back into electrical energy by an alternator or a dynamo. Each transformation proceeds at the cost of wasted energy. For this reason experimenters, both professional and amateur, have long dreamed of developing an inexpensive, compact and durable electrochemical cell that would make the transformation in a single step.

In theory such a cell could be made. The first promising step toward its development was taken by Alessandro Volta 175 years ago. Volta's apparatus, the predecessor of the ordinary dry cell, consisted of small pieces of cloth moistened with brine and sandwiched between alternating disks of zinc and silver. The device was an effective converter of energy, as indicated by Volta's report of an early experiment: "I have finally succeeded in stimulating my sense [of hearing] with my new apparatus. I introduced into my ears two metal rods with rounded ends and joined them to the terminals of the apparatus. At the moment the circuit was completed I received a shock in the head: and a few moments afterward, the circuit remaining closed, I began to hear a noise which I cannot well describe. It was a crackling...or boiling. This disagreeable sensation, which I feared might be dangerous, has deterred me so that I have not repeated the experiment." The energy responsible for Volta's discomfort was liberated at high efficiency in a single step by a chemical reaction in which the metal, particularly the zinc, served as fuel.

A cell that demonstrates essentially the same properties can be assembled inexpensively at home by substituting copper for the silver. The experiment can serve as an introduction to the basic properties of electrochemical cells in general. Both copper and zinc, in the form of sheet metal known as "flashing," can be bought from tinsmiths and from most dealers in hardware.

In order to make a small cell cut the sheets into two-inch squares and scour the surfaces with steel wool. Cut a few similar squares of cotton cloth or paper toweling. Soak them in a saturated solution of table salt and tap water. (Such a solution, at a given temperature, will dissolve no more salt.) Sandwich a sheet of wet cloth or paper between a copper plate and a zinc plate. Place the sandwich between flat wooden blocks and squeeze it with a C-clamp or a vise. Connect the positive terminal of a voltmeter to the copper plate and the negative terminal to the zinc plate. The pointer of the meter will swing to about .8 volt. An ammeter connected in the same way will indicate a current of about 15 milliamperes. The current will drop to approximately five milliamperes within a minute or two as reaction products accumulate in the cell.

Higher voltages can be generated by building a pile of cells. Place the copper plate of one cell on top of the zinc plate of its neighbor below, and so on. Clamp the completed pile and attach lead wires to the end plates. The output potential will increase in direct proportion to the number of cells in the battery. The maximum current delivered by the battery will vary directly with the area of the plates. Volta assembled batteries of 100 or more cells.

With a somewhat similar battery the English chemist Sir Humphry Davy sent electric current through molten salts and in 1807 succeeded in isolating the alkali metals sodium and potassium by electrolysis. Shortly thereafter the Royal Society of London constructed a battery of 2,000 cells, the plates of which measured 2 1/2 feet by six feet. This giant powered the first carbon arc light and led to the discovery of the laws of electrolysis.

Volta's battery, although it was primitive in design, must not be dismissed as a harmless toy. The experimenter working with more than 20 cells must exercise caution. As Volta learned, electricity can make one's head roar; it can also be lethal.

Two factors have limited the usefulness of Volta's apparatus and of its lineal descendants as sources of electrical energy. One is the relatively high cost of the metallic fuel; the other is the fact that the cell consumes itself. The ideal cell would be kept fully charged by a supply of inexpensive fuel such as alcohol or gasoline, and its working parts would have a long service life.

Substantial progress toward meeting these objectives has been made in recent years. Some of the resulting cells are simple enough for amateur construction. For example, Sol M. Gruner of Elmer, N.J., has made working models of two types. One uses hydrogen as fuel and the other uses alcohol.

"My cells," Gruner writes, "were built as an experiment rather than as power sources. Both are small, comparatively inexpensive and designed for easy modification so that various chemical systems can be tested conveniently. The power output is limited to a few milliwatts but is sufficient for accurate measurement by instruments of modest cost. Both cells operate at room temperature and atmospheric pressure.

"Each cell consists of a glass container that can be a large test tube, a beaker or a similar vessel; a cover made of an insulating material such as plastic or rubber, and a pair of electrodes, which are suspended from the cover. The electrodes of the hydrogen cell were made of carbon rods from used dry cells. The rods were drilled lengthwise to form slender cups with walls somewhat less than a sixteenth of an inch thick. The carbons were heated to about 1,500 degrees centigrade to drive off the ammonium chloride and other substances carried over from the dry cells and were then impregnated with two metals that function as catalysts enabling the hydrogen gas to combine with oxygen at room temperature.

"The oxygen electrode, which is the positive terminal of the cell, requires a catalyst of finely divided silver oxide. It was prepared by injecting a concentrated solution of silver nitrate into one of the hollow carbons. The electrode was then drained, dried and heated to redness with a gas torch to decompose the silver nitrate thermally into silver and nitric oxides. The finely divided particles of silver oxide remained in the carbon as the catalyst and the nitric oxide was liberated as gas. I have also experimented with an alternate oxygen catalyst consisting of one part of nickel oxide to 10 parts of cobalt oxide. A concentrated solution of the nitrates of these metals is applied to the electrode and decomposed by the procedure just described.

"Finely divided platinum serves as the catalyst of the hydrogen electrode. Chloroplatinic acid is applied to the carbon and decomposed into platinum black by heat. The acid costs about $10 per gram, but a little goes a long way. A few milligrams of acid adequately coats an electrode made from the carbon of a size-D flashlight cell.

"The open ends of the electrodes are slipped into tightly fitting tubes of rubber or plastic through which the gases are fed to the cell. Leads of copper wire are wrapped in contact with the carbon adjacent to the tubing. The electrodes are then spaced a few millimeters apart and clamped in parallel alignment by a fixture improvised from rigid plastic that is fastened to the cover of the cell. The tubes and leads pass snugly through holes in the cover.

"The cell is completed by immersing the electrodes in a solution made by dissolving 300 grams of potassium hydroxide in one liter of distilled water. A sufficient quantity of this electrolyte is transferred to the cell container for immersing the electrodes. When fuel gas and oxygen are admitted, the cell develops a potential of about 3/4 volt. I generate the hydrogen and oxygen by the electrolysis of water. Gas from the electrolysis apparatus is fed directly to the electrodes through flexible tubing. The rate of gas flow is regulated by adjusting the direct current that energizes the electrolysis apparatus.

"The alcohol cell is based on a demonstration cell that was first described by the Esso Research and Engineering Company. It is more convenient to use than the hydrogen-oxygen cell and appears to operate at higher efficiency. It is also somewhat easier to make because the electrodes consist of 150-mesh nickel screening. They are two inches wide and five inches long. (Nickel screening of this mesh can be obtained from the Newark Wire Cloth Company, 351 Verona Avenue, Newark, N.J. 07104. A sheet six inches square is currently priced at $1.75.)

"One end of each electrode is bent to a right angle and pierced for a nickel-plated machine screw that attaches the screening to the cover of the cell [see Figure 2]. The electrodes must also be coated with catalysts of platinum and silver. The fuel electrode, which is the negative terminal of the cell, is prepared by immersion for one hour in a solution of chloroplatinic acid dissolved in 100 milliliters of distilled water. During immersion the electrode is turned over several times to ensure a uniform coating. Platinum ions in the solution deposit on the nickel in the form of platinum black. Some nickel goes into solution as nickel ions. The oxygen electrode is similarly coated with silver by immersing the second piece of screening for an hour in a solution consisting of five grams of silver nitrate dissolved in 100 milliliters of distilled water. Avoid touching the surfaces of the coated electrodes.

"Both cells use the same electrolyte: a 5.5-molar solution of potassium hydroxide. Any glass vessel that will accommodate the electrodes can be used as the container. I prefer a beaker with a volume of one liter. The container should be filled so that the electrodes will be immersed almost up to the heads of the machine screws. The fuel consists of 35 milliliters of methyl alcohol, which is mixed with the electrolyte. (My experiments indicate that denatured ethyl alcohol works about as well.) A sheet of white filter paper or blotting paper should be inserted between the electrodes to prevent the screens from making accidental contact, which would short-circuit the cell.

"After the fuel has been added a potential of .5 volt will appear across the electrodes. A milliammeter connected to the terminals will indicate an initial current of about 20 milliamperes. At this current the terminal voltage will fall almost to zero because the oxygen electrode will quickly accumulate a coating of fine bubbles that are released by the reaction. Most of the voltage will appear between the electrolyte and the oxygen electrode, across the layer of bubbles.

"The coating can be disrupted by playing a stream of air bubbles continuously over the surfaces of the oxygen electrode. I accomplish this by installing an air dispenser immediately below the electrode. It consists of a short length of rubber tubing, tied closed at one end, that has been pierced several hundred times by a sewing needle. Air from an aquarium compressor is fed to the perforated tubing. The rate of airflow is adjusted by applying a pinch clamp to the supply hose from the compressor to produce a rising cloud of bubbles of pinhead size. The effect of the bubbles on the performance of the cell can be observed by connecting a 100 ohm resistor across the cell as a load and measuring the voltage with and without the air supply. When the switch is closed in the absence of air, the output potential will quickly drop to about .1 volt. When the compressor is started, the voltage will rise almost to its open-circuit value and the power output will approach 10 milliwatts. If the compressed air is replaced by pure oxygen, the output will increase to 30 milliwatts or more. I found that the output can be increased still more by adding 15 milliliters of concentrated sodium hypochlorite to the electrolyte and then slowly injecting hydrogen peroxide under the oxygen electrode at a rate of about five milliliters per hour. The sodium hypochlorite dissociates the hydrogen peroxide, yielding nascent oxygen.

"The cell generates electric current by 'burning' alcohol into formic acid. At the oxygen electrode a molecule of oxygen combines with two molecules of water and four electrons, which are supplied by the electrode, to form four hydroxyl ions. The hydroxyl ions migrate through the electrolyte to the fuel electrode, where they combine with a molecule of alcohol to yield one molecule of formic acid, three molecules of water and four electrons, which make their way back to the oxygen electrode through the external circuit [see illustration above]. The formic acid promptly reacts with the potassium hydroxide to form its salt.

"Although the cell is not intended as a power source, it will operate a small transistor-radio receiver continuously on a single charge of fuel for more than 1,500 hours. At the end of the period the cell can be recharged immediately by adding alcohol. The circuit of an appropriate receiver that can be assembled easily at home is shown in the accompanying illustration [below]. The construction can be simplified by buying a ready-made antenna coil and a variable capacitor from a dealer in radio supplies. The coil-capacitor combination should be capable of tuning from 540 to 1,600 kilocycles."

Every generation includes a substantial number of amateurs who design sundials, a hobby that continues to recruit enthusiasts even in these days when wristwatches are almost as common as shoes. To the collection of unusual dials that have appeared in recent years is now added one that tells clock time and daylight saving time. William C. Boyd, professor of immunochemistry at the Boston University School of Medicine, is the designer. He writes:

"Considering the thousands of years that sundials have been used, it seems unlikely that an amateur could invent a new design. It may well be that mine is not new, but I have never come across one like it, even though it is based on a simple principle. Its novel feature is an adjustable dial. The time, as indicated by the shadow of the gnomon, can be advanced or retarded by rotating the dial, just as a clock can be reset by moving the hour hand.

"The dial must be reset almost every day to keep the indicated time in step with clock time, because the shadow cast by the gnomon 'runs' faster or slower than clocks by a predictable amount that varies throughout the year. This v predictable variation, known as the equation of time, can be recorded as a table-of corrections that dictates the setting of the dial for every day of the year. Data for compiling the table are available in standard references such as The American Ephemeris and Nautical Almanac. (This reference is available in most public libraries and can be bought from the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.) I engraved the table on a metal plate that is mounted on the base of the dial. A photocopy of the table posted indoors would serve as well.

"The instrument can be built by anyone with access to modest workshop facilities. My model was made largely of do-it-yourself aluminum that I bought at a hardware store. The apparatus is held together by brass machine screws that were tapped into the aluminum. I sidestepped the most difficult part of the job-graduating the dial-by using part of a carpenter's square. The square, made of stainless steel, had 1/12-inch graduations. I used a hacksaw to cut a two-foot length, which I then bent into a semicircle [see illustration below]. The semicircle corresponds to a 12-hour interval; the smallest division represents 2 1/2 minutes. All the other dimensions of the instrument are determined by the size of the dial.

"The graduated dial slides on the surface of a semicircular aluminum support and is loosely attached to the support by brass screws that move in slots. The dial is restrained laterally by stops at the edges of the support and is rotated back and forth on its support by a brass rack bent to the same radius and soldered to the dial. The rack is engaged by a pinion gear fixed on one end of a shaft. The opposite end of the shaft is fitted with a knob that extends beyond the edge of the base. To reset the time indicated by the dial one merely turns the knob one way or the other.

"Another handy feature that increases the accuracy of the instrument is a time-equation mechanism that displays the setting of the dial. The mechanism consists of a flat graduated scale, geared to the dial by a pair of straight racks that engage a pair of gears mounted on the adjustment shaft. The graduated scale slides in a set of ways. The driving gears have three times as many teeth as the pinion that engages the rack of the dial, hence the linear displacement of the flat scale exceeds by threefold the movement of the dial. This multiplication of motion increases by threefold the precision with which the dial can be set. A change of 1/4 inch corresponds to a time interval of 2 1/2 minutes. The scale of the indicator was cut from a machinist's steel rule. I ruled a vernier scale by hand. The vernier is fixed to the base of the instrument, adjacent to the graduated edge of the machinist's rule.

"The gnomon consists of a 9.4-inch length of No. 26-gauge silver wire supported 7.64 inches above the dial by a pair of adjustable blocks carried by arms made of aluminum strips. The base of the instrument is constructed for rotation in both declination and azimuth, so that the gnomon can be pointed both to true north and parallel to the earth's axis. When the gnomon is so aligned, it is possible even without reference to the vernier scale to set the dial to within 15 seconds of local clock time. On July 11 of this year I made a total of 18 readings, spaced roughly 40 minutes apart, and checked each reading against a good watch that had been set by reference to time signals broadcast by radio station WWV of the National Bureau of Standards. The maximum error amounted to +.5 minute and the average error to +/-.17 minute, or about 10 seconds. Many watches are not as good. Moreover, errors made by the sundial are not cumulative. On the other hand, one does need the sun."

Bibliography

HOW TO MAKE A DEMONSTRATION FUEL CELL. Esso Research and Engineering Company, 1961.

SYMPOSIUM ON FUEL CELLS. Ernst G. Baars, Chairman. 12th Annual Battery Research and Development Conference Proceedings. United States Army Signal Research and Development Laboratory, Fort Monmouth, N.J., 1958.

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