Speaker 1: Section twenty five of the Science History of the Universe,
Speaker 1: Volume three. This is a LibriVox recording. All LibriVox recordings
Speaker 1: are in the public domain. For more information or to volunteer,
Speaker 1: please visit LibriVox dot org. The Science History of the Universe,
Speaker 1: Volume three, edited by Francis Rolt Wheeler. Electricity, Chapter seven
Speaker 1: The development of electrochemistry. The striking effects brought about by
Speaker 1: electricity formed the subject of much study about the middle
Speaker 1: of the eighteenth century. At that time, friction electrical machines
Speaker 1: were in use, and in order to intensify the effects produced,
Speaker 1: very large machines were constructed. The most famous of these
Speaker 1: is still to be seen in the Taylor Museum in Harlem.
Speaker 1: Pater Baccaria some one hundred and thirty years ago. By
Speaker 1: using such machines, found that metals could be revivified, that is,
Speaker 1: reduced from their calcis oxides, when the electric spark was
Speaker 1: passed between two pieces. In this way, he obtained zinc
Speaker 1: and mercury. Some time later, Priestley investigated the action of
Speaker 1: the electric spark on air and observed that an acid
Speaker 1: was produced. He mistook this for carbonic acid until Cavendish
Speaker 1: recognized it as nitric acid. Van Marum studied the behavior
Speaker 1: of several other gases in this path of the electric spark,
Speaker 1: which led him to notice the formation of ozone, and
Speaker 1: made experiments also by passing the spark through liquids. Before him,
Speaker 1: Priestley had discovered that in oil and ether, the electric
Speaker 1: spark produces gas, and proved that this gas contained hydrogen.
Speaker 1: The first actual electrolysis was made by Demon and Pates
Speaker 1: von Truswick and Harlem in seventeen eighty nine, in which
Speaker 1: they successfully decomposed water into hydrogen and oxygen. In their experiments,
Speaker 1: the water was contained in a cylindrical tube, closed at
Speaker 1: the top and having a metal wire sealed into its
Speaker 1: upper end. Another metal wire was interduced into the lower
Speaker 1: end of the tube, which dipped into a basin of water.
Speaker 1: When the spark struck through the water, bubbles of gas
Speaker 1: were disengaged from the metal wires and rising in the
Speaker 1: tube gradually displaced the water. As soon as the column
Speaker 1: of water sank below the upper electrode, the gas, which
Speaker 1: was a mixture of hydrogen and oxygen, exploded. This experiment
Speaker 1: was later repeated by Ritter using silver wires and a
Speaker 1: solution of a silver salt, and he observed that the
Speaker 1: negative pole became coated with precipitated silver. On changing the poles,
Speaker 1: silver was dissolved from one and deposited on the other,
Speaker 1: now the negative pole. In Deemon's experiment, oxygen and hydrogen
Speaker 1: were simultaneously formed both at the positive and at the
Speaker 1: negative poles, so that the process was not a true
Speaker 1: electrolytic one like that of Fritters. The whole state of
Speaker 1: the science was changed in a great degree by the
Speaker 1: discoveries of Galvani, and particularly by those of Volta. In
Speaker 1: seventeen ninety five, Volta arranged the metals in a series
Speaker 1: according to the their behavior in galvanic experiments, and in
Speaker 1: seventeen ninety eight Ritter showed that the same series is
Speaker 1: obtained when the properties of the metals to separate other
Speaker 1: metals from their salt solutions are compared. Quote. After the
Speaker 1: introduction of Volta's pile in eighteen hundred, the physiological and
Speaker 1: optical phenomena were less studied quote remarks Spen Aarnius in
Speaker 1: his textbook of Electric Chemistry quote, and more attention was
Speaker 1: paid to the chemical actions as opposed to the electrical machines.
Speaker 1: These piles gave large quantities of electricity at a comparatively
Speaker 1: low potential. Nicholson and Carlisle in eighteen hundred studied the
Speaker 1: evolution of oxygen and hydrogen in salt solutions at immersed
Speaker 1: gold electrodes which were connected with the poles of a
Speaker 1: voltaic pile, and observed that litmis in the neighborhood of
Speaker 1: the positive pole was turned red by the acid produced there.
Speaker 1: Some years later, Davy made his brilliant electrochemical discoveries. He
Speaker 1: succeeded in decomposing the oxides of the alkali and alkaline
Speaker 1: earth metals, which had previously been regarded as elementary substances,
Speaker 1: and in preparing the pure metals. Further progress in obtaining
Speaker 1: the more difficultly reducible metals in this way was later
Speaker 1: made by Bunsen and his pupils. At the time of
Speaker 1: Davy's discovery of the alkali metals, Brasilius was just beginning
Speaker 1: his scientific investigations. In one of the first of these,
Speaker 1: carried out jointly with Hissinger, he studied the action of
Speaker 1: the electric current upon solutions of various inorganic substances, resulting
Speaker 1: chiefly in the establishment of the first electrochemical theory. This
Speaker 1: theory dominated the science of chemistry for many decades. According
Speaker 1: to it, each chemical atom, when in contact with another, possesses,
Speaker 1: like a magnet, an electropositive and an electronegative pole. Moreover,
Speaker 1: one of these poles is usually much stronger than the other. Consequently,
Speaker 1: an atom behaves as if it possessed but one pole,
Speaker 1: either electropositive or electronegative, according as the positive or negative pull, respectively,
Speaker 1: predominates in strength. The magnitude and sign of this resultant
Speaker 1: polarity upon the atoms of a given element determines its
Speaker 1: chemical behavior. If, for instance, the atoms of an element
Speaker 1: are electropositive, it will react with elements whose atoms are electronegative,
Speaker 1: and conversely, during this reaction, the two kinds of electricity
Speaker 1: neutralize each other more or less completely, according to the
Speaker 1: degree of inequality existing between the positive and negative charges
Speaker 1: upon the reacting atoms. If complete neutralization does not take place,
Speaker 1: the resulting compound itself is electropositive or electronegative, according as
Speaker 1: the electropositive are greater or less than the electronegative charges
Speaker 1: upon the component atoms. Compounds which thus possess a resultant polarity,
Speaker 1: may then enter into further combinations with each other in
Speaker 1: such a way as to form a complex compound which
Speaker 1: is more nearly or quite neutral. Thus, the theory explains
Speaker 1: not only the formation of simple compounds from their elements,
Speaker 1: but also the formation of complex compounds such as double salts,
Speaker 1: from their component simple compounds. According to this theory, chemical
Speaker 1: and electrical processes are closely related, and all compounds have
Speaker 1: a dualistic nature, being formed of an electropositive and an
Speaker 1: electronegative component. This theory is therefore known as the electrochemical
Speaker 1: or dualistic theory. It was applied throughout the domain of
Speaker 1: inorganic chemistry, which at that time was practically the entire
Speaker 1: science of chemistry, and although it contained many arbitrary assumptions,
Speaker 1: it performed a great service to science because of its
Speaker 1: systematizing influence. For several decades after the establishment of the
Speaker 1: dualistic theory, no considerable advance was made in electrochemistry. This
Speaker 1: lack of progress was soon counterbalanced by the important discoveries
Speaker 1: which were made by Faraday about the year eighteen thirty five.
Speaker 1: He was the first to show that whether electricity is
Speaker 1: produced by friction or by means of a voltaic pile,
Speaker 1: it is capable of producing the same effects. This fact
Speaker 1: convinced him that there exists but one kind of positive
Speaker 1: and one of negative electricity. He next attempted to discover
Speaker 1: a relation between the quantity of electricity flowing through a
Speaker 1: circuit and the magnitude of the chemical and magnetic effects
Speaker 1: which it could produce. His results may be expressed as follows.
Speaker 1: The magnitude of the chemical and magnetic effects produced in
Speaker 1: a circuit by an electric current is proportional to the
Speaker 1: quantity of electricity which passes through the current. A further
Speaker 1: discovery was made by Faraday by comparing the quantities of
Speaker 1: different substances and solution which are decomposed by the same
Speaker 1: quantity of electricity. This comparison may be made in a
Speaker 1: very simple manner by connecting into one circuit a series
Speaker 1: of solutions of different substances, so that the same quantity
Speaker 1: of electricity passes through each solution. The chemical decomposition produced
Speaker 1: by the electric current in each solution may then be
Speaker 1: ded determined by analysis. Their results obtained may be summarized
Speaker 1: as follows. The quantities of the different substances which separate
Speaker 1: at the electrodes throughout the circuit are directly proportional to
Speaker 1: their equivalent weights, and are independent of the concentration and
Speaker 1: the temperature of the solutions, the size of the electrodes,
Speaker 1: and all other circumstances. Those who first recognized the decomposition
Speaker 1: of water by the electric current sought an explanation for
Speaker 1: the simultaneous appearance of hydrogen at one electrode and of
Speaker 1: oxygen at the other. It was not until eighteen o five, however,
Speaker 1: that a comprehensive theory for this phenomenon was put forward.
Speaker 1: During that year, such a theory was published by Grotus.
Speaker 1: According to this theory, the electric current charges one electrode
Speaker 1: positively and the other negatively, and these charged electrodes then
Speaker 1: exert an electrical influence upon the water molecules. Under this influence,
Speaker 1: the water molecules acquire a polarity, the hydrogen atom becoming
Speaker 1: charged with positive and the oxygen atom with negative electricity.
Speaker 1: The positive electrode then attracts the negatively charged oxygen atom
Speaker 1: and the negative electrode the positively charged hydrogen atom, causing
Speaker 1: the water molecules to arrange themselves in a row or chain.
Speaker 1: As science gradually developed, the imperfections of the theory advanced
Speaker 1: by Grotis became more and more apparent. According to this theory,
Speaker 1: the splitting of the molecule, which is necessary for the
Speaker 1: conduction of electricity, cannot take place until the electromotive force
Speaker 1: is sufficiently great to overcome the affinity or cohesion between
Speaker 1: the two components of a given compound. As a matter
Speaker 1: of fact, however, it was found that under suitable conditions
Speaker 1: of experiment, it is possible to cause an electric current
Speaker 1: to pass through a solution even when the electromotive force
Speaker 1: of the current is extremely small. Clausius was the first
Speaker 1: to direct attention to the disagreement of the Grotis theory
Speaker 1: or conception of all electrolysis with facts. Basing his conclusions
Speaker 1: upon the experimental results already obtained, he declared, quote every
Speaker 1: assumption to be inadmissible which requires the natural condition of
Speaker 1: a solution of an electrolyte to be one of equilibrium,
Speaker 1: in which every positive ion is firmly combined with its
Speaker 1: negative ion, and which at the same time requires the
Speaker 1: action of a definite force in order to change this
Speaker 1: condition of equilibrium, into another, differing from it only in
Speaker 1: that some of the positive ions have combined with other
Speaker 1: negative ions than those with which they were formerly combined.
Speaker 1: Every such assumption is in contradiction to Ohm's law. At
Speaker 1: about the same time that Clausius advanced this theory, Hitchhorf
Speaker 1: began work upon the migration of the ions, and a
Speaker 1: little later coal Rausch commenced experiments upon the electrical conduction
Speaker 1: of solution. The work of these investigators greatly increased the
Speaker 1: knowledge of the process of electrolysis. Making use of their work,
Speaker 1: Ireneus in eighteen eighty seven replaced the theory of vibrating
Speaker 1: ions of Clausius by the theory of free ions. According
Speaker 1: to the material conception of electricity, an ion may be
Speaker 1: considered to be a compound of positive or negative electrons
Speaker 1: with the element in question. The formation of an ion
Speaker 1: is then entirely analogous to the formation of a compound
Speaker 1: from two ordinary elements. For instance, in the formation of
Speaker 1: ions from sodium iodide, the sodium atoms combined with positive
Speaker 1: and the iodine atoms with negative electrons. This conception is
Speaker 1: very comprehensive, for, according to it, the law of electrochemical change.
Speaker 1: Faraday's law appears as a consequence of the laws of
Speaker 1: definite and multiple proportion. Although the theory of electrolytic disassociation
Speaker 1: was not spared great opposition in its early years, it
Speaker 1: has successfully advanced until at the present time, by far
Speaker 1: the greater number of investigators accept it and recognize its value.
Speaker 1: It would be impotois possible to give, in a few
Speaker 1: words a clear conception of all the reasons which led
Speaker 1: Erhnius to adopt his now almost universally accepted views. Unquote,
Speaker 1: says Langbine in his Electrodeposition of metals quote, and a
Speaker 1: short statement of these views must therefore suffice. He discovered that,
Speaker 1: according to the degree of dilution and the nature of
Speaker 1: their combination, salts and aqueous solutions are, to a more
Speaker 1: or less far reaching extent, decomposed into independent portions, that is,
Speaker 1: the ions, and the term electrolytic dissociation is applied to
Speaker 1: this phenomenon. Only combinations which dissociate are decomposed, and thus
Speaker 1: form ions can be conductors of the current, the progressive
Speaker 1: motion of the latter being solely taken care of and
Speaker 1: affected by the ions. The ions are supposed to be
Speaker 1: charged with a certain quantity of electricity, the cathions with
Speaker 1: positive the anions with negative electricity, and so long as
Speaker 1: current passes through to the electrolyte, they move free in
Speaker 1: the latter. However, when a current is conducted through the electrolyte,
Speaker 1: the ions are attracted by the electrodes, the positively charged
Speaker 1: cathions by the negatively charged cathode, and the negatively charged
Speaker 1: anions by the positively charged anode. By reason of these
Speaker 1: movements of the ions to the electrodes, this phenomenon is
Speaker 1: called migration of the ions. The ions, on reaching the
Speaker 1: electrodes are freed of their charge, that is, they yield
Speaker 1: their electricity to the electrodes. They lose thereby their ion nature,
Speaker 1: being transformed by their separation on the electrodes into the
Speaker 1: allotropic or isomeric form of the element or combination. After
Speaker 1: the true action of Volta's pile had been discovered, the
Speaker 1: first modification was to immerse the plates of copper and
Speaker 1: zinc in the liquid. This arrangement gave a more powerful
Speaker 1: and lasting effect than the original pile. Volta arranged the
Speaker 1: cells in a circle and called such a battery a
Speaker 1: crown of cups. In eighteen o six, the Royal Institution
Speaker 1: of London became possessed of a battery of two thousand
Speaker 1: elements on the trough system. It was with this apparatus
Speaker 1: that Davy succeeded in decomposing potash and soda. This simple
Speaker 1: type of cell would, however, only work for a short
Speaker 1: time on account of the collection of bubbles of gas
Speaker 1: on the plates. That is, the cells became polarized. Beccarel
Speaker 1: studied this effect and succeeded in overcoming it to a
Speaker 1: great extent in eighteen twenty nine by employing two different
Speaker 1: liquids separated by a porous partition, each of which enclosed
Speaker 1: one of the electrodes. In eighteen sixty three, Professor Daniel
Speaker 1: invented the cell known by his name, and which is
Speaker 1: one of the most constant current cells ever made, although
Speaker 1: not so powerful as some. The zinc and copper electrodes
Speaker 1: are here separated by a jar of porous earthenware, the
Speaker 1: zinc being surrounded by dilute sulphuric acid, and the copper
Speaker 1: by a saturated solution of sulfates copper. This latter solution
Speaker 1: is the depolarizer, acting to prevent the bubbles of hydrogen
Speaker 1: from collecting on the copper plate, as would be the
Speaker 1: case in the simple cell. Instead of hydrogen being thrown
Speaker 1: out at the copper pole, copper is deposited from the
Speaker 1: sulfate of copper depolarizer, so that this solution becomes constantly
Speaker 1: weaker and the copper heavier. To prevent the weakening, sulfate
Speaker 1: crystals are added Occasionally. This battery has been much employed
Speaker 1: in telegraphic work. A form of this cell, known as
Speaker 1: the gravity cell, has been much used for this purpose,
Speaker 1: the porous partition having here been done away with, and
Speaker 1: the separation of the liquids affected by the difference in
Speaker 1: their densities. In eighteen thirty nine, Grove introduced a cell
Speaker 1: in which the depolarizer was strong nitric acid, which surrounded
Speaker 1: a platinum plate. This is a much more powerful depolarizer
Speaker 1: than sulfate of copper, and the cell was very energetic.
Speaker 1: It had, however, the disadvantage of high cost and gave
Speaker 1: off disagreeable fumes. The first drawback was overcome by Professor
Speaker 1: Bunsen in eighteen forty three, who substituted for the platinum
Speaker 1: plate one of gas retort carbon. The fumes however, still remained.
Speaker 1: This battery was useful to the early experimenters as it
Speaker 1: furnished a strong and constant current. Another good depolarizer is
Speaker 1: chromic acid. This is used in the same manner as
Speaker 1: nitric acid in the carbon zinc cell of Bunsen. It
Speaker 1: does not, however, give off fumes, and yet is almost
Speaker 1: as powerful as the Bunsen cell. Various forms of this
Speaker 1: cell have been made, and they have been extensively used,
Speaker 1: especially for telephone work. They deteriorate only slightly on standing.
Speaker 1: Perhaps the most extensively used primary cell is the laclants.
Speaker 1: This is also a zinc carbon cell, but cell ammoniac
Speaker 1: is used to replace the sulphuric acid of the preceding cells,
Speaker 1: and the depolarizer is the black oxide of manganese. This
Speaker 1: depolarizer is celow in its action, and the cell is
Speaker 1: therefore not good for constant current work, but it has
Speaker 1: a very slow rate of deterioration. This cell is very
Speaker 1: extensively manufactured in the dry form, in which the exciting
Speaker 1: fluid is held as a moist paste. The cell is
Speaker 1: not entirely dry, however, as is sometimes supposed, for if
Speaker 1: it dries out, it ceases to work. One of the
Speaker 1: most recent primary cells, as well as the best, is
Speaker 1: the zinc copper oxide cell of the land. In the
Speaker 1: Edison form of this cell, the copper oxide is pressed
Speaker 1: into plates and mounted in the cell between two zinc plates.
Speaker 1: The exciting fluid is caustic potash. The copper oxide acts
Speaker 1: as the depolarizer and is reduced to metallic copper. The
Speaker 1: cell is very efficient, has a long life, and does
Speaker 1: not deteriorate on standing. Thousands are now in use for
Speaker 1: such work as operating railway signals, sparking gas engines, et cetera.
Speaker 1: The existence of secondary currents was discovered by Ritter in
Speaker 1: eighteen o three, having substituted to the actions of a
Speaker 1: volta's pile another pile formed only of discs of copper
Speaker 1: separated by moist cloth. He remarked that this second pile,
Speaker 1: though enacted by itself, gave in its turn an electric
Speaker 1: current in the opposite direction to the current of the
Speaker 1: first pile. This current was of but short duration, and
Speaker 1: the electromotive force was lower than that of the pile
Speaker 1: used in charging it. In eighteen twenty six, De la
Speaker 1: Revee also found that a secondary or inverse current could
Speaker 1: be obtained from plates of platinum upon which oxygen and
Speaker 1: hydrogen had been disengaged in the experiment of the decomposition
Speaker 1: of water by a battery. This phenomenon took the name
Speaker 1: of polarization of the electrodes, and the current itself that
Speaker 1: of the current of polarization. After that, secondary currents were
Speaker 1: the object of many researches made by physicists, among whom
Speaker 1: many may be mentioned Faraday, Grove, Wheatstone, Pogendwarf E. Becquerel,
Speaker 1: and Gaugene. In eighteen fifty nine, gastone Plant studied the
Speaker 1: influence of different metals and different liquids on the production
Speaker 1: of secondary currents and on their intensity. Since that date,
Speaker 1: the question has assumed great importance, having received scientific and
Speaker 1: practical applications, due mainly to the researches of this acute observer.
Speaker 1: He experimented on voltameters with wires of copper, silver, tin, aluminium, iron, zinc, gold,
Speaker 1: and platinum, and for each of them varied the nature
Speaker 1: of the liquid into which the electrodes were placed. He
Speaker 1: found that quote all the metals oxidizing at the positive
Speaker 1: pole of the cell, the secondary current obtained after the
Speaker 1: interruption of the primary current was as much more intense
Speaker 1: as the oxidation was more complete if the oxide form
Speaker 1: remained adherent and insoluble in the ascidulated liquid of the voltameter.
Speaker 1: Even gold and silver did not resist the action of
Speaker 1: the oxygen of the pile. They were covered with dark
Speaker 1: deposits of oxide and furnished an energetic secondary current. Platinum
Speaker 1: did not oxidize, it is true in a visible manner,
Speaker 1: but the secondary inverse current was of shorter duration than
Speaker 1: that of the metals which were covered with a layer
Speaker 1: of adherent oxide, an effect which was explained by the
Speaker 1: rapid decomposition of the oxygenated water produced around the positive
Speaker 1: electrode of the voltameter. The action of the hydrogen was,
Speaker 1: on the other hand, stronger with platinum than with all
Speaker 1: the other metals, for the electrode around which this gas
Speaker 1: was disengaged furnished with another neutral electrode a more intense
Speaker 1: secondary current than when any other metal was employed. The
Speaker 1: most important result of these interesting researches is that which
Speaker 1: assigns the greatest intensity to this secondary current produced by
Speaker 1: a voltameter with electrodes of lead and dilute sulphuric acid
Speaker 1: as the liquid. Measuring the electromode of forest developed in
Speaker 1: such a voltameter after the rupture of the primary current,
Speaker 1: plot found it was equal to about one and a
Speaker 1: half half times more exactly one point four eight to
Speaker 1: one point four nine that of the most energetic voltaic element,
Speaker 1: such as a grove or bunsen. This suggested the idea
Speaker 1: of constructing secondary cells and uniting them in a battery
Speaker 1: so as to store up or accumulate the work of
Speaker 1: the voltaic pile, in the same way that static electricity
Speaker 1: is condensed by the aid of conductors of great surface
Speaker 1: separated by an insulating material. The action in a storage
Speaker 1: cell is as follows. When the battery is charged, the
Speaker 1: positive plate consists of lead peroxide and the negative of
Speaker 1: pure lead in a spongy condition. When the cell discharges,
Speaker 1: both plates become a form of lead sulfate. Upon being
Speaker 1: charged by having a reverse current sent through them, they
Speaker 1: are reformed into lead peroxide and sponge lead. If the
Speaker 1: plates were platinum, oxygen would be given off where the
Speaker 1: current enters and hydrogen were it leaves, but with the
Speaker 1: lead sulfate plates, the oxygen and hydrogen combine thus oxidizing
Speaker 1: one and reducing the other. Storage cells have many uses.
Speaker 1: They are employed in large sizes and central power stations
Speaker 1: to equalize the load on the machinery, serving to help
Speaker 1: the engines carry the maximum loads so that they are
Speaker 1: not strained. Electric automobiles are largely used, but the weight
Speaker 1: of the battery seriously handicaps their other excellent qualities. They
Speaker 1: also find application in lighting trains, operating industrial locomotives, supplying
Speaker 1: telephone lines, and igniting gas engines. End of Section twenty
Speaker 1: five Electricity, Chapter seven