See also:

• ELECTROLYSIS (formed from Gr. Xbety, to loosen)

ELECTROLYSIS (formed from Gr. Xbety, to loosen)  . When the passage of an electric current through a substance is accompanied by definite chemical changes which are See also:

• INDEPENDENT

independent of the See also:

• HEATING

heating effects of the current, the See also:

• PROCESS

process is known as See also:

• ELECTROLYSIS (formed from Gr. Xbety, to loosen)

electrolysis, and the substance is called an electrolyte . As an example we may take the See also:

• CASE
• CASE, JOHN (d. 1600)

case of a See also:

• SOLUTION (from Lat. solvere, to loosen, dissolve)

solution of a See also:

• SALT (a common Teutonic word, cf. Dutch zout, Ger. Salz, Scand. salt; cognate with Gr. &Xs, Lat. sal)
• SALT, SIR TITUS, BART

salt such as See also:

• COPPER (symbol Cu, atomic weight 63.1, H=1, or 63.6, O = 16)

copper sulphate in See also:

• WATER

water, through which an electric current is passed between copper plates . We shall then observe the following phenomena . (I) The bulk of the solution is unaltered, except that its temperature may be raised owing to the usual heating effect which is proportional to the square of the strength of the current . (2) The copper See also:

• PLATE

plate by which the current is said to enter the solution, i.e. the plate attached to the so-called See also:

• POSITIVE (or PORTABLE) ORGAN

positive terminal of the See also:

• BATTERY (Fr. batterie, from battles, to beat)

battery or other source of current, dissolves away, the copper going into solution as copper sulphate . (3) Copper is deposited on the See also:

• SURFACE

surface of the other plate, being obtained from the solution . (4) Changes in concentration are produced in the neighbourhood of the two plates or electrodes . In the case we have chosen, the solution becomes stronger near the anode, or electrode at which the current enters, and weaker near the See also:

• CATHODE

cathode, or electrode at which it leaves the solution . If, instead of using copper electrodes, we take plates of See also:

• PLATINUM [symbol Pt, atomic weight 145.0 (0=16)]

platinum, copper is still deposited on the cathode; but, instead of the anode dissolving, See also:

• FREE

free sulphuric See also:

• ACID (from the Lat. root ac-, sharp; acere, to be sour)

acid appears in the neighbouring solution, and See also:

• OXYGEN (symbol 0, atomic weight 16)

oxygen See also:

• GAS

gas is evolved at the surface of the platinum plate . With other electrolytes similar phenomena appear, though the See also:

• PRIMARY

primary chemical changes may be masked by secondary actions . Thus, with a dilute solution of sulphuric acid and platinum electrodes, See also:

• HYDROGEN [symbol H, atomic weight x-oo8 (0=16)]

hydrogen gas is evolved at the cathode, while, as the result of a secondary See also:

• ACTION

action on the anode, sulphuric acid is there re-formed, and oxygen gas evolved .

Again, with the solution of a salt such as See also:

• SODIUM [symbol Na, from Lat. natrium; atomic weight 23.00 (0=16)]

sodium chloride, the sodium, which is primarily liberated at the cathode, decomposes the water and evolves hydrogen, while the See also:

• CHLORINE (symbol Cl, atomic weight 35`46 (0=16)

chlorine may be evolved as such, may dissolve the anode, or may liberate oxygen from the water, according to the nature of the plate and the concentration of the solution . See also:

• EARLY
• EARLY, JUBAL ANDERSON (1816-1894)

Early See also:

• HISTORY

History of Electrolysis.—Alessandro See also:

• VOLTA
• VOLTA, ALESSANDRO (1745-1827)

Volta of See also:

• PAVIA (anc. Ticinum, q.v.)

Pavia discovered the electric battery in the See also:

• YEAR

year 1800, and thus placed the means of maintaining a steady electric current in the hands of investigators, who, before that date, had been restricted to the study of the isolated electric charges given by frictional electric See also:

• MACHINES

machines . Volta's See also:

• CELL (from Lat. cella, probably from an Indo-European kal —seen in Lat. celare, to hide; another suggestion connects the word with Lat. cera, wax, taking the original meaning to refer to the honeycomb)

cell consists essentially of two plates of different metals, such as See also:

• ZINC

zinc and copper, connected by an electrolyte such as a solution of salt or acid . Immediately on its See also:

• DISCOVERY

discovery intense See also:

• INTEREST

interest was aroused in the new invention, and the chemical effects of electric currents were speedily detected . W . See also:

• NICHOLSON, HENRY ALLEYNE (1844-1899)
• NICHOLSON, JOHN (1822-18J7)
• NICHOLSON, WILLIAM (1753-1815)
• NICHOLSON, WILLIAM (1784-1844)

Nicholson and See also:

• SIR

Sir A . See also:

• CARLISLE
• CARLISLE, EARLS OF

Carlisle found that hydrogen and oxygen were evolved at the surfaces of See also:

• GOLD
• GOLD [symbol Au, atomic weight 195.7(H = 1),197.2(0 =16)]

gold and platinum wires connected with the terminals of a battery and dipped in water . The See also:

• VOLUME

volume of the hydrogen was about See also:

• DOUBLE
• DOUBLE (from the Mid. Eng. duble, the form which gives the present pronunciation, through the Old Er. duble, from Lat. duplus, twice as much)

double that of the oxygen, and, since this is the ratio in which these elements are combined in water, it was concluded that the process See also:

• CON

con-sisted essentially in the, decomposition of water . They also noticed that a similar See also:

• KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind of chemical action went on in the battery itself . Soon afterwards, See also:

• WILLIAM
• WILLIAM (1143-1214)
• WILLIAM (1227-1256)
• WILLIAM (1J33-1584)
• WILLIAM (A.S. Wilhelm, O. Norse Vilhidlmr; O. H. Ger. Willahelm, Willahalm, M. H. Ger. Willehelm, Willehalm, Mod.Ger. Wilhelm; Du. Willem; O. Fr. Villalme, Mod. Fr. Guillaume; from " will," Goth. vilja, and " helm," Goth. hilms, Old Norse hidlmr, meaning
• WILLIAM (c. 1130-C. 1190)
• WILLIAM, 13TH

William Cruickshank decomposed the See also:

• MAGNESIUM [symbol Mg, atomic weight 24.32 (0 = 16)]

magnesium, sodium and ammonium chlorides, and precipitated See also:

• SILVER

silver and copper from their solutions—an observation which led to the process of See also:

• ELECTROPLATING

electroplating . He also found that the liquid See also:

• ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round the anode became acid, and that round the cathode alkaline . In 1804 W .

Hisinger and J . J . See also:

• BERZELIUS, JONS JAKOB (1779-1848)

Berzelius stated that neutral salt solutions could be decomposed by See also:

• ELECTRICITY

electricity, the acid appearing at one See also:

• POLE (FAMILY)
• POLE, REGINALD (1500-1558)
• POLE, RICHARD DE LA (d. 1525)
• POLE, WILLIAM (1814—1900)

pole and the See also:

• METAL
• METAL (through Fr. from Lat. metallum, mine, quarry, adapted from Gr. µATaXAov, in the same sense, probably connected with ,ueraAAdv, to search after, explore, µeTa, after, aAAos, other)

metal at the other . This observation showed that nascent hydrogen was not, as had been supposed, the primary cause of the separation of metals from their solutions, but that the action consisted in a See also:

• DIRECT

direct decomposition into metal and acid . During the earliest investigation of the subject it was thought that, since hydrogen and oxygen were usually evolved, the electrolysis of solutions of acids and alkalis was to be regarded as a direct decomposition of water . In 18o6 Sir See also:

• HUMPHRY, OZIAS (1742-1810)

Humphry See also:

• DAVY, SIR HUMPHRY

Davy proved that the formation of acid and See also:

• ALKALI

alkali when water was electrolysed was due to saline impurities in the water . He had shown previously that decomposition of water could be effected although the two poles were placed in See also:

• SEPARATE

separate vessels connected by moistened threads . In 1807 he decomposed potash and soda, previously considered to be elements, by passing the current from a powerful battery through the moistened solids, and thus isolated the metals See also:

• POTASSIUM [symbol K (from kalium), atomic weight 39.114 0=16)]

potassium and sodium . The electromotive force of Volta's See also:

• SIMPLE

simple cell falls off rapidly when the cell is used, and this phenomenon was shown to be due to the See also:

• ACCUMULATION (from Lat. accumulare, to heap up)

accumulation at the metal plates of the products of chemical changes in the cell itself . This See also:

• REVERSE

reverse electromotive force of polarization is produced in all electrolytes when the passage of the current changes the nature of the electrodes . In batteries which use acids as the electrolyte, a film of hydrogen tends to be deposited on the copper or platinum electrode; but, to obtain a See also:

• CONSTANT, BENJAMIN (1845-1902)

constant electromotive force, several means were soon devised of preventing the formation of the film . Constant cells may be divided into two See also:

• GROUPS
• GROUPS, THEORY

groups, according as their action is chemical (as in the bichromate cell, where the hydrogen is converted into water by an oxidizing See also:

• AGENT (from Lat. agere, to act)

agent placed in a porous pot round the See also:

• CARBON (symbol C, atomic weight 12)

carbon plate) or electrochemical (as in See also:

• DANIELL, JOHN FREDERIC (1790-1845)
• DANIELL, THOMAS (1749–1840)

Daniell's cell, where a copper plate is surrounded by a solution of copper sulphate, and the hydrogen, instead of being liberated, replaces copper, which is deposited on the plate from the solution) .

See also:

• FARADAY, MICHAEL (1791-1867)

Faraday's See also:

• LAWS

Laws.—The first exact quantitative study of electrolytic phenomena was made about 183o by See also:

• MICHAEL
• MICHAEL (1596-1645)
• MICHAEL (Hebrew Sn,q, " Who is like God? ")

Michael Faraday (Experimental Researches, 1833) . When an electric current flows round a See also:

• CIRCUIT (Lat. circuitus, from circum, round, and ire, to go)

circuit, there is no accumulation of electricity any-where in the circuit, hence the current strength is every-where the same, and we may picture the current as analogous to the flow of an incompressible fluid . Acting on this view, Faraday set himself to examine the relation between the flow of electricity round the circuit and the amount of chemical decomposition . He passed the current driven by a voltaic battery ZnPt (fig . 1) through two branches containing the two electrolytic cells A and B . The reunited cur-See also:

• RENT

rent was then led through another cell C, in which the strength of the current must be the sum of those in the arms A and B . Faraday found that the See also:

• MASS (O.E. maesse; Fr. messe; Ger. Messe; Ital. messa; from eccl. Lat. missa)
• MASS, IN

mass of substance liberated at the electrodes in the cell C was equal to the sum of the masses liberated in the cells A and B . He also found that, for the same current, the amount of chemical action was independent of the See also:

• SIZE

size of the electrodes and proportional to the See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

time that the current flowed . Regarding the current as the passage of a certain amount of electricity per second, it will be seen that the results of all these experiments may be summed up in the statement that the amount of chemical action is proportional to the quantity of electricity which passes through the cell . Faraday's next step was to pass the same current through different electrolytes in See also:

• SERIES (a Latin word from serere, to join)

series . He found that the amounts of the substances liberated in each cell were proportional to the chemical See also:

• EQUIVALENT

equivalent weights of those substances . Thus, if the current be passed through dilute sulphuric acid between hydrogen electrodes, and through a solution of copper sulphate, it will be found that the mass of hydrogen evolved in the first cell is to the mass of copper deposited in the second as i is to 31.8 .

Now this ratio is the same as that which gives the relative chemical equivalents of hydrogen and copper, for i gramme of hydrogen and 31.8 grammes of copper unite chemically with the same See also:

• WEIGHT

weight of any acid radicle such as chlorine or the sulphuric See also:

• GROUP

group, SO4 . Faraday examined also the electrolysis of certain fused salts such as See also:

• LEAD
• LEAD (pronounced iced)

lead chloride and silver chloride . Similar relations were found to hold and the amounts of chemical See also:

• CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change to be the same for the same electric See also:

• TRANSFER (from Lat. transferre, to bear across, carry over)

transfer as in the case of solutions . We may sum up the See also:

• CHIEF (from Fr. chef, head, Lat. caput)

chief results of Faraday's See also:

• WORK

work in the statements known as Faraday's laws: The mass of substance liberated from an electrolyte by the passage of a current is proportional (1) to the See also:

• TOTAL

total quantity of electricity which passes through the electrolyte, and (2) to the chemical equivalent weight of the substance liberated . Since Faraday's time his laws have been confirmed by See also:

• MODERN

modern See also:

• RESEARCH (O. Fr. recerche, from recercher, re- and cercer, mod. chercher, to search; Late Lat. circare, to go round in a circle, to explore)

research, and in favourable cases have been shown to hold See also:

• GOOD, JOHN MASON (1764-1827)

good with an accuracy of at least one See also:

• PART

part in a thousand . The See also:

• PRINCIPAL

principal See also:

• OBJECT

object of this more See also:

• RECENT

recent research has been the determination of the quantitative amount of chemical change associated with the passage for a given time of a current of strength known in electromagnetic See also:

• UNITS, DIMENSIONS OF
• UNITS, PHYSICAL

units . It is found that the most accurate and convenient apparatus to use is a platinum bowl filled with a solution of silver nitrate containing about fifteen parts of the salt to one See also:

• HUNDRED

hundred of water . Into the solution dips a silver plate wrapped in See also:

• FILTER (a word common in various forms to most European languages, adapted from the medieval Lat. fi-ltrum, felt, a material used as a filtering agent)

filter See also:

• PAPER
• PAPER (Fr. papier, from Lat. papyrus)

paper, and the current is passed from the silver plate as anode to the bowl as cathode .. The bowl is weighed before and after the passage of the current, and the increase gives the mass of silver deposited . The mean result of the best determinations shows that when a current of one See also:

• AMPERE, ANDRE MARIE (1775–1836)
• AMPERE, JEAN JACQUES (1800-1864)

ampere is passed for one second, a mass of silver is deposited equal to 0•0o1118 gramme . So accurate and convenient is this determination that it is now used conversely as a See also:

• PRACTICAL

practical See also:

• DEFINITION (Lat. definitio, from de-finire, to set limits to, describe)

definition of the ampere, which (defined theoretically in terms of magnetic force) is defined practically as the current which in one second deposits 1.118 milligramme of silver . Taking the chemical equivalent weight of silver, as determined by chemical experiments, to be 1o7.92, the result described gives as the electrochemical equivalent of an See also:

• ION

ion of unit chemical equivalent the value 1 •o36 X ro 5 .

If, as is now usual, we take the equivalent weight of oxygen as our See also:

• STANDARD
• STANDARD, BATTLE OF THE

standard and See also:

• CALL (from Anglo-Saxon ceallian, a common Teutonic word, cf. Dutch kallen, to talk or chatter)

call it 16, the equivalent weight of hydrogen is i •oo8, and its electrochemical equivalent is 1.044 X 10—5 . The electrochemical equivalent of any other substance, whether See also:

• ELEMENT (Lat. elementum)

element or See also:

• COMPOUND
• COMPOUND (from Lat. componere, to combine or put together)

compound, may be found by multiplying its chemical equivalent by r .o36 X io-2 . If, instead of the ampere, we take the C.G.S. electromagnetic unit of current, this number becomes i •o36 X ro 4 . Chemical Nature of the Ions.—A study of the products of decomposition does not necessarily lead directly to a knowledge of the ions actually employed in carrying the current through the electrolyte . Since the electric forces are active throughout the whole solution, all the ions must come under its See also:

• INFLUENCE (Late Lat. influentia, from influere, to flow in)

influence and therefore move, but their separation from the electrodes is determined by the electromotive force needed to liberate them . Thus, as See also:

• LONG, GEORGE (1800-1879)
• LONG, JOHN DAVIS (1838– )

long as every ion of the solution is See also:

• PRESENT

present in the layer of Iiquid next the electrode, the one which responds to the Ieast electromotive force will alone be set free . When the amount of this ion in the surface layer becomes too small to carry all the current across the junction, other ions must also be used, and either they or their secondary products will appear also at the electrode . In aqueous solutions, for instance, a few hydrogen(H) and hydroxyl (OH) ions derived from the water are always present, and will be liberated if the other ions require a higher decomposition voltage and the current be kept so small that hydrogen and hydroxyl ions can be formed fast enough to carry all the current across the junction between solution and electrode . The issue is also obscured in another way . When the ions are set free at the electrodes, they may unite with the substance of the electrode or with some constituent of the solution to See also:

• FORM (Lat. forma)

form secondary products . Thus the hydroxyl mentioned above decomposes into water and oxygen, and the chlorine produced by the electrolysis of a chloride may attack the metal of the anode . This leads us to examine more closely the part played by water in the electrolysis of aqueous solutions .

Distilled water is a very See also:

• BAD, BCD

bad conductor, though, even when See also:

• GREAT

great care is taken to remove all dissolved bodies, there is See also:

• EVIDENCE (Lat. evidentia, evideri, to appear clearly)

evidence to show that some part of the trace of conductivity remaining is due to the water itself . By careful redistillation F . Kohlrausch has prepared water of which the conductivity compared with that of See also:

• MERCURY
• MERCURY (MERCU1uus)
• MERCURY (symbol Hg, atomic weight = 2oo)

mercury was only o•4oXio—11 at 18° C . Even here some little impurity was present, and the conductivity of chemically pure water was estimated by thermodynamic reasoning as o•36X lo—it at 18° C . As we shall see later, the conductivity of very dilute salt solutions is proportional to the concentration, so that it is probable that, in most cases, practically all the current is carried by the salt . At the electrodes, however, the small quantity of hydrogen and hydroxyl ions from the water are liberated first in cases where the ions of the salt have a higher decomposition voltage . The water being present in excess, the hydrogen and hydroxyl are re-formed at once and therefore are set free continuously . If the current be so strong that new hydrogen and hydroxyl ions cannot be formed in time, other substances are liberated; in a solution of sulphuric acid a strong current will evolve See also:

• SULPHUR

sulphur dioxide, the more readily as the concentration of the solution is increased . Similar phenomena are seen in the case of a solution of hydrochloric acid . When the solution is weak, hydrogen and oxygen are evolved; but, as,the concentration is increased, and the current raised, more and more chlorine is liberated . An interesting example of secondary action is shown by the See also:

• COMMON

common technical process of electroplating with silver from a See also:

• BATH
• BATH, THOMAS THYNNE
• BATH, WILLIAM

bath of potassium silver See also:

• CYANIDE

cyanide . Here the ions are potassium and the group Ag(CN)z 1 Each potassium ion as it reaches the cathode precipitates silver by reacting with the solution in accordance with the chemical See also:

• EQUATION (from Lat. aequatio, aequare, to equalize)

equation K+ KAg(CN)2 =2KCN +Ag, while the anion Ag(CN)2 dissolves an See also:

• ATOM (Gr. &rows, indivisible, from a- privative, and TE,aPfw, to cut)

atom of silver from the anode, and re-forms the complex cyanide KAg(CN)2 by combining with the 2KCN produced in the reaction described in the equation .

If the anode consist of platinum, See also:

• CYANOGEN (Gr. ebavos, blue 'yevvav, to produce), C2N2

cyanogen gas is evolved thereat from the anion Ag(CN)zi and the platinum becomes covered with the insoluble silver cyanide, AgCN, which soon stops the current . The coating of silver obtained by this process is coherent and homogeneous, while that deposited from a solution of silver nitrate, as the result of the primary action of the current, is crystalline and easily detached . In the electrolysis of a concentrated solution of sodium acetate, hydrogen is evolved at the cathode and a mixture of ethane and carbon dioxide at the anode . According to H . See also:

• JAHN, FRIEDRICH LUDWIG (1778-1852)
• JAHN, JOHANN (1750—1816)
• JAHN, OTTO (1813—1869)

Jahn? the processes at the anode can be represented by the equations 2CH,•COO+See also:

• H2O (combined)

H2O =2CH,•000H +O 2CH,•000H -f-0 = See also:

• C2H6

C2H6+2CO2+H20 . The hydrogen at the cathode is See also:

• DEVELOPED

developed by the secondary action 2Na +2H20 =2 NaOH +H2 . Many organic compounds can be prepared by taking See also:

• ADVANTAGE

advantage of secondary actions at the electrodes, such as reduction by the cathodic hydrogen, or oxidation at the anode (see See also:

• ELECTROCHEMISTRY

ELECTROCHEMISTRY) . It is possible to distinguish between double salts and salts of compound acids . Thus J . W . Hittorf showed that when a current was passed through a solution of sodium platino-chloride, the platinum appeared at the anode . The salt must therefore be derived from an acid, chloroplatinic acid, H2PtCI6, and have the See also:

• FORMULA
• FORMULA (Lat. diminutive of forma, shape, pattern, &c., especially used of rules of judicial procedure)

formula Na2PtCl6, the ions being Na and PtCI4", for if it were a double salt it would decompose as a mixture of sodium chloride and platinum chloride and both metals would go to the cathode .

1 See Hittorf, Pogg . See also:

• ANN

Ann. cvi . 517 (1859) . 2 Grundriss der Elektrochemie (1895), p . 292; see also F. kaufler and C . See also:

• HERZOG, HANS (1819–1894)
• HERZOG, JOHANN JAKOB (1805-1882)

Herzog, Ber., 1909, 42, p . 3858 . Early Theories of Electrolysis.—The obvious phenomena to be explained by any theory of electrolysis are the liberation of the products of chemical decomposition at the two electrodes while the intervening liquid is unaltered . To explain these facts, Theodor Grotthus (1785-1822) in 18o6 put forward an See also:

• HYPOTHESIS (from Gr. inrorcOivat, to put under; cf. Lat. suppositio, from sub-ponere)

hypothesis which supposed that the opposite chemical constituents of an electrolyte interchanged partners all along the See also:

• LINE

line between the electrodes when a current passed . Thus, if the See also:

• MOLECULE (from mod. Lat. molecula, the diminutive of moles, a mass)

molecule of a substance in solution is represented by AB, Grotthus considered a See also:

• CHAIN (through the O. Fr. citable, chcene, &c., from Lat. catena)

chain of AB molecules to exist from one electrode to the other . Under the influence of an applied electric force, he imagined that the B part of the first molecule was liberated at the anode, and that the A part thus isolated See also:

• UNITED

united with the B part of the second molecule, which, in its turn, passed on its A to the B of the third molecule . In this manner, the B part of the last molecule of the chain was seized by the A of the last molecule but one, and the A part of the last molecule liberated at the surface of the cathode .

Chemical phenomena throw further See also:

• LIGHT

light on this question . If two solutions containing the salts AB and CD be mixed, double decomposition is found to occur, the salts AD and CB being formed till a certain part of the first pair of substances is transformed into an equivalent amount of the second pair . The proportions between the four salts AB, CD, AD and CB, which exist finally in solution, are found to be the same whether we begin with the pair AB and CD or with the pair AD and CB . To explain this result, chemists suppose that both changes can occur simultaneously, and that See also:

• EQUILIBRIUM (from the Lat. aequus, equal, and libra, a balance)

equilibrium results when the See also:

• RATE

rate at which AB and CD are transformed into AD and CB is the same as the rate at which the reverse change goes on . A freedom of interchange is thus indicated between the opposite parts of the molecules of salts in solution, and it follows reasonably that with the solution of a single salt, say sodium chloride, continual interchanges go on between the sodium and chlorine parts of the different molecules . These views were applied to the theory of electrolysis by R . J . E . See also:

• CLAUSIUS, RUDOLF JULIUS EMMANUEL (1822-1888)

Clausius . He pointed out that it followed that the electric forces did not cause the interchanges between the opposite parts of the dissolved molecules but only controlled their direction . Interchanges must be supposed to go on whether a current passes or not, the See also:

• FUNCTION

function of the electric forces in electrolysis being merely to determine in what direction the parts of the molecules shall work their way through the liquid and to effect actual separation of these parts (or their secondary products) at the electrodes . This conclusion is supported also by the evidence supplied by the phenomena of electrolytic See also:

• CONDUCTION, ELECTRIC

conduction (see CONDUCTION, ELECTRIC, § II.) .

If we eliminate the reverse electromotive forces of polarization at the two electrodes, the conduction of electricity through electrolytes is found to conform to See also:

• OHM, GEORG SIMON (1787-1854)

Ohm's See also:

• LAW
• LAW (0. Eng. lagu, M. Eng. lawe; from an old Teutonic root lag, " lie," what lies fixed or evenly; cf. Lat. lex, Fr. loi)
• LAW, JOHN (1671—1729)
• LAW, WILLIAM (1686-1761)

law; that is, once the polarization is overcome, the current is proportional to the electromotive force applied to the bulk of the liquid . Hence there can be no reverse forces of polarization inside the liquid itself, such forces being confined to the surface of the electrodes . No work is done in separating the parts of the molecules from each other . This result again indicates that the parts of the molecules are effectively separate from each other, the function of the electric forces being merely directive . See also:

• MIGRATION

Migration of the Ions.—The opposite parts of an electrolyte, which work their way through the liquid under the action of the electric forces, were named by Faraday the ions—the travellers . The changes of concentration which occur in the solution near the two electrodes were referred by W . Hittorf (1853) to the unequal speeds with which he supposed the two opposite ions to travel . It is clear that, when two opposite streams of ions move past each other, equivalent quantities are liberated at the two ends of the See also:

• SYSTEM

system . If the ions move at equal rates, the salt which is decomposed to See also:

• SUPPLY (through Fr. from Lat. supplere, to fill up)

supply the ions liberated must be taken equally from the neighbourhood of the two electrodes . But if one ion, say the anion, travels faster through the liquid than the other, the end of the solution from which it comes will be more exhausted of salt than the end towards which it goes . . ..... See also:

• WHITE
• WHITE, ANDREW DICKSON (1832– )
• WHITE, GILBERT (1720–1793)
• WHITE, HENRY KIRKE (1785-1806)
• WHITE, HUGH LAWSON (1773-1840)
• WHITE, JOSEPH BLANCO (1775-1841)
• WHITE, RICHARD GRANT (1822-1885)
• WHITE, ROBERT (1645-1704)
• WHITE, SIR GEORGE STUART (1835– )
• WHITE, SIR THOMAS (1492-1567)
• WHITE, SIR WILLIAM ARTHUR (1824--1891)
• WHITE, SIR WILLIAM HENRY (1845– )
• WHITE, THOMAS (1628-1698)
• WHITE, THOMAS (c. 1550-1624)

white ones, the See also:

• STATE
• STATE, GREAT OFFICERS OF

state of things o 0 0 0 0 o o a; '0 0 o a o after the passage of a current ` '- - will be represented by the See also:

• LOWER

lower part of the figure .

Here the See also:

• MIDDLE

middle part of the solution is unaltered and the number of ions liberated is the same at either end, but the amount of salt See also:

• LEFT

left at one end is less than that at the other . On the right, towards which the faster ion travels, five molecules of salt are left, being a loss of two from the See also:

• ORIGINAL

original seven . On the left, towards which the slower ion moves, only three molecules remain—a loss of four . Thus, the ratio of the losses at the two ends is two to one—the same as the ratio of the assumed ionic velocities . It should be noted, however, that another cause would be competent to explain the unequal dilution of the two solutions . If either ion carried with it some of the unaltered salt or some of the solvent, concentration or dilution of the liquid would be produced where the ion was liberated . There is See also:

• REASON (Lat. ratio, through French raison)

reason to believe that in certain cases such complex ions do exist, and interfere with the results of the differing ionic velocities . Hittorf and many other observers have made experiments to determine the unequal dilution of a solution round the two electrodes when a current passes . Various forms of apparatus have been used, the principle of them all being to secure efficient separation of the two volumes of solution in which the changes occur . In some cases porous diaphragms have been employed; but such diaphragms introduce a new complication, for the liquid as a whole is pushed through them by the action of the current, the phenomenon being known as electric endosmose . Hence* experiments without separating diaphragms are to be preferred, and the apparatus may be considered effective when a consideraable bulk of intervening solution is left unaltered in See also:

• COMPOSITION
• COMPOSITION (Lat. compositio, from componere, to put together)

composition . It is usual to See also:

• EXPRESS (through the French from the past participle of the Lat. exprimere, to press out, by transference used of representing objects in painting or sculpture, or of thoughts, &c. in words)

express the results in terms of what is called the migration constant of the anion, that is, the ratio of the amount of salt lost by the anode See also:

• VESSEL (O. Fr. vaissel, from a rare Lat. vascellum, dim. of vas, vase, urn)

vessel to the whole amount lost by both vessels .

Thus the statement that the migration constant or transport number for a decinormal solution of copper sulphate is o•632 implies that of every gramme of copper sulphate lost by a solution containing originally one-tenth of a gramme equivalent per litre when a current is passed through it between platinum electrodes, o•632 gramme is taken from the cathode vessel and x.368 gramme from the anode vessel . For certain concentrated solutions the transport number is found to be greater than unity; thus for a normal solution of See also:

• CADMIUM (symbol Cd, atomic weight 112.4 (0=16))

cadmium iodide its value is 1.12 . On the theory that the phenomena are wholly due to unequal ionic velocities this result would mean that the cation like the anion moved against the conventional direction of the current . That a See also:

• BODY

body carrying a positive electric See also:

• CHARGE
• CHARGE (through the Fr. from the Late Lat. carricare, to load in a carrus or wagon; cf. " cargo ")

charge should move against the direction of the electric intensity is contrary to all our notions of electric forces, and we are compelled to seek some other explanation . An alternative hypothesis is given by the See also:

• IDEA (Gr. Ibia, connected with i&eiv, to see; cf. Lat. species from specere, to look at)

idea of complex ions . If some of the anions, instead of being simple See also:

• IODINE (symbol I, atomic weight '26.92)

iodine ions represented chemically by the See also:

• SYMBOL (Gr. o-uµ(3oXov, a sign)

symbol I, are complex structures formed by the See also:

• UNION
• UNION (known locally as Union Hill and officially as Town of Union)

union of iodine with unaltered cadmium iodide—structures represented by some such chemical formula as I(CdI2), the concentration of the solution round the anode would be increased by the passage of an electric current, and the phenomena observed would be explained . It is found that, in such cases as this, where it seems necessary to imagine the existence of complex ions, the transport number changes rapidly as the concentration of the original solution is changed . Thus, diminishing the concentration of the cadmium iodine solution from normal to one-twentieth normal changes the transport number from 1.12 to o'64 . Hence it is probable that in cases where the transport number keeps constant with If we assume that no other cause is at work, it is easy to prove that, with non-dissolvable electrodes, the ratio of salt lost at the anode to the salt lost at the cathode must be equal to the ratio of the velocity of the cation to the velocity of the anion . This result may be illustrated by fig . 2 . The See also:

• BLACK
• BLACK, ADAM (1784-1874)
• BLACK, JEREMIAH SULLIVAN (1810–1883)
• BLACK, WILLIAM (1841-1898)

black circles represent one ion and the white circles the other .

If the black ions move twice as fast as the 0000000,000000.0000006 changing concentration the hypothesis of complex ions is unnecessary, and we may suppose that the transport number is a true migration constant from which the relative velocities of the two ions may be calculated in the See also:

• MATTER

matter suggested by Hittorf and illustrated in fig . 2 . This conclusion is confirmed by the results of the direct visual determination of ionic velocities (see CONDUCTION, ELECTRIC, § II.), which, in cases where the transport number remains constant, agree with the values calculated from those See also:

• NUMBERS, BOOK OF
• NUMBERS, PARTITION OF

numbers . Many solutions in which the transport numbers vary at high concentration often become simple at greater dilution . For instance, to take the two solutions to which we have already referred, we have of ions between molecules at the instants of molecular collision only; during the See also:

• REST (O. Eng. rest, reste, bed, cognate with other Teutonic forms, e.g. Ger. Rast, Riiste, rest, and probably Gothic Rasta, league, i.e. resting or stopping place)

rest of the See also:

• LIFE

life of the ions they were regarded as linked to each other to form electrically neutral molecules . In 1887 Svante See also:

• ARRHENIUS, SVANTE AUGUST (1859– )

Arrhenius, See also:

• PROFESSOR (the Latin noun formed from the verb profiteri, to declare publicly, to acknowledge, profess)

professor of physics at See also:

• STOCKHOLM

Stockholm, put forward a new theory which supposed that the freedom of the opposite ions from each other was not a See also:

• MERE
• MERE, ADALBERT (1838-1909)

mere momentary freedom at the instants of molecular collision, but a more or less permanent freedom, the ions moving independently of each other through the liquid . The evidence which led Arrhenius to this conclusion was based on See also:

• VAN

van 't Hoff's work on the osmotic pressure of solutions (see SOLUTION) . If a solution, let us say of See also:

• SUGAR

sugar, be confined in a closed vessel through the walls of Concentration . 2.O 1.5 I.0 0.5 0.2 0•I 0.05 0.02 o•o1 normal Copper sulphate transport numbers 0.72 0.714 0.696 0.668 o•643 0.632 0.626 0.62 . . Cadmium iodide I •22 I.18 I•I2 P00 0.83 0.71 o•64 0.59 0-56 It is probable that in both these solutions complex ions exist at fairly high concentrations, but gradually gets less in number and finally disappear as the dilution is increased . In such salts as potassium chloride the ions seem to be simple throughout a wide range of concentration since the transport numbers for the same series of concentrations as those used above run Potassium chloride- 0'515, 0.515, 0.514, 0.513, 0.509, 0.508, 0.507, 0.507, 0.506 . The next important step in the theory of the subject was made by F .

Kohlrausch in 1879 . Kohlrausch formulated a theory of electrolytic conduction based on the idea that, under the action of the electric forces, the oppositely charged ions moved in opposite directions through the liquid, carrying their charges with them . If we eliminate the polarization at the electrodes, it can be shown that an electrolyte possesses a definite electric resistance and therefore a definite conductivity . The conductivity gives us the amount of electricity conveyed per second under a definite electromotive force . On the view of the process • of conduction described above, the amount of electricity conveyed per second is measured by the product of the number of ions, known from the concentration of the solution, the charge carried by each of them, and the velocity with which, on the See also:

• AVERAGE

average, they move through the liquid . The concentration is known, and the conductivity can be measured experimentally; thus the average velocity with which the ions move past each other under the existent electromotive force can be estimated . The velocity with which the ions move past each other is equal to the sum of their individual velocities, which can therefore be calculated . Now Hittorf's transport number, in the case of simple salts in moderately dilute solution, gives us the ratio between the two ionic velocities . Hence the See also:

• ABSOLUTE (Lat. absolvere, to loose, set free)

absolute velocities of, the two ions can be determined, and we can calculate the actual See also:

• SPEED, JOHN (1552–1629)

speed with which a certain ion moves through a given liquid under the action of a given potential gradient or electromotive force . The details of the calculation are given in the See also:

• ARTICLE (from Lat. articulus, a joint)

article CONDUCTION, ELECTRIC, § II., where also will be found an See also:

• ACCOUNT
• ACCOUNT (through O. Fr. acont, Late Lat. comptum, cornputare, to calculate)

account of the methods which have been used to measure the velocities of many ions by direct visual observation . The results go to show that, where the existence of complex ions is not indicated by varying transport numbers, the observed velocities agree with those calculated on Kohlrausch's theory . See also:

• DISSOCIATION

Dissociation Theory.—The verification of Kohlrausch's theory of ionic velocity verifies also the view of electrolysis which regards the electric current as due to streams of ions moving in opposite directions through the liquid and carrying their opposite electric charges with them .

There remains the question how the necessary migratory freedom of the ions is secured . As we have seen, Grotthus imagined that it was the electric forces which sheared the ions past each other and loosened the chemical bonds holding the opposite parts of each dissolved molecule together . Clausius extended to electrolysis the chemical ideas which looked on the opposite parts of the molecule as always changing partners independently of any electric force, and regarded the function of the current as merely directive . Still, the necessary freedom was supposed to be secured by interchangeswhich the solvent can pass but the solution cannot, the solvent will enter till a certain equilibrium pressure is reached . This equilibrium pressure is called the osmotic pressure of the solution, and thermodynamic theory shows that, in an ideal case of perfect separation between solvent and solute, it should have the same value as the pressure which a number of molecules equal to the number of solute molecules in the solution would exert if they could exist as a gas in a space equal to the volume of the solution, provided that the space was large enough (i.e. the solution dilute enough) for the intermolecular forces between the dissolved particles to be inappreciable . Van 't Hoff pointed out that measurements of osmotic pressure confirmed this 'value in the case of dilute solutions of See also:

• CANE

cane sugar . Thermodynamic theory also indicates a connexion between the osmotic pressure of a solution and the depression of its freezing point and its vapour pressure compared with those of the pure solvent . The freezing points and vapour pressures of solutions of sugar are also in conformity with the theoretical numbers . But when we pass to solutions of See also:

• MINERAL

mineral salts and acids—to solutions of electrolytes in fact—we find that the observed values of the osmotic pressures and of the allied phenomena are greater than the normal values . Arrhenius pointed out that these exceptions would be brought into line if the ions of electrolytes were imagined to be separate entities each capable of producing its own pressure effects just as would an See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary dissolved molecule . Two relations are suggested by Arrhenius' theory . (I) In very dilute solutions of simple substances, where only one kind of dissociation is possible and the dissociation of the ions is cdmplete, the number of pressure-producing particles necessary to produce the observed osmotic effects should be equal to the number of ions given by a molecule of the salt as shown by its See also:

• ELECTRICAL
• ELECTRICAL (or ELECTROSTATIC) MACHINE

electrical properties .

Thus the osmotic pressure, or the depression of the freezing point of a solution of potassium chloride should, at extreme dilution, be twice the normal value, but of a solution of sulphuric acid three times that value, since the potassium salt contains two ions and the acid three . (2) As the concentration of the solutions increases, the ionization as measured electrically and the dissociation as measured osmotically might decrease more or less together, though, since the thermodynamic theory only holds when the solution is so dilute that the dissolved particles are beyond each other's See also:

• SPHERE (Gr. vclsa?pa, a ball or globe)

sphere of action, there is much doubt whether this second relation is valid through any appreciable range of concentration . At present, measurements of freezing point are more convenient and accurate than those of osmotic pressure, and we may test the validity of Arrhenius' relations by their means . The theoretical value for the depression of the freezing point of a dilute solution per gramme-equivalent of solute per litre is 1.857° C . Completely ionized solutions of salts with two ions should give double this number or 3.714°, while electrolytes with three ions should have a value of 5.57° . The following results are given by H . B . Loomis for the concentration of o•o1 gramme-molecule of salt to one thousand grammes of water . The salts tabulated are those of which the equivalent conductivity reaches a limiting value indicating that See also:

• COMPLETE

complete ionization is reached as dilution is increased . With such salts alone is a valid comparison possible . Molecular Depressions of the Freezing Point . Electrolytes with two Ions .

Potassium chloride . 3.6o Nitric acid 3.73 Sodium chloride . 3.67 Potassium nitrate 3.46 Potassium See also:

• HYDRATE

hydrate . 3.71 Sodium nitrate . 3'55 Hydrochloric acid . 3.61 Ammonium nitrate . 3.58 Electrolytes with three Ions . 5•o4 Sulphuric acid . . 4.49 See also:

• CALCIUM [symbol Ca, atomic weight 40.0 (o= x6)]

Calcium chloride . . Sodium sulphate . . 5.09 Magnesium chloride . 5.08 At the concentration used by Loomis the electrical con- ductivity indicates that the ionization is not complete, particularly in the case of the salts with divalent ions in the second See also:

• LIST (O.E. lisle, a Teutonic word, cf. Dut. lust, Ger. Leiste, adapted in Ital. lista and Fr. lisle)
• LIST, FRIEDRICH (1789-1846)

list .

Allowing for incomplete ionization the See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

general See also:

• CONCORDANCE (Late Lat. concordantia, harmony, from cum, with, and car, heart)

concordance of these numbers with the theoretical ones is very striking . The measurements of freezing points of solutions at the extreme dilution necessary to secure complete ionization is a matter of great difficulty, and has been overcome only in a research initiated by E . H . Griffiths.' Results have been obtained for solutions of sugar, where the experimental number is 1.858, and for potassium chloride, which gives a depression of 3.72o . These numbers agree with those indicated by theory, viz . 1.857 and 3.714, with astonishing exactitude . We may take Arrhenius' first relation as established for the case of potassium chloride . The second relation, as we have seen, is not a strict consequence of theory, and experiments to examine it must be treated as an investigation of the limits within which solutions are dilute within the thermodynamic sense of the word, rather than as a test of the soundness of the theory . It is found that divergence has begun before the concentration has become great enough to enable freezing points to be measured with any ordinary apparatus . The freezing point See also:

• CURVE (Lat. curvus, bent)

curve usually lies below the electrical one, but approaches it as dilution is increased' Returning once more to the See also:

• CONSIDERATION (from Lat. considerare, to look at closely, examine, generally taken to be from con-, and the base seen in sidus, sideris, a star, the word being supposed to be originally an astrological or astronomical term)

consideration of the first relation, which deals with the comparison between the number of ions and the number of pressure-producing particles in dilute solution, one caution is necessary . In simple substances like potassium chloride it seems evident that one kind of dissociation only is possible . The electrical phenomena show that there are two ions to the molecule, and that these ions are electrically charged .

Corresponding with this result we find that the freezing point of dilute solutions indicates that two pressure-producing particles per molecule are present . But the converse relation does not necessarily follow . It would be possible for a body in solution to be dissociated into non-electrical parts, which would give osmotic pressure effects twice or three times the normal value, but, being uncharged, would not See also:

• ACT (Lat. actus, actum)

act as ions and impart electrical conductivity to the solution . L . Kahlenberg (Jour . Phys . Chem., 19o1, v . 344, 1902, vi . 43) has found that solutions of diphenylamine in methyl cyanide possess an excess of pressure-producing particles and yet are non-conductors of electricity . It is possible that in complicated organic substances we might have two kinds of dissociation, electrical and non-electrical, occurring simultaneously, while the possibility of the association of molecules accompanied by the electrical dissociation of some of them into new parts should not be overlooked . It should be pointed out that no measurements on osmotic pressures or freezing points can do more than tell us that an excess of particles is present; such experiments can throw no light on the question whether or not those particles are electrically charged . That question can only be answered by examining whether or not the particles move in an electric See also:

• FIELD (a word common to many West German languages, cf. Ger. Feld, Dutch veld, possibly cognate with O.E. f olde, the earth, and ultimately with root of the Gr. irAaror, broad)
• FIELD, CYRUS WEST (1819-1892)
• FIELD, DAVID DUDLEY (18o5-1894)
• FIELD, EUGENE (1850-1895)
• FIELD, FREDERICK (18o1—1885)
• FIELD, HENRY MARTYN (1822-1907)
• FIELD, JOHN (1782—1837)
• FIELD, MARSHALL (183 1906)
• FIELD, NATHAN (1587—1633)
• FIELD, STEPHEN JOHNSON (1816-1899)
• FIELD, WILLIAM VENTRIS FIELD, BARON (1813-1907)

field .

The dissociation theory was originally suggested by the osmotic pressure relations . But not only has it explained satisfactorily the electrical, properties of solutions, but it seems to be the only known hypothesis which is consistent with the experimental relation between the concentration of a solution and its electrical conductivity (see CONDUCTION, ELECTRIC, 1 Brit . See also:

• ASS (O.E. assa; Lat. asinus)
• ASS, FEAST OF THE

Ass . See also:

• REP, REPP, or REPS

Rep., 1906, See also:

• SECTION
• SECTION (Lat. sectio, cutting, secare, to cut)

Section A, Presidential Address . ' See Theory of Solution, by W . C . D . Whetham (1902), p . 328 . § II., " Nature of Electrolytes ") . It is probable that the electrical effects constitute the strongest arguments in favour of the theory . It is necessary to point out that the dissociated ions of such a body as potassium chloride are not in the same See also:

• CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition as potassium and chlorine in the free state .

The ions are associated with very large electric charges, and, whatever their exact relations with those charges may be, it is certain that the See also:

• ENERGY (from the Gr. ivipyela; iv, in, ipyov, work)

energy of a system in such a state must be different from its energy when unelectrified . It is not unlikely, therefore, that even a compound as See also:

• STABLE

stable in the solid form as potassium chloride should be thus dissociated when dissolved . Again, water, the best electrolytic solvent known, is also the body of the highest specific inductive capacity (See also:

• DIELECTRIC

dielectric constant), and this See also:

• PROPERTY

property, to whatever cause it may be due, will reduce the forces between electric charges in the neighbourhood, and may therefore enable two ions to separate . This view of the nature of electrolytic solutions at once explains many well-known phenomena . Other See also:

• PHYSICAL

physical properties of these solutions, such as See also:

• DENSITY (Lat. densus, thick)

density, See also:

• COLOUR (Lat. color, connected with celare, to hide, the root meaning, therefore, being that of a covering)

colour, See also:

• OPTICAL

optical rotatory See also:

• POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power, &c., like the conductivities, are additive, i.e. can be calculated by adding together the corresponding properties of the parts . This again suggests that these parts are independent of each other . For instance, the colour of a salt solution is the colour obtained by the superposition of the See also:

• COLOURS, MILITARY

colours of the ions and the colour of any undissociated salt that may be present . All copper salts in dilute solution are See also:

• BLUE (common in different forms to most European languages)

blue, which is therefore the colour of the copper ion . Solid copper chloride is See also:

• BROWN
• BROWN, CHARLES BROCKDEN (1771-181o)
• BROWN, FORD MADOX (1821-1893)
• BROWN, FRANCIS (1849- )
• BROWN, GEORGE (1818-188o)
• BROWN, HENRY KIRKE (1814-1886)
• BROWN, JACOB (1775–1828)
• BROWN, JOHN (1715–1766)
• BROWN, JOHN (1722-1787)
• BROWN, JOHN (1735–1788)
• BROWN, JOHN (1784–1858)
• BROWN, JOHN (1800-1859)
• BROWN, JOHN (1810—1882)
• BROWN, JOHN GEORGE (1831— )
• BROWN, ROBERT (1773-1858)
• BROWN, SAMUEL MORISON (1817—1856)
• BROWN, SIR GEORGE (1790-1865)
• BROWN, SIR JOHN (1816-1896)
• BROWN, SIR WILLIAM, BART
• BROWN, THOMAS (1663-1704)
• BROWN, THOMAS (1778-1820)
• BROWN, THOMAS EDWARD (1830-1897)
• BROWN, WILLIAM LAURENCE (1755–1830)

brown or yellow, so that its concentrated solution, which contains both ions and undissociated molecules, is See also:

• GREEN, A
• GREEN, ALEXANDER HENRY (1832—1896)
• GREEN, DUFF (1791—1875)
• GREEN, JOHN RICHARD (1837—1883)
• GREEN, MATTHEW (1696-1737)
• GREEN, THOMAS HILL (1836-1882)
• GREEN, VALENTINE (1739–1813)
• GREEN, WILLIAM HENRY (.1825–1900)

green, but changes to blue as water is added and the ionization becomes complete . A series of equivalent solutions all containing the same coloured ion have absorption spectra which, when photographed, show identical absorption bands of equal intensity.3 The colour changes shown by many sub-stances which are used as indicators (q.v.) of acids or alkalis can be explained in a similar way . Thus See also:

• PARA
• PARA (officially BELEM; sometimes BELEM DO PARA)

para-nitrophenol has colour-less molecules, but an intensely yellow negative ion . In neutral, and still more in acid solutions, the dissociation of the See also:

• INDICATOR (from Lat. indicare, to point out)

indicator is practically nothing, and the liquid is colourless .

If an alkali is added, however, a highly dissociated salt of para-nitrophenol is formed, and the yellow colour is at once evident . In other cases, such as that of See also:

• LITMUS (apparently a corruption of lacmus, Dutch lacmoes, lac, lac, and moes, pulp, due to association with " lit," an obsolete word for dye, colour; the Ger. equivalent is Lac/emus, Fr tournesol)

litmus, both the ion and the undissociated molecule are coloured, but in different ways . Electrolytes possess the power of coagulating solutions of colloids such as albumen and arsenious sulphide . The mean values of the relative coagulative See also:

• POWERS, HIRAM (1805-1873)

powers of sulphates of mono-, di-, and tri-valent metals have been shown experimentally to be approximately in the ratios 1 :35:1023 . The dissociation theory refers this to the action of electric charges carried by the free ions . If a certain minimum charge must be collected in See also:

• ORDER
• ORDER (through Fr. ordre, for earlier ordene, from Lat. ordo, ordinis, rank, service, arrangement; the ultimate source is generally taken to be the root seen in Lat. oriri, rise, arise, begin; cf. " origin ")
• ORDER, HOLY

order to start coagulation, it will need the See also:

• CONJUNCTION (from Lat. conjungere, to join together)

conjunction of 6n monovalent, or 311 divalent, to equal the effect of 211 trivalent ions . The ratios of the coagulative powers can thus be calculated to be 1:x:x', and putting x=32 we get 1 :32 :1024, a satisfactory agreement with the numbers observed.4 The question of the application of the dissociation theory to the case of fused salts remains . While it seems clear that the conduction in this case is carried on by ions similar to those of solutions, since Faraday's laws apply equally to both, it does not follow necessarily that semi-permanent dissociation is the only way to explain the phenomena . The evidence in favour of dissociation in the case of solutions does not apply to fused salts, and it is possible that, in their case, a series of molecular interchanges, somewhat like Grotthus's chain, may represent the mechanism of conduction . An interesting relation appears when the electrolytic conductivity of solutions is compared with their chemical activity . The readiness and speed with which electrolytes react are in W . Ostwald, Zeits. physikal .

Chemie, 1892, vol . Ix. p . 579; T . Ewan, Phil . Mag . (5), 1892, vol. xxxiii. p . 317; G . D . Liveing, See also:

• CAMBRIDGE
• CAMBRIDGE, EARLS AND DUKES OF
• CAMBRIDGE, RICHARD OWEN (1717-1802)

Cambridge Phil . Trans., 1900, vol. xviii. p . 298 . 4See W .

B . See also:

• HARDY, ALEXANDRE (1569?-1631)
• HARDY, SIR THOMAS DUFFUS (1804-1878)
• HARDY, SIR THOMAS MASTERMAN
• HARDY, THOMAS (1840- )

Hardy, See also:

• JOURNAL
• JOURNAL (through Fr. from late Lat. diurnalis, daily)

Journal of See also:

• PHYSIOLOGY (from Gr. 4 i s, nature, and koyos, discourse)

Physiology, 1899, vol. See also:

• XXIV

xxiv. p . 288; and W . C . D . Whetham, Phil . Mag., See also:

• NOVEMBER (Lat. novem, nine)

November 1899 . See also:

• SHARP, GRANVILLE (1735-1813)
• SHARP, JAMES (1618-1679)
• SHARP, JOHN (1645-1714)
• SHARP, RICHARD (1759-1835)
• SHARP, WILLIAM (1749-1824)
• SHARP, WILLIAM (1856-1905)

sharp contrast with the difficulty experienced in the case of non-electrolytes . Moreover, a study of the chemical relations of electrolytes indicates that it is always the electrolytic ions that are concerned in their reactions . The tests for a salt, potassium nitrate, for example, are the tests not for KNO3, but for its ions K and NO3, and in cases of double decomposition it is always these ions that are exchanged for those of other substances . If an element be present in a compound otherwise than as an ion, it is not interchangeable, and cannot be recognized by the usual tests . Thus neither a chlorate, which contains the ion C1O3, nor monochloracetic acid, shows the reactions of chlorine, though it is, of course, present in both substances; again, the sulphates do not See also:

• ANSWER (derived from and, against, and the same root as swear)

answer to the usual tests which indicate the presence of sulphur as sulphide .

The chemical activity of a substance is a quantity which may be measured by different methods . For some substances it has been shown to be independent of the particular reaction used . It is then possible to assign to each body a specific coefficient of See also:

• AFFINITY (Lat. affinitas, relationship by marriage, from offinis, bordering on, related to; finis, border, boundary)
• AFFINITY, CHEMICAL

affinity . Arrhenius has pointed out that the coefficient of affinity of an acid is proportional to its electrolytic ionization . The See also:

• AFFINITIES

affinities of acids have been compared in several ways . W . Ostwald (Lehrbuch der allg . Chemie, vol. ii., See also:

• LEIPZIG

Leipzig, 1893) investigated the relative affinities of acids for potash, soda, and See also:

• AMMONIA (NH3)

ammonia, and proved them to be independent of the See also:

• BASE

base used . The method employed was to measure the changes in volume caused by the action . His results are given in See also:

• COLUMN (Lat. columna)

column I. of the following table, the affinity of hydrochloric acid being taken as one hundred . Another method is to allow an acid to act on an insoluble salt, and to measure the quantity which goes into solution . Determinations have been made with calcium oxalate, CaC2O4+H20, which is easily decomposed by acids, oxalic acid and a soluble calcium salt being formed .

The affinities of acids relative to that of oxalic acid are thus found, so that the acids can be compared among themselves (column II.) . If an aqueous solution of methyl acetate be allowed to stand, a slow decomposition goes on . This is much quickened by the presence of a little dilute acid, though the acid itself remains unchanged . It is found that the influence of different acids on this action is proportional to their specific coefficients of affinity . The results of this method are given in column III . Finally, in column IV. the electrical conductivities of normal solutions of the acids have been tabulated . A better basis of comparison would be the ratio of the actual to the limiting conductivity, but since the conductivity of acids is chiefly due to the mobility of the hydrogen ions, its limiting value is nearly the same for all, and the general result of the comparison would be unchanged . Acid . I . I I . III . IV .

Hydrochloric See also:

• LOO (formerly called " Lanterloo," Fr. lanturlu, the refrain of a popular 17th-century song)

loo loo too loo Nitric 302 See also:

• ITO, HIROBUMI, PRINCE (1841-1909)

Ito 92 99'6 Sulphuric 68 67 74 65.1 Formic 4.0 2.5 1.3 1.7 Acetic 1.2 1•o 0.3 0.4 Propionic 1.1 .. 0.3 0.3 Monochloracetic 7.2 5•I 4•3 4'9 Dichloracetic . 34 18 23.0 25.3 Trichloracetic 82 63 68.2 62.3 Malic 3.0 5.o P2 1.3 Tartaric 5'3 6.3 2.3 2.3 Succinic 0.1 0.2 o'5 o•6 It must be remembered that, the solutions not being of quite the same strength, these numbers are not strictly comparable, and that the experimental difficulties involved in the chemical measurements are considerable . Nevertheless, the remarkable general agreement of the numbers in the four columns is quite enough to show the intimate connexion between chemical activity and electrical conductivity . We may take it, then, that only that portion of these bodies is chemically active which is electrolytically active—that ionization is necessary for such chemical activity as we are dealing with here, just as it is necessary for electrolytic conductivity . The ordinary laws of chemical equilibrium have been applied to the case of the dissociation of a substance into its ions . Let x be the number of molecules which dissociate per second when the number of undissociated molecules in unit volume is unity, then in a dilute solution where the molecules do not interfere with each other, xp is the number when the concentration is p . Recombination can anly occur when two ions meet, and since the frequency with which this will happen is, in dilute solution, proportional to the square of the ionic concentration, we shall get for the number of molecules re-formed in one second yqz where q is the number of dissociated molecules in one cubic centimetre: When there is equilibrium, xp = yqz . Ifµ be the molecular conductivity, and µcp its value at See also:

• INFINITE (from Lat. in, not, finis, end or limit; cf. findere, to deave)

infinite dilution, the fractional number of molecules dissociated isµ/µco , which we may write as a . The number of undissociated moleculesis then i — a, so that if V be the volume of the solution containing t gramme-molecule of the dissolved substance, we get q=a/V and p= (1 —a)/V, hence x(I —a) V =ya2/V2, and V(I_a) y=constant =k . This constant k gives a numerical value for the chemical affinity, and the, equation should represent the effect of dilution on the molecular conductivity of binary electrolytes . In the case of substances like ammonia and acetic acid, where the dissociation is very small, I —a is nearly equal to unity, and only varies slowly with dilution .

The equation then becomes See also:

• A2(z)

a2/V = k, or a= a/ Vk, so that the molecular conductivity is proportional to the square See also:

• ROOT (late O.E. rot, adopted from Scand., cf. Norw. and Swed. rot, Dan. rod; the true O.E. word was wyrt, plant, represented in Ger. Wurz or Wurzel; the ultimate root is the same in both words, and is seen in Lat. radix)
• ROOT, ELIHU (1845– )

root of the dilution . Ostwald has confirmed the equation by observation on an enormous number of weak acids (Zeits. physikal . Chemie, 1888, ii. p . 278; 1889, iii. pp . 170, 241, 369) . Thus' in the case of cyanacetic acid, while the volume V changed by doubling from 16 to 1024 litres, the values of k were o.00 (376, 373, 374, 361, 362, 361, 368) . The mean values of k for other common acids were—formic, 0.0000214; acetic, o•o0oot8o; monochloracetic, 0.00155; dichloracetic, 0.051; trichloracetic, 1.21; propionic, 0.0000134 . From these numbers we can, by help of the equation, calculate the conductivity of the acids for any dilution . The value of k, however, does not keep constant so satisfactorily in the case of highly dissociated substances, and empirical formulae have been constructed to represent the effect of dilution on them . Thus the values of the expressions az/(I —a V) (Rudolphi, Zeits. physikal . Chemie, 1895, vol. xvii. p . 385) and a3/(1—a)2V (van 't Hoff, ibid., 1895, vol. xviii. p .

300) are found to keep constant as V changes . Van 't Hoff's formula is equivalent to taking the frequency of dissociation as proportional to the square of the concentration of the molecules, and the frequency of recombination as proportional to the See also:

• CUBE (Gr. K46os, a cube)

cube of the concentration of the ions . An explanation of the failure of the usual dilution law in these cases may be given if we remember that, while the electric forces between bodies like undissociated molecules, each associated with equal and opposite charges, will vary inversely as the See also:

• FOURTH

fourth power of the distance, the forces between dissociated ions, each carrying one charge only, will be inversely proportional to the square of the distance . The forces between the ions of a strongly dissociated solution will thus be considerable at a dilution which makes forces between undissociated molecules quite insensible, and at the concentrations necessary to test Ostwald's formula an electrolyte will be far from dilute in the thermodynamic sense of the See also:

• TERM

term, which implies no appreciable intermolecular or interionic forces . When the solutions of two substances are mixed, similar considerations to those given above enable us to calculate the resultant changes in dissociation . (See Arrhenius, See also:

• LAC

lac. cit.) The simplest and most important case is that of two electrolytes having one ion'in common, such as two acids . It is evident that the undissociated part of each acid must eventually be in equilibrium with the free hydrogen ions, and, if the concentrations are not such as to secure this condition, readjustment must occur . In order that there should be no change in the states of dissociation on mixing, it is necessary, therefore, that the concentration of the hydrogen ions should be the same in each separate solution . Such solutions were called by Arrhenius isohydric." The two solutions, then, will so act on each other when mixed that they become isohydric . Let us suppose that we have one very active acid like hydrochloric, in which dissociation is nearly complete, another like acetic, in which it is very small . In order that the solutions of these should be isohydric and the concentrations of the hydrogen ions the same, we must have a very large quantity of the feebly dissociated acetic acid, and a very small quantity of the strongly dissociated hydrochloric, and in such proportions alone will equilibrium be possible . This explains the action of a strong acid on the salt of a weak acid .

Let us allow dilute sodium acetate to react with dilute hydrochloric acid . Some acetic acid is formed, and this process will go on till the solutions of the two acids are isohydric: that is, till the dissociated hydrogen ions are in equilibrium with both . In order that this should hold, we have seen that a considerable quantity of acetic acid must be present, so that a corresponding amount of the salt will be decomposed, the quantity being greater the less the acid is dissociated . This " replacement &