Chapter LXIII: repeats the promise of freedom to the English church (1)

and of their rights and liberties to all.

Magna Carta is an elaboration of the accession charter of Henry I., and is based upon the Articles of the Barons. It is, however, very much longer than the former charter and somewhat longer than the Articles. Moreover, it differs in several particulars from the Articles, these differences being doubtless the outcome of deliberation and of compromise. For instance, the provisions in Magna Carta concerning the freedom of the church find no place in the Articles, while a comparison between the two documents suggests that in other ways also influences favourable to the church and the clergy were at work while the famous charter was being framed. When one reflects how active and prominent Langton and other prelates were at Runnimede the change is not surprising. Another difference between the two documents concerns the towns and the trading classes. Certain privileges granted to them in the Articles are not found in Magna Carta, although, it must be noted, this document bestows exceptionally favoured treatment on the citizens of London. The conclusion is that the friends of the towns and the traders were less in evidence at Runnimede than they were at the earlier meetings of the barons, but that the neighbouring Londoners were strong enough to secure a good price for their support.

Magna Carta throws much light on the condition of England in the early 13th century. By denouncing the evil deeds of John and the innovations practised by him, it shows what these were and how they were hated; how money had been raised, how forest areas had been extended, how minors and widows had been cheated and oppressed. By declaring, as it does, what were the laws and customs of a past age wherein justice prevailed, it shows what was the ideal of good government formed by John's prelates and barons. Magna Carta can hardly be said to have introduced any new ideas. As Pollock and Maitland (_History of English Law_) say "on the whole the charter contains little that is absolutely new. It is restorative." But although mature study has established the truth of this proposition it was not always so. Statesmen and commentators alike professed to find in Magna Carta a number of political ideas which belonged to a later age, and which had no place in the minds of its framers. It was regarded as having conferred upon the nation nothing less than the English constitution in its perfect and completed form. Sir Edward Coke finds in Magna Carta a full and proper legal answer to every exaction of the Stuart kings, and a remedy for every evil suffered at the time. Sir William Blackstone is almost equally admiring. Edmund Burke says "Magna Carta, if it did not give us originally the House of Commons, gave us at least a House of Commons of weight and consequence." Lord Chatham used words equally superlative. "Magna Carta, the Petition of Rights and the Bill of Rights form that code, which I call the Bible of the English Constitution." Modern historians, although less rhetorical, speak in the highest terms of the importance of Magna Carta, the view of most of them being summed up in the words of Dr Stubbs: "The whole of the constitutional history of England is a commentary on this charter."

Many regard Magna Carta as giving equal rights to all Englishmen. J. R. Green says "The rights which the barons claimed for themselves they claimed for the nation at large." As a matter of fact this statement is only true with large limitations. The villains, who formed the majority of the population, got very little from it; in fact the only clauses which protect them do so because they are property--the property of their lords--and therefore valuable. They get neither political nor civil rights under Magna Carta. The traders, too, get little, while preferential treatment is meted out to the clergy and the barons. Its benefits are confined to freemen, and of the benefits the lion's share fell to the larger landholders; the smaller landholders getting, it is true, some crumbs from the table. It did not establish freedom from arbitrary arrest, or the right of the representatives of the people to control taxation, or trial by jury, or other conceptions of a later generation.

The story of Magna Carta after the death of John is soon told. On the 12th of November 1216 the regent William Marshal, earl of Pembroke, reissued the charter in the name of the young king Henry III. But important alterations were made. War was being waged against Louis of France, and the executive must not be hampered in the work of raising money; moreover the personal equation had disappeared, the barons did not need to protect themselves against John. Consequently the chapter limiting the power of the crown to raise scutages and aids without the consent of the council vanished, and with it the complementary one which determined the method of calling a council. Other provisions, the object of which had been to restrain John from demanding more money from various classes of his subjects, were also deleted, and the same fate befell such chapters as dealt with mere temporary matters. The most important of these was Chapter LXI., which provided for the appointment of 25 executors to compel John to observe the charter. The next year peace was made at Lambeth (Sept. 11, 1217) between Henry III. and Louis and another reissue of the charter was promised. This promise was carried out, but two charters appeared, one being a revised issue of Magna Carta proper, and the other a separate charter dealing with the forests, all references to which were omitted from the more important document. The date of this issue appears to have been the 6th of November 1217. The issue of a separate forest charter at this time led subsequently to some confusion. Roger of Wendover asserts that John issued a separate charter of this kind when Magna Carta appeared. This statement was believed by subsequent writers until the time of Blackstone, who was the first to discover the mistake.

As issued in 1217 Magna Carta consists of 47 chapters only. It declares that henceforward scutages shall be taken according to the precedents of Henry II.'s reign. New provisions were introduced for the preservation of the peace--unlawful castles were to be destroyed--while others were directed towards making the administration of justice by the visiting justices less burdensome. With regard to the land and the services due therefrom a beginning was made of the policy which culminated in the statutes of Mortmain and of Quia Emptores. The sheriffs were ordered to publish the revised charter on the 22nd of February 1218. Then in February 1225 Henry III. again issued the two charters with only two slight alterations, and this is the final form taken by Magna Carta, this text being the one referred to by Coke and the other early commentators. Subsequently the charters were confirmed several times by Henry III. and by Edward I., the most important occasion being their confirmation by Edward at Ghent in November 1297. On this occasion some supplementary articles were added to the charter; these were intended to limit the taxing power of the crown.

There are at present in existence four copies of Magna Carta, sealed
with the great seal of King John, and several unsealed copies. Of the
four two are in the British Museum. Both came into the possession of
the Museum with the valuable collection of papers which had belonged
to Sir Robert Cotton, who had obtained possession of both. One was
found in Dover castle about 1630. This was damaged by fire in 1731;
the other is undamaged. The two other sealed copies belong to the
cathedrals of Lincoln and of Salisbury. Both were written evidently in
a less hurried fashion than those in the British Museum, and the one
at Lincoln was regarded as the most perfect by the commissioners who
were responsible for the appearance of the _Statutes of the Realm_
1810. The British Museum also contains the original parchment of the
Articles of the Barons. Magna Carta was first printed by Richard
Pynson in 1499. This, however, was not the original text, which was
neglected until the time of Blackstone, who printed the various issues
of the charter in his book _The Great Charter and the Charter of the
Forest_ (1759). The earliest commentator of note was Sir Edward Coke,
who published his _Second Institute_, which deals with Magna Carta, by
order of the Long Parliament in 1642. Modern commentators, who also
print the various texts of the charter, are Richard Thomson, _An
Historical Essay on the Magna Carta of King John_ (1829); C. Bémont,
in his _Chartes des libertés anglaises_ (1892); and W. Stubbs in his
_Select Charters_ (1895). A more recent book and one embodying the
results of the latest research is W. S. McKechnie, _Magna Carta_
(1905). The text of Magna Carta is also printed in the _Statutes of
the Realm_ (1810-1828), and in T. Rymer's _Foedera_ (1816-1869). In
addition to Blackstone, Coke and these later writers, the following
works may also be consulted: John Reeves, _History of English Law_
(1783-1784); L. O. Pike, _A Constitutional History of the House of
Lords_ (1894); W. Stubbs, _Constitutional History of England_ (1897);
Sir F. Pollock and F. W. Maitland, _The History of English Law_
(1895); W. S. Holdsworth, _A History of English Law_ (1903), and Kate
Norgate, _John Lackland_ (1902). (A. W. H.*)

MAGNA GRAECIA ([Greek: he megale Hellas]), the name given (first, apparently, in the 6th century B.C.) to the group of Greek cities along the coast of the "toe" of South Italy (or more strictly those only from Tarentum to Locri, along the east coast), while the people were called Italiotes ([Greek: Italiôtai]). The interior, which the Greeks never subdued, continued to be in the hands of the Bruttii, the native mountaineers, from whom the district was named in Roman times ([Greek: Brettia] also in Greek writers). The Greek colonies were established first as trading stations, which grew into independent cities. At an early time a trade in copper was carried on between Greece and Temesa (Homer, _Od._ i. 181).[1] The trade for a long time was chiefly in the hands of the Euboeans; and Cyme (Cumae) in Campania was founded in the 8th century B.C., when the Euboean Cyme was still a great city. After this the energy of Chalcis went onward to Sicily, and the states of the Corinthian Gulf carried out the colonization of Italy, Rhegium having been founded, it is true, by Chalcis, but after Messana (Zancle), and at the request of the inhabitants of the latter. Sybaris (721) and Crotona (703) were Achaean settlements; Locri Epizephyrii (about 710) was settled by Ozolian Locrians, so that, had it not been for the Dorian colony of Tarentum, the southern coast of Italy would have been entirely occupied by a group of Achaean cities. Tarentum (whether or no founded by pre-Dorian Greeks--its founders bore the unexplained name of Partheniae) became a Laconian colony at some unknown date, whence a legend grew up connecting the Partheniae with Sparta, and 707 B.C. was assigned as its traditional date. Tarentum is remarkable as the only foreign settlement made by the Spartans. It was industrial, depending largely on the purple and pottery trade. Ionian Greeks fleeing from foreign invasion founded Siris about 650 B.C., and, much later, Elea (540).

The Italian colonies were planted among friendly, almost kindred, races, and grew much more rapidly than the Sicilian Greek states, which had to contend against the power of Carthage. After the Achaean cities had combined to destroy the Ionic Siris, and had founded Metapontum as a counterpoise to the Dorian Tarentum, there seems to have been little strife among the Italiotes. An amphictyonic league, meeting in common rites at the temple of Hera on the Lacinian promontory, fostered a feeling of unity among them. The Pythagorean and Eleatic systems of philosophy had their chief seat in Magna Graecia. Other departments of literature do not seem to have been so much cultivated among them. The poet Ibycus, though a native of Rhegium, led a very wandering life. They sent competitors to the Olympic games (among them the famous Milo of Croton); and the physicians of Croton early in the 6th century (especially in the person of Democedes) were reputed the best in Greece; but politically they appear to have generally kept themselves separate. One ship of Croton, however, fought at Salamis, though it is not recorded that Greece asked the Italiotes for help when it sent ambassadors to Gelon of Syracuse. Mutual discord first sapped the prosperity of Magna Graecia. In 510 Croton, having defeated the Sybarites in a great battle, totally destroyed their city. Croton maintained alone the leading position which had belonged jointly to the Achaean cities (Diod. xiv. 103); but from that time Magna Graecia steadily declined. In the war between Athens and Syracuse Magna Graecia took comparatively little part; Locri was strongly anti-Athenian, but Rhegium, though it was the headquarters of the Athenians in 427, remained neutral in 415. Foreign enemies pressed heavily on it. The Lucanians and Bruttians on the north captured one town after another. Dionysius of Syracuse attacked them from the south; and after he defeated the Crotoniate league and destroyed Caulonia (389 B.C.), Tarentum remained the only powerful city. Henceforth the history of Magna Graecia is only a record of the vicissitudes of Tarentum (q.v.). Repeated expeditions from Sparta and Epirus tried in vain to prop up the decaying Greek states against the Lucanians and Bruttians; and when in 282 the Romans appeared in the Tarentine Gulf the end was close at hand. The aid which Pyrrhus brought did little good to the Tarentines, and his final departure in 274 left them defenceless. During these constant wars the Greek cities had been steadily decaying; and in the second Punic war, when most of them seized the opportunity of revolting from Rome, their very existence was in some cases annihilated. Malaria increased in strength as the population diminished. We are told by Cicero (_De am._ 4), _Magna Graecia nunc quidem deleta est_. Many of the cities completely disappeared, and hardly any of them were of great importance under the Roman empire; some, like Tarentum, maintained their existence into modern times, and in these only (except at Locri) have archaeological investigations of any importance been carried on; so that there still remains a considerable field for investigation. (T. As.)

FOOTNOTE:

[1] This passage should perhaps be referred to the 8th century B.C.
It is the first mention of an Italian place in a literary record.

MAGNATE (Late Lat. _magnas_, a great man), a noble, a man in high position, by birth, wealth or other qualities. The term is specifically applied to the members of the Upper House in Hungary, the _Förendihaz_ or House of Magnates (see HUNGARY).

MAGNES (_c._ 460 B.C.), Athenian writer of the Old Comedy, a native of the deme of Icaria in Attica. His death is alluded to by Aristophanes (_Equites_, 518-523, which was brought out in 424 B.C.), who states that in his old age Magnes had lost the popularity which he had formerly enjoyed. The few titles of his plays that remain, such as the _Frogs_, the _Birds_, the _Gall-flies_, indicate that he anticipated Aristophanes in introducing grotesque costumes for the chorus.

See T. Kock, _Comicorum atticorum fragmenta_, i. (1880); G. H. Bode,
_Geschichte der hellenischen Dichtkunst_, iii. pt. 2 (1840).

MAGNESIA, in ancient geography the name of two cities in Asia Minor and of a district in eastern Thessaly, lying between the Vale of Tempe and the Pagasaean Gulf.

(1) MAGNESIA AD MAEANDRUM, a city of Ionia, situated on a small stream flowing into the Maeander, 15 Roman miles from Miletus and rather less from Ephesus. According to tradition, reinforced by the similarity of names, it was founded by colonists from the Thessalian tribe of the Magnetes, with whom were associated, according to Strabo, some Cretan settlers (Magnesia retained a connexion with Crete, as inscriptions found there attest). It was thus not properly an Ionic city, and for this reason, apparently, was not included in the Ionian league, though superior in wealth and prosperity to most of the members except Ephesus and Miletus. It was destroyed by the Cimmerii in their irruption into Asia Minor, but was soon after rebuilt, and gradually recovered its former prosperity. It was one of the towns assigned by Artaxerxes to Themistocles for support in his exile, and there the latter ended his days. His statue stood in its market-place. Thibron, the Spartan, persuaded the Magnesians to leave their indefensible and mutinous city in 399 B.C. and build afresh at Leucophrys, an hour distant, noted for its temple of Artemis Leucophryne, which, according to Strabo, surpassed that at Ephesus in the beauty of its architecture, though inferior in size and wealth. Its ruins were excavated by Dr K. Humann for the Constantinople Museum in 1891-1893; but most of the frieze of the temple of Artemis Leucophryne, representing an Amazon battle, had already been carried off by Texier (1843) to the Louvre. It was an octostyle, pseudo-dipteral temple of highly ornate Ionic order, built on older foundations by Hermogenes of Alabanda at the end of the 3rd century B.C. The platform has been greatly overgrown since the excavation, but many bases, capitals, and other architectural members are visible. In front of the west façade stood a great altar. An immense _peribolus_ wall is still standing (20 ft. high), but its Doric colonnade has vanished. The railway runs right through the precinct, and much of Magnesia has gone into its bridges and embankments. South and west of the temple are many other remains of the Roman city, including a fairly perfect theatre excavated by Hiller von Gärtringen, and the shell of a large gymnasium. Part of the Agora was laid open to Humann, but his trenches have fallen in. The site is so unhealthy that even the Circassians who settled there twenty years ago have almost all died off or emigrated. Magnesia continued under the kings of Pergamum to be one of the most flourishing cities in this part of Asia; it resisted Mithradates in 87 B.C., and was rewarded with civic freedom by Sulla; but it appears to have greatly declined under the Roman empire, and its name disappears from history, though on coins of the time of Gordian it still claimed to be the seventh city of Asia.

See K. Haumann, _Magnesia am Maeander_ (1904).

(2) MAGNESIA AD SIPYLUM (mod. _Manisa_, q.v.), a city of Lydia about 40 m. N.E. of Smyrna on the river Hermus at the foot of Mt Sipylus. No mention of the town is found till 190 B.C., when Antiochus the Great was defeated under its walls by the Roman consul L. Scipio Asiaticus. It became a city of importance under the Roman dominion and, though nearly destroyed by an earthquake in the reign of Tiberius, was restored by that emperor and flourished through the Roman empire. It was one of the few towns in this part of Asia Minor which remained prosperous under the Turkish rule. The most famous relic of antiquity is the "Niobe of Sipylus" (_Suratlu Tash_) on the lowest slopes of the mountain about 4 m. east of the town. This is a colossal seated image cut in a niche of the rock, of "Hittite" origin, and perhaps that called by Pausanias the "very ancient statue of the Mother of the Gods," carved by Broteas, son of Tantalus, and sung by Homer. Near it lie many remains of a primitive city, and about half a mile east is the rock-seat conjecturally identified with Pausanias' "Throne of Pelops." There are also hot springs and a sacred grotto of Apollo. The whole site seems to be that of the early "Tantalus" city. (D. G. H.)

MAGNESITE, a mineral consisting of magnesium carbonate, MgCO3, and belonging to the calcite group of rhombohedral carbonates. It is rarely found in crystals or crystalline masses, being usually compact or earthy and intermixed with more or less hydrous magnesium silicate (meerschaum). The compact material has the appearance of unglazed porcelain, and the earthy that of chalk. In colour it is usually dead white, sometimes yellowish. The hardness of the crystallized mineral is 4; sp. gr. 3.1. The name magnesite as originally applied by J. C. Delamétherie in 1797 included several minerals containing magnesium, and at the present day it is used by French writers for meerschaum. The mineral has also been called baudisserite from the locality Baudissero near Ivrea in Piedmont. Breunnerite is a ferriferous variety.

Magnesite is a product of alteration of magnesium silicates, and
occurs as veins and patches in serpentine, talc-schist or
dolomite-rock. It is extensively mined in the island of Euboea in the
Grecian Archipelago, near Salem in Madras, and in California, U.S.A.
It is principally used for the manufacture of highly refractory
fire-bricks for lining steel furnaces and electric furnaces; also for
making plaster, tiles and artificial stone; for the preparation of
magnesium salts (Epsom salts, &c.); for whitening; paper-pulp and
wool; and as a paint.

MAGNESIUM [symbol Mg, atomic weight 24.32 (O = 16)], a metallic chemical element. The sulphate or "Epsom salts" (q.v.) was isolated in 1695 by N. Grew, while in 1707 M. B. Valentin prepared _magnesia alba_ from the mother liquors obtained in the manufacture of nitre. Magnesia was confounded with lime until 1755, when J. Black showed that the two substances were entirely different; and in 1808 Davy pointed out that it was the oxide of a metal, which, however, he was not able to isolate. Magnesium is found widely distributed in nature, chiefly in the forms of silicate, carbonate and chloride, and occurring in the minerals olivine, hornblende, talc, asbestos, meerschaum, augite, dolomite, magnesite, carnallite, kieserite and kainite. The metal was prepared (in a state approximating to purity) by A. A. B. Bussy (_Jour. de pharm._ 1829, 15, p. 30; 1830, 16, p. 142), who fused the anhydrous chloride with potassium; H. Sainte Claire Deville's process, which used to be employed commercially, was essentially the same, except that sodium was substituted for potassium (_Comptes rendus_, 1857, 44, p. 394), the product being further purified by redistillation. It may also be prepared by heating a mixture of carbon, oxide of iron and magnesite to bright redness; and by heating a mixture of magnesium ferrocyanide and sodium carbonate, the double cyanide formed being then decomposed by heating it with metallic zinc. Electrolytic methods have entirely superseded the older methods. The problem of magnesium reduction is in many respects similar to that of aluminium extraction, but the lightness of the metal as compared, bulk for bulk, with its fused salts, and the readiness with which it burns when exposed to air at high temperatures, render the problem somewhat more difficult.

Moissan found that the oxide resisted reduction by carbon in the
electric furnace, so that electrolysis of a fusible salt of the metal
must be resorted to. Bunsen, in 1852, electrolysed fused magnesium
chloride in a porcelain crucible. In later processes, carnallite (a
natural double chloride of magnesium and potassium) has commonly,
after careful dehydration, been substituted for the single chloride.
Graetzel's process, which was at one time employed, consisted in
electrolysing the chloride in a metal crucible heated externally, the
crucible itself forming the cathode, and the magnesium being deposited
upon its inner surface. W. Borchers also used an externally heated
metal vessel as the cathode; it is provided with a supporting collar
or flange a little below the top, so that the upper part of the vessel
is exposed to the cooling influence of the air, in order that a crust
of solidified salt may there be formed, and so prevent the creeping of
the electrolyte over the top. The carbon anode passes through the
cover of a porcelain cylinder, open at the bottom, and provided with a
side-tube at the top to remove the chlorine formed during
electrolysis. The operation is conducted at a dull red heat (about
760° C. or 1400° F.), the current density being about 0.64 amperes per
sq. in. of cathode surface, and the pressure about 7 volts. The
fusing-point of the metal is about 730° C. (1350° F.), and the
magnesium is therefore reduced in the form of melted globules which
gradually accumulate. At intervals the current is interrupted, the
cover removed, and the temperature of the vessel raised considerably
above the melting-point of magnesium. The metal is then removed from
the walls with the aid of an iron scraper, and the whole mass poured
into a sheet-iron tray, where it solidifies. The solidified chloride
is then broken up, the shots and fused masses of magnesium are picked
out, run together in a plumbago crucible without flux, and poured into
a suitable mould. Smaller pieces are thrown into a bath of melted
carnallite and pressed together with an iron rod, the bath being then
heated until the globules of metal float to the top, when they may be
removed in perforated iron ladles, through the holes in which the
fused chloride can drain away, but through which the melted magnesium
cannot pass by reason of its high surface tension. The globules are
then re-melted. F. Oettel (_Zeit. f. Elektrochem._, 1895, 2, p. 394)
recommends the electrolytic preparation from carnallite; the mineral
should be freed from water and sulphates.

Magnesium is a silvery white metal possessing a high lustre. It is malleable and ductile. Sp. gr. 1.75. It preserves its lustre in dry air, but in moist air it becomes tarnished by the formation of a film of oxide. It melts at 632.7° C. (C. T. Heycock and F. H. Neville), and boils at about 1100°C. Magnesium and its salts are diamagnetic. It burns brilliantly when heated in air or oxygen, or even in carbon dioxide, emitting a brilliant white light and leaving a residue of magnesia, MgO. The light is rich in the violet and ultra-violet rays, and consequently is employed in photography. The metal is also used in pyrotechny. It also burns when heated in a current of steam, which it decomposes with the liberation of hydrogen and the formation of magnesia. At high temperatures it acts as a reducing agent, reducing silica to silicon, boric acid to boron, &c. (H. Moissan, _Comptes rendus_, 1892, 114, p. 392). It combines directly with nitrogen, when heated in the gas, to form the nitride Mg3N2 (see ARGON). It is rapidly dissolved by dilute acids, with the evolution of hydrogen and the formation of magnesium salts. It precipitates many metals from solutions of their salts.

_Magnesium Oxide_, magnesia, MgO, occurs native as the mineral
periclase, and is formed when magnesium burns in air; it may also be
prepared by the gentle ignition of the hydroxide or carbonate. It is a
non-volatile and almost infusible white powder, which slowly absorbs
moisture and carbon dioxide from air, and is readily soluble in dilute
acids. On account of its refractory nature, it is employed in the
manufacture of crucibles, furnace linings, &c. It is also used in
making hydraulic cements. A crystalline form was obtained by M.
Houdard (_Abst. J. C. S._, 1907, ii. p. 621) by fusing the oxide and
sulphide in the electric furnace. _Magnesium hydroxide_ Mg(OH)2,
occurs native as the minerals brucite and némalite, and is prepared by
precipitating solutions of magnesium salts by means of caustic soda or
potash. An artificial brucite was prepared by A. de Schulten (_Comptes
rendus_, 1885, 101, p. 72) by boiling magnesium chloride with caustic
potash and allowing the solution to cool. Magnesium hydroxide is a
white amorphous solid which is only slightly soluble in water; the
solubility is, however, greatly increased by ammonium salts. It
possesses an alkaline reaction and absorbs carbon dioxide. It is
employed in the manufacture of cements.

When magnesium is heated in fluorine or chlorine or in the vapour of
bromine or iodine there is a violent reaction, and the corresponding
halide compounds are formed. With the exception of the fluoride, these
substances are readily soluble in water and are deliquescent. The
fluoride is found native as sellaïte, and the bromide and iodide occur
in sea water and in many mineral springs. The most important of the
halide salts is the _chloride_ which, in the hydrated form, has the
formula MgCl2·6H2O. It may be prepared by dissolving the metal, its
oxide, hydroxide, or carbonate in dilute hydrochloric acid, or by
mixing concentrated solutions of magnesium sulphate and common salt,
and cooling the mixture rapidly, when the less soluble sodium
sulphate separates first. It is also formed as a by-product in the
manufacture of potassium chloride from carnallite. The hydrated salt
loses water on heating, and partially decomposes into hydrochloric
acid and magnesium oxychlorides. To obtain the anhydrous salt, the
double magnesium ammonium chloride, MgCl2·NH4Cl·6H2O, is prepared by
adding ammonium chloride to a solution of magnesium chloride. The
solution is evaporated, and the residue strongly heated, when water
and ammonium chloride are expelled, and anhydrous magnesium chloride
remains. Magnesium chloride readily forms double salts with the
alkaline chlorides. A strong solution of the chloride made into a
thick paste with calcined magnesia sets in a few hours to a hard,
stone-like mass, which contains an oxychloride of varying composition.
Magnesium oxychloride when heated to redness in a current of air
evolves a mixture of hydrochloric acid and chlorine and leaves a
residue of magnesia, a reaction which is employed in the
Weldon-Pechiney and Mond processes for the manufacture of chlorine.

_Magnesium Carbonate,_ MgCO3.--The normal salt is found native as the
mineral magnesite, and in combination with calcium carbonate as
dolomite, whilst hydromagnesite is a basic carbonate. It is not
possible to prepare the normal carbonate by precipitating magnesium
salts with sodium carbonate. C. Marignac has prepared it by the action
of calcium carbonate on magnesium chloride. A salt MgCO3·3H2O or
Mg(CO3H)(OH)·2H2O may be prepared from the carbonate by dissolving it
in water charged with carbon dioxide, and then reducing the pressure
(W. A. Davis, _Jour. Soc. Chem. Ind._ 1906, 25, p. 788). The carbonate
is not easily soluble in dilute acids, but is readily soluble in water
containing carbon dioxide. _Magnesia alba_, a white bulky precipitate
obtained by adding sodium carbonate to Epsom salts, is a mixture of
Mg(CO3H)(OH)·2H2O, Mg(CO3H)(OH) and Mg(OH)2. It is almost insoluble in
water, but readily dissolves in ammonium salts.

_Magnesium Phosphates._--By adding sodium phosphate to magnesium
sulphate and allowing the mixture to stand, hexagonal needles of
MgHPO4·7H2O are deposited. The _normal phosphate_, Mg3P2O8, is found
in some guanos, and as the mineral wagnerite. It may be prepared by
adding normal sodium phosphate to a magnesium salt and boiling the
precipitate with a solution of magnesium sulphate. It is a white
amorphous powder, readily soluble in acids. _Magnesium ammonium
phosphate_, MgNH4PO4·6H2O, is found as the mineral struvite and in
some guanos; it occurs also in urinary calculi and is formed in the
putrefaction of urine. It is prepared by adding sodium phosphate to
magnesium sulphate in the presence of ammonia and ammonium chloride.
When heated to 100° C., it loses five molecules of water of
crystallization, and at a higher temperature loses the remainder of
the water and also ammonia, leaving a residue of magnesium
pyrophosphate, Mg2P2O7. _Magnesium Nitrate_, Mg(NO3)2·6H2O, is a
colourless, deliquescent, crystalline solid obtained by dissolving
magnesium or its carbonate in nitric acid, and concentrating the
solution. The crystals melt at 90° C. _Magnesium Nitride_, Mg3N2, is
obtained as a greenish-yellow amorphous mass by passing a current of
nitrogen or ammonia over heated magnesium (F. Briegleb and A. Geuther,
_Ann._, 1862, 123, p. 228; see also W. Eidmann and L. Moeser, _Ber._,
1901, 34, p. 390). When heated in dry oxygen it becomes incandescent,
forming magnesia. Water decomposes it with liberation of ammonia and
formation of magnesium hydroxide. The chlorides of nickel, cobalt,
chromium, iron and mercury are converted into nitrides when heated
with it, whilst the chlorides of copper and platinum are reduced to
the metals (A. Smits, _Rec. Pays Bas_, 1896, 15, p. 135). _Magnesium
sulphide_, MgS, may be obtained, mixed with some unaltered metal and
some magnesia, as a hard brown mass by heating magnesia, in sulphur
vapour. It slowly decomposes in moist air. _Magnesium sulphate_,
MgSO4, occurs (with IH2O) as Kieserite. A hexahydrate is also known.
The salt may be obtained from Kieserite: formerly it was prepared by
treating magnesite or dolomite with sulphuric acid.

Grignard Reagent.

_Organic Compounds._--By heating magnesium filings with methyl and
ethyl iodides A. Cahours (_Ann. chim. phys._, 1860, 58, pp. 5, 19)
obtained magnesium methyl, Mg(CH3)2, and magnesium ethyl, Mg(C2H5)2,
as colourless, strongly smelling, mobile liquids, which are
spontaneously inflammable and are readily decomposed by water. The
compounds formed by the action of magnesium on alkyl iodides in the
cold have been largely used in synthetic organic chemistry since V.
Grignard (_Comptes rendus_, 1900 et seq.) observed that magnesium and
alkyl or aryl halides combined together in presence of anhydrous ether
at ordinary temperatures (with the appearance of brisk boiling) to
form compounds of the type RMgX(R = an alkyl or aryl group and X =
halogen). These compounds are insoluble in ether, are non-inflammable
and exceedingly reactive. A. V. Baeyer (_Ber._, 1902, 35, p. 1201)
regards them as oxonium salts containing tetravalent oxygen
(C2H5)2:O:(MgR) (X), whilst W. Tschelinzeff (_Ber._, 1906, 39, p. 773)
considers that they contain two molecules of ether. In preparing the
Grignard reagent the commencement of the reaction is accelerated by a
trace of iodine. W. Tschelinzeff (_Ber._, 1904, 37, p. 4534) showed
that the ether may be replaced by benzene containing a small quantity
of ether or anisole, or a few drops of a tertiary amine. With
unsaturated alkyl halides the products are only slightly soluble in
ether, and two molecules of the alkyl compound are brought into the
reaction. They are very unstable, and do not react in the normal
manner. (V. Grignard and L. Tissier, _Comptes rendus_, 1901, 132, p.
558).

The products formed by the action of the Grignard reagent with the
various types of organic compounds are usually thrown out of solution
in the form of crystalline precipitates or as thick oils, and are then
decomposed by ice-cold dilute sulphuric or acetic acids, the magnesium
being removed as a basic halide salt.

_Applications._--For the formation of primary and secondary alcohols
see ALDEHYDES and KETONES. Formaldehyde behaves abnormally with
magnesium benzyl bromide (M. Tiffeneau, _Comptes rendus_, 1903, 137,
p. 573). forming ortho-tolylcarbinol, CH3·C6H4·CH2OH, and not
benzylcarbinol, C6H5CH2·CH2OH (cf. the reaction of formaldehyde on
phenols: O. Manasse, _Ber._ 1894, 27, p. 2904). Acid esters yield
carbinols, many of which are unstable and readily pass over into
unsaturated compounds, especially when warmed with acetic anhydride:
R·CO2R´(R´´)2·R·:C·OMgX -> (R´´)2R·:C·OH.

Formic ester yields a secondary alcohol under similar conditions. Acid
chlorides behave in an analogous manner to esters (Grignard and
Tissier, _Comptes rendus_, 1901, 132, p. 683). Nitriles yield ketones
(the nitrogen being eliminated as ammonia), the best yields being
given by the aromatic nitriles (E. Blaise, ibid., 1901, 133, p. 1217):
R·CN -> RR´:C:NMgI -> R·CO·R´. Acid amides also react to form ketones
(C. Béis, ibid., 1903, 137, 575):

R·CONH2 -> RR´:C(OMgX)·NHMgX + R´H -> R·CO·R´;

the yield increases with the complexity of the organic residue of the
acid amide. On passing a current of dry carbon dioxide over the
reagent, the gas is absorbed and the resulting compound, when
decomposed by dilute acids, yields an organic acid, and similarly with
carbon oxysulphide a thio-acid is obtained:

RMgX -> R·CO2MgX -> R·CO2H; COS -> CS(OMgX)·R -> R·CSOH.

A. Klages (_Ber._, 1902, 35, pp. 2633 et seq.) has shown that if one
uses an excess of magnesium and of an alkyl halide with a ketone, an
ethylene derivative is formed. The reaction appears to be perfectly
general unless the ketone contains two ortho-substituent groups.
Organo-metallic compounds can also be prepared, for example

SnBr4 + 4MgBrC6H5 = 4MgBr2 + Sn(C6H5)4.

For a summary see A. McKenzie, _B. A. Rep._ 1907.

_Detection._--The magnesium salts may be detected by the white
precipitate formed by adding sodium phosphate (in the presence of
ammonia and ammonium chloride) to their solutions. The same reaction
is made use of in the quantitative determination of magnesium, the
white precipitate of magnesium ammonium phosphate being converted by
ignition into magnesium pyrophosphate and weighed as such. The atomic
weight of magnesium has been determined by many observers. J.
Berzelius (_Ann. chim. phys._, 1820, 14, p. 375), by converting the
oxide into the sulphate, obtained the value 12.62 for the equivalent.
R. F. Marchand and T. Scheerer (_Jour. prakt. Chem._, 1850, 50, p.
358), by ignition of the carbonate, obtained the value 24.00 for the
atomic weight, whilst C. Marignac, by converting the oxide into the
sulphate, obtained the value 24.37. T. W. Richards and H. G. Parker
(_Zeit. anorg. Chem._, 1897, 13, p. 81) have obtained the value 24.365
(O = 16).

_Medicine._--These salts of magnesium may be regarded as the typical _saline purgatives_. Their aperient action is dependent upon the minimum of irritation of the bowel, and is exercised by their abstraction from the blood of water, which passes into the bowel to act as a diluent of the salt. The stronger the solution administered, the greater is the quantity of water that passes into the bowel, a fact to be borne in mind when the salt is administered for the purpose of draining superfluous fluid from the system, as in dropsy. The oxide and carbonate of magnesium are also invaluable as antidotes, since they form insoluble compounds with oxalic acid and salts of mercury, arsenic, and copper. The result is to prevent the local corrosive action of the poison and to prevent absorption of the metals. As alkaloids are insoluble in alkaline solutions, the oxide and carbonate--especially the former--may be given in alkaloidal poisoning. The compounds of magnesium are not absorbed into the blood in any appreciable quantity, and therefore exert no remote actions upon other functions. This is fortunate, as the result of injecting a solution of a magnesium salt into a vein is rapid poisoning. Hence it is of the utmost importance to avoid the use of salts of this metal whenever it is necessary--as in diabetic coma--to increase the alkalinity of the blood rapidly. The usual doses of the oxide and carbonate of magnesium are from half a drachm to a drachm.

MAGNETISM. The present article is a digest, mainly from an experimental standpoint, of the leading facts and principles of magnetic science. It is divided into the following sections:

1. General Phenomena.

2. Terminology and Elementary Principles.

3. Magnetic Measurements.

4. Magnetization in Strong Fields.

5. Magnetization in Weak Fields.

6. Changes of Dimensions attending Magnetization.

7. Effects of Mechanical Stress on Magnetization.

8. Effects of Temperature on Magnetism.

9. Magnetic Properties of Alloys and Compounds of Iron.

10. Miscellaneous Effects of Magnetization:--Electric
Conductivity--Hall Effect--Electro-Thermal Relations--Thermo-electric
Quality--Elasticity--Chemical and Voltaic Effects.

11. Feebly Susceptible Substances.

12. Molecular Theory of Magnetism.

13. Historical and Chronological Notes.

Of these thirteen sections, the first contains a simple description of the more prominent phenomena, without mathematical symbols or numerical data. The second includes definitions of technical terms in common use, together with so much of the elementary theory as is necessary for understanding the experimental work described in subsequent portions of the article; a number of formulae and results are given for purposes of reference, but the mathematical reasoning by which they are obtained is not generally detailed, authorities being cited whenever the demonstrations are not likely to be found in ordinary textbooks. The subjects discussed in the remaining sections are sufficiently indicated by their respective headings. (See also ELECTROMAGNETISM, TERRESTRIAL MAGNETISM, MAGNETO-OPTICS and UNITS.)

1. GENERAL PHENOMENA

Pieces of a certain highly esteemed iron ore, which consists mainly of the oxide Fe3O4, are sometimes found to possess the power of attracting small fragments of iron or steel. Ore endowed with this curious property was well known to the ancient Greeks and Romans, who, because it occurred plentifully in the district of Magnesia near the Aegean coast, gave it the name of _magnes_, or the _Magnesian stone_. In English-speaking countries the ore is commonly known as _magnetite_, and pieces which exhibit attraction as _magnets_; the cause to which the attractive property is attributed is called _magnetism_, a name also applied to the important branch of science which has been evolved from the study of phenomena associated with the magnet.

If a magnet is dipped into a mass of iron filings and withdrawn, filings cling to certain parts of the stone in moss-like tufts, other parts remaining bare. There are generally two regions where the tufts are thickest, and the attraction therefore greatest, and between them is a zone in which no attraction is evidenced. The regions of greatest attraction have received the name of _poles_, and the line joining them is called the _axis_ of the magnet; the space around a magnet in which magnetic effects are exhibited is called the _field of magnetic force_, or the _magnetic field_.

Up to the end of the 15th century only two magnetic phenomena of importance, besides that of attraction, had been observed. Upon one of these is based the principle of the mariner's compass, which is said to have been known to the Chinese as early as 1100 B.C., though it was not introduced into Europe until more than 2000 years later; a magnet supported so that its axis is free to turn in a horizontal plane will come to rest with its poles pointing approximately north and south. The other phenomenon is mentioned by Greek and Roman writers of the 1st century: a piece of iron, when brought into contact with a magnet, or even held near one, itself becomes "inductively" magnetized, and acquires the power of lifting iron. If the iron is soft and fairly pure, it loses its attractive property when removed from the neighbourhood of the magnet; if it is hard, some of the induced magnetism is permanently retained, and the piece becomes an artificial magnet. Steel is much more retentive of magnetism than any ordinary iron, and some form of steel is now always used for making artificial magnets. Magnetism may be imparted to a bar of hardened steel by stroking it several times from end to end, always in the same direction, with one of the poles of a magnet. Until 1820 all the artificial magnets in practical use derived their virtue, directly or indirectly, from the natural magnets found in the earth: it is now recognized that the source of all magnetism, not excepting that of the magnetic ore itself, is electricity, and it is usual to have direct recourse to electricity for producing magnetization, without the intermediary of the magnetic ore. A wire carrying an electric current is surrounded by a magnetic field, and if the wire is bent into the form of an elongated coil or spiral, a field having certain very useful qualities is generated in the interior. A bar of soft iron introduced into the coil is at once magnetized, the magnetism, however, disappearing almost completely as soon as the current ceases to flow. Such a combination constitutes an _electromagnet_, a valuable device by means of which a magnet can be instantly made and unmade at will. With suitable arrangements of iron and coil and a sufficiently strong current, the intensity of the temporary magnetization may be very high, and electromagnets capable of lifting weights of several tons are in daily use in engineering works (see ELECTROMAGNETISM). If the bar inserted into the coil is of hardened steel instead of iron, the magnetism will be less intense, but a larger proportion of it will be retained after the current has been cut off. Steel magnets of great strength and of any convenient form may be prepared either in this manner or by treatment with an electromagnet; hence the natural magnet, or _lodestone_ as it is commonly called, is no longer of any interest except as a scientific curiosity.

Some of the principal phenomena of magnetism may be demonstrated with very little apparatus; much may be done with a small bar-magnet, a pocket compass and a few ounces of iron filings. Steel articles, such as knitting or sewing needles and pieces of flat spring, may be readily magnetized by stroking them with the bar-magnet; after having produced magnetism in any number of other bodies, the magnet will have lost nothing of its own virtue. The compass needle is a little steel magnet balanced upon a pivot; one end of the needle, which always bears a distinguishing mark, points approximately, but not in general exactly, to the north,[1] the vertical plane through the direction of the needle being termed the _magnetic meridian_. The bar-magnet, if suspended horizontally in a paper stirrup by a thread of unspun silk, will also come to rest in the magnetic meridian with its marked end pointing northwards. The north-seeking end of a magnet is in English-speaking countries called the _north pole_ and the other end the _south pole_; in France the names are interchanged. If one pole of the bar-magnet is brought near the compass, it will attract the opposite pole of the compass-needle; and the magnetic action will not be sensibly affected by the interposition between the bar and the compass of any substance whatever except iron or other magnetizable metal. The poles of a piece of magnetized steel may be at once distinguished if the two ends are successively presented to the compass; that end which attracts the south pole of the compass needle (and is therefore north) may be marked for easy identification.

Similar magnetic poles are not merely indifferent to each other, but exhibit actual repulsion. This can be more easily shown if the compass is replaced by a magnetized knitting needle, supported horizontally by a thread. The north pole of the bar-magnet will repel the north pole of the suspended needle, and there will likewise be repulsion between the two south poles. Such experiments as these demonstrate the fundamental law that _like poles repel each other_; _unlike poles attract_. It follows that between two neighbouring magnets, the poles of which are regarded as centres of force, there must always be four forces in action. Denoting the two pairs of magnetic poles by N, S and N´, S´, there is attraction between N and S´, and between S and N´; repulsion between N and N´, and between S and S´. Hence it is not very easy to determine experimentally the law of magnetic force between poles. The difficulty was overcome by C. A. Coulomb, who by using very long and thin magnets, so arranged that the action of their distant poles was negligible, succeeded in establishing the law, which has since been confirmed by more accurate methods, that _the force of attraction or repulsion exerted between two magnetic poles varies inversely as the square of the distance between them_. Since the poles of different magnets differ in strength, it is important to agree upon a definite unit or standard of reference in terms of which the strength of a pole may be numerically specified. According to the recognized convention, the unit pole is that which acts upon an equal pole at unit distance with unit force: a north pole is reckoned as positive (+) and a south pole as negative (-). Other conditions remaining unchanged, the force between two poles is proportional to the product of their strengths; it is repulsive or attractive according as the signs of the poles are like or unlike.

If a wire of soft iron is substituted for the suspended magnetic needle, either pole of the bar-magnet will attract either end of the wire indifferently. The wire will in fact become temporarily magnetized by induction, that end of it which is nearest to the pole of the magnet acquiring opposite polarity, and behaving as if it were the pole of a permanent magnet. Even a permanent magnet is susceptible of induction, its polarity becoming thereby strengthened, weakened, or possibly reversed. If one pole of a strong magnet is presented to the like pole of a weaker one, there will be repulsion so long as the two are separated by a certain minimum distance. At shorter distances the magnetism induced in the weaker magnet will be stronger than its permanent magnetism, and there will be attraction; two magnets with their like poles in actual contact will always cling together unless the like poles are of exactly equal strength. Induction is an effect of the field of force associated with a magnet. Magnetic force has not merely the property of acting upon magnetic poles, it has the additional property of producing a phenomenon known as _magnetic induction_, or _magnetic flux_, a physical condition which is of the nature of a flow continuously circulating through the magnet and the space outside it. Inside the magnet the course of the flow is from the south pole to the north pole; thence it diverges through the surrounding space, and again converging, re-enters the magnet at the south pole. When the magnetic induction flows through a piece of iron or other magnetizable substance placed near the magnet, a south pole is developed where the flux enters and a north pole where it leaves the substance. Outside the magnet the direction of the magnetic induction is generally the same as that of the magnetic force. A map indicating the direction of the force in different parts of the field due to a magnet may be constructed in a very simple manner. A sheet of cardboard is placed above the magnet, and some iron filings are sifted thinly and evenly over the surface: if the cardboard is gently tapped, the filings will arrange themselves in a series of curves, as shown in fig. 1. This experiment suggested to Faraday the conception of "lines of force," of which the curves formed by the filings afford a rough indication; Faraday's lines are however not confined to the plane of the cardboard, but occur in the whole of the space around the magnet. A _line of force_ may be defined as an imaginary line so drawn that its direction at every point of its course coincides with the direction of the magnetic force at that point. Through any point in the field one such line can be drawn, but not more than one, for the force obviously cannot have more than one direction; the lines therefore never intersect. A line of force is regarded as proceeding from the north pole towards the south pole of the magnet, its direction being that in which an isolated north pole would be urged along it. A south pole would be urged oppositely to the conventional "direction" of the line; hence it follows that a very small magnetic needle, if placed in the field, would tend to set itself along or tangentially to the line of force passing through its centre, as may be approximately verified if the compass be placed among the filings on the cardboard. In the internal field of a long coil of wire carrying an electric current, the lines of force are, except near the ends, parallel to the axis of the coil, and it is chiefly for this reason that the field due to a coil is particularly well adapted for inductively magnetizing iron and steel. The older operation of magnetizing a steel bar by drawing a magnetic pole along it merely consists in exposing successive portions of the bar to the action of the strong field near the pole.

Faraday's lines not only show the direction of the magnetic force, but also serve to indicate its magnitude or strength in different parts of the field. Where the lines are crowded together, as in the neighbourhood of the poles, the force is greater (or the field is stronger) than where they are more widely separated; hence the strength of a field at any point can be accurately specified by reference to the concentration of the lines. The lines presented to the eye by the scattered filings are too vague and ill-defined to give a satisfactory indication of the field-strength (see Faraday, _Experimental Researches_, § 3237) though they show its direction clearly enough. It is however easy to demonstrate by means of the compass that the force is much greater in some parts of the field than in others. Lay the compass upon the cardboard, and observe the rate at which its needle vibrates after being displaced from its position of equilibrium; this will vary greatly in different regions. When the compass is far from the magnet, the vibrations will be comparatively slow; when it is near a pole, they will be exceedingly rapid, the frequency of the vibrations varying as the square root of the magnetic force at the spot. In a refined form this method is often employed for measuring the intensity of a magnetic field at a given place, just as the intensity of gravity at different parts of the earth is deduced from observations of the rate at which a pendulum of known length vibrates.