Images de page
PDF
ePub

144

CHEEVER

CHELONIA

extremely fond of attention, and seems to repay became tutor to the Prince, afterwards Edward VI., kindness with affection.

whose elevation to the throne secured him rank, Cheever, GEORGE BARRELL, American clergy.

wealth, and honour-a seat in parliament (1547 man, born in Maine in 1807, was educated at

the provostship of King's College (1548), and Bowdoin College and Andover Theological Semi. knighthood (1552). He was stripped of everything nary, and from 1832 to 1870 was pastor of Con. at Mary's accession, and went abroad, but in 1556 gregational and Presbyterian churches in Salem

was treacherously seized in Belgium, and brought (Massachusetts) and New York. He delivered

to the Tower. Fear of the stake induced him to numerous lectures on religious, literary, and social

abjure Protestantism, and fresh lands were given questions, and published a number of works, the 1 to him in the place of those he had tortei most popular of which is his Lectures on the Pil. his recantation preyed on his mind, and he died in grim's Progress (1844), which, with his Wander.

the course of the following year, 13th Septemler ings of a "Pilgrim in the Shadow of Mont Blanc 1557. Of more than thirty Latin and English (1845 46), has had a wide circulation in England

books by him, one is a translation of St Matthews as well as in America. In his prime Dr Cheever

Gospel (edited by Goodwin, 1843), exemplifying a was an active and uncompromising opponent of plan for reforming the language by eradicating all intemperance and slavery. Died October 1, 1890.

words save those of English origin. See his Life Che-foo (properly the name of the European

by Strype (best ed. Oxford, 1821). colony of the Chinese town of Yen-Tai), a treaty

Che-keang, an eastern and maritime province port on the north side of the peninsula of Shan-tung,

of China (q.v.). Capital, Hang-chow. at the entrance to the Gulf of Pechili, in which it Cheli'ceræ, a technical term usually restricted is the only port that remains open throughout the to the biting organs which form the first pair of winter. The foreign quarter, with about 120 Euro- appendages in spiders, scorpions, and other Arachpeans and Americans, is in some sense a colony of nida. Shanghai, and, having the wholesomest climate of Chelifer. See BOOR-SCORPION. all the treaty ports, it is much resorted to by conval. escents. The Chinese town, built on the sandy

Chelmsford, the county town of Essex, at shore, with exceedingly dirty streets, has a fort, a

the confluence of the Chelmer and the Cam, 29 signal-station, and about 32,000 inhabitants. As a

miles NE. of London. It has a corn exchange market for foreign manufactured goods, particularly

(1857), a shire hall (1792), a grammar-school, English cotton yarn and American sheetings, Che.

founded by Edward VI. in 1551, and a parish foo is of great and increasing importance. In 1887

church, which, all but the tower and spire, was the value of imports was £1,760,967, of which

rebuilt between 1803 and 1878. There is a con£1,145,749 were foreign goods; of exports, £1,347,427.

siderable trade in agricultural produce. On a The principal articles of import besides those men

small island in the Chelmer there has long been tioned are sugar, paper, iron, edible seaweed,

a ludicrous mock-election during the county elecmatches, and opium. The chief exports are silk,

tions. Pop. (1851) 6033; (1881) 9885. straw-braid, bean-cake, and vermicelli. The total Chelmsford, FREDERIC THESIGER, BAROX, number of vessels entered and cleared during 1887 born in 1794, was a midshipman in the navy, but was 2081, of 1,656,075 tons, of which 1130, of 958,821 exchanged the sea for law, and was called to the tons, were British. The Che-foo Convention, which bar in 1818. He was knighted and made solicitor settled several disputed points between China and general in 1844, attorney-general in 1845 and 1832 Great Britain, and extended certain commercial and lord chancellor in 1838 and 1866. He died advantages to the latter country, besides throwing October 5, 1878.--His son, FREDERIC AUGUSTU: open four new treaty ports, was signed 13th Sep THESIGER, second BARON, was born in 1827, entered tember 1876.

the Rifle Brigade in 1844, became major in the Cheiranthus. See WALLFLOWER.

Grenadier Guards in 1855, and served through the Cheiro'lepis, a genus of fossil ganoid fishes,

Crimea, the Indian Mutiny, and the Abyssinian characteristic of the Devonian strata. The generic

campaign of 1868. He was adjutant-general in name, meaning "scaly-hand,' was given in allusion

Bengal (1869-74), and commanded the forces in the to the large pectoral scaly fins.

Kaffir war of 1878 and in the unfortunate Zulu war

of 1879, having resigned the governorship of Cape Cheiromys. See AYE-AYE.

Colony. Appointed lieutenant-general in 1882, he Cheironectes, an aberrant genus of Opossums

was made lieutenant of the Tower of London in (9.v.), with webbed hind feet and of unique aquatic

1884. habit. There is but one species, C. variegatus, palmatus, or Yapock (q.v.).

Chelonia, an order of reptiles including the

various forms of, tortoise and turtle. Their most Cheiroptera (wing-handed'), the technical

distinctive character is the more or less complete name for the order of Bats (q.v.).

inclosure of the body by a dorsal and a ventral Cheirothe'rium (Gr., 'hand-beast'), the name shield, of which the former is in part due to a originally given to the Labyrinthodont (q.v.), from modification of the vertebral spines and of the the peculiar hand-like impressions left by it in the ribs. Within these shields the head, limbs, and Triassic rocks.

tail can be more or less retracted. The absence of Cheke, SIR Jonx, one of the revivers of Greek teeth is also very characteristic. The Chelonia learning in England, was born in 1514 at Cam. ) include marine, fresh-water, and terrestrial forms; bridge, and in 1329 obtained a fellowship of St the known living species number about 200, the John's ('ollege, where he embraced the Reformed majority occurring in warm countries; they are doctrines. He laboured earnestly to advance the represented by numerous fossil forms from the study of the Greek language and literature ; and lpper Jurassic onwards. The large family Te when a regius professorship of Greek was founded tudinidæ, with oval, horny-plated dorsal Shield, at Cambridge in 1540, Cheke was appointed its first includes both terrestrial and marsh forms, such occupant. A new mode of pronouncing Greek | as Testudo-eg. the Greek tortoise. Terrapin. which he introduced was assailed by Bishop Emys, Chelys; a second small family, Trionychida, Gardiner, the chancellor of the university ; but with oval, softer shield, includes river forms, such notwithstanding, (heke's system prevailed. It as the well-known snapping turtle (Trionyr ferari; resembled that still in vogue in England, as a third family, (Chelonidze, with heart shaped opposed to the continental system. In 1544 Cheke I shield, includes five species of marine turtles-eg. CHELSEA

CHEMICAL AFFINITY

145

Chelone riridis. The order will be chiefly discussed again, and there are always very many men seeking under the titles TORTOISE and TURTLE.

the position so vacated. Chelsea Hospital is locally Chelsea, a suburb of London, on the north known as Chelsea College '—the Hospital having bank of the Thames, here crossed by bridges to been erected nearly on the site of James I.'s shortBattersea (q.v.). In the 16th century the village lived ‘College for Re

| lived College for Religious Controversy' (1610). of Chelsea was the residence of Sir Thomas More, See the official Early History of the Royal Hospital Queen Catharine Parr, the Princess Elizabeth, and at Chelsea (1872), and Martin's Old Chelsea (1888). Anne of Cleves. Afterwards Walpole, Swift, Steele, || Chelsea in Massachusetts, U.S., is a northAnd Sir Hans Sloane, and, in later years, Leigheastern suburb of Boston, from which it is sepaHant, Carlyle, Rossetti, and George Eliot lived rated by the estuary of Mystic River (see BOSTON). here. In the 18th century Ranelagh was much Pop. (1870) 18,547 ; (1880) 21,782; (1890) 27,909. resorted to, and Cremorne (closed 1877) was at Cheltenham, a fashionable watering place of one time a popular attraction. Besides its Hospital,

s Hospital, Gloucestershire, on the Chelt, a little affluent of ("helsea has a Royal Military Asylum for soldiers' chukiren, large barracks for the Foot Guards, a

the Severn, 44 miles NNE. of Bristol, 47 SSW. of

Birmingham, and 121 WNW. of London (by road botanie garden, water-works (1722) to supply

only 95). It lies in a picturesque and fertile valley, London, & river-pier, and an embankment (1873)

on the east and south-east half encircled by the extending to Battersea Bridge on the west. The

Coteswolds. A saline spring was discovered here famous 18th-century porcelain is noticed under POTTERY.

in 1716, and from a mere village the place gradually The borough has returned one member increased till 1788, when the benefit derived by to parliament since 1885, when its limits were

George III. from its waters suddenly made it a pratly reduced. Pop. of parish (1887) 112,316.

resort of fashion. The four spas-Royal Old Well, CHELSEA HOSPITAL is an asylum for old and disabled soldiers of the British army.

Montpellier, Pittville, and Cambray-are all saline The gradual

but the last, which is chalybeate; they are deemed dreay of the feudal system rendered it necessary

efficacious for liver complaints and dyspepsia. to make some new provision for sick and maimed

With its squares, crescents, and terraces, its garsoldiers, consequently various statutes were passed

dens and promenades, its clubs and pump-rooms, during the reigns of Elizabeth, James I., and

its August. cricket week,' its healthy climate, the burles L. throwing their maintenance on their mwpective parishes, under directions from

cheapness of living, and the happy absence of manuthe

factures, the town offers many attractions both to romanty justices. This system was abrogated during

visitors and residents, the former largely foxhunters the (onmonwealth as a matter of policy, and the

in winter, the latter retired Anglo-Indians. It is, expense met out of moneys arising from sequestratuins of the estates of the vanquished royalists.

tra besides, a great educational centre, the seat of the After the Restoration a new act was passed (1662)

Proprietary College, for 700 boys, founded in 1840,

and occupying a splendid Tudor pile of 1843; á in throwing their maintenance on the parishes,

grammar-school (1586; reconstituted 1883); a large but this was so burdensome that it was never re

ladies' college (1854); a Church of England training enacted. Sir Stephen Fox, the first paymaster

| college for schoolmasters (1847); and private schools gebrnal of the forces, who had long been an exile

beyond number. Noticeable buildings are the in France, and was no doubt well acquainted with the erection in 1671 of the Hôpital des Invalides

14ih-century parish church; the Roman Catholic

Church (1837), with a spire 205 feet high; the Corn a: Paris, first suggested the building of Chelsea Hotel

Exchange (1863); and the handsome Free Library. The foundation stone was laid by

Cheltenham has memories of Lord Tennyson, (harles II. in 1682, and the building, designed by

Frederick Robertson, Sydney Dobell, and Dean Wren, was opened in 1692.

Close, under whom (1824-56) it became a strong. The funds for its lands and buildings, and for

| hold of Evangelicalism. It was incorporated many year the maintenance of its inmates, were derived chiefly by deductions from the pay of the

| as a municipal borough in 1876, and has returned trop themselves-viz. Is. in the £1, as well as

one member to parliament since 1832, the

| parliamentary boundary having been extended one day'* pay in each year. Since 1783 it has, brever, been almost entirely supported

in 1885. Pop. (1804) 3076 ; (1841) 31,411; (1881)

by aantal parliamentary grants. All Pensions (q.v.)

by 50,842. kranted to soldiers are awarded by the Commis.' Chelyuskin, CAPE (formerly North-east Cape, Eners of Chelsea Hospital, who are appointed and sometimes called Cape Serero), the most by the crown. Originally it was contemplated northerly point of Asia, on a peninsula of the same that all pensioners would become inmates of name, which forms the western arm of the eastern (hrles Hospital, but this was soon found im half of the Taimyr peninsula. It is named after a parable, and thus those who could not gain | Russian officer who led an expedition thus far in Nimittance were granted allowances termed out. | 1742, and here succumbed, with his wife, to the enjen. The out-pensioners in 1889 numbered fatigues of the journey ; it was not revisited till 4.703 men, including negroes in the West Indies |

| 1878, when Nordenskjold, in the Vega, spent the West Africa, Maltese, Singhalese, and Lascars,

19 and 20th of August here. He found it a low and were estimated to cost £1,770,000. The in promontory, divided into two parts by a small hay; jensioners numbered about 530. They are selected the lat. of the western is 77 36' 37" X., that of trom such out-pensioners as desire to become in the eastern 77 41' X. mates, according to merit, age, and sufferings from Chemical Affinity is the name given to the Wand- or other disabilities, and are provided tendency to combine with one another which is with board, lodging, clothing, including the well. exhibited by many substances; or to the force by kan red coat and cocked hat, nursing and which the substances constituting a compound are betaal attendance, together with a small weekly held together. The tendency of any given element Nuwance in money according to rank. The to unite with a number of other elements varies

pa bon vote for the year 1888-89 amounted greatly. Chlorine, for instance, unites with great 19luling, however, charges relating to the grant readiness with most metals and with many non

t-pensions, but excluding cost of repairs to metallic elements, much heat being proluced dur. lin , &c.) to £27,083, against which there is ing the union; but it has little or no affinity to set off the amount of the out-pensions, which for, or tendency to combine with, oxygen, so that

2 by statute be surrendered on admission. I compounds of chlorine with oxygen can only be Thome within can at any time become out-pensioners i obtained by roundabout methods, and are very

[blocks in formation]

liable to sudden and explosive decomposition into dupes by more or less clumsy experiments, which chlorine and oxygen. Where the affinity of ele- appeared to demonstrate the production of gold ments for each other is great, the compounds pro from baser metal. Others, however, were really duced by their union are decomposed with difficulty, earnest and untiring in their labours, and held the and where the affinity is feeble, decomposition is fullest belief in the prospects of the ultimate easily effected. See also CHEMISTRY.

success of some fortunate worker. The new subChemistry. Although chemistry has only stances obtained by the alchemists were frequently taken its place as an exact science based upon

used in medicine, and it is to these infatuated accurate experimental investigation within a com

workers, therefore, that we owe our first knowledge paratively recent period, yet its origin dates back of many potent medicines. The writings of many to the earliest times of philosophical study. It of the alchemists are preserved, but numbers of will be convenient to give in the first place a short them are entirely worthless from a scientific point sketch of the history of chemistry, and then to

of view, as the descriptions of processes are mixed state some of the principles of the science, illustrat

up with so much of mystery and extravagance that ing these from the simplest facts. When possible, they present a wholly unintelligible jargon. For such illustrations will be chosen as are likely more detail, however, regarding this remarkable to be not altogether unfamiliar to non-scientific period in the history of chemistry, see the article readers.

ALCHEMY. Historical Sketch.The word chemistry has As Geber has been called the patriarch of chemcome to us from the Greek through the Arabic, istry, so Robert Boyle (1627-91) has been called as shown in our article ALCHEMY. With regard the father of modern chemistry, since it was to the chemistry of the ancients, we know Boyle who first tried to free chemistry from the that the ancient Egyptians, Phænicians, Greeks, trammels of alchemy and to place it upon a true and Romans were acquainted with a very con scientific basis. Boyle in his Sceptical Chemist siderable number of useful substances, and that tried to discredit the salt, sulphur, and mercury of their processes for preparing some of these did not the alchemists (as well as the Aristotelian earth, differ in any essential particular from those now in air, fire, and water) as elements or ultimate conuse. It does not appear, however, that they have stituents of substances, and he gave a scientific left any chemical records behind them, or that they | definition of an element. Boyle was an experi. knew anything of the science of chemistry. Several | mental investigator of considerable skill, and to metals were known to, and employed by, these him we owe the introduction of the air-pump and ancient peoples, who were acquainted with processes the thermometer into this country. His experifor reducing them from their ores. Amongst these ments upon the physical properties of gases led to metals were gold, silver, mercury, copper, tin, lead,

the formulation of the law concerning the relation and iron ; whilst they also knew and worked with

of the volume of a gas to the pressure, which is brass, although they were not aware that it was commonly known as Boyle's Law. an alloy of copper and zinc. Various alloys were Theory in modern chemistry begins with Becher employed for bronzes for statues, and these usually

(1635–82) and Stahl (1660-1734). The latter contained copper, lead, and tin. The processes for adopted, with some modifications, a theory promanufacturing soap, starch, glass, leather, vari. pounded by the former concerning elements and ous mineral and vegetable pigments, stoneware, compounds, and formulated the phlogiston theory and other useful substances, were all known and of combustion. The views of Becher and Stahl carried on in very early times; and wine and beer regarding elements were not so enlightened as appear likewise to have been prepared and used as

those of Boyle, and must be considered as retrobeverages long before the process of distillation, grade. Stahl's phlogiston theory (1697) was at once which was unknown to the ancients, had been

adopted almost universally by chemists, and for introduced. Vinegar, sulphur, and carbonate of

fifty years it was held to give the full explanation soda were also known.

of the phenomena of combustion. According to We find the application in medicine of many this theory phlogiston was a constituent of all comchemical products at a comparatively early period, bustible substances. When a substance burned, and the Arabians appear to have been the first the phlogiston made its escape, and the product of who tried to prepare new medicines by chemical combustion was regarded as the other substance methods. Geber, who lived in the 8th century A.D.,

with which the phlogiston had been previously is the most noted of the Arabian chemists, and he united. When a metal such as lead was heated in has left some writings which show us what was the the air, it lost its phlogiston, and the oxide formed state of chemistry at that early date. Geber knew, was looked upon as the other constituent of lead for instance, how to make and distil vinegar and besides phlogiston. The process of reduction of nitric acid, and even sulphuric acid was made and lead from its oxide by means of charcoal was the used as a solvent by him. He knew, amongst

transfer of phlogiston from the charcoal to the lead. other substances, white arsenic, borax, common It did not present itself to the adherents of the salt, alum, sal-ammoniac (ammonium chloride), cop-| theory as an absurdity that a metal, in losing its

rrous sulphate), nitre (potassium nitrate). | phlogiston on oxidation, gained weight, although and corrosive sublimate (mercuric chloride), and some of them at least were aware of the fact. The was acquainted with a number of their properties. idea of gain of matter being a necessary accompani. He used almost all the kinds of apparatus that ment of gain of weight is so familiar to us that we were commonly in use down till the 18th century, can scarcely realise that it was not always so and understood the processes of distillation, filtra regarded. To this may fairly be attributed the tion, sublimation, and crystallisation. In one of persistence with which the phlogiston theory held his works he describes the construction of furnaces its ground for so long a period. for chemical purposes.

The Dutch chemist Boerhaave (1668-1738), who From the 8th till the 17th century but little did not accept Stahl's theory, published in 1732 his real progress was made in chemistry as a science. system of chemistry, which was a compilation of The new knowledge that was gained during this

practically all that was known up till that date, period was mainly due to the assiduity of the collected with great labour from a large variety of alchemists, who, in their vain search for the philo alchemical and other writings. sopher's stone, necessarily made useful discoveries The interval between the introduction of the from time to time. Many of the alchemists so phlogiston theory and its overthrow by Lavoisier in called were mere tricksters who deceived their I 1772-85 was one of great advance in chemical

pe

[blocks in formation]

knowledge, and a number of very eminent chemists were carried out by Klaproth (1743-1817), Vauque. i preceded and were contemporaries of Lavoisier. lin (1763-1829), Fourcroy (1755-1809), and others;

In Germany, Marggraf (1709-82) studied the and many quantitative observations of all kinds properties of the almost unknown alumina and were made about the end of the 18th century, all magnesia, and made considerable advances in the preparing the way for Dalton's statement of the qualitative analysis of substances in solution. Atomic Theory (q.v.) in 1803-4.

Amongst British chemists of note may be men The progress of chemistry during the present tind Hales (1677-1761), who was amongst the century has been immense, and it is not possible to first to experiment on gases; Black (1728-99), who do much more than mention the names of some of in 116 published his research on Magnesia Alba, the most prominent workers. A stimulus was given stating the nature of fixed air or carbonic acid to research by the publication of Dalton's atomic PR, and of the difference between caustic and mild theory; and the labours of Gay Lussac (1778-1850), ar cartonated) alkalies; Priestley (1733-1804), who experimented with gases, of Dulong (1785wbo, in addition to his discovery of oxygen in 1774, 1838), and Petit (1791-1820), who pointed out the investigated nitric oxide, nitrous oxide, sulphurous | relation between specific heats and atomic weights acid, carbonic oxide, hydrochloric acid, and of elements, and of others, supported and amplified ammonia gases, being specially attracted to the Dalton's views.

wly of gaseous substances and their properties ; Wollaston (1767-1829) discovered palladium in and Cavendish (1731-1810), who investigated the 1803, and rhodium in 1804. The first alkaloid nature and properties of hydrogen, analysed atmo. (morphine) was obtained pure by Sertürner in 1816, spheric air, and discovered the compound nature and this led to the discovery of a number of others and composition of water and of nitric acid,

| in a short time. Lavoisier ( 1743-94) was one of the ablest chemists The decomposition by electricity of the bases of hus time, and his labours include a vast variety potash and soda by Davy (1778-1829) in 1807, and of subjects. His attack upon, and eventual deinoli the separation from these of the metals potassium tion of the phlogiston theory, and his experiments and sodium, threw an entirely new light on the in connection with his new theory of combustion, nature of these substances. The metals were more orrupied him for a considerable number of years. fully investigated by Gay-Lussac and Thénard He taught that combustion was the union of the (1777-1857). Davy is noted also as the inventor of rulmastible substance with atmospheric oxygen ; the miners' safety-lamp, and for experiments on the bor was the first to introduce system into chemistry respiration of nitrous oxide and other gases. and ebemical research; he determined the con. Amongst the foremost chemists of the earlier part statuents of a large number of substances, including of the 19th century was the Swede Berzelius (1779sulphurie, phosphoric, and carbonic acids, numerous 1848), whose careful and exact analyses of mineral brtalle oxides, and many animal and vegetable substances contributed a good deal to the confirmasuletances; and he, along with Berthollet, Four. tion of the law of constant proportions and to the Croy, and Morvean (1737-1816), introduced a new fixing of the atomic weights (see ATOMIC THEORY) and consistent system of chemical nomenclature of the elements. Berzelius was very conservative Two contemporary Swedish chemists, Bergman with regard to new theories, which he declined to • 1735-*4) and Scheele (1742-86), must be men. accept without putting them to the strictest experi. Bued before leaving the phlogiston age. Berg. mental tests. He formulated the electro-chemical muan investigated, amongst other things, carbonic theory of the constitution of salts, introduced great arid gas, studied the phenomena of affinity, and improvements into the methods of quantitative made advances in the processes and reagents used analysis, increased the value of the blowpipe as an ma qualitative analysis. Scheele was one of the aid in mineral analysis, discovered many new sub

net laborious chemists of his time. He discovered stances, and further examined and elucidated points atnr, malic, tartaric, oxalic, lactic, hydrocyanic, concerning many already known, both inorganic

air and other acids, and chlorine, besides in. and organic. vestigating the nature of a large number of other The artificial production of urea in 1828 by bemties and independently discovering oxygen. Wöhler (1800-82) marks the beginning of a new

It was towards the end of the 18th century that era in the branch of organic chemistry, and enor. the value of quantitative analysis of substances mous strides have been made in this department began to be generally recognised. The question as since that time by Dumas (1800 84), Liebig (1803– to whether the quantitative composition of a given 73), Laurent (1807-53), Gerhardt (1816-56), Wurtz watataner was always the same gave rise to a dis. (1817-84), Kolbe (1818 84), Baeyer, Cannizzaro,

o which lasted for several years, and was at Frankland, Hofmann, Kekulé, Williams length decided in favonr of constant composition. many others. Advances in general inorganic

The searches of Richter (1762-1807) on the chemistry and analysis have been made by Leopold quantities of various acids neutralised by a given ' Gmelin (1788-1853), H. Rose (1795 - 1864), Saintequantity of a base, and of varions bases neutralised (laire Deville (1818-81), and Bunsen ; whilst in

a niven quantity of an acid, led him to the connection with advances in chemical physics may oral conclusion that the quantities of two acids, I be mentioned Faraday (1791-1867), Mitscherlich

and a', which form neutral salts, a b, and a' b', (1794-1863), Graham (1805-69), Regnault (1810-78), with the quantities of two bases, b and ', are just | Andrews (1813-85), and Berthelot. These lists do the quantities required to form two other neutral | not include all of even the most prominent names te ab and ab. This fundamental discovery that might be mentioned in connection with each

erroneously attributed to Wenzel by Berzelius department.

*19, and the error has been carefully per. The most striking feature of modern chemistry is tuated in a considerable number of text-books the extraordinary development of organic chemistry,

that time (Kopp, Entrickelung der Chemie | the account of one branch of it-the chemistry of en der neueren Zeit, p. 251).

the coal-tar products constituting of itself quite a Berthollet (1748-1822), who was one of the most literature which receives additions every day

opponents of the theory of the constant com. | Amongst the most recent triumphs of chemical matus of chemical substances, contributed valu. research may be mentioned the artificial provluction de trearches into the laws of chemical affinity, of indigo and grape-sugar, and the isolation, in

ed applied chlorine to processes of bleaching. The sufficient quantities to study its properties, of the Pred of chemical analysis were improved, and hitherto all but unknown element fluorine.

numbers of analyses, especially of minerals, 1 Of the greatest possible interest from a theoretical

n. 21

[blocks in formation]

point of view is the fact that since 1870 three new first the saltpetre and then the sulphur, and thus elements have been discovered---gallium, scandium, recover all three ingredients separately. The explo and germanium—the existence of all of which had sion of gunpowder when heated to a sufficiently been predicted, and the properties of which had high temperature is due to the occurrence of a series to a certain extent been described beforehand by of changes of the kind we call chemical, for these Mendeleëff. (See periodic law in article ATOMIC changes result in the production of new kinds dd THEORY.)

matter, gaseous and solid, which possess propertie Of late much attention has been given to in no way resembling those of sulphur, charcoal, or measurements of the quantity of heat produced saltpetre, and from which these substances cannot in various chemical changes, notably by Berthelot now be dissolved out. and Thomsen.

A mixture possesses to a greater or less extent Elementary Principles of Chemistry.-The science the properties of its respective ingredients of chemistry deals with a certain class of changes pound, on the other hand, has not as a rule any which matter undergoes when subjected to par: properties resembling those of its constituents. A ticular conditions. Similar treatment may produce piece of magnesium wire heated in the air to a very different effects upon different substances, as, sufficiently high temperature takes fire and burns. for instance, the effect of strong heat upon a piece This is a chemical change in which the metal magof quartz, a piece of limestone, and a piece of sugar. nesium combines with the oxygen of the air to form The quartz does not suffer any permanent change, a white, brittle, solid compound called magnesis et that is, it has the same properties after it is cold magnesium oxide. This magnesia does not in the again as it had before the action of heat. The least resemble either magnesium or oxygen in it limestone, although not necessarily much altered in properties, and the most powerful microscope fails appearance, has its properties entirely changed, and to reveal particles of either of these substances to what remains is a new kind of matter-quicklime. our vision. The sugar melts, darkens, and chars, and becomes The Atomic Theory (q.v.) is based upon the quite manifestly changed into more than one new assumption that matter of every kind is made kind of matter, for gaseous products, having the up of extremely minute indivisible particles called smell characteristic of burnt sugar,' go off, whilst atoms. The atoms which exist in a substance may a black coaly mass remains.

be all of the same kind, as in elements, or of differThe first of the above changes is merely a ent kinds, as in compounds. Chemists believe that physical change, from cold to hot; the other two the element hydrogen consists of molecula or are chemical changes, which result in the pro aggregates of atoms--each molecule consisting of duction of new kinds of matter having properties two atoms ; further, that the compound substance entirely different from those of the kinds of matter water consists of molecules, each composed of two from which they were obtained. The existence of atoms of hydrogen and an atom of oxygen united chemistry depends upon the existence of different to each other by that force which is called Chemist kinds of matter, and it is with such different kinds cal Affinity (q.v.); and that similarly every other of matter and the change from one kind to another compound substance is composed of molecules that chemistry has to do.

each molecule consisting of two or more different When the properties of matter are studied, it is kinds of atoms united by chemical affinity. The found that for chemical purposes all kinds of weight of a new compound formed by the union of matter may be divided into two great classes, two or more substances is in every case equal to which are called respectively elements and com. the sum of the weights of its constitnents. In pounds. The name element is applied to any chemical actions it is only the kind of matter kind of matter that has not been proved to be com which is changed, whilst, as in every physical posed of more than one simpler kind of matter. change, the quantity of matter concerned remains This conception of an elementary substance we constant and unalterable. owe to Boyle, and it will be noted that some of It has already been seen that one of the char those substances which are now looked upon as acteristics of the chemical combination of two sub elements (see article ATOMIC THEORY for a list of stances is that the properties of both disappear and the 68 known elements) may hereafter be proved are not observable in the compound. Another and to be compounds, or kinds of matter composed of a most important characteristic is the evolution of more than one simpler kind, just as some sub heat, which is a very frequent although not an instances which were at one time rightly classed as variable accompaniment of chemical action. The elements (according to Boyle's definition) are now best examples of this may be seen in the ordinary known to be compounds of two or more elements. phenomena of ('ombustion (q.v.). All combustion,

The compound nature of a specimen of matter whether it be of magnesium wire, coal, phosphoras, may be proved in one or other (or both) of two paraffin oil, or a candle, is nothing more than a ways. One of these methods is called Synthesis chemical action accompanied by the evolution of (q.v.), and consists in building up the compound heat and light, oxygen gas of the atmosphere being from the component simpler kinds; the other is almost invariably one of the substances taking called Analysis (q.v.), and consists in separating part in such action. more than one simpler kind from the compound The conditions under which substances act chemi kind.

cally upon each other are very various for different The distinction between chemical compounds 'substances. In the first place, certain substances and mere mechanical mixtures is a fundamental cannot be got to act upon each other at all. Such one, and must be fully understood. The substance substances may have little affinity for each other gunpowder, for instance, is an intimate mixture of as chlorine and oxygen, or no athinity, as fluorine finely powdered sulphur, charcoal, and saltpetre and oxygen. Other substances, again, only act as (potassium nitrate), certain precautions being each other with difficulty. The main conditions observed during the mixing in order to avoid · upon which action of one substance upon another explosion. These substances are not combined, depends are the state of physical aggregation and together chemically in gunpowder, but are only the temperature. (ertain chemical actions take mired, a fact as to which we can easily satisfy . place at ordinary temperatures, as, for instance, ourselves in various ways. We may examine the the combination of chlorine with metallic antimony punpowder under the microscope and identify the · or copper, or the spontaneous ignition of one of the separate particles of the ingredients; or, by the compounds of phosphorus and hydrogen when use of appropriate solvents, we may dissolve out / brought into contact with oxygen. Other actions

« PrécédentContinuer »