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these systems of belief and practice and their relation He has been called the pupil and follower of Joseph to human progress.

Part Second of his work, pub- Jefferson, but is more pronounced in his action than lished in 1883, is called A Comparison of all Relig. Jefferson, and hence more purely a low comedian than ions. Another notable work is The Legend of that artist. Clarke's repertoire covers a wide range Thomas Didymus, the Jewish Sceptic (1881), in which of character, his most noted impersonations being Dr. Clarke attempts to set forth in a narrative the Toodles, Pangloss, Waddilove, and Major de Boots. opinions, beliefs, and prejudices of the Jewish sects in

(F. H. W.) the time of Jesus and the characters which surrounded CLARKSBURG, the county-seat of Harrison co., him. Dr. Clarke has also published a volume of W. Va., is on the west fork of the Monongahela River Memorial and Biographical Sketches (1878), Self and on the Parkersburg branch of the Baltimore and Culture, Physical, Intellectual, Moral, and Spiritual Ohio Railroad, 122 miles S. of Wheeling and $2 miles (1880), and The Ideas of the Apostle Paul Translated E. of Parkersburg. It has a court-house, six churches, into their Modern Equivalents (1884). His writings a female college, two weekly newspapers, a national on every subject are clear, earnest, and inspiring. bank, one other bank, two foundries and machine-shops,

CLARKE, JOHN SLEEPER, an American comedian, a woollen-mill, two flour-mills, and gas-works. There was born in Baltimore, Md., in 1835. At an early are coal-mines in the vicinity. Population, 2307. age he lost his father and was thrown upon his CLARKSVILLE, the county-seat of Montgomery own resources. While still a boy, he developed a co., Tenn., is on the N. bank of the Cumberland strong inclination for the stage and became a member River, at the mouth of Red River, 60 miles below of a company of amateur tragedians, of which Edwin Nashville. It is on the Louisville and Memphis RailBooth, who subsequently became his brother-in-law, road, which here crosses both rivers. The city has a was also a member. By the desire of his mother he fine court-house, a hotel, two national banks and two took up the study of law, reading industriously for other banks, one semi-weekly and two weekly news about a year in the office of Elisha R. Sprague, in papers, thirteen churches, and six schools. The Baltimore, Md. But after a brave effort to meet his South-western University (Presbyterian) was estabmother's wishes, he abandoned law and turned his lished here in 1874, the citizens contributing liberally attention earnestly to the stage. Although tragedy for its endowment. There is also a female academy, had attracted his boyish fancy, it soon became evident The industries comprise a foundry, several flour- and that low comedy offered the most inviting field for the planing-mills, and manufactures of ploughs, wagons, exercise of his peculiar powers. Not wanting, in carriages, and ice. The city was incorporated in 1830, pathos, and, indeed, having a nature singularly alive and, though it suffered severely by a fire in 1878, has to emotional influences, he yet possessed that keen revived and presents a fine appearance. It is lighted sense of the ludicrous, conjoined with an extraordinary with gas, and supplied with water by public watermimetic faculty, which fitted him for comic activity. works. The surrounding country furnishes a large His first regular engagement began at the Old Chest- amount of tobacco and other products for shipment by nut Street Theatre, in Philadelphia, Aug. 28, 1852, river or by rail. Population, chiefly of American birth, the play being “She Would and She Would Not," in 3880. which Clarke assumed the rôle of Soto. He rose in

CLAUSEN, HENRIK NICOLAI (1793-1877), a favor, and in January, 1853, became leading man in Danish theologian, was born April 22, 1793, in the Chestnut Street stock company-a position which Marebo, where his father was pastor. The father, he held for a year. In 1854 he went to Baltimore, who was a man of ability, became afterward chief taking the place of first low comedian at the Front preacher in the Lady church at Copenhagen, and Street Theatre in that city. He became so general a published several volumes of sermons. The son disfavorite that the Baltimoreans forced upon him a tinguished himself at the University of Copenhagen, complimentary benefit in the autumn of 1854, which and after graduating, in 1818, travelled extensively in became, indeed, a popular ovation. In August, 1855, France, Italy, and Germany. While in Berlin he he returned to Philadelphia, and took the position of came under the influence of Schleiermacher. In 1821 leading comedian at the Arch Street Theatre until he began to lecture on theology at Copenhagen, and in 1858, when he entered into partnership with William the next year was made professor in the university Wheatley and became joint-lessee of that house. The there. He soon took part in the agitation for a conbusiness was successfully conducted until 1861, when stitutional government, and in 1840 he became a the partnership was dissolved, and Clarke arranged to member of the provincial assembly at Roestilde, of appear as a star in New York. He made his debut in which from 1842 to 1846 he was president. He was this capacity at the Winter Garden and secured an afterward elected to a constitutional assembly, and instant and unequivocal success.

from 1848 to 1851 was a member of the state council. The critics with one accord hailed him as a great In 1876 he resigned his professorship, and he died at artist and the legitimate successor of W. E. Burton, Copenhagen March 28, 1877. His reputation as a whose loss had been felt as nearly irreparable. Clarke's writer was first cstablished by his Catholicism and fame was now

secure, and he began a starring-tour of Protestantism in their Eccesiastical Organization, Docthe principal American cities, rapidly acquiring for trine, and Ritual (1825). This work involved the tune. He became part-proprietor of the three lead-author in a famous controversy with Bishop Grundtvig, ing theatres of the country, the Boston Theatre, the one of the results of which was a libel suit against the New York Winter Garden, and the Walnut Street latter. Clausen published several other works against Theatre, Philadelphia, from each of which he reaped Grundtvig and his followers. He was also the author large financial returns. In 1868, Clarke went to Eng- of numerous exegetical and dogmatic works. Among land, making his appearance at the St. James's these are treatises on the Synoptical Gospels (1847Theatre in the autumn of that year. London re- 50), on John (1855), on Romans (1863). - After his ceived him with an enthusiasm equal to that accorded death a volume of autobiography was published. him by New York, and, with the exception of a brief

CLAUSIUS, RUDOLF JULIUS EMANUEL, a German visit to his native country in 1881, he has since made physicist, was born at Köslin. Pomerania, Jan. 2, England

his home. He has played at nearly all the 1822. He studied at the University of Berlin, and be leading English theatres.

came a privat docent there, as well as professor of Mr. Clarke married a sister of Edwin Booth, and physics in a military school. In 1855 a polytechnic has always been noted for his strong domestic attach- school was established at Zurich, and Clausius was apments and exemplary personal character. As an artist pointed to the chair of physics. He also obtained a he may be said to have created a school of his own, professorship in the University of Zurich. In 1867 he although he approaches in his methods more nearly to accepted a call to a similar position at Würzburg, and the late William E. Burton than to any other actor. two years later became professor at Bonn. Besides

some investigations in optics and on the elasticity of lif they possess a spherical instead of an angular form, bodies, Professor Clausius's labors have been chiefly and we state it as the result of numerous examinadirected to the subject of heat, which he maintains to tions that the ultimate particles of the clay-substance be a state of matter in motion. His essays on this proper are of spherical shape. Being so very small — subject appeared first in Poggendorff's Annalen, but that is, less than the totoo part of an inch, a diameter he afterwards published separate treatises-Ueber das for which the ratio of surface to mass is very largeWesen der Wärme (Zurich, 1857), Die Mechanische it follows that this substance can remain suspended in Wärmetheorie (Brunswick, 1864; 2d ed. 1876), Veber water for a long time. The peculiar milky opalesden zueiten Hauptsatz der mechanischen Wärmetheorie cence which river-water shows many days after the

Brunswick, 1867). His work Die Potentialfunktion subsidence of a freshet is owing to the suspension in it und das Potential, first published at Leipsic in 1850, of these minutest clay-globules. reached its third edition in 1877.

The other components of clay are best designated CLAVICLE (Lat. clavis, a key, claricula, a small in common as sand. They are fragments of different key), the collar-bone. In man this bone is rather mineral species-quartz, felspar, mica chiefly, tourmasiender for its length, curved somewhat like an italic f, line, hornblende, magnetite, ilmenite or titaniferous and extends from the acromion process of the scapula iron, rutile, and others. These minerals are hard, to the manubrium of the sternum; it is movably ar- their fragments angular and of all degrees of fineness. ticulated at each end, and the sternal end furnishes the They may be reduced to grains not much larger than only body connection of the arm with the trunk proper the globules of the clay-substance and remain suspendof the body. From its exposed situation in the neck ed with them in water, whilst the sand proper settles the collar-bone is peculiarly liable to fracture. In nearly very quickly, and may be thus separated from the all Mammalia the clavicles, when perfect, repeat the kaolin. The mineral nature and chemical composition same connections they have in man, but they are fre- of the sandy portions of a clay and their relative quanquently defective or wanting altogether. They are con- tity determines whether a given clay is serviceable for sequently of little value in morphological classification, a specified purpose. Besides the sand, there are being present and perfect, or in varying imperfection, other compounds present in clays, such as coaly matter, or absent, in closely-related animals, eren of neighbor- the red, brown, and yellow oxides of iron, pyrite, fosing genera. They are best developed, as a rule, in those sil ros'n, bitumen, black oxide of manganese, alum, quadrupeds which use the fore limbs as arms and gypsum, calcite, dolomite. They produce the many hands, rudimentary or lacking in those which the same colored varieties of clay, and are either quite harmless limbs are exclusively devoted to ordinary locomotion. or more or less hurtful to the uses to which clay may In birds the clavicles are usually present and perfect, be put. but very seldom join the sternum, being united with According to their place of occurrence, clays are each other on the middle line of the body to form the divided into those of primary and secondary deposits. furculum or merrythought, usually developing at their According to structure, physical condition, and comjunction a special process called the hypocleidium. parison, clays are said to be fat, lean, plastic, argylThey are absent or rudimentary or separate in Ratito lites

, cluy-slates

, marls, and loams. To gain a proper and some parrots; ankylosed with the keel of the ster- idea of these differences we must consider thenum in some Steganopodes, as the pelican and frigate- Origin of Clay.The so-called primitive rocks, bird; with the body of the sternum in Opisthocomus. which have been proven by all deep mining and by When perfected they serve to bear the shoulders apart; the study of the sequence of rocks to underlie .ail and their degree of curvature and solidity bear some re- other rocks, are composed chiefly of three species of lation to power of strong or protracted flight. (E. C.) minerals, quartz, felspar, and mica. Quartz is pure

CLAY, in its purest state, is a mineral substance of silica (S10,), yery hard, compact, and very indifferent perfect snow-white color; it feels to the touch like toward chemical agencies at ordinary temperature. soap, is very soft and brittle ; it sticks to the tongue, Felspar is a more complex compound, containing at and emits a peculiar odor when the moist breath is least four elements—.e. potassium (K), aluminuni blown upon it. Kneaded together with water, it (Al), silicon (Si), and oxygen (O). These_elements absorbs the latter in considerable quantity, and passes are combined in the ratio K,A1,Się016- Potassium into a peculiar condition which is designated plastic. may be replaced by sodium wholly or in part, and also In this state the clay has lost its brittleness, the parti- by calciuni, in felspar. It is a white, vitreous, easily. cles adhere with considerable force and yet possess a cleavable substance only one degree less hard than remarkable freedom of motion against each other, and quartz. Mica is composed of the same elements, may thus receive any arbitrary shape from the mould- with the addition of iron and magnesium. But the ing hand of man. This is a quality not possessed by ratio of combination is different, likewise, for the any other mineral substance, and gives to clay its several species of mica: muscovite, the white mica ; great importance as raw material in the arts. Clay, biotite, the dark-colored mica. Thé micas crystallize however, is not a uniform mineral matter.

in the same system with the felspar, but possess only The above characters belong only to one of its com- one eminent cleavage. The cleavage laminæ are posing parts, which may be named the clay-substance, flexible, elastic, and much softer than felspar. The or, in conformity with mineral nomenclature, kaolin. same or very similar minerals form the component Kaolin is made up of minute loosely-aggreated parti- parts of a number of igneous or volcanic rocks. When cles invisible to the naked eye and impalpable to the these minerals are aggregated in more or less parallel touch-that is, without grit. Under a magnifying layers, they form gneiss, whose structure is schistose or power of 1100 diameters these particles look like slaty; when in granular, irregular aggregation, they globules, and in appearance their aggregate is not form granite; when developed with porphyric strucunlike to fish-roe. The writer's observations harmon- ture, they compose the volcanic rocks porphyry and ize in this respect entirely with Aron's, who examined trachyte. The researches in chemical geology have them under a power of 760 diameters. They differ proved that all other rocks have been formed by the from those of other observers, who conclude that the chemical and mechanical destruction of those just clay-substance is composed of fragments of crystal. mentioned. It is not asserted by the writer that they The writer could not observe any effect which this are original rocks; they are merely the oldest and material is said by some to have on polarized light, deepest we have any cognizance of. At all places which would be a proof of their crystalline nature. where the felspathic rocks have been at the surface This substance, on the contrary, resembles much more for any length of time a peculiar change becomes the globules of starch, being capable of absorbing noticeable. Especially the coarse-grained granite, in water, of swelling, and of passing into a plastic paste. which the felspar is fonn I very pure, and often in The extreme mobility of the particles is accounted for large masses, shows this change more markedly. The glassy surface of the mineral turns to a pulverulent partly altered felspar, quartz, and the fragments of chalk-like substance, and this is due to its conversion all other and less easily decomposable minerals of the into the clay-substance, or kaolin. In chemistry the original rock. It will be understood that this residue law prevails that the more complex a composition a as a whole is therefore a rock- i. e, an aggregate of given compound possesses, the more ready it is to minerals--and not a species of mineral—that is, a unisuccumb to the action of chemical agencies. Likewise, form and homogeneous substance. Among the minthe more a ternary compound or salt is acid—that is, erals in the granite and gneiss are black tourmaline, the more the ratio of that acid portion increases over black hornblende, and black mica, or biotite. These are that of normal saturation—the less will be its chemical silicates containing ferrous oxide (protoxide of iron). stability. In the felspar we have a case exactly cor. Undergoing the process of hydration like the felspar, responding. The composition of the orthoclase felspar this iron becomes altered into ferric hydrate or brown has been stated as K,A1,Si6016. This formula may be hydrated sesquioxide of iron-iron-rust; sometimes, written K,0+A1,03+65i0g.

also, into the red oxide. This imparts to the kaolin Under the action of water, which penetrates into its color and produces all shades, from the faintest the smallest cracks and by its freezing in wintertime buff to a deep-brown color. Owing to this cause, few expanding with irresistible force, the most compact localities furnish a pure white kaolin, which alone is minerals are finally broken and ground into the finest desirable in the arts, and commands a ready sale. powder. After this physical disintegration the chemi- The word kaolin is accepted as the Chinese term for cal action begins. Many writers of high authority designating an earth serviceable in the manufacture ascribe the principal role in this action to the carbonic of porcelain. In England and this country the word dioxide contained in the air to the amount of 0.03 of China-clay is mostly used to designate a deposit of one per cent. They believe that a body of acid chemi- kaolin which is still in situ—that is, above or between cal nature is indispensable in the decomposition of the granite or gneissic rocks from whose decomposimineral compounds, and this fractional percentage of tion it was derived. One of the most notable deposits carbonic dioxide is the only available body of this kind. of this kind is that of St. Austel in Cornwall, where it The writer does not share in this belief. The observa- has been mined for many years in a huge open quarry tion in the laboratory that pure water (obtained by along the tops of a long hill. In Delaware and Chesdistillation) alone will slowly decompose_i, e destroy ter counties, Pa., in the neighborhood of Wilmington, and rearrange the molecules of a substance like hard Delaware, and around Baltimore, Md., are examples Bohemian glass if the latter be very finely pulverized in this country. Neither of these compares in extent - seems entirely sufficient to account for the decompo- with that of St. Austel. All these deposits may be sition in nature of a body like felspar by water alone. looked at as products of the present geological periods, Water acts in the capacity of an acid as well as a base, during which the rocks have been exposed to atmoand the strongest affinity undoubtedly, exists to exert spheric agencies. Their bulk is constantly decreasing, this capacity, especially toward supersilicated minerals under the washing energy of rains and floods. Suslike felspar. In this case the attack by water is sup- pended in the current, both kaolin and mineral fragported by the possibility of forming a compound soluble ments are carried into the rivers. As soon as the in water-potassium silicate ; for if the white pulver- carrying-power of the current decreases by reason of ulent substance forming from the felspar be examined, lessened velocity the heavier sandy materials fall out, it is seen that only fractions of one per cent. of K20 mostly along the banks of the rivers, if they have are left, whilst the fresh felspar contains sixteen per risen above those banks, whilst at a distance, on the cent. The result of the completed decomposition so-called flood-plain, the velocity decreases apace, and may be represented by an equation : KASI,O6+ more and more the finer grains fall out, until at last, HO- AlSi, 07,2H,0 (kaolin or pure clay-substance) in nearly quiet water—that is, in the bays and estua+K,S,0,31,0 +Si0,2H,0: of these three prodries, where the counter-current of the tide checks the ucts, the first and last are insoluble in water; the river-current—the deposition of the clay-particles takes middle one is soluble in it. The silicic hydrate may place together with the very finest sand. These are be separated from the clay-substance by digestion with the mud-bars at the mouth of very large rivers. As a dilute solution of sodium carbonate. (It is not the dredgings show, they are composed of clay, not of proper to take the hydrates of sodium or potassium, sand. Instead of emptying into the sea, the waters because they will decompose and dissolve the clay- may empty into a large lake or fresh-water basin, or substance also.) The above formula for the first-named into huge swamps. At all events, these are Nature's body, Al,Si,0,+2H,0, gives the percentage compo- settling-vats. And thus we account for the numerous sition: sílica (SiO2), 46.40; alumina (Al2O3), 39.68 ; clay-strata which are encountered in all geological forwater (H,0), 13.92 (Rammelsberg Mineral" Chemie

, mations, from the earliest palæozoic to the most recent 2d edit., 642). But this formula is not generally ac- tertiary and quaternary. These deposits are clays, in cepted. C. Bischof, in his excellent treatise on The the more restricted sense of the word. They occur Refractory Clays (Leipzig, 1876), assumes more mostly in beds of varying thickness as well as purity, basic silicate: $1,0,.Si0, +2H,0 or 2A1,03,3Si0,+ which follow the stratification in dips and strike of the 44,0 (when silica = $io,). This yields the percentage surrounding rocks, sandstones, limestones, etc. Concomposition : silica, 39.33; alumina, 44.93; water, taining the kaolinized product of the entire geologic 15.73. The percentages of alumina and silica are very time, their magnitude in superficial extension is very nearly reversed in the two formulas. Bischof follows great. But there can be no doubt that many of the Malagutti, who treated the kaolin with potassic hydrate late clay-formations are made by redepositing the maand then analyzed the residue. But this method isterial of one or more older deposits, through which incorrect, as stated above. There are, however, cer- stretches the drainage of a river-system. According tain very refractory clays whose analysis leads nearly to collateral circumstances, the repeated transportation to Bischofs formula ; they are exceptions, and it must and deposition of clays may result in a purification or be assumed that they contain aluminic hydrate mixed in a degeneration ; the probability is in favor of the with the silicate. The whole subject, however, is by latter. The structure and general physical condition no means clear. Investigations of a still more critical of these transported, or secondary, clays is very varycharacter and more comprehensive than those on jpg, as well as their ultimate chemical composition. All record might possibly shed a better light upon the have preserved the one common stamp of their origin true composition of this highly useful mineral. --that is, a decided bedding or separation in layers,

Such, then, is the process of the hydration and kaolini- each of which undoubtedly corresponds to one flood. zation of the felspathic rocks. It is plain that the bulk But pressure and the influence of surrounding or of the insoluble residue cannot be pure kaolin, but penetrating volcanic rocks has largely modified the must be

mixture of this with grains of fresh or original bedding. In the older clays these layers



are so much compressed and hardened that they independent of the water contained in the clay and is form_slates. The well-known black roofing-slates of constant for all plastic clays; and, further, that the the Blue Mountain, belonging to No. 3, or Hudson cubical shrinkage is equal to the volume of water lost River, group-formation, are simply highly compressed by evaporation up to the limit of linear shrinkage. and hardened clay. This slate, when finely ground Aron found further that if the purest clay-substance is and in contact with water, returns after a time into mixed with very fine quartz sand the shrinkage will plastic clay. Between this hard slate and the soft increase up to a certain point, which he calls the point clays of tertiary or quaternary age we find all degrees of "greatest density." From this point the shrinkof slaty structure. The whole of these are compre- age decreases again, with increasing leanness, while hended under the generic term “argillites.” They the porousness increases. are clay-slates at the one extreme end, and slaty cluys Exposure to red heat destroys the plasticity of clay, at the other. It is well known that the outcrops of because the two molecules of water are eliminated from roofing-slate beds are too rotten for serviceable ma- the aluminum silicate at that temperature, and as a terial, The slate must be gotten by underground consequence the clay shrinks a second time; that is mining at a considerable depth. Being exposed to the "fire-shrinkage.". Addition of quartz sand neurain and frost, the slate absorbs water along the out- tralizes this second shrinking, and even reverts it into crops, swells, and becomes a lean clay.

expansion. Aron found that a clay-mass made lean Properties of Clay.—Under this head we shall with quartz sand shows a larger volume at a red heat speak of the qualities of the clay as a rock-mass- not than it had shown in the air-dry state, and that from so much of the clay-substance as of the various modi- a given point of leanness the volume will grow infications which the properties of that substance are versely as the temperature. Finely pulverized pure subject to by the admixture of the sandy fragments. limestone is an excellent means to counteract the fireAs such, we mean the fragments of all possible min-shrinkage, since it imparts to the burnt mass a certain erals. In absolute quantities the quartz always pre- uniformity in expansion and porousness within temperdominates in the sandy part.

atures of considerable range. If the temperature be Physical properties are such as may be at once carried to a white heat, these facts suffer modificanoticed by the eye-color and lustre ; opaqueness or tion, because new chemical affinities are provoked ; horny translucency; touch, sectility; the dimensions the materials of a clay-mass lose their former identity of the granular admixtures; the presence or absence more or less completely. This leads to the consideraof efforescences, of concretions; the fracture and tion of the most important physical property of pure general structure. Other physical properties, or at clay-substance and of clay, its resistance to the action least their causes, are not at once observable. Among of very intense heat. them the most prominent and important is the plas- The two proximate components are alumina (A1,03) ticity, in whose train many other phenomena may be and silica (SiO2). Both are found in a very pure state considered the shrinkage; the binding capacity, the as crystallized minerals, the first as corundum, and cohesion; the fatness or leanness; the capacity for with water as diaspore (A1,H,02); the second as quartz, absorbing water-capillarity or porousness; the stiff- hornstone, chalcedony, fint, and opal. Exposed to ness or resistance against water, etc.

highest temperature which can be realized in furnaces, Plasticity is the most valuable property of clay. It at which pure platinum fuses, neither corundum nor means the power to pass with water into a dough diaspore shows the least change or tendency to fusion. which may be moulded into any convenient and desira- Artificially-prepared alumina purified to the utmost ble shape. This power decreases with the percent behaves in the same way. Exposed to the same heat, age of increase of the sandy admixtures. It is strong- quartz (as rock-crystal) becomes rounded at the sharp est in the fat and weakest in the lean clays. A clay edges and comers, while its whole surface appears may be, however, too plastic; it dries very slowly and covered with a lustrous glaze. This mineral is there. unevenly. Objects after moulding will warp and fore less refractory than corundum. The other varie crack. Lean clays absorb water readily and become ties mentioned are always more or less impure from plastic; fat clays rather resist the water. Many of admixture of other bodies. They are decidedly more the latter class show the peculiarity which may be fusible than the pure rock-crystal

. The glazing takes called water-tightness—that is, they will not take up place at the temperature of melting wrought iron, and any more water after a certain quantity has been some varieties even fuse to a transparent or milky glass. absorbed. Such clays are used with advantage in the There is a general law that if two bodies enter into construction of temporary dams and weirs, in making chemical combination the resulting compound will have a shaft water-tight when sinking through loose or a lower fusing-point than the arithmetical mean of swimming rock. When first taken from the deposits their individual fusing-points. The combination of near the surface, the clays are mostly in this condition silica and alumina is no exception to this. Its fusingof water-saturation.

point is lower than that of quartz; it glazes readily as Experimenting upon the purest clay-substance ob- it approaches melting heat of wrought iron. It retained by careful washing in Schöne's apparatus, Dr. mains to be seen now how the relative proportions of Jul. Aron found that the linear shrinking does not the two compounds affect the fusing-point. The conprogress apace with the drying of the clay, as might cordant results of extended experiments by C. Bishave been expected, but only follows up to a certain chof and Richters show that the refractory character point, which he calls “limit of shrinkage ;', the water increases with the preponderance of alumina. Up to evaporated to this point is “the water of shrinkage;' a certain point the addition of silica increases the the remainder of the water given out until the weight fusibility (about 1: 6); beyond this point it decreases of the sample remains constant at a tem ature of again toward the same as in the ratio 1:1. 130° C. as the water of pores.' The sum of both The natural clays are rarely or never pure A1,03, is the total water. Under the supposition that the 2SiO, +2H,0. As explained above, they contain fragsmallest material particles of clay-substance possess ments of a number of other minerals with varying globular shape, this behavior is explicable. In a meas- composition, but generally silicates, and carbonates of ure, as the water which separates those particles passes the metals iron, calcium, magnesium, and maganese ; off, these will approach until they touch each other. more rarely sulphates of calcium, magnesium, iron, But each particle will be touched only at six points of and aluminum; phosphates of calcium and aluminum, its surface, and therefore the interstices between all chloride of sodium, oxides like those of iron. as hemthe other points will still be filled with the water of the atite (Fe,O3), limonite (Fe,1,08), ilmenite or titanifer" pores ;" *its evaporation cannot produce any further ous iron Fe_0s + TiO2), magnetite (Fez0.), rutile shrinkage of the clay. It follows as an important rule (Ti0,); sulphides, as pyrite (FeS,); rarely galenite for the potter that the number and size of the pores is (PbS) and blende (Zns). Materials of organic origin

VOL. 11.-1

are, seldom wanting in clays. They are hydrocarbons found that No. 1 (containing magnesia) bad completely (bitumen), sometimes in such quantities that they im- melted to a vitreous slag; Nos. 2, 3, and 4 followed, sü part a very peculiar and disagreeable odor when the that portion 4 (containing potassa) had been least clay is rubbed (stinking clays). They are oxidized melted. But the order of these samples corresponds hydrocarbons, such as humic acid. Graphite and to the atomic weights of these oxides in ascending amorphous carbon are very often present in clays. All series: Mg0-40; Ca0-56; 1 (Fe,0)=80; K,0= these materials have little influence on the fusing-point 94. Richters formulates this result as a law, thus: as they are destroyed in the furnace, except graphite, Equivalent quantities of different flucing ocides prowhich rather raises the fusing-point. The potassium duce the same effect upon the fusibility of a clay. For which is always present in clays is contained in the example: If the analysis had shown that a certain fragments of orthoclase. These substances more or clay contains magnesia=0.3 per cent., and that anless modify the refractory character of kaolin and sec- other clay contains potassa = 0.70, we could deduce ondary clays; they lower the fusing-points, and are with certainty that both would stand equally in the most properly comprised under one term as “fluxing fire, all other conditions being the same. According agents.

to the same observer, the presence of several fluxing Richters mixed one part by weight of pure alumina oxides in a clay does not influence the effect produced with two parts of silica, and exposed the mixture for by each singly; the fusibility increases only with the considerable time to the highest heat attainable in the higher sum of their equivalent weight. As the manufurnace until a partial fusion took place, showing that facture of fire-resisting bricks and vessels of many dethe two bodies had formed a chemical union. The scriptions forms the foremost use of clays, the properproduct was again pulverized, and equal portions of ties of clays just described are practically the most it were intimately mixed with four per cent. of the important. fluxing oxides, one part with percentage of magnesia, one with oxide of calcium (lime), one with ferric oxide, The following table is taken from C. Bischof's and one with potassium oxide (potassa). When the work, (1. c.). It gives the composition of seven clays four mixtures, made into small cylinders, were ex- which he takes as types of seven classes as far as posed to the same highest heat, the experimenter / refractoriness and plasticity are concerned :

[blocks in formation]


50 10-11

45 9-10




Deg. of refractoriness... 100 70-50

20 Degree of plasticity..... 1-2

8-9 100 parts of steam-dry clay absorb water.... |



6.55 CLASS I. Clay from Saarau, in Upper Silesia. - CLASS III. Best Belgian Clays. These clays are The tests were made with carefully selected pieces from found in irregular elliptic basins in the limestone forseveral hundredweights of clay from this locality. They nation which underlies the coal-measures in the provrepresent a slaty material of deep-blue color, not ince of Namur. There are several belts of such basins. easily friable. It looks somewhat hornlike, is of very The best quality is furnished by the second belt, touchuniform and mild grain, and shows no admixtures to ing the villages of Wez, Moget, Coutisse. The clay the eye. The clays belonging to this type are very has a blue or black-blue slate-color and is remarkable compact; the pores are reduced to a minimum (ab- for its binding power-that is, the large amount of sand sorbing only three per cent. of water), and are not that it will take up without losing its plastic force. It plastic. They become slightly plastic when soaking in has a very soap-like touch and assumes a vivid lustre coal-measures belong to this class more than others, water, it falls to small pieces, while large numbers of notably the celebrated prime-quality clay from Garn- air-bubbles escape with a hissing sound. Rubbed in kirk and Gartsherie, in Scotland. The New Jersey the mortar, it shows grit (one per cent. of small clay-beds of the cretaceous formation include a few quartz-grains). This clay is mined by shafts (140 feet) localities furnishing a quality very little inferior to this and underground workings. Number 1. The celebrated Stourbridge clay is notably | Class IV. Clay from Mühlheim, near Coblenz, on inferior. This prime quality is only used for glass- the Rhine.--It lies at the bottom of the brown-coal or pots, steel crucibles, and the best grade of fire-brick. lignite formation, and is mined by means of so-called

Class II. Kaolin from Zettlitz, near Carlsbad, in "hoop-shafts.” They are sunk from 30 to 80 feet, Bohemia. - This material is found in the highly fels- and pass through a layer of pumice-sand before reachpathic granite. It is a china-clay, and does not come ing the clay. In all physical properties it is like the to market in its crude form. It is first subjected to a Belgian clay, except that the degree of fusibility is washing process. The crude kaolin is grayish-white ; lower. it feels rough and gritty between the fingers. The re- CLASS V. Clay from Grünstadt, in the Pulalinate. fined material, when dry, forms very uniform pieces -Occurs in nests in the tertiary limestone, probably with a conchoidal fracture. It shows mild touch and derived from the decomposition of porphyry, which somewhat soapy; it cuts smoothly, and the cut surface constitutes the Donnersberg Mountain, some miles disis lustrous. When heated, it turns black at first (from or- tant, the kaolin being carried thence by floods. It is ganic woody admixtures); but soon the fine carbon burns, of light-bluish color, is free from grit, and otherwise is and the clay is almost snow-white. Thischina-clay is used like the two preceding clays. After burning has a almost exclusively in the manufacture of porcelain (on yellowish- and grayish-white color. account of the white color). Of similar grade are some Class VI. From Oberkauffungen, near Cassel, in washed china-clays of Delaware and Pennsylvania, and Prussia.—This and the next class are characteristic the well-known product of St. Austel, in Cornwall. representatives of clay-beds from the brown coal, lying

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