Jefferson, and hence more purely a low comedian than CLARKSBURG, the county-seat of Harrison co., W. Va., is on the west fork of the Monongahela River and on the Parkersburg branch of the Baltimore and Ohio Railroad, 122 miles S. of Wheeling and 82 miles E. of Parkersburg. It has a court-house, six churches, a female college, two weekly newspapers, a national bank, one other bank, two foundries and machine-shops, a woollen-mill, two flour-mills, and gas works. There are coal-mines in the vicinity. Population, 2307. CLARKSVILLE, the county-seat of Montgomery co., Tenn., is on the N. bank of the Cumberland River, at the mouth of Red River, 60 miles below Nashville. It is on the Louisville and Memphis Railroad, which here crosses both rivers. The city has a fine court-house, a hotel, two national banks and two other banks, one semi-weekly and two weekly newspapers, thirteen churches, and six schools. The South-western University (Presbyterian) was estab lished here in 1874, the citizens contributing liberally for its endowment. There is also a female academy, The industries comprise a foundry, several flour- and planing-mills, and manufactures of ploughs, wagons, carriages, and ice. The city was incorporated in 1830, and, though it suffered severely by a fire in 1878, has revived and presents a fine appearance. It is lighted with gas, and supplied with water by public waterworks. The surrounding country furnishes a large amount of tobacco and other products for shipment by river or by rail. Population, chiefly of American birth, 3880. 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 Religions. Another notable work is The Legend of Thomas Didymus, the Jewish Sceptic (1881), in which Dr. Clarke attempts to set forth in a narrative the opinions, beliefs, and prejudices of the Jewish sects in the time of Jesus and the characters which surrounded him. Dr. Clarke has also published a volume of Memorial and Biographical Sketches (1878), Self Culture, Physical, Intellectual, Moral, and Spiritual (1880), and The Ideas of the Apostle Paul Translated into their Modern Equivalents (1884). His writings on every subject are clear, earnest, and inspiring. CLARKE, JOHN SLEEPER, an American comedian, was born in Baltimore, Md., in 1835. At an early age he lost his father and was thrown upon his own resources. While still a boy he developed a strong inclination for the stage and became a member of a company of amateur tragedians, of which Edwin Booth, who subsequently became his brother-in-law, was also a member. By the desire of his mother he took up the study of law, reading industriously for about a year in the office of Elisha R. Sprague, in Baltimore, Md. But after a brave effort to meet his mother's wishes, he abandoned law and turned his attention earnestly to the stage. Although tragedy had attracted his boyish fancy, it soon became evident that low comedy offered the most inviting field for the exercise of his peculiar powers. Not wanting in pathos, and, indeed, having a nature singularly alive to emotional influences, he yet possessed that keen sense of the ludicrous, conjoined with an extraordinary mimetic faculty, which fitted him for comic activity. His first regular engagement began at the Old Chestnut Street Theatre, in Philadelphia, Aug. 28, 1852, the play being "She Would and She Would Not," in which Clarke assumed the role of Soto. He rose in favor, and in January, 1853, became leading man in the Chestnut Street stock company-a position which he held for a year. In 1854 he went to Baltimore, taking the place of first low comedian at the Front Street Theatre in that city. He became so general a favorite that the Baltimoreans forced upon him a complimentary benefit in the autumn of 1854, which became, indeed, a popular ovation. In August, 1855, he returned to Philadelphia, and took the position of leading comedian at the Arch Street Theatre until 1858, when he entered into partnership with William Wheatley and became joint-lessee of that house. The business was successfully conducted until 1861, when the partnership was dissolved, and Clarke arranged to appear as a star in New York. He made his debut in this capacity at the Winter Garden and secured an instant and unequivocal success. The critics with one accord hailed him as a great artist and the legitimate successor of W. E. Burton, whose loss had been felt as nearly irreparable. Clarke's fame was now secure, and he began a starring-tour of the principal American cities, rapidly acquiring fortune. He became part-proprietor of the three leading theatres of the country, the Boston Theatre, the New York Winter Garden, and the Walnut Street Theatre, Philadelphia, from each of which he reaped large financial returns. In 1868, Clarke went to England, making his appearance at the St. James's Theatre in the autumn of that year. London received him with an enthusiasm equal to that accorded him by New York, and, with the exception of a brief visit to his native country in 1881, he has since made England his home. He has played at nearly all the leading English theatres. Mr. Clarke married a sister of Edwin Booth, and has always been noted for his strong domestic attach ments and exemplary personal character. As an artist he may be said to have created a school of his own, although he approaches in his methods more nearly to the late William E. Burton than to any other actor. CLAUSEN, HENRIK NICOLAI (1793-1877), a Danish theologian, was born April 22, 1793, in Marebo, where his father was pastor. The father, who was a man of ability, became afterward chief preacher in the Lady church at Copenhagen, and published several volumes of sermons. The son distinguished himself at the University of Copenhagen, and after graduating, in 1818, travelled extensively in France, Italy, and Germany. While in Berlin he came under the influence of Schleiermacher. In 1821 he began to lecture on theology at Copenhagen, and in the next year was made professor in the university there. He soon took part in the agitation for a constitutional government, and in 1840 he became a member of the provincial assembly at Roestilde, of which from 1842 to 1846 he was president. He was afterward elected to a constitutional assembly, and from 1848 to 1851 was a member of the state council. In 1876 he resigned his professorship, and he died at Copenhagen March 28, 1877. His reputation as a writer was first established by his Catholicism and Protestantism in their Eccesiastical Organization, Doctrine, and Ritual (1825). This work involved the author in a famous controversy with Bishop Grundtvig, one of the results of which was a libel suit against the latter. Clausen published several other works against Grundtvig and his followers. He was also the author of numerous exegetical and dogmatic works. Among these are treatises on the Synoptical Gospels (184750), on John (1855), on Romans (1863). After his death a volume of autobiography was published. CLAUSIUS, RUDOLF JULIUS EMANUEL, a German physicist, was born at Köslin. Pomerania, Jan. 2, 1822. He studied at the University of Berlin, and became a privat docent there, as well as professor of physics in a military school. In 1855 a polytechnic school was established at Zurich, and Clausius was appointed to the chair of physics. He also obtained a professorship in the University of Zurich. In 1867 he accepted a call to a similar position at Würzburg, and two years later became professor at Bonn. Besides some investigations in optics and on the elasticity of | if 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 smallsubject appeared first in Poggendorff's Annalen, but that is, less than the Too 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), Ueber water for a long time. The peculiar milky opalesden zweiten 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 in common as sand. They are fragments of different mineral species-quartz, felspar, mica chiefly, tourmaline, hornblende, magnetite, ilmenite or titaniferous iron, rutile, and others. These minerals are hard, their fragments angular and of all degrees of fineness. They may be reduced to grains not much larger than the globules of the clay-substance and remain suspended with them in water, whilst the sand proper settles very quickly, and may be thus separated from the kaolin. The mineral nature and chemical composition of the sandy portions of a clay and their relative quantity determines whether a given clay is serviceable for a specified purpose. Besides the sand, there are other compounds present in clays, such as coaly matter, the red, brown, and yellow oxides of iron, pyrite, fossil ros'n, bitumen, black oxide of manganese, alum, gypsum, caleite, dolomite. They produce the many colored varieties of clay, and are either quite harmless or more or less hurtful to the uses to which clay may be put. CLAVICLE (Lat. clavis, a key, clavicula, a small key), the collar-bone. In man this bone is rather slender for its length, curved somewhat like an italic f, and extends from the acromion process of the scapula to the manubrium of the sternum; it is movably articulated at each end, and the sternal end furnishes the only bony connection of the arm with the trunk proper of the body. From its exposed situation in the neck the collar-bone is peculiarly liable to fracture. In nearly all Mammalia the clavicles, when perfect, repeat the same connections they have in man, but they are frequently defective or wanting altogether. They are consequently of little value in morphological classification, being present and perfect, or in varying imperfection, or absent, in closely-related animals, even of neighboring genera. They are best developed, as a rule, in those quadrupeds which use the fore limbs as arms and hands, rudimentary or lacking in those which the same limbs are exclusively devoted to ordinary locomotion. In birds the clavicles are usually present and perfect, 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 Ratite and some parrots; ankylosed with the keel of the sternum in some Steganopodes, as the pelican and frigatebird; with the body of the sternum in Opisthocomus. When perfected they serve to bear the shoulders apart; and their degree of curvature and solidity bear some relation to power of strong or protracted flight. (E. C.) CLAY, in its purest state, is a mineral substance of perfect snow-white color; it feels to the touch like soap, is very soft and brittle; it sticks to the tongue, and emits a peculiar odor when the moist breath is blown upon it. Kneaded together with water, it absorbs the latter in considerable quantity, and passes into a peculiar condition which is designated plastic. In this state the clay has lost its brittleness, the particles adhere with considerable force and yet possess a remarkable freedom of motion against each other, and may thus receive any arbitrary shape from the moulding hand of man. This is a quality not possessed by any other mineral substance, and gives to clay its great importance as raw material in the arts. Clay, however, is not a uniform mineral matter. The above characters belong only to one of its composing parts, which may be named the clay-substance, or, in conformity with mineral nomenclature, kaolin. Kaolin is made up of minute loosely-aggreated particles invisible to the naked eye and impalpable to the touch-that is, without grit. Under a magnifying power of 1100 diameters these particles look like globules, and in appearance their aggregate is not unlike to fish-roe. The writer's observations harmonize in this respect entirely with Aron's, who examined them under a power of 760 diameters. They differ from those of other observers, who conclude that the clay-substance is composed of fragments of crystal. The writer could not observe any effect which this material is said by some to have on polarized light, which would be a proof of their crystalline nature. This substance, on the contrary, resembles much more the globules of starch, being capable of absorbing water, of swelling, and of passing into a plastic paste. The extreme mobility of the particles is accounted for lites, clay-slates, marls, and loams. To gain a proper idea of these differences we must consider the— Potassium Origin of Clay.-The so-called primitive rocks, which have been proven by all deep mining and by the study of the sequence of rocks to underlie all other rocks, are composed chiefly of three species of minerals, quartz, felspar, and mica. Quartz is pure silica (SiO), very hard, compact, and very indifferent toward chemical agencies at ordinary temperature. Felspar is a more complex compound, containing at least four elements-e. potassium (K), aluminum (Al), silicon (Si), and oxygen (O). These elements are combined in the ratio KAlSi¿O16may be replaced by sodium wholly or in part, and also by calciumi, in felspar. It is a white, vitreous, easily cleavable substance only one degree less hard than quartz. Mica is composed of the same elements, with the addition of iron and magnesium. But the ratio of combination is different, likewise, for the several species of mica: muscovite, the white mica; biotite, the dark-colored mica. The micas crystallize in the same system with the felspar, but possess only one eminent cleavage. The cleavage laminæ are flexible, elastic, and much softer than felspar. The same or very similar minerals form the component parts of a number of igneous or volcanic rocks. When these minerals are aggregated in more or less parallel layers, they form gneiss, whose structure is schistose or slaty; when in granular, irregular aggregation, they form granite; when developed with porphyric structure, they compose the volcanic rocks porphyry and trachyte. The researches in chemical geology have proved that all other rocks have been formed by the chemical and mechanical destruction of those just mentioned. It is not asserted by the writer that they are original rocks; they are merely the oldest and deepest we have any cognizance of. At all places where the felspathic rocks have been at the surface for any length of time a peculiar change becomes noticeable. Especially the coarse-grained granite, in which the felspar is found very pure, and often in 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 into the clay-substance, or kaolin. In chemistry the law prevails that the more complex a composition a given compound possesses, the more ready it is to succumb to the action of chemical agencies. Likewise, the more a ternary compound or salt is acid-that is, the more the ratio of that acid portion increases over that of normal saturation-the less will be its chemical stability. In the felspar we have a case exactly corresponding. The composition of the orthoclase felspar has been stated as K,Al,SiO16. This formula may be written K2O+Al2O3 + 6SiO2. all other and less easily decomposable minerals of the original rock. It will be understood that this residue as a whole is therefore a rock- i, e. an aggregate of minerals and not a species of mineral that is, a uniform and homogeneous substance. Among the minerals in the granite and gneiss are black tourmaline, black hornblende, and black mica, or biotite. These are silicates containing ferrous oxide (protoxide of iron). Undergoing the process of hydration like the felspar, this iron becomes altered into ferric hydrate or brown hydrated sesquioxide of iron-iron-rust; sometimes, 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 K,O 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: KAlSiO8+ more and more the finer grains fall out, until at last, H2OAL,S,O,2H,O (kaolin or pure clay-substance) in nearly quiet water-that is, in the bays and estua+K2Si,O,,3H2O+SiO,.2H,O: of these three prod-ries, 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 be separated from the clay-substance by digestion with a dilute solution of sodium carbonate. (It is not proper to take the hydrates of sodium or potassium, because they will decompose and dissolve the claysubstance also.) The above formula for the first-named body, Al, Si,O,+2H,O, gives the percentage composition: silica (SiO2), 46.40; alumina (Al2O3), 39.68; water (H2O), 13.92 (Rammelsberg Mineral Chemie, 2d edit., 642). But this formula is not generally accepted. C. Bischof, in his excellent treatise on The Refractory Clays (Leipzig, 1876), assumes a more basic silicate: Al2O3,SiO, +2H20 or 2A1,O,,3SiO2+ 4H,O (when silica-SiO). This yields the percentage composition: silica, 39.33; alumina, 44.93; water, 15.73. The percentages of alumina and silica are very nearly reversed in the two formulas. Bischof follows Malagutti, who treated the kaolin with potassic hydrate and then analyzed the residue. But this method is incorrect, as stated above. There are, however, certain very refractory clays whose analysis leads nearly to Bischof's formula; they are exceptions, and it must be assumed that they contain aluminic hydrate mixed with the silicate. The whole subject, however, is by no means clear. Investigations of a still more critical character and more comprehensive than those on record might possibly shed a better light upon the true composition of this highly useful mineral. = Such, then, is the process of the hydration and kaolinization of the felspathic rocks. It is plain that the bulk of the insoluble residue cannot be pure kaolin, but must be a mixture of this with grains of fresh or place together with the very finest sand. These are the mud-bars at the mouth of very large rivers. As the dredgings show, they are composed of clay, not of sand. Instead of emptying into the sea, the waters may empty into a large lake or fresh-water basin, or into huge swamps. At all events, these are Nature's settling-vats. And thus we account for the numerous clay-strata which are encountered in all geological formations, from the earliest palæozoic to the most recent tertiary and quaternary. These deposits are clays, in the more restricted sense of the word. They occur mostly in beds of varying thickness as well as purity, which follow the stratification in dips and strike of the surrounding rocks, sandstones, limestones, etc. Containing the kaolinized product of the entire geologic time, their magnitude in superficial extension is very great. But there can be no doubt that many of the late clay-formations are made by redepositing the material of one or more older deposits, through which stretches the drainage of a river-system. According to collateral circumstances, the repeated transportation and deposition of clays may result in a purification or in a degeneration; the probability is in favor of the latter. The structure and general physical condition of these transported, or secondary, clays is very varying, as well as their ultimate chemical composition. All have preserved the one common stamp of their origin -that is, a decided bedding or separation in layers, each of which undoubtedly corresponds to one flood. But pressure and the influence of surrounding or penetrating volcanic rocks has largely modified the 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 clays at the other. It is well known that the outcrops of roofing-slate beds are too rotten for serviceable material. The slate must be gotten by underground mining at a considerable depth. Being exposed to rain and frost, the slate absorbs water along the outcrops, swells, and becomes a lean clay. Properties of Clay.-Under this head we shall speak of the qualities of the clay as a rock-mass-not so much of the clay-substance as of the various modifications which the properties of that substance are subject to by the admixture of the sandy fragments. As such, we mean the fragments of all possible minerals. In absolute quantities the quartz always predominates in the sandy part. · Physical properties are such as may be at once noticed by the eye-color and lustre; opaqueness or horny translucency; touch, sectility; the dimensions of the granular admixtures; the presence or absence of efflorescences, of concretions; the fracture and general structure. Other physical properties, or at least their causes, are not at once observable. Among them the most prominent and important is the plasticity, in whose train many other phenomena may be considered the shrinkage; the binding capacity, the cohesion; the fatness or leanness; the capacity for absorbing water-capillarity or porousness; the stiffness or resistance against water, etc. Exposure to red heat destroys the plasticity of clay, because the two molecules of water are eliminated from the aluminum silicate at that temperature, and as a consequence the clay shrinks a second time; that is the "fire-shrinkage.' Addition of quartz sand neutralizes this second shrinking, and even reverts it into expansion. Aron found that a clay-mass made lean with quartz sand shows a larger volume at a red heat than it had shown in the air-dry state, and that from a given point of leanness the volume will grow inversely as the temperature. Finely pulverized pure limestone is an excellent means to counteract the fireshrinkage, since it imparts to the burnt mass a certain uniformity in expansion and porousness within temperatures of considerable range. If the temperature be carried to a white heat, these facts suffer a modification, because new chemical affinities are provoked; the materials of a clay-mass lose their former identity more or less completely. This leads to the consideration of the most important physical property of pure clay-substance and of clay, its resistance to the action of very intense heat. The two proximate components are alumina (Al2O3) and silica (SiO2). Both are found in a very pure state as crystallized minerals, the first as corundum, and with water as diaspore (Al,H2O,); the second as quartz, hornstone, chalcedony, flint, and opal. Exposed to 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 corners, 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 it approaches melting heat of wrought iron. It remains to be seen now how the relative proportions of the two compounds affect the fusing-point. The concordant results of extended experiments by C. Bischof and Richters show that the refractory character increases with the preponderance of alumina. Up to a certain point the addition of silica increases the fusibility (about 1: 6); beyond this point it decreases again toward the same as in the ratio 1: 1. Experimenting upon the purest clay-substance obtained by careful washing in Schöne's apparatus, Dr. Jul. Aron found that the linear shrinking does not progress apace with the drying of the clay, as might have been expected, but only follows up to a certain point, which he calls "limit of shrinkage;" the water evaporated to this point is "the water of shrinkage;" the remainder of the water given out until the weight of the sample remains constant at a temperature of 130° C. as the "water of pores." The sum of both is the total water. Under the supposition that the smallest material particles of clay-substance possess globular shape, this behavior is explicable. In a measure, as the water which separates those particles passes off, these will approach until they touch each other. But each particle will be touched only at six points of its surface, and therefore the interstices between all the other points will still be filled with the water of the "pores;" its evaporation cannot produce any further shrinkage of the clay. It follows as an important rule for the potter that the number and size of the pores is VOL. II.-I The natural clays are rarely or never pure Al2O3, 2SiO,+2H2O. As explained above, they contain fragments of a number of other minerals with varying composition, but generally silicates, and carbonates of the metals iron, calcium, magnesium, and maganese; more rarely sulphates of calcium, magnesium, iron, and aluminum; phosphates of calcium and aluminum, chloride of sodium, oxides like those of iron. as hematite (Fe,O,), limonite (Fe,H,O), ilmenite or titaniferous iron (Fe,O,+TiO2), magnetite (FeO.), rutile (TiO,); sulphides, as pyrite (FeS2); rarely galenite (PbS) and blende (ZnS). Materials of organic origin are, seldom wanting in clays. They are hydrocarbons found that No. 1 (containing magnesia) had completely (bitumen), sometimes in such quantities that they im- melted to a vitreous slag; Nos. 2, 3, and 4 followed, so 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: MgO=40; CaO-56; } (FeO3)=80; K2O= 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 fluxing oxides 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 oxides in a clay does not influence the effect produced by each singly; the fusibility increases only with the higher sum of their equivalent weight. As the manufacture of fire-resisting bricks and vessels of many descriptions forms the foremost use of clays, the properties of clays just described are practically the most important. Richters mixed one part by weight of pure alumina with two parts of silica, and exposed the mixture for considerable time to the highest heat attainable in the furnace until a partial fusion took place, showing that the two bodies had formed a chemical union. The product was again pulverized, and equal portions of it were intimately mixed with four per cent. of the fluxing oxides, one part with percentage of magnesia, one with oxide of calcium (lime), one with ferric oxide, and one with potassium oxide (potassa). When the four mixtures, made into small cylinders, were exposed to the same highest heat, the experimenter III. The following table is taken from C. Bischof's work (l. c.). It gives the composition of seven clays which he takes as types of seven classes as far as refractoriness and plasticity are concerned : VII. 3.26 Degree of plasticity..... 100 parts of steam-dry 8.90 clay absorb water.... CLASS I. Clay from Saarau, in Upper Silesia.The tests were made with carefully selected pieces from several hundredweights of clay from this locality. They represent a slaty material of deep-blue color, not easily friable. It looks somewhat hornlike, is of very uniform and mild grain, and shows no admixtures to the eye. The clays belonging to this type are very compact; the pores are reduced to a minimum (absorbing only three per cent. of water), and are not plastic. They become slightly plastic when soaking in water for a greater length of time. The clays of the coal-measures belong to this class more than othersnotably the celebrated prime-quality clay from Garnkirk and Gartsherie, in Scotland. The New Jersey clay-beds of the cretaceous formation include a few localities furnishing a quality very little inferior to this Number 1. The celebrated Stourbridge clay is notably inferior. This prime quality is only used for glass pots, steel crucibles, and the best grade of fire-brick. CLASS II. Kaolin from Zettlitz, near Carlsbad, in Bohemia. This material is found in the highly felspathic granite. It is a china-clay, and does not come to market in its crude form. It is first subjected to a washing process. The crude kaolin is grayish-white; it feels rough and gritty between the fingers. The refined material, when dry, forms very uniform pieces with a conchoidal fracture. It shows mild touch and somewhat soapy; it cuts smoothly, and the cut surface is lustrous. When heated, it turns black at first (from organic woody admixtures); but soon the fine carbon burns, and the clay is almost snow-white. This china-clay is used almost exclusively in the manufacture of porcelain (on account of the white color). Of similar grade are some washed china-clays of Delaware and Pennsylvania, and the well-known product of St. Austel, in Cornwall. 10.73 CLASS III. Best Belgian Clays.-These clays are found in irregular elliptic basins in the limestone formation which underlies the coal-measures in the province of Namur. There are several belts of such basins. The best quality is furnished by the second belt, touching the villages of Wez, Moget, Coutisse. The clay has a blue or black-blue slate-color and is remarkable for its binding power—that is, the large amount of sand that it will take up without losing its plastic force. It has a very soap-like touch and assumes a vivid lustre on the face of a cut, almost like graphite. Placed in water, it falls to small pieces, while large numbers of air-bubbles escape with a hissing sound. Rubbed in the mortar, it shows grit (one per cent. of small quartz-grains). This clay is mined by shafts (140 feet) and underground workings. CLASS IV. Clay from Mühlheim, near Coblenz, on the Rhine.-It lies at the bottom of the brown-coal or lignite formation, and is mined by means of so-called "hoop-shafts." They are sunk from 30 to 80 feet, and pass through a layer of pumice-sand before reaching the clay. In all physical properties it is like the Belgian clay, except that the degree of fusibility is lower. CLASS V. Clay from Grünstadt, in the Palatinate. -Occurs in nests in the tertiary limestone, probably derived from the decomposition of porphyry, which constitutes the Donnersberg Mountain, some miles distant, the kaolin being carried thence by floods. It is of light-bluish color, is free from grit, and otherwise is like the two preceding clays. After burning has a yellowish- and grayish-white color. CLASS VI. From Oberkauffungen, near Cassel, in Prussia.-This and the next class are characteristic representatives of clay-beds from the brown coal, lying |