Yarn is usually dyed in the hank, in rectangular vats of wood, stone, or metal, heated by steam coils, and provided with false bottoms to prevent the yarn from coming into direct contact with the steam. The hanks are suspended on rods placed across the vats at intervals of one or more inches, and turned, usually by hand, until all the yarn has absorbed a sufficient amount of dye. In yarn-dyeing machines the hand-turned rods are usually replaced by porcelain rollers operated from a single shaft by means of spur wheels. Yarn is sometimes dyed in the warp, either in hank form or in specially constructed warp-dyeing machines. Cotton yarn is frequently dyed in cops, just as it is wound from the spinning frame, the dye being forced through the mass of the cop by pressure or suction. Slubbing is made into hanks and dyed in the same manner as yarn.

Loose fibres are sometimes dyed in vats or boilers, in which they are turned by hand with poles or forks; or they may be placed in a perforated drum through which the dye is forced by means of a circulating pump or other device. In another type of machine, similar to that used for hank dyeing, the drum is made to revolve in such a manner that the fibres are alternately dipped into the dye and lifted out to drain.

With some colors-notably alizarin reds. Turkey red, and aniline blacks-the dyed goods are treated with steam to develop the color, but in general this is not necessary. Most goods, however, require washing to remove the excess of coloring solution which they mechanically retain. In some cases this is done in the same machine that has been employed for dyeing, the dye liquor having been drawn off and water substituted. In others it is done by hand or in specially designed machines. Drying is plished by hydro-extractors, tentering machines, etc. (see DRYING MACHINES).

accom

The Supply of Dyestuffs.-Prior to the European war (see EuROPE, GREAT WAR OF) only onefifth of the artificial dyestuffs used in the United States were produced there, by far the largest part of the supply being imported from Germany, where the product of 22 establishments represented three-fourths of the world's output. Since August, 1914, the importation has been seriously interrupted, while the prices have advanced 25 to 50 per cent. and more. Many American dye firms have been obliged to return to the use of natural

dyes, or to change or abandon some of their products; and the textile, leather, paper, paint and varnish, and ink industries have suffered seriously.

Many efforts have been made toward relieving the resulting shortage. The few American establishments devoted to the manufacture of artificial dyestuffs have greatly increased their output; new plants have been established; and the erection of adequate by-product recovery plants in connection with coke works has made rapid progress. A second means of meeting the shortage has been the increased use of natural dyestuffs. As a rule, these require more manipulation than artificial colors; but in many cases the total cost is no greater, and standardized extracts frequently assure a degree of uniformity equal to that afforded by the coal tars. In spite of these efforts, however, a decided shortage of dyestuffs still exists, and the present domestic production supplies little more than half the demand, while the variety of colors is seriously limited.

On Aug. 1, 1914, there were 6 establishments in the United States engaged in the manufacture of artificial dyestuffs, which produced about 3,300 short tons annually. In January, 1916, there were 12 establishments, and about 15,000 short tons were produced in 1915. During the first eleven months of 1915, coal-tar colors valued at $3,200,000 (as compared with $6,400,000 in 1914), and coal-tar distillates valued at $700,000 (as compared with $1,300,000 in 1914), were imported into the United States. During the same period there were also imported 53,513 tons of logwood, valued at $725,000; and 19.555 tons of other dyewoods, valued at $300,000.

To alleviate or to avert a famine in dyestuffs, the U. S. Department of State has sought to secure the free passage of dyestuffs from Germany. The Department of Commerce has urged economy in the use of dyes; has emphasized the desirability of using natural coloring matters; and has encouraged the development of a national coal-tar chemical industry by stimulating cooperation among inventors, dyers, and capitalists. It is said that the natural resources of the United States can be made to furnish all the raw materials required in the manufacture of dyestuffs.

See CALICO PRINTING; COALTAR DYES.

Bibliography-Consult Rawson, Gardner, and Laycock's Dictionary of Dyes and Mordants; Schultz and Julius' Systematic Survey of Organic Coloring Matters

(Eng. trans.); Fraps' Principles of Dyeing; Cain and Thorpe's The Synthetic Dyestuffs (1905); Kent, Rawson, and Loewenthal's A Manual of Dyeing (2 vols., 1910); Martin's Industrial and Manufacturing Chemistry (1913); Pellew's Dyes and Dyeing (1913); Matthews' Laboratory Manual of Dyeing and Textile Chemistry (1913).

Dyer, di'er, Eliphalet (17211807), American soldier and legislator, was born in Windham, Conn. He was graduated from Yale in 1740, and was admitted to the bar in 1746. During the French and Indian War he was lieutenant-colonel of a Connecticut regiment, and in 1763 was sent to England as the agent of the Susquehanna Land Company. He was a delegate to the Stamp Act Congress in 1765; and served as member of the Continental Congress during the Revolutionary War. He was raised to the bench of the superior court in 1766, and was chief justice from 1789 to 1793.

Dyer, GEORGE (1755-1841). English scholar and historian, was born in London. He edited two plays of Euripides and a Greek Testament, and assisted Valpy in his great edition of the classics, a work which caused the total loss of his eyesight. He was an intimate friend of Charles Lamb. He also wrote Poems (1792); Four Letters on the English Constitution (1812); History of the Universities and Colleges of Cambridge (1814).

Dyer, ISADORE (1865), American dermatologist, was born in Galveston, Texas. He was graduated from the Sheffield Scientific School (1887), and in medicine from Tulane University (1889). He has been lecturer (1892-1905), associate professor (1905-08), and professor (since 1908) of diseases of the skin, and associate dean (1907-08) and dean (since 1908) of the School of Medicine, at Tulane University. He is editor of The New Orleans Medical and Surgical Journal (since 1896), and associate editor of The American Journal of Tropical Diseases (since 1913). He has published The Art of Medicine (1913).

Dyer, JOHN (1700-58), British poet, was born in Aberglasney, Carmarthenshire, Wales. In 1727 he published Grongar Hill, a short poem, possessing even now a certain charm. While studying painting in Italy he composed The Ruins of Rome (1740). His longest work is The Fleece (1757).

Dyer, LOUIS (1851-1908), American author and educator. was born in Chicago, Ill., and was graduated from Harvard (1874) and from Oxford (1878). He was assistant professor of Greek at Harvard (1881-7); lec

turer at Lowell Institute (1889); lecturer at Balliol College, Oxford (1893-6); and acting professor of Greek at Cornell University (1895-6). After 1900 he lectured on art at the principal educational institutions of the United States. His publications include: The Greek Question and Answer (1884); Plato's Apology and Crito (1886); Oxford as It Is (1902); Machiavelli and the Modern State (1904).

Dyer, or DYAR, MARY (d. 1660), American Quaker, was a victim of religious persecution in Massachusetts under a statute sentencing to death any Quaker returning to the colony after being once expelled. On her first return she was reprieved after the rope was around her neck, and again exiled. On her second return she was publicly hanged on Boston Common (June 1, 1660).

Dyer, NEHEMIAH MAYO (18391910), American naval officer, was born in Provincetown, Mass., and went to sea at an early age. At the outbreak of the Civil War he volunteered as a soldier, but was later transferred to the Navy, where he served with distinction, and was promoted to the rank of acting ensign in 1863, and acting master in 1864. He became lieutenant-commander in 1883, commander in 1884, and captain in 1897; and commanded the Baltimore in the Battle of Manila Bay (May 1, 1898). He retired in 1901 with the rank of rear-admiral.

Dyer, SIR WILLIAM TURNER THISTLETON (1843), English botanist, was born in Westminster. He was professor of natural history at Cirencester (1868), and professor of botany at the Royal College of Science in Ireland (1870). In 1875 he became assistant director of the Royal Gardens at Kew, and was director from 1885 to 1905. He is joint author of The Flora of Middlesex (1869); prepared the English edition of Sachs' Text Book of Botany (1875); and was editor of Flora Capensis and The Flora of Tropical Africa.

Dyersburg, di'erz-burg, city, Tennessee, county seat of Dyer county, on the Forked Deer River, and the Illinois Central, the Birmingham and Northwestern, and the Chicago, Memphis, and Gulf Railroads; 70 miles northeast of Memphis. The chief industries are the manufacture of cottonseed oil, machinery, wagons, flour, tobacco, brick, tile and barrels. Pop. (1900) 3,647; (1910) 4,149.

Dyes. See COAL-TAR DYES; DYEING.

Dyke, or DIKE, an artificially constructed embankment of earth, stone, brush, or other material

erected along river banks or seashores: either (1) for the improvement of channels for navigation by contracting them over shoals, correcting excessive curvature, or securing a more evenly distributed depth of water than occurs naturally; or (2) for the protection of the banks or shores against erosion, and the prevention of inundation.

Dykes for the improvement of river channels are of two main types: longitudinal dykes, which follow the general direction of the current, and spur dykes, which are erected at intervals of from 200 to 650 feet, and at angles of from 75 to 110 degrees with the channel. They are constructed of stone, piles, brush, masonry, concrete, etc., and their average height is a few feet above low water. Dykes of loose stone are sometimes confined in timber cribs.

Dykes for the protection of river banks and seashores may be similar in construction to those for correcting river channels, or they may consist of high embankments of earth. Such dykes are found in most low-lying countries, and are especially numerous in the Netherlands, where there are more than 1,500 miles of sea dykes, erected and maintained at enormous cost. One of these, the West Kappel Dyke, is 12,648 feet long, and 23 feet high, with a seaward slope of 300 feet; it is protected by piles and stone work, and has a road and a railway on top.

In 1574 the Prince of Orange raised the siege of Leyden by breaking down the dykes, flooding the country, and drowning many of the besieging Spaniards; and in 1914 the Belgians adopted a similar plan to arrest the advance of the Germans. The fearful damage caused by the bursting of dykes is illustrated in the destruction of Szegedin, in Hungary, in 1879, and the flooding of a vast area in China by the inundation of the Yellow River in 1887. In January, 1916, a tidal wave from the North Sea caused the bursting of the Zuider Zee dykes, and the inundation of a large area of the province of North Holland. A number of towns in the vicinity of Amsterdam were flooded, and the island of Marken was submerged.

See DRAINAGE; MISSISSIPPI RIVER; RECLAMATION. Consult Thomas and Watt's The Improvement of Rivers (vol. I., 1913).

Dykes, or DIKES, masses of igneous rock that fill fissures in the earth's crust in more or less vertical, wall-like sheets. They occur as the result of volcanic action, and their method of origin may be seen in such active vol

canoes as Etna and Vesuvius. The powerful internal forces at work both during and after active eruption produce numerous radiating fissures in the volcanic mass, into which the fluid lava forces its way, and there consolidates. As a rule, the lava which constitutes these masses is more crystalline than that poured out from the crater of the volcano; and it may show extreme variations in structure, from the glassy material formed by rapid cooling in contact with other rocks, to perfectly crystalline or granitic varieties in the centre of the intrusive mass. When the lava is

which they occur. A dyke may become horizontal for a space, or follow the bedding, when it is to be regarded as an intrusive sheet. Some dykes are many yards broad, but more commonly they do not exceed a few feet. There are dykes which can be traced running across country in a nearly straight line for a hundred miles. Their form depends much on the nature of the rocks they cut; for if these have a perfect jointing, they will split open in a regular manner. On account of the high temperature to which they are raised by contact with the molten material in the dyke, the adjacent rocks are altered to a greater or less degree. Occasionally they have been fused or recrystallized; more frequently they are merely indurated and baked. See IGNEOUS ROCKS.

Dynamical Units. See UNITS. Dynamics, di nam'iks, a branch of mechanics (q.v.) conveniently subdivided into the two great branches kinetics and statics, which treat respectively of the motion and the equilibrium of material systems. The principles of dynamics are contained in Newton's definitions and laws of motion (see MOTION, LAWS OF), as given in the Principia. They depend upon the recognition of mass and its correlative force.

now

Since the discovery of the great principle of the conservation of energy, physical science has become essentially dynamical; and, in addition to the comparatively limited field originally covered by dynamics, there are recognized the important branches of thermodynamics or the dynamics of heat, and electrodynamics, including the whole theory of electricity and magnetism. Hydrodynamics is the branch of the subject which deals with liquids, and aerodynamics that which deals with gases.

In the study of dynamics it is usual, though possibly not necessary, to form the conception of force as producing change of motion. Attention is fixed upon a small body, say a stone falling towards the earth, and its motion is conceived to be governed by the action of the so-called force of gravity. This constitutes the simplest problem in what is known as the dynamics of a particle. Then follow dynamics of connected particles of rigid bodies, of flexible strings, and of elastic bodies, solid, liquid, and gaseous. See KINETICS and STATICS; also the following articles:

There are few complete treatises in English on the subject of the dynamics of material systems, even in the more limited sense, excluding thermal and electrical effects. Thomson and Tait's Natural Philosophy, Tait's Dynamics, Routh's Dynamics of a System of Rigid Bodies and Dynamics of a Particle are among the best. Appell's Mécanique rationnelle complete work in four volumes. Newton's Principia (1687) and Lagrange's Méchanique analytique (1788) must always take first rank; the latter especially, though nearly a century old, is in close touch with the highest analytical developments of the subject.

a very

Dy'namite, a term covering a great number of nitroglycerin explosives, which may be divided into two main classes: (1) dynamites with an inert base acting merely as an absorbent of the liquid nitroglycerin; (2) dynamites with an active (i.e.. an explosive or combustible) base.

(1) Of the first class, ordinary dynamite, in which the absorbent is almost invariably kieselguhr (q.v.), in the proportion of about seventy-five per cent. of nitroglycerin to twenty-five per cent. of kieselguhr, may be taken as an example. Kieselguhr, a clay of almost pure silica, consists of the scales and frustules of diatoms; these minute tubes serve to hold the nitroglycerin by capillary attraction. The kieselguhr is calcined, crushed, and sifted; it will then absorb from three to four times its weight of nitroglycerin. The mixture is thoroughly incorporated by hand by kneading and rubbing through wire sieves, and is then pressed through a cylindrical mould and made up into suitably sized cartridges by wrapping in waterproof paper. This is called dynamite No. 1, or giant powder, and forms a somewhat greasy, plastic mass. It has usually a reddish color, from the presence of impurities in the kieselguhr, or from added coloring matter, and has all the poisonous properties of nitroglycerin. The latter partially separates on immersion in water.

Dynamite, when set on fire in small quantities, burns quietly, unless the temperature rises rapidly, when it explodes. It is less sensitive to shock than nitroglycerin, though it can be exploded by sharp blows between hard substances. In practice, it is invariably exploded by a detonator containing fulminate of mercury (q.v.) fired by a fuse. Its explosion is very rapid, being prop

gated at 20,000 feet per second; thus producing the so-called 'downward effect.' and making it quite unsuitable as a propulsive agent in guns. The flame produced by its explosion is capable of firing fire-damp, and the fumes given off are noxiousdefects that have been more or less obviated by the addition of other components to the mixture. The explosive powers of dynamite are not affected by damp, but it readily freezes (40° F.), and is then much less easily exploded, so that in such a case it must be thawed before it can be used. It is best thawed in a warm room; it should never be placed near a fire, since it explodes at 356° F. Weaker dynamites contain 10 to 50 per cent. of nitroglycerin.

Dynamite was invented in 1866 by Alfred Nobel (q.v.). It is used exclusively for blasting, being three or four times as powerful as gunpowder, and having a greater pulverizing effect. It can be destroyed by spreading it out in small quantities in long rolls, covering with paraffin oil, and setting on fire.

(2) Of the second class of dynamites, a variety of explosives with an active dope are in use. These consist of mixtures of nitroglycerin with sulphur, sodium or potassium nitrate, charcoal, wood pulp, etc. They are sold under such names as Vulcan, Atlas, Hercules, Hecla powders. Blasting gelatin is made by dissolving nitrated cellulose (collodion) in nitroglycerin. It is not affected by water, hence is much used for mines and torpedoes. Gelatin dynamite consists of blasting gelatin, wood pulp, and potassium nitrate.

See BLASTING; EXPLOSIVES; NITROGLYCERIN, Consult Guttmann's Manufacture of Explosives: Walke's Lectures on Explosives; Bernadou's Smokeless Powder; Eissler's Handbook of Modern Explosives.

Dynamo and Motor, di'na-mō. All electric generators and motors are classed together as DynamoElectric Machinery. Under this head are two main groups of machines: (1) those for directcurrent circuits, and (2) those for alternating current.

A dynamo, as the term is commonly used, converts the energy of mechanical motion into electrical energy, and a motor converts electrical energy into mechanical. In general, under proper conditions, dynamos can be used as motors, and motors as dynamos-though in most cases it would not be practicable to attempt the interchange, as a generator might be designed for certain conditions which would never be met with for a motor.

If we supply to a direct-current dynamo, direct current at or near the same voltage produced when driven at rated speed, then the dynamo will run as a motor at or near that speed. A common single-phase or polyphase alternator supplied with alternating current of the same frequency and voltage as normally generated will run at normal speed, as a motor, provided it is brought up to speed first, and the connections are made when the frequencies of the alternator are alike, and the voltages have their maximum values at the same time. (See ELECTRIC CIRCUIT.) An induction motor can be mechanically driven and made to furnish electric power to a circuit having also some other type of generator to give a fixed frequency.

When a conductor is moved across a field of magnetic force, an electro-motive force (E.M.F.) is caused between the ends of the conductor. A current flows if the conductor is part of a complete closed circuit. The mechanical energy required to sustain such relative motion between conductor and magnetic field is very largely transformed into electric energy. This is the principle of the dynamo. When an electric current is forced through a conductor located in a magnetic field. a mechanical force is produced tending to move the conductor. If motion can follow, then the electric energy furnished the conductor will very largely become energy of mechanical motion. This is the principle of the motor. The efficiency of these conversions is commonly about 90 per cent. in modern machines, and may rise to 98 per cent. in the largest types.

Dynamo-Electric Machines.The essential elements of a dynamo-electric machine are (1) a field magnet for producing the magnetic flux (see MAGNETISM), and (2) an armature or system of conductors which move in the magnetic field. A simple arrangement of these elements is shown in Fig. 1, typical of some early

field-magnet and across the airgap between the poles. The aim is to have all the lines of flux across the air-gap traverse the armature. There is always, however, some leakage of lines of flux as they pass from the highly permeable iron to the less permeable air.

In Fig. 2 is shown a pair of connecting armature conductors (forming a complete armature coil, in this case) being rotated so as to cut across the magnetic flux. The coil as shown is moving so as to decrease the number of lines of flux passing through it, and the resultant induced E.M.F. tends to cause a current to flow so as to resist the movement and to strengthen the field. (See ELECTRICITY, CURRENT.) The upper conductor is seen cutting lines downward, and the lower cutting upward. This produces E.M.F. in opposite directions on the conductors, but as shown they are connected so that the E.M.F.'s are additive, and the E.M.F between the collector rings is double that between the ends of either con

ductor. The E.M.F. increases directly with the rate of cutting lines of flux. In one particular position, horizontal in this case, the coil is cutting across the greatest number of lines of flux during any chosen short interval of time. The induced E.M.F. is therefore a maximum. In another particular position, in this case vertical, the conductors momentarily move along the lines, but do not cut them, and the induced E.M.F. is zero. After half a revolution from any position, the E.M.F. is induced in an opposite direction in the coil, SO that an alternating E.M.F. is generated.

The E.M.F. (volts) generated by an armature coil like this is proportional to the number of lines of magnetic force cut per second. Expressed as a formula: E.M.F. «Νηρ (AV.) = where is 100,000,000,' total magnetic flux from a pole (see MAGNETISM); N is the number of conductors in an armature coil (here two, the upper and lower ones); n is the number of revolutions per second and p is the number of poles. This gives the average E.M.F., and not the instantaneous or the effective. (See ELECTRIC CIR

tained. When. however, the in-. sulated split ring arrangement shown in Fig. 3 is used, and so adjusted that. at the moment wher the E.M.F. is about to change its direction, the brushes which connect the inductor with the external circuit make contact with the other segment of the ring. the current in the external circuit still continues to flow in the same direction through that circuit. These segments are known as the commutator. If the armature consisted of only one coil, the E.M.F., and consequently the current, would vary periodically in strength. from value zero to a maximum value. But this is easily remedied by using an armature of many distinct coils or loops suitably arranged, as explained below. all practical machines the magnetic flux is increased by winding the armature coils around a soft iron core which has a smaller reluctance to the flux than air.

In

Considering the actions in a motor, the force developed tending to move a conductor, which carries current through a magnetic field, is proportional to the product of current and magnetic flux, (I) (see ELECTRICITY, CURRENT). The armature turns in the magnetic field, and in so doing the conductors must move across the magnetic flux and must generate an E.M.F., acting against the motor current. The Es-Ec current now flowing is R where Es is the voltage of the supply, E, is the generated or internal counter-voltage, and R is the resistance. Should the speed reach a point where the impressed and internally generated voltages are equal, no current would flow. What actually happens, with direct current flowing in an armature of the type in Fig.