forms of Staphylococcus pyogenes aureus. Grützner and Haffner have shown that the casein precipitated in milk by the addition of acids depends on the degree of dissociation of the latter, and that the presence of salts modified this relation in accordance with the theory of dissociation. The researches of Jacques Loeb have shown the importance of the applications of the electrolytic theory to the physiology of man and of the lower animals. Consult Talbot and Blanchard, Electrolytic Dissociation Theory (New York, 1905). See ELECTRO-CHEMISTRY; SOLUTION; ACIDS.

DISSOLVING VIEWS. Pictures on a screen produced by a mechanical device attached to the magic lantern or stereopticon which causes the image furnished by one slide to dissolve, as it were, or blend into that of the following slide. Two lanterns are generally employed to secure this effect, which is obtained by gradually covering one of the projection lenses and allowing the rays from the other to fall on the screen.

DISSONANCE (Lat. dissonantia, from dissonare, to sound harshly). The simultaneous sounding of two or more tones foreign to a major or minor triad. Dissonance produces a feeling of unrest requiring a resolution into consonance (q.v.). This feeling of unrest is attributed to the complex ratios existing between the number of vibrations of dissonant intervals; whereas the ratios of consonant intervals are always simple. In reality it is impossible to set up any exact limits of dissonance, as what may seem dissonant to one person may seem consonant to another. But it is easy to establish certain landmarks within which each individual will, to a certain extent, determine the bounds of dissonance. Dissonant intervals are the major and minor second and all'augmented or diminished intervals. (See INTERVAL.) Chords containing one or more dissonant intervals are dissonant chords and require resolution. The dissonant chords are all augmented and diminished triads, as well as all chords of the seventh and ninth. See ACOUSTICS; CHORD; HARMONY; TRIAD.

DISTAFF (AS. distæf, from * dise, OE. dizen, to dress with flax for spinning, to bedizen, Low Ger. diesse, flax on the distaff + stof, staff). The staff on which the flax or wool is fastened, and from which the thread is drawn in spinning. As represented in ancient art, and still used by Greek peasants, it is a straight rod, from either side of which projects near one end a semicircle of cane or withes, forming a bed to which the wool or flax is attached. In both ancient and

modern art, the Fates are usually represented with it, engaged in spinning the thread of life. It has ever been considered as the peculiar enblem of feminine as opposed to masculine occupations, and is sometimes used figuratively for a woman. DISTAFF'S DAY, SAINT. A name given to January 7, because it marks the return of the women to their usual daily occupation after the Christmas festivities terminating on the Twelfth Day, January 6.

DISTANCE (OF., Fr. distance, from Lat. distantia, from distare, to be distant, from dis-, apart stare, Gk. iorával, histanai, OChurch Slav. stati, Skt. stha, to stand; connected with OHG. sten, Ger. stehen, to stand, and ultimately with Goth., AS, standan, Engl. stand). In navigation (q.v.), the distance between any two

places is the length of the rhumb-line (q.v.) between the places. On the ordinary sailing chart (Mercator's projection) the rhumb-line is straight. Also, the angular distance between heavenly bodies measured on the arc of the great circle passing through them.

The limit of view in a picture, or point of distance, as it is called in perspective, is that portion of the picture where the visual rays meet; the middle distance being the central portion between the extreme distance and the foreground. Distance, in a picture, is obtained by painting the tones that express the relative remoteness of a distant object with the same directness and truth that is employed in portraying those objects that are near at hand, or in the foreground, as it is called. When distant objects are thus true in color, the quality of distance will be produced by the diminution in size which obedience to the laws of perspective exacts. See PERSPECT

IVE.

DISTANCE, or DEPTH, PERCEPTION OF. When we look at objects we think that we sce how far away they are. Yet their distance is not directly given with the act of vision. It is true that a few writers, e.g. Hering and James, believe that the primitive field of view was not altogether flat, and that distance is 'a genuinely opti cal feeling'; but the majority agree that it is derivative, built up by the association of tactual ideas with certain 'signs,' visual and strain sensations arising in the use of the eyes. In either case it is admitted that the 'optical signs' themselves, the 'criteria of distance,' as they are called, are essential to the complete development of the idea. We must distinguish between the primary,' immediately given, and the 'secondary,' or indirect criteria. The former are (1) dissimilarity of retinal images; (2) converg ence strains; (3) accommodation strains; and (4) dispersion circles. The last must be taken together with the third. Alone, it is of minor importance; for accommodation, which clarifies moderately distant objects, will occasion dispersion circles for both nearer and farther objects. The strain set up in the ciliary muscle as it focuses the lens may, however, serve as a definite empirical criterion of distance. The second factor results from the functioning of the eyes in binocular vision. If we are to have a single clear image of near objects, the eyes must converge. The intensity of the strain sensations thus engendered increases in proportion to the proximity of the fixated point. Experimental investigawell as the anatomical arrangement of the twelve tions of the sensitivity to strain sensations, as eye-muscles, warrant the assumption that such distance of objects, at least up to a few hundred sensations may give accurate indications of the feet. Convergence, together with accommodation, is, according to Wundt and Arrer, the essential basis of the perception of depth. other authorities, notably Wheatstone, Hering, and Hillebrand, lay stress upon the dissimilarity of retinal images. We have given us, in our two eyes, two pictures of every object seen. difference between the two pictures increases with the nearness of the object. The testing of the part played by this disparity in the perception of distance led to the invention of the stereoscope, which enables us artificially to reconstruct the actual retinal conditions of binocular vision.

But

The

DISTANCE.

In our daily life, it is perhaps true that the secondary criteria become most important; they are at least most in evidence. These indirect data of distance are seven in number: (1) linear perspective, i.e. the perspective of drawing, the course of the contour lines of objects in the visual field; (2) aërial perspective, i.e. distinctness of outline and color-tone; (3) the number of intervening objects, or the partial covering of the distant by the nearer; (4) movement of objects in the visual field, e.g. swiftly moving objects seen from the window of a moving train are known to be near; (5) movement of our own head or body, with consequent relative displacement of objects differently distant; (6) distribution of light and shade, e.g. the illusion of depth given by appropriately shaded stage-settings; and (7) visual angle, i.e. the apparent size of known objects. The two last are the most influential. Consult: Berkeley, An Essay Toward a New Theory of Vision (London, 1709); Wundt, Human and Animal Psychology, trans. by Creighton and Titchener (London, 1896); Titchener, An Outline of Psychology (New York, 1902); James, Principles of Psychology (New York, 1890).

DISTEMPER (OF. destemprer, to distemper, ML. distemperare, from Lat. dis-, apart`+ temperare, to temper, from tempus, time). A typhoid inflammation affecting the upper airpassages of young dogs, and resembling in many respects the strangles of young horses, and the scarlatina and other such complaints of children. Like these, it is contagious, runs a definite course, is accompanied by low fever and debility, and is most successfully treated by good nursing and attention to diet and regimen. The eyes are red, weak, and watery; the nose dry and hot; draughts of air or movements of the animal readily excite sneezing or cough; there is dullness, fever, and loss of appetite. The thickened slimy mucus which the inflamed membrane, after some days, secretes, accumulates about the eyes, nostrils, and respiratory passages, and, lodging in the bronchial tubes, prevents the free access of air and the proper purification of the blood. Hence ensue distressed breathing, increasing weakness, and symptoms of nervous disturbance, such as staggering gait, chorea (q.v.), and fits. All dogs are liable to distemper, but the delicate, highly bred, and artificially treated varieties suffer most severely. All irritating and reducing remedies must be carefully avoided, and a good dry bed in a comfortable airy place provided. The stomach, which is generally overloaded, should be relieved of its contents by an emetic, which for an ordinary-sized English terrier may consist of two grains each of tartar emetic and ipecacuanha, with eight or ten grains of common salt, given in a wineglassful of tepid water. If no effect is produced, the dose must be repeated in twenty minutes. Constipation, if present, should be corrected by half an ounce each of castor and olive oil, to which, in large dogs, a few grains of gray powder is a useful addition. The febrile symptoms, if acute, may be alleviated by giving four times daily, in cold water, two drops of tincture of aconite, and five grains each of nitre and extract of belladonna. In cases where the pulse is very weak care should be exercised in the administration of aconite. Piorkowski has recently recommended

DISTILLATION.

a serum for use in the treatment of dog distemper, claiming that it is successful in a majority of cases. This has been confirmed in a few cases, while others report that the serum has no effect. The throat may also be rubbed with hartshorn and oil, and the nostrils sponged and steamed occasionally. Give frequently, and in small quantities at a time, milk and bread, or any other such simple and digestible food; and when recovery is tardy, and weakness ensues, endeavor by nursing, and by the use of tonics and stimulants, to support the strength.

The term distemper is sometimes applied to influenza (q.v.) in horses, and epizootic pleuropneumonia (q.v.) in cattle. For an account of distemper in pigs, see HOG CHOLERA.

DISTEMPER (IN PAINTING). See TEMPERA. DISTICH, dis'tik (Lat. distichon, Gk. diorixov, distichon, distich, from di-, di-, double + oTiXOS, The classical name given to any couplet, but stichos, row, from oreixew, steichein, to tread). especially to a hexameter and pentameter, makGreeks and Romans as a vehicle for the expresing complete sense. It was much used by the sion of single thoughts and sentiments; and hence became almost exclusively employed for the classical epigram. The great poets of modern Germany, Goethe, Schiller, etc., have also shown a fondness for the distich, and a remarkable skill in the use of it. A collection of moral maxims in Latin, ascribed to a certain Dionysius Cato (q.v.), are called Disticha, and were highly popular during the Middle Ages.

DISTILLATION (Lat. destillatio, from destillare, to distil, from de, down + stillare, to drop, from stilla, drop). A process consisting in the evaporation of liquids by boiling and the subsequent liquefaction of their vapors by cooling. The purpose of distillation is to separate

different substances from one another more or less

completely. The process has been in use

tically pure water may be isolated from wine and other liquid mixtures by distillation. The al chemists obtained the mineral acids and other valuable substances by processes of distillation, and at the present day distillation is one of the most potent processes in the hands of the scientific and industrial chemist.

FIG. 3. MODERN DISTILLING APPARATUS.

What usually takes place during the distillation of a mixture is very simple: The given liquid becomes divided into portions of unequal volatility, every portion that distils over being more volatile than the portion that still remains behind. And as less volatile liquids boil at higher temperatures than more volatile ones, it is obvious that the boiling-point of a distilling mixture must continually rise. If the mixture were allowed to evaporate at constant temperature its vapor-tension must continually decrease. A liquid whose vapor-tension, during evaporation, might increase, is an impossibility for almost obvious reasons. Such a liquid and its vapor would constitute a system whose volume would increase, and not diminish, if some compressing power was brought to act upon it; which is absurd. Further, by means of such a liquid, it would be easy to obtain a form of what physicists call 'perpetual motion of the second kind,' which the science of thermodynamics recognizes as no less impossible than the creation of mechanical work out of nothing. (See THERMODYNAMICS.) But while the vapor-tension of an evaporating mixture cannot possibly increase, it may, and in certain cases does, remain constant. Thus a mixture of three parts of water and 97 parts of absolute alcohol will evaporate without change of vapor-tension. The question therefore remains, what mixtures are subject to decrease of vapor-tension, and what mixtures evaporate without such change. The answer is: If the ingredients are present in such proportions that the vapor-tension of the mixture is either the highest or the lowest that can be obtained with the given substances, then the vapor-tension will remain constant during evapoiation; in every other case it will decrease. If for a certain proportion of the ingredients the vapor-tension of the mixture is lower than for any other proportion, the composition of the boiling liquid will approach nearer and nearer to that proportion as a limit; once that limit reached, the vapor-tension cannot decrease any further, and thenceforward the composition of the distilling liquid must remain unchanged: the vapor passing off and the liquid remaining be

hind will have precisely the same relative composition. Again, if at a certain temperature a given mixture has the highest vapor-tension that can possibly be obtained with its ingredients, then a separation into more and less volatile por tions is evidently impossible, and hence the distillation can produce no change of composition. A mixture of 3 parts of water and 97 parts of absolute alcohol has, at its boiling-temperature, a higher vapor-tension than any other mixture of water and alcohol at the same temperature; and this is why that mixture distils over without change of composition.

From the above it may be seen that the possible changes of the total vapor-tension of a mixture determine in a general manner the direction in which the changes of composition will proceed in course of a distillation. To recapitu late, distillation can effect a change in the composition of a given mixture only if both of the following conditions are fulfilled: (1) If there exist mixtures of the same substances, whose vapor-tensions are less than that of the given mixture; (2) if there also exist mixtures of the same substances, whose vapor-tensions are greater than that of the given mixture. Distillation will then divide the given mixture into, say, two portions, one of which will be more, the other less, volatile than the given mixture. But the exact course of a distillation is far from being determined by these laws. For example, no answer is thus furnished to the question: being given a mixture of a pound of water and a pound of alcohol, and supposing that half the mixture has distilled over, what is the composition of the distillate? The total vapor-tension of a mixture, it must be remembered, is the sum of the 'partial' vapor-tensions of its ingredients. The relative amounts of the ingredients passing over at any moment are proportional to their partial vaportensions at that moment. The partial vaportensions in a mixture are known to be lower than the vapor-tensions of the ingredients in an isolated state. But what they are exactly is but seldom known. To determine them experimentally is a matter of considerable difficulty; and no theory is known which would permit of calculating them in all ordinary cases. our knowledge of the process of distillation is as yet extremely meagre. An empirical rule capable of yielding some practical results has been proposed by Brown, and has been somewhat developed by Thomas, Barrell, and Young. But it is by no means sufficiently established to require explanation here. The modern theory of solutions, too, has been brought to bear on the problem of distillation; but that theory permits of calculating the partial vapor-tensions only in mixtures containing a very large excess of one of the ingredients ('dilute solutions'), and hence cannot furnish a sufficiently general solution of the problem of distillation.

Hence

It remains to notice briefly the processes of fractional distillation and distillation with a reflex condenser kept at constant temperature. In fractional distillation, which is very frequently employed by organic chemists, a mixture is first divided into a series of fractions' by distillation; then the fractions are subdivided by further separate distillations; then some of the fractions are mixed together in pairs or threes, the resulting liquids again distilled separately, and so forth until the required separation has

DISTILLATION.

been effected. If a condenser is attached to the still in such a manner that any liquid forming in it may flow back into the still, and if the temperature in this condenser is kept constant, then the vapors passing out of it uncondensed are found to have the same relative composition, no matter what changes of composition are taking place in the distilling liquid. In most cases examined (but not in mixtures of alcohol and water), the distillate thus obtained is found to boil exactly at the temperature at which the condenser has been kept. See CHEMISTRY; BOILINGPOINT; EVAPORATION; DISTILLED LIQUOrs.

DESTRUCTIVE DISTILLATION. This is quite different from the process described above. For while that process is purely physical and involves no chemical change whatever, destructive distillation, as implied by the term, causes profound chemical changes in the materials subjected to it. Examples of destructive distillation are: the heating of coal in gas-works at a red heat, when it resolves itself into coke, which is left in the retort, and coal-gas, naphtha, tar, etc., which distil over into suitable receivers; the treatment of coal at and below a red heat, when it yields much paraffin oil; and the distillation of wood in close vessels, at a red heat, when charcoal is left in the vessel, and wood-vinegar, wood-spirit, tar, etc., pass over in vapor, and are condensed. See TAR; COAL-TAR; GAS, ILLU MINATING; PARAFFIN; ACETIC ACID; DIPPEL'S ANIMAL OIL; etc.

DISTILLED LIQUORS, or ARDENT SPIRITS. Alcoholic liquors manufactured by the process of distillation (q.v.). They may be produced from fermented liquors or directly from the raw materials, which must contain a large percentage either of sugar or of starch. An example of the first class is brandy, which is made by distilling wine. An example of spirit produced from saccharine material is rum, which is made from molasses, while whisky, made from corn, rye, barley, or other cereal, is an example of spirit made from a starchy material. The process of distillation may be so conducted as to produce an alcoholic beverage or simply a 'raw spirit.' From the latter, by a process described below, is obtained the rectified spirit which is used as a basis in the manufacture of various alcoholic beverages. Rectified spirit is also employed in the arts, and from it, by a process of purifica tion, is obtained the absolute ethyl alcohol of the chemist. See ALCOHOL.

HISTORY. All the intoxicating drinks used in ancient times seem to have been the product of fermentation only. The art of distilling liquors is first mentioned by an Arabian physician of the tenth century, Albukassen by name, though the invention is attributed by some to the northern nations. The name aqua vitæ, given to distilled spirits, shows what an estimate was put upon the discovery by early physicians and alchemists. One of them "declares this admirable essence to be an emanation from divinity, an element newly revealed to man, but hid from antiquity because the human race were then too young to need this beverage destined to revive the energies of modern decrepitude."

PROCESS OF MANUFACTURE. Spirits were first distilled from wine, but an endless variety of substances are now used in their manufacture. Alcohol, however, is the essential element in all

DISTILLED LIQUORS.

spirits. It results from the decomposition of sugar, which, by the process of fermentation, is resolved into carbonic acid and alcohol. Sugar is therefore the direct source of alcohol, and for this reason sweet vegetables and fruits may be converted into spirits. But starch is readily converted into sugar by means of the substance called diastase, which is found in malt and in germinating seeds generally. (See BEER and BREWING.) Hence, starchy as well as sweet vegetables may be used in the manufacture of spirits. In making distilled liquors, when the raw material is a fermented liquor, it is ready to be distilled without further preparation; when it is a sugar, however, it must first be fermented and then distilled; when it is a starch, another initial process, to convert the starch into sugar, is necessary.

MASHING OR PREPARATION OF THE WORT. TO saccharify the starch is the object of the initial process, technically known as mashing. This process consists in mixing the raw grain, properly ground, with malt and with water at a temperature of about 150° F. Barley, oats, and rye are the grains commonly used. In England and the United States most distillers use a mixture of raw and malted grain, in which the larger proportion is raw. The first mashing requires from one to four hours, during which time the mash is kept at a uniform temperature of 145° F. by successive additions of hot water. After this saccharine infusion, technically called wort, has acquired its maximum density, as inFresh water is then poured upon the residue and dicated by a saccharometer, it is drawn off.

allowed to stand to form a second wort. This is added to the first. A third wort, used to infuse a new mixture of grain, is sometimes made. In this method of direct mashing, nearly 10 per cent. of the grain is not decomposed. The waste may be reduced to 5 per cent. by heating the grain and water before the malt is added.

In Germany, where potatoes are used for the manufacture of spirits, the potatoes are steamed before the malt is applied. This is advisable because potatoes contain a much smaller proportion of starch than the cereals. By steaming, the starch-cells are thoroughly broken and the starch reduced to a condition in which it is

easily acted upon. Several different forms of In that of Henze, which is largely used, the apparatus have been devised for this purpose. steam is applied under pressure and the potatoes are reduced to a pulpy liquid, in which form they run into the mash-tub from an opening in the bottom of the apparatus. After this mass has cooled to the proper temperature, the malt

is added and the wort formed as described above.

FERMENTATION. This is effected by adding either brewer's or compressed yeast to the wort prepared as described above; or to a saccharine liquid obtained from molasses, beets, or other sugar-producing fruits or vegetables. Eight to ten parts of brewer's yeast are mixed with 1000 parts of grain mash, and with a larger proportion of yeast for potato mash. The chemical processes involved in fermentation, by which the sugar is resolved into carbon and alcohol, are discussed under YEAST and FERMENTATION. From three to nine days are consumed in fermentation. The process is continued until the density of the liquid ceases to lessen, as indicated by the saccharometer. Hydrofluoric acid is quite gen

erally used in the fermentation process. Sadtler states, in his Industrial Organic Chemistry (New York, 1896), that the following advantages are claimed for its use: "(1) by preventing the losses due to secondary fermentation the alcoholic yield is increased; (2) this yield is especially maintained when raw materials of somewhat inferior quality are used, when, without the hydrofluoric acid, the yield would be diminished; (3) the development of foaming in the fermentation is largely prevented."

In

In making spirit from beets, sulphuric acid is used during the fermentative process. Much of the beet-spirit is made from molasses derived as a by-product from the manufacture of beetsugar. But in France it is customary to make inferior beets directly into spirit. Only a small quantity of yeast is required, and fermentation is completed in about twenty-four hours. the West Indies, the molasses produced in making cane-sugar is utilized in the manufacture of rum. (See the article RUM for a description of its manufacture.) The addition of yeast to the saccharine liquid is unnecessary, because enough wild yeast is present in the molasses to produce spontaneous fermentation.

DISTILLATION. The operations thus far described are merely preliminary. They differ from those employed in the two fermentation industries, wine and beer making, in that in preparing the liquor for distillation the fermentation process is carried to its furthest limit in order to produce the greatest possible amount of alcohol. The liquid thus prepared for distillation is technically known as the wash. The still is the apparatus in which the wash is reduced to vapor and then condensed. In its oldest and simplest form the still consists of a copper vessel, provided with a closed head, connected with a spiral tube, called the worm. The latter is placed in a refrigeratory, or closed, chamber, through which cold water is constantly passing. When heat is applied at the still the spirit begins to rise in vapor, along with more or less steam; these vapors pass through the worm, become condensed by the cold, and drop or trickle down into the receiver. The product of the first distillation in a simple still is a weak and impure liquid technically known as low wines. This is then redistilled at a lower temperature to deprive it of the water and of the fetid oils which have passed with the alcohol.

In 1801 the first great improvement in distilling was invented by a workman of Montpellier named Adam. By making the vapors rise from the still through a series of winding passages, maintained at a determinate degree of heat, and deposit part of the water and other impurities, he was able to obtain from wine a spirit of any required degree of purity at one operation. This device was applied by Pistorius to the distillation of washes made from grains. Within recent years many inventions have been made to produce the purest and strongest alcohol at the lowest possible cost. Sadtler divides the different forms of distilling apparatus into five general classes: (1) The simple stills already described, with worm-condenser heated by direct firing. (2) The simple stills with closed 'washwarmer.' This is a device for saving fuel by causing the pipe containing the hot vapors on their way to the refrigerator coil to pass through a vessel containing the wash. Thus the wash

is heated to a considerable degree before it enters the still at all. (3) Stills with rectifying 'wash-warmer.' This is a device invented by Dorn, in which the vessel through which the vapor pipe passes is divided into two compartments by a sheet of copper. The upper and larger compartment serves as a wash-warmer. Through it the tube conveying the vapors from the still passes into the lower compartment, where at first the distillate is condensed. But as the wash is warmed by the vapors from the still, the distillate in this compartment gives off alcoholic vapors which pass on and are condensed in the worm, while the watery portion is allowed to run back into the still. This rectifying action can be increased by introducing two or more chambers between the still and the final condenser. (4) Stills with washwarmer, rectifying, and dephlegmator apparatus for intermittent working. (5) Stills with similar apparatus for continuous working. A dephlegmator is an apparatus for partially condensing the vapor, by means of metallic diaphragms. The vapor, coming in contact with these metallic sheets, is chilled, and the watery portion, which condenses most readily, separates and flows back, while the alcoholic vapors pass on through the pipes to the condenser. The Pistorius apparatus, already referred to, is an intermittent dephlegmator. The original invention has been improved successively by Gall, Schwartz, and Siemens, and is much used in Germany in making potato spirit. Examples of the fifth class of stills, those with a continuous dephlegmator apparatus, are the Coffey still, used in England for making grain spirit, and the Savalle still, used in France in distilling brandy. The Coffey still is particularly well adapted to the manufacture of what is known as 'silent spirit,' that is a spirit which is very strong and pure, but nearly destitute of flavor. For the manufacture of beverages it is not so well fitted because it removes, along with other impurities, a large proportion of the volatile oils which give them their peculiar flavor. For the principles involved in the process see DISTILLATION; EVAPORATION; BOILING-POINT.

PURIFYING THE DISTILLED SPIRIT. If alcohol and water were the only substances that pass over in distillation, all spirits, from whatever source, would be the same. But, except to a partial extent in the Coffey still, this is not the case. Brandy, rum, and whisky owe their distinctive flavors to essential oils derived from the grape, from sugar, or from grain. Other impurities also pass over which are unpleasant and unwholesome. The mellowing effect of age upon spirits is said to be due to the evaporation or spontaneous combustion of these oils. Newly distilled spirits are in general fiery and unwholesome. The process of removing the impurities from the spirit, by fractional or repeated distillation, is known as rectifying the spirit. The spirit that is first condensed, in rectifying, is crude and milky. Next comes the clear alcohol, which is caught separately. Last of all comes a weak spirit called faints, which is returned to the still. There are certain impurities which cannot be removed by distillation. Fusel oil is one of these persistent impurities. Several chemical methods have been proposed for its removal, but the method usually employed is to filter the alcohol, diluted with equal parts of