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one was then entirely filled with the aleoholic liquor combined with the acid ferment, and called the vinegar mixture, and the other cask was only half filled. After 12 hours, half the liquor was drawn out from the full cask, and poured into the other, and this process was repeated every 12 hours. The acelification proceeded with great rapidity in the vessel that was only half full, as was evident from the escape of suffocating fumes of vinegar; the temperature within it far exceeded that of the vinegar room, while in the full cask it was scarcely if at all higher. An improvement on this method consisted in changing the liquors in the two casks every 3 or 4 hours instead of 12, and it was found that in the course of 14 days, such a vinegar was obtained as would have required some months by the slow method. The effect of this contrivance will be evident, when it is considered that every particle of the aleohol in the mixture must be brought into contact with the oxygen of the air, in order to be converted into vinegar, and that the porous mass formed by the grape husks presented an enormous surface to the air in the half filled cask, so that in slowly filtering through it, the mixture was broken up and divided, and the points of contact with the air multiplied to an indefinite extent. In the full cask, on the contrary, the air was in contact with the liquid only at the top of the cask; hence it will be understood why the acetification proceeded much more slowly in the full cask than in the one only half filled, for in the latter case the surface of the liquid was covered by a wet acid spongy mass full of air, and in filling it up, this mass was well washed of its acid particles, and the air renewed. The heat, also, which by the old method was maintained at great expense of fuel, was by the new method generated during the rapid acetification of the mixture, the heat thus liberated being usefully employed to maintain the temperature of the mixture. For example, in converting 10 lbs. of aleohol into vinegar, the same amount of heat is liberated, whether the change be slow or rapid; but in the one case it is distributed over a larger portion of time—say fifty days, and that 500° of the heat of temperature is set free. In such case there would be an accession of heat to the mixture, amounting to only 10° per day, and this would probably be carried off by the surrounding air. But if the fifty days were by the quick method reduced to ten, the mixture would have the heating effect of 50° per day; and if this 10 days were reduced to 1 day of 12 hours, it would have the whole 500° in that time, which would be at (he rate of 41 per hour, which could not all be dissipated into the surrounding air, so that the mixture could be maintained at a tolerably high temperature without any or much assistance from artificial heat.

Boerhaave's plan has been carried to its greatest point of perfection by a new method of constructing the casks. They are now made of oak, and are from 5 to 7 feet high, and from 2£ to 3 feet in diameter, but somewhat narrower at the bottom than at the top. About a foot from the bottom, and just above the

syphon/used for drawing off the acid liquor, each tub is perforated by holes a about an inch wide, and sloping downwards, so that the air may enter without allowing the liquor to escape. Each tub is closed by a cover, with a hole in the centre 2 or 3 inches square. Instead of the grape husks and stalks before noticed, each cask is filled with curled beech shavings; but before they or the casks are used, they are repeatedly scalded with hot water to get out all soluble matters, and when dried, are imbued with hot vinegar. The casks are ranged on wooden frames or brick piers sufficiently high to allow the liquor to be conveniently drawn off.

[graphic]

According to another arrangement thecask, A (Fig. 9), called a graduation vessel, is furnished with an inner hoop of beech-wood (c), about six inches from the mouth (d), supporting a perforated shelf. Through the perforations, which are numerous, cotton wicks are drawn and secured by a knot at the upper extremities ; they are just thick enough to allow the liquid poured upon the shelf to pass through and drop from their lower ends. The edges of the shelf are packed with tow to prevent the escape of liquid at the side. The lower compartment is filled with beech-wood shavings nearly up to the ends of the wicks. By this means the vinegar mixture is divided into drops, and thus exposed more intimately to the oxygen of the air of the cask.

The vinegar mixture consists of 20 quarts aleohol, 40 of vinegar, and 120 water; or 15 £ quarts aleohol, 20 vinegar, and 137 water. The water is first heated to 100° or 104°, and then the vinegar and aleohol are added, so that the temperature of the mixture may be about 86° or 90° before it is poured into the casks. From 2j to 5 quarts of the mixture, according to the size of the casks, are poured upon the shavings every half hour. The cover is then put on, but the hole in the centre is left open. When all the mixture has filtered through, the liquor is drawn off into the mixing vessel, and a few quarts of aleohol are added; it is passed a second time through the shavings, then drawn off and a smaller quantity of aleohol added; it is then sent through the shavings a third time. The liquor after the first percolation becomes changed into a weak vinegar; after the second percolation it becomes greatly increased in strength; and after the third, it is perfectly good and very strong vinegar. Tho reason why the aleohol is not added all at once, is, that even nnder favourable circumstances a portion of the aleohol escapes the acetifying action. Indeed in some cases the manufacturer finds that all his alcohol has disappeared, and that no vinegar has been produced. This may occur when the supply of air has not been sufficient to allow the aleohol to be converted into acetic acid. In such case the aleohol becomes transformed into aldehyde, which being extremely volatile, (its boiling point being 72°,) escapes, and leaves nothing but water in the cask. Hence the supply of air to the cask should be abundant, and this is the object of perforating the cask near the bottom, and having the hole in the cover open. If all goes on favourably, the vinegar is rapidly formed, and the temperature rises. With a vinegar room at 77°, and the mixture at 82°, the interior of the casks will often be 95° or 100°. The internal temperature of the casks should not be less than 95°, or the vinegar mixture will not breathe enough oxygen. The escape of heat from the casks is prevented by covering them with paper or linen jackets; the airholes being of course left open. In general it may be remarked that the higher the temperature, and the larger the quantity of air conveyed in the shortest time to the mixture, the more rapidly is the hydrogen of the aleohol oxidised and vinegar formed. The more aleohol there is in the mixture, the stronger will be the vinegar; but the quantity of aleohol in the mixture ought not to exceed 10 per cent. The temperature must not be below 72° nor above 113°. When fruit or malt vinegar is prepared by this process, the liquor must be as clear as possible, or the shavings will become coated with a slimy substance.1

There is another quick process of making vinegar which has been partially introduced into this country. This plan, which was patented in 1824, by Mr. Ham, of Norwich, differs in many respects from the process just described. The apparatus consists of a large vat, in the centre of which is a revolving pump, having two or more shoots pierced with holes so as to cause a constant shower of wash to descend from the top. The lower part of the vat contains the wash, and in the upper part are birch twigs properly prepared and arranged so as not to interfere with the revolving shoots. Between the surface of the wash and the joists which support the birch, is a vacant space of 3 or 4 inches, into which air is let or forced by holes made in the vat. By means of steam pipes the wash is maintained at the temperature of from 90° to 100°, and being kept in motion by the constant action of the pump, it is so fully exposed to the oxygen of the air in trickling through the twigs, that it becomes acetified in the course of 48 houre; but in practice, it is usual to occupy from 15 to 20 days, according to the season and the state of the atmosphere, in obtaining the complete acetification of the charge.

(1) Chemical Gazette, Vol. i. Rose, Lecture* on Organic Chemistry- Otto, Lehrbuch der rationelle Praxil.

In 1841, a patent was taken out by Mr. Neale, and others, for the manufacture of vinegar from beet root. The roots are reduced to pulp, and the saccharine juice extracted by pressure. Water is added to the juice, and the whole is boiled. It is next cooled to 60°, and fermented with yeast. The fermented wash is pumped into an acidulating vessel, which is a strong vat of the capacity of 24,000 gallons, in the centre of which, near the bottom, is a small inverted dome, pierced with a multitnde of holes, and connected with a blowing apparatus outside. The temperature of the wash is maintained by a coil of steam pipe within the vat, and the interior of the vat is divided into several compartments by means of false bottoms pierced with small holes. The cover is furnished with a valve opening outwards, which yields to a slight internal pressure from the air within.

The total number of vinegar factories in the United Kingdom was, a few years ago, only 48, of which the 5 principal were in London. Vinegar is known in commerce by the numbers 18, 20, 22, and 24, which originally represented the number of pence per gallon, at which it was sold; but these numbers now represent merely a certain quality of the article. About 3,000,000 gallons of vinegar are annually manufactured in the United Kingdom, of which quantity more than half is made by four London firms. An excise duty of 2d. is levied on every gallon of proof vinegar, which is represented by No. 24; this, at the specific gravity of 1.0085, contains 5 per cent. of real acid. Vinegar is sometimes made double proof, and then pays id. per gallon duty. The strength may be estimated by a species of HydroMeter, called an acetometer, but as the specific gravity of vinegar depends more upon foreign matters than upon the actual quantity of acetic acid contained in it, the best method is to saturate a given quantity of the vinegar with dry carbonate of soda; and the quantity of that salt required for the purpose indicates the proportion of real acetic acid present, 54 parts of dry carbonate of soda being equivalent to 51 of true, or anhydrous acetic acid. Another method is to saturate the vinegar with lime. "The equivalent of carbonate of lime, which is 50, is so near that of acetic acid, as to furnish a ready mode of ascertaining the value of vinegar, or other dilute acetic acid. For this purpose a piece of clean white marble is selected and accurately weighed; it is then suspended by a thread in a proper quantity of the vinegar to be examined, which is occasionally cautiously stirred, so as to mix its parts without chipping the marble; when it is no longer acted on, it is removed, washed, dried, and weighed; its loss is equivalent to the acetic acid."1

Vinegar may be made stronger by exposure to a low temperature, for the aqueous portion freezes first, and may be removed; and the part which remains unfrozen will be found to be greatly increased in strength.

The quantity of real acid in vinegar is difficult to ascertain, from its being often adulterated with sul(i) Brande'» Manual of Chemistry, p. U17*

phuric, nitric, and hydrochloric acids. Indeed the manufacturers are allowed by law to mix one thousandth of sulphuric acid with the weight of the vinegar. The presence of sulphuric acid may be detected by nitrate of baryta, which occasions a white precipitate. Nitric acid is present, if a bit of gold leaf, wetted with hydrochloric acid, be dissolved on gently heating a portion of the vinegar in a wateh glass. Hydrochloric acid is present, if a white precipitate be produced on adding a solution of nitrate of silver to the vinegar. Pepper, and other acrid substances used to adulterate vinegar may be detected by neutralising the vinegar with carbonate of soda, when their undisguised pungency will detect them. Vinegar is apt to be infested with flies (Musca cellaris), and with animaleules commonly termed eels (Vibrio aceti); these may be destroyed by passing the vinegar through a spiral tube immersed in boiling water. Vinegar exposed to the air gradually becomes turbid or mothery; it loses its acid, and deposits a slippery gelatinous substance, which when dried resembles gum. The vinegar becomes weak and mouldy as this change goes on.

The use of vinegar as a condiment may be understood from the properties of acetic acid. In its concentrated state, this acid acts on living tissues as a caustic, producing heat, redness, and rapid inflammation of the skin. It dissolves many organic products, such as camphor, gluten, gelatine, gum resins, resins, fibrine of blood, white of egg, &c. When properly diluted, as in vinegar, and used in moderation, it promotes digestion. The property of the acid in dissolving gelatine shows the use of vinegar as a condiment with veal, young meats, and fish. It also assists the digestion of crnde vegetables, such as salads. Its powers are heightened by having aromatic or pungent substances dissolved in it, such as chilies or tarragon. Persons who use much vinegar with the view of preventing corpulency, may do themselves much injury, and even engender cancer in the stomach. The saits of vinegar sold at the druggists' shops as a reviving scent in sickness and fainting, consist of sulphate of potash impregnated with acetic acid, and scented with oil of rosemary, or lavender.

A pure variety, called distilled vinegar, was formerly produced by distilling common vinegar, a plan now almost entirely superseded by mixing pure acetic acid with water. Colour can be imparted to it by means of burnt sugar.

ACIDS (Lat. aeidus, sour) form a very numerous and important class of bodies in chemistry, and in many of those arts and manufactures in which chemical processes are concerned. Perhaps the most important acid in a manufacturing point of view is the Sulphuric. Nitric, Hydrochloric, Acetic, CarBonic, TARTARIC, CITRIC, OXALIC, ARSENIOUS, and

other acids, are also important objects of commerce.

The common idea of an acid, is a soluble substance possessing the property of sourness. The chemist, however, disregards this property, and considers all those substances to be acids which impart a red

colour to blue litmus paper, and form stable, neutral and crystallizable compounds with bases, such as alkalies and earths, or metals or their oxides. Indeed, all acids are remarkable for their great powers of combination. Many acids are natural or organic products, of very complex structure: these cannot be formed synthetically, that is, by artificially uniting their elements; others are not found in nature, but result entirely from chemical processes. Acids occur in all three kingdoms of nature: phosphoric acid is found in bone; citric and oxalic acids are vegetable products, and chromic and arsenic are of mineral origin. Those acids which are produced by the oxidation of a metal, are termed metallic acids.

The states and properties of acids are of the most varied description; some are gaseous, as carbonic acid; others fluid, as nitrous; others solid, as tartaric: some cannot exist except in combination with water or with a base, such as acetic; others exist without either, as anhydrous sulphuric acid. Most of the acids are colourless, but chromic acid is red; some are inodorous, as sulphuric; others pungent, as hydrochloric: some are comparatively fixed, as the phosphoric; others can be converted into vapour at a moderate heat, as sulphuric; others are volatile at all temperatures, as the hydrochloric.

No simple or elementary substance has the properties of an acid. Hence all acids are compounds of two or more elements. When oxygen was first discovered, it was observed that by its union with phosphorus, sulphur, nitrogen, &c. acids were produced; hence it was supposed that oxygen was the principle of acidity, and it was named accordingly acidproducer, from 6£i>s, acid, and ytvvaa, I generate or produce. But when it was discovered that the union of oxygen with an element produced in some cases an alkali instead of an acid, and that muriatic and some other acids contained no oxygen at all, this theory was abandoned, although the name of oxygen was retained.

The union of one elementary substance with another, is termed a binary compound; as for example, oxygen with sulphur in sulphuric acid, or oxygen with sodinm in soda. Combinations of binary compounds with each other, as of sulphuric acid with soda, are termed ternary compounds; three elements being concerned, as in the instance just given, viz. sulphur, oxygen, and sodinm. Most of the mineral salts are ternary compounds. Combinations of salts with one another, or double salts, such as alum, are named quaternary compounds.

In binary compounds of oxygen which possess acid properties, the name of the acid is derived from that of the substance which combines with the oxygen, with the termination ic. When the same element forms two aeid compounds with oxygen, the term ous is applied to that which contains the less proportion of oxygen, as in sulphurous and sulphuric acids. When these acids combine with bases to form salts, the ous of the acid is changed into ite, and the ic into ale. Thus a salt of sulphurous acid is a sulphite; of sulphuric acid, a sulphate.

This sort of nomenclature served to distinguish these acids and their salts until, as chemistry advanced, an acid was discovered containing less oxygen than the sulphurous, and then a new name was required: it was therefore called hyposulphurous acid, and the salt formed with it was termed a hyposulphite, (from the Greek virb, under;) so also when an acid was discovered containing less oxygen than the sulphuric but more than the sulphurous, it was called hyposulphuric acid, and its salt a hyposulphaie. In some cases acids have been discovered containing more oxygen than those already named with terminations in ic: to these the prefix hyper (from the Greek virip, over) is attached, as hyperchloric acid, and its salts hyperchloraies. A similar system is adopted for all analogous acids.

There is a class of acids called sulphur acids, in which sulphur takes the place of oxygen. In such cases the names of the corresponding oxacids are sometimes applied to them with the prefix sulph; as sulpharscnious and sulpharsenic acids, which resemble arsenious and arsenic acids in composition, but contain sulphur instead of oxygen.

Most acids contain cither oxygen or hydrogen; those which contain the former are termed oxygen acids or oxyacids; those which contain the latter are named hydrogen acids or hydracids. Oxygen, as already stated, combines with the same element in various proportions, forming several distinct acids therewith; but hydrogen does not combine with the same element to form more than one acid. In the nomenclature of the hydracids, the names of both constituents are usually given:—thus the acid compound of hydrogen and chlorine is named hydrochloric acid, (a more systematic term than the name muriatic, formerly applied to it;) the acid compound of hydrogen and sulphur is named hydrosulphuric acid, and so on. The salts of these acids are termed hydrochlorates and hydrosulphates. The subject of salts will be taken up more in detail hereafter. The processes concerned in the manufacture of the most important commercial acids, will be found under the respective heads indicated at the commencement of this article.

ADHESION. The force by which two dissimilar substances resist separation, although their contact does not produce any permanent change in them. It is distinguished on the one hand from Cohesion, which is applied to a force of the same kind between similar substances, or parts of the same body; and on the other hand from Affinity, which acting between dissimilar substances, not only resists their separation, but renders it impossible by mere mechanical force.

The undisguised action of adhesion generally requires one of the bodies to be solid, because if both were fluid they would mix, and the phenomenon would come under the head of affinity. On the other hand, it commonly requires one body at least to be soft, plastic or semifluid if not fluid, for when both are completely solid we know of no case of decided adhesion which is not referable to electrical or

magnetic attraction, or the pressure of the air or other surrounding fluid. Two pieces of clean lead, or of glass, adhere independently of these causes,«'. e. by the action of cohesion; but with dissimilar metals or other hard bodies, however we may press them, no such phenomenon occurs, for the removal of the atmospheric pressure causes them to fall asunder. Hence it would appear that the "attraction of adhesion," as it has been called, is limited to shorter distances than that of cohesion; since two pieces of the same hard solid can be brought near enough to cohere, while two different solids, no harder or more rigid, cannot be brought near enough to adhere. To produce adhesion generally requires one of the solids to be rendered by heat semifluid or ductile, and then its return to a hard state (if not attended with crystallization) does not diminish the adhesion, unless the unequal contractions of the two substances, by the same fall of temperature, force them to separate. Hence the fitness of different cements to join different substances, depends mainly on their equal expansibility by heat. Metals, being more expansible than solids in general, will not adhere to ordinary cements, but require metallic ones (called solders); and each of these does not adhere to all metals indifferently, but only to those having nearly the same rate of expansion. Glass and stones, being both less expansible and less various in their rates of expansion, adhere to a greater variety of substances; and light porous solids, being very little affected by change of temperature, adhere still more generally to those of the same kind which may be softened by heat or liquid solvents, and return to the solid state gradually and without tendency to crystallize. The most universally adhesive bodies (as piteh) are those which retain, even at low temperatures, a certain ductility by which they may readily yield to the various expansions and contractions of the rigid bodies in contact with them; and the rigid bodies most readily made to adhere are the worst conductors of heat; because they cannot undergo very sndden changes of temperature or of bulk, and so allow time for the adhering body to accommodate itself. The non-adhesiveness of animal membranes is very remarkable, and probably a provision for their cleanliness and freedom from foreign matter. Crystallization, by requiring a body while solidifying to obey with rigour certain internal laws of its own, is a great bar to adhesion.

The adhesion of two solids is generally stronger than the cohesion of at least the weaker one. Hence if two pieces of wood be glued, gummed, or pasted together, and then separated, a layer of cement adheres to each; and if there be a bank note in the midst of the cement, it will be split into two layers, simply because its own cohesion is less than that of the cement, or of the wood, or the adhesion between the cement and either wood or paper. [See Cements, Mortars, and Solders.]

The adhesion between a solid and liquid is often greater than a cohesion of the liquid, so that on separating them a film of liquid remains attached to the solid, and it is said to be wetted. Aeriform fluids will wet as well as liquids. Thus on plunging the finger (or any non-metallic body) into mereury, it does not touch that liquid, but retains a film of air; just as it would retain, in air, a film of water with which it had been wetted. Some few bodies, generally of a fatty nature, adhere to air in preference to water, and thus cannot be wetted by the latter, except in vacuo, or when plunged to a great depth. Iron requires the pressure of a certain small depth of water to remove its air-film, for small particles of it, and even a needle, carefully placed on water, retain air enough to float them. A body plunged from air into a liquid may behave in three different ways. H its attraction for the liquid be such as to overeome both the adhesion of the air and the cohesion of the liquid, it will raise the liquid all round it with a eoncave slope, as happens with silver dipped into mereury, or perfectly clean glass into water, but such cases are not common. If the attraction for the liquid be not sufficient to overeome the adhesion of the air, the liquid will be depressed, with a convex slope, to that depth at which its hydrostatic pressure enables it to expel the air-film; and yet after once touching the solid, it may adhere thereto with foree enough to overeome its own cohesion, and so may wet it. This is the commonest case with water, and it occurs also with platinum dipped into mereury. The third case is when the adhesion of the solid to the liquid being weaker than the cohesion of the latter, it cannot be wetted even though the intervening air-film be expelled. 'This occurs with iron, brass and cobalt made to touch mereury; and even in such cases adhesion is not absent, and is more easily measured than in any other case. Guyton-Morveau took disks of these metals 1 inch in diameter, and having suspended them from one arm of a balance, and counterpoised them by weights, made them touch the surface of mereury, when it required the addition to the other scale of 115 grains, 142 grains, and 8 grains to detach them. Gay-Lnssac found that when such disks can be wetted by the fluid, they always require (with the same fluid) the same foree, however different their materials may be, for this does not measure their adhesion but only the cohesion of the fluid, a film of which has to be torn from the rest. But in the case of mereury and metals wetted by it, Morveau found various forees necessary to detach them, because affinity is here concerned, for the adhering film is not pure mercury, but an amalgam of the two metals, and the foree measured is either the cohesion of this amalgam, or its adhesion to the pure mereury, or to the more liquid amalgam left behind. He found these forees nearly proportional to the affinities of the metals for mereury, or the readiness with which they combine with it; and adhesion may doubtless be considered proportional to, or even identical with that kind of affinity to which the term affinity is most proper, because it acts most between bodies having some resemblance; but both this and adhesion are totally independent of the foree commonly called affinity by chemists, which acts most between bodies widely differing from each other. This distinction must

be borne in mind, and for this purpose, besides the difference above mentioned there are two others equally broad and important: the affinity that bears a relation to adhesion produces compounds whose properties are in every respect intermediate between those of the ingredients, as alloys, solutions, &c.; but the other affinity produces compounds with new properties unlike either of the ingredients, as oxides from a gas and a metal, salts from acids and alkalies, &c.; and lastly, the former kind of affinity produces compounds in which the proportions of the ingredients may vary, as sugar and water in syrup, copper and zinc in brass, &c.; while the other kind leads to definite compounds, whose proportions are always the same. [See Affinity.]

Tor a further account of the effects resulting from the adhesion of liquids to solids, see Capillarity.

ADIT, a passage or entrance, (Latin aditus, from ad-ire, to go to.) [See Mine.]

ADJUTAGE. [See Hydraulics.]

ADZE or ADDICE, a cutting tool or pereussive chisel with a thin arehing blade, and its edge at right angles to the handle. In the Axe the edge is in the same plane with the handle. These tools are always used with pereussion, and hence differ from chisels, which act by pressure. The axe differs from the adze in being a splitting wedge, not a cutting instrument; for if driven into a block of wood as at a (Fig. 10) it will split it into two parts through the natural line of the fibres, leaving rough uneven surfaces, and the rent will precede the tool. A similar effect will be produced on removing a stout chip from the side of a block of wood with the hatchet, adze, or paring chisel. So long as the chip is too rigid to bend to the edge of the tool, the rent will precede it. If the instrument is thin and sharp, so that the shaving can bend to the tool, the wood will not split; it will be cut. In paring tools, one face of the wedge or tool is nearly parallel with the face of the work. In tools ground with only one chamfer this position not only assists in giving direction to the tool, but also places the strongest line of the tool in the linfldf resistance, or of the work to be done. Thus the axe or hatchet with two bevils a, which is intended for hewing and splitting and not for cutting, must, when required for the purpose of paring the surface, be applied at the angle a', which is a much less convenient and effective position than (A) that of the side hatchet with only one chamfer; but for paring a large or a nearly horizontal surface, the side hatchet is inferior to the adze c. This instrument is held in both hands by the handle, which is from 24 to 30 inches long, while the operator stands upon his work in a stooping position. The weight of the blade is from 2 to 4 pounds. "The adze is swung in a cireular path almost of the same curvature as the blade, the shoulder-joint being the centre of motion, and the entire arm and tool forming as it were one inflexible radius; the tool therefore makes a succession of small ares, and in each blow the arm of the workman is brought in contact with the thigh, which thus serves as a stop to prevent accident. Tji coarse preparatory works, the workman

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