Page images

by the Bill of Rights on the accession of William and


Bispersion. Light, as we receive it from the sun or from other original sources as a star, a fire, a candle, &c., appears to the senses as a o undecomposable element by the instrumentality of which objects are perceived ; and as for the peculiar colours of bodies, we naturally consider them, according to our early impressions, as belonging to the bodies themselves, or inherent in them. We are partly undeceived in this view by the changing colours of birds' feathers, soap-bubbles, compound silk textures, &c., but we are enabled to trace the immediate cause of the colours of bodies, whether permanent or transient, by the analysis of light furnished by the well-known experiments of the glass-prism.

The triangular prism used for this purpose is a solid, terminated by two equal and exactly similar triangles, and having besides three plane faces of a rectangular form, contained by the sides of the triangles and by right lines or edges joining corresponding angles of the two triangular bases above-mentioned: and any imaginary right line withia it parallel to these edges around which the prism is capable of revolving is called the aa is of the prism.

[ocr errors][subsumed]

In the annexed figure the triangle B A C represents a section of the prism parallel to its basis or perpendicular to its axis. DE we shall suppose to be a ray or exceedingly narrow beam of solar light incident from vacuo or air on the prism at E3 this ray of white light enters the prism at that point, and having undergone refraction by the dense medium of the glass, no longer proceeds as a simple ray E F, but is dispersed or divided into various rays of different colours over the space represented in the figure by f E F, and emerging at f F from the prism, undergoes another refraction, such that the portion of g of the ray proceeding from f is still more refracted than the portion FG from F, since the sines of the angles of incidence and refraction being in a constant ratio, that portion will be most refracted which has the greatest incidence: let now this dispersed beam g f FG be intercepted by a screen or wall P K, and from which extraneous light is as much as possible excluded, we shall then find the elongated space FG brilliantly painted over with tints passing gradually and insensibly from deep red to an attenuated violet, in the following order, as described by Newton, and since very generally concurred in, red, orange, yellow, green, blue, indigo, violet. This experiment, which first opens the analysis of light, is easily made by letting a beam of light pass through a small circular hole in a shutter, in a darkened room, on a glass prism such as above described, the refracted and dispersed ray being received on the opposite wall, ceiling, or floor, according to the position of the prism. It would be still more effective by concentrating |. light incident on a double convex lens in its focus, so that the beam E F may emanate more nearly from a point than it can when received through the hole of a shutter; for in the latter case rays are admitted which are inclined to each other at the angle subtended by the sun's disc to the eye. This primary experiment is, however, so familiar to almost all amateurs of science, that it will not be here necessary to enter into details respecting its most successful application.

When the image of the sun or a star, candle, &c., is thus formed by admission through a small hole or narrow line, and the refraction of the prism, the coloured space G g, which has the same angular breadth as the object in a direction parallel to the axis of the prism (the screen being sup

* For the history of this abuse see Prynne's ‘Animadversions on the Fourth Institute;' Petyt's Jus Parliam.", c. 7; and ‘Ladies Tracts, 327; the “Birth and Parentage, Rise and Fall, of Nonobstante.”

posed also parallel to it), but which is considerably elongated in the perpendicular direction, is called the spectrum ; and that angle of the prism B A C the sides containing which BA, AC, have been traversed by the ray DEFG is called the refracting angle of the prism.

Suppose, now, that a small orifice O is made in the screen at some point of the spectrum, so that rays of any particular colour, green for example, may be transmitted through it; and let the transmitted portion be again subjected to refraction through another prism, this beam being supposed very small, to ensure its purity or near uniformity of colour. It will not, after refraction, be again decomposed, or undergo any alteration of colour, except in respect to brilliancy, arising from absorption by the second prism: thus showing that light incident on the first prism, when once decomposed into homogeneous elements by refraction, is then, at least by refraction, not further decomposable.

If the original prism BAC be turned gradually round its axis, preserving always to the incident light the same refracting angle A, the spectrum Gg may be made to descend towards K, but after arriving at a certain point where the deviation, that is the inclination of DE produced to FG, is a minimum, it then reascends, and it is usual to make the chromatic experiments in this definite position of minimum deviation. }. occurs when the position of the prism is such that the angles of incidence and emergence, or their complements DEB, G FC, are equal; for when the moving point G has reached its lowest place, it is for a moment in the condition of a fixed point like the point D, through which we may suppose the incident beam admitted; hence rays proceeding from D, notwithstanding a small variation of incidence arising from the rotation of the prism, reach G, as if it were a fixed point; and since in dioptrics it is of no consequence to the path in what direction we suppose the rays to move, it follows that rays proceeding from G, notwithstanding a small alteration of the angle C F G, would arrive at the fixed point or orifice D; and consequently the data for the determination of the angles DE B, § C, in the position of minimum deviation, are precisely the same, and therefore these angles must then be equal.

This being premised, the following easy calculus will give the necessary angle of incidence to produce a minimum deviation

[ocr errors]

Since the angles of incidence and emergence are equal, the angles formed by the interior ray EF with both sides of the prism are equal, or the triangle A E F is an isosceles; let 2 a be the refracting angle of the prism, then drawing A M perpendicular to E F, we have Z E A M = a, which, being the complement of AEM, is necessarily the angle of refraction; if therefore H be the index of refraction for rays of any given colour, the angle of incidence P, corresponding to a minimum deviation, is given by the equation,

Sin. (P) = p sin. (a)

For distinctness, suppose the preceding index of refraction p to belong to the extreme red rays, and let H' be the index for the extreme violet rays of the spectrum; then, if P' denote the angle of incidence corresponding to the minimum deviation of the latter, we have

Sin. P'-p' sin. a ;

and since a is always less than a right angle, and p' is greater than n, therefore P’ is greater than P. In other words, when the red rays of the spectrum, having arrived at their lowest position on the screen, begin to reascend by the continued rotation of the prism, the violet rays will still descend a little before they arrive at their lowest position. Under these circumstances, the extent of the spectrum contracts from both ends, and an angle of incidence P, intermediate to P and P', which do not greatly differ, corresponds to the minimum or brightest spectrum; and it would be probably useful to observe what class of rays, defined by Fraunhofer's lines, had then obtained their minimum deviation; that is, such whose index of refraction Sin. P, * Sin, a We have seen that compound light, the sun's for example, may be decomposed into its homogeneous constituent rays by refraction through a transparent prism. Conversely it may be recompounded into light similar to the original, merely by making the rays, thus separated, by another refraction to occupy the same place. This may be effected by placing a prism of exactly similar material and form to that already used, with its refracting angle turned in a direction opposite to that of the former, so that the near faces of both prisms may be parallel; for the rays entering the second prism are in the same condition as if we supposed their direction inverted, that they may repass through the first; and therefore they emerge in a similar compound ray with the original, which may also be easily confirmed by experiment. The rays issuing from the second face of the refracting prism may also be collected by means of a double convex lens, so as all to meet very nearly in its principal focus, where, if the image be received on a sheet of paper, the original compound light will be reproduced. When the light of the sky, admitted through a small hole in a shutter in a dark room, is refracted by a prism, if an eye is placed behind the prism in the position which the spectrum would occupy on a screen, the hole will appear of the particular colour of the ray which reaches . eye, changing continually from one colour to another as the eye occupies different parts of the spectrum. The prismatic analysis of light, together with the phenomena relative to the transmission and absorption of light, enabled Newton to conclude that the colours of natural bodies are not inherent qualities of those bodies, but depend on their powers of reflecting, transmitting, or absorbing the rays of some colours more than others from the compound light incident on them; for all bodies, placed in homogeneous light of any colour appear themselves to be of that colour, though the vividness of tint is greatest when placed in that coloured light which they reflect most copiously. Hence also arise the different colours of the liquids exhibited frequently in chemists' shops, according as they are viewed by transmitted or reflected light which would necessarily be complementary colours if no absorption or extinction of light occurred in its passage through the fluid. Many of the prismatic colours may be imitated by mixing colours taken as in the spectrum of greater and less refrangibility, as orange from red and yellow, &c., but such compound colours are not identical with the homogeneous light of the same colour, being immediately decomposable when viewed through a prism. It would be difficult, if not altogether impracticable, to judge of the dispersive powers of o: media by measuring the length of the spectra which they produce in a prismatic form, in consequence of the indefiniteness of their termini. The light at the violet end is so feeble that it requires some continued application of the eye to perceive a colour where we had first imagined the spectrum terminated: and, on the other hand, the influence of imagination, after we have recognised it, is apt to extend it momentarily far beyond its limits. Fortunately Nature has herself furnished a scale of definite limits in the beautiful discovery made by Wollaston and Fraunhofer of the existence of dark spaces, bands transverse to the length of the spectrum, and now generally designated Fraunhofer's lines. . . These bands are best observable by forming the spectrum of a luminous line instead of a point, by means of a prism of great purity, and viewing it through a telescope of good magnifying power, though some of them may, when carefully pointed out, be recognised by the unassisted eye, and after one recognition are in future easily found. They are spaces totally deficient of light, of very unequal width, and exceedingly numerous; the large bands near the extremities of the spectrum serve, however, as definite limits, so as to furnish the requisite criteria for the dispersive powers of different substances; it is also very remarkable that these bands, always the same in number and relative position for the same light, are different when the source of light is varied. Thus sun-light, moon-light, planet-light, sky-light, derived from a common source, have the same lines, but they are different from those of star-light, fire light, candle-light,


&c., each essentially different source having a peculiar system of deficient rays. Substances which have not a great difference of refractive powers possess frequently very #. dispersive powers, and the angular dispersion by a medium is not proportional to the angular deviation, and therefore by a system of prisms, two or more, white light incident on the first may be reproduced from the last, though on the whole refracted from its original direction. Such a system is called achromatic. Conversely, by forming an achromatic system experimentally, where the angles of the prisms are small, and in the position of minimum deviation, if the dispersive power of the material of one of them be taken as a standard, that of the other may be readily obtained, the dispersion being

§ measured by #, p being the index of refraction, and 3 p.

the difference of its extreme values for any class of rays. This method has been much used in practice, particularly by Dollond. The formulae for achromaticity in systems of prisms or lenses, though not difficult of investigation, are in general too complicated and tedious for a popular work; (see moires }. l'Acad. de Sciences, 1765; Mém. par D'Alembert.) The rainbow is a beautiful natural exhibition of the dispersion of light into the spectral colours. [RAINBow.] To find the longitudinal chromatic aberration of a lens, or the interval of the axis between the foci of extreme red and violet rays: Let the red rays converge to the point R, and the violet to the point V in the axis.

[ocr errors][merged small][merged small][merged small][ocr errors][ocr errors]

To find, in the same case, the radius of the circle of least chromatic dispersion By referring to the same figure, we may observe that the foci. R V are respectively the vertices of red and violet conical surfaces, having the lens as a common base. Let these surfaces intersect in a circle, of which the radius is DE; then it is plain that all the intermediate coloured rays pass through this circle. It is therefore that of least dispersion: he preceding figure, representing a plane section of the whole system taken through the axis, it is obvious that, from the smallness of RV relative to CR, the angles CVB, CRA, are sensibly equal, or the triangle VR D is exceedingly nearly isosceles, and therefore D E bisects VR, or

[ocr errors][merged small]
[ocr errors]

ER =% and DE = ER . CA, and for paIt is an art equally applicable to both divisions of the organic kingdom, and indispensable alike to the discovery of the structure of plants and animals. The grounds on which, for the well-being of the community, every facility should be afforded to the cultivation of this art, as far as regards human dissection, have been already fully stated. [ANATOMY.] It is satisfactory to observe that the prejudices which formerly obstructed this practice are rapidly disappearing, and that even the most uneducated are beginming to appreciate its great importance and its signal utility. DISSEISIN... [SEisin.]

DISSENTERS, the general name for the various Protestant religious sects in this country that disagree in doctrine, discipline, or mode of worship with the established church. The Jews and Roman Catholics are not commonly called dissenters. The origin of Protestant dissent from the church of England is usually traced back to the year 1548, in the reign of Edward VI., when a controversy arose among the adherents of the new Reformation in consequence of the excellent Hooper (afterwards the martyr) scrupling to be consecrated as bishop of Gloucester in the customary canonical habit, which he deemed objectionable as a relic of Romanism. Hooper eventually received consecration without being attired in canonicals. At this time the two parties received the names of Conformists and Nonconformists. Very soon after that of Puritans came into use as the general appellation of the dissenters; and it continued to be that by which they were commonly distinguished down to the close of the civil wars in the next century. The toleration of the dissenters, even in the most limited extent, dates only from the Revolution; during the century and a half that elapsed between the Reformation and that event, with the exeeption only of the short period of the Commonwealth, during which first the Presbyterians and afterwards the Independents had the ascendency, they continued to be persecuted by a succession of restrictive and penal laws of almost constantly increasing severity. It has taken almost the century and a half more, that has passed since the revolution, to raise the dissenters from being a merely tolerated body to a free participation in the rights of their fellow subjects by the abolition of the Test and Corporation Acts, in 1828. If the relaxation of the marriage law, that has since taken place, shall be followed by the abolition of church rates, the dissenters will be placed as nearly on an equality in all respects with the adherents of the established church as it is possible that they should be, without the established church itself being abolished. In the early times of dissent the great classes of dissenters were the Presbyterians, the Independents, the Baptists, and the Quakers, and they still continue to be the most numerous sects, unless we are to include the Methodists, or followers of Wesley and Whitfield, some of whom are avowedly dissenters, and others not, and are also subdivided into Wesleyan Methodists, Primitive, &c. The minor sects of dissenters now make a long list; but many of them may be considered as only subdivisions of or included in the four leading denominations. From an examination of the best materials (which are however very imperfect) that exist for the statistics of dissent, Mr. Macculloch is inclined to think that the entire number of Protestant dissenters in England and Wales does not exceed 2,200,000, or, at most, 2,500,000, even including the Methodists, who may amount to about 1,200,000. (Statistical Account of the British Empire, ii., 413, 416.) But this estimate, we are inclined to think, is too low. The most numerous classes of dissenters in Scotland originated in a separation from the established church in 1740. They are called generally Seceders, and are divided into Burghers, Anti-Burghers, Original Burghers, and Original Seceders. There are also the body of dissenters called the Relief Church, who separated from the establishment in 1758. The only considerable body of Scottish dissenters of older standing, with the exception of the Episcopalians, are the Cameronians, or Reformed Presbyterian Synod, who are the representatives of the Covenanters of the seventeenth century. Mr. Macculloch calculates the whole number of dissenters in Scotland (exclusive of about 140,000 Roman Catholics) at about 360,000 or 380,000 persons. In Ireland, exclusive of the Roman Catholics, who alone outnumber the adherents of the established church in the proportion of 7% to one, the principal dissenters are the Presbyterians, who are mostly confined to the province of Ulster. The Irish Presbyterians amount to between 600,000 nd 700,000, and are more than twenty times as numerous

as all the other bodies of dissenters in that country taken together. (Report of Commissioners of Religious Instruction in Ireland, 1835.) [DonDRIDGE.] DISSEPIMENTS, the partitions in the inside of a fruit which are formed by the union of the sides of its constituent carpels. Dissepiments are therefore necessarily alternate with the stigma. When partitions which do not bear this relation to the stigma occur in the inside of a fruit they are called phragmata or spurious dissepiments, as in the cathartocarpus fistula where they are horizontal, and in verbena where they are vertical. DISSONANCE, in music, a term synonymous with discord. [DiscoRD.] DISTANCE. The only remark which we need make upon this common word is that it is very frequently applied to angular distance, meaning the angle of separation which the directions of two bodies include. Thus the spectator's eye being at O, the angle A O B is the angular distance (frequently simply called the distance) of the two points A ...}. In the apparent sphere of the heavens, distance always means angular distance. The term apparent distance is frequently applied in the same case. DISTEM p;|. an inferior kind of colouring used for both intermal and external walls, but principally for the former, instead of oil colour, being a cheap substitute. It is composed of whitening mixed with size of a coarse quality, in the proportions of twelve pounds of whitening to one of size. The size is boiled and reduced to a proper working consistency by the addition of water, after which the colour is added to form the necessary tint. Coarser colours are used for distemper than are employed in oil painting and colouring. Scene painting is executed in distemper, and paper stainers employ distemper colour in printing and staining papers for walls. The colours used in these cases are however of a better quality, and the size employed is made from the hide of the buffalo, or parchment cuttings. . The proportions of size and whitening in paper staining depend on the strength of the size. In five quarts of distemper, if the size is strong, one-fourth part will be sufficient; if weak, about .# In mixing the size and whitening much depends on the judgment of the workman. The distemper is used in a chilled state. Five quarts will stain about eighty-four yards of paper. DISTHENE, a variety of KYANITE. DI'STICHOUS, a term in botany, signifies arranged in two rows, as the grains in an ear of barley, and the florets in a spikelet of quaking-grass. DISTILLATION is a chemical process for applying a regulated heat to fluid substances in covered vessels of a peculiar form called ALEMBics, in order to separate their more volatile constituents in vapour: and for condensing them immediately by cold into the liquid state, in a distinct vessel, styled a refrigerator. The Arabians seem to have practised, in the remotest ages, the art of extracting the aromatic essences of plants and their flowers, in the form of distilled waters, to supply the luxuries of oriental baths. They are also supposed to have been the first to extract from wine a colourless intoxicating liquor by distillation. The term alcohol, now applied to such distilled spirit, and which is supposed to be Arabic”, appears at first sight to favour that idea, but as it was antiently employed to designate merely the extremity, tenuity, or impalpable state of pulverulent substances, it affords no just ground for the above conclusion. From certain passages in É. and Galen there can be no doubt that the Greeks and Romans were well acquainted with the distillation of aromatic waters. Indeed Nicander, a Greek poet and physician who lived 140 years before the Christian aera, employs the terms duðić ambia and distillation in describing the preparation of rose-water. From ambix, which signifies a pot, the Arabic name alambic or alembic is derived. The words pot and poteen are used in the same way by the modern Irish to designate a still and its spirituous product. It is obvious that distillation must have been a familiar process to the countrymen of Avicenna, since, in his treatise of catarrh, he compares the human body to an alembic; he regards the belly as the cucurbit or body, and the head as its capital, through which the humours distil, passing off by the nostrils as its beak, Arnoldus de Villa Nova, a chemical physician of the thirteenth century, is the first author who speaks explicitly of an intoxicating spirit obtained by the distillation of wine, and he describes it as a recent discovery. He considers it to be the universal panacea so long sought after in vain. His disciple Raymond Lully, of Majorca, declares this admirable essence of wine to be an emanation of the 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. He further imagined that the discovery of this aqua vitae, as it was called, indicated the approaching consummation of all things—the end of the world. However much he erred as to the value of this remarkable essence, he truly foresaw its vast influence upon the condition of man, since to both civilized and uncivilized nations it has realized infinitely greater evils than were threatened in the fabled box of Pandora. In his “Chemical Theatre,’ written towards the conclusion of the thirteenth century, Raymond Lully describes the distillation of ardent spirits thus:— ‘Limpid and well-flavoured red or white wine,’ says he, “is to be digested during 20 days in a close vessel by the heat of fermenting horse-dung, and to be then distilled in a sand bath with a very gentle fire. The true water of life will come over in precious drops, which, being rectified by three or four successive distillations, will afford the wonderful quintessence of wine.” - - “To prove its purity,” adds he, “if a rag be dipped in it, and kindled, it will not become moist, but consume away.” All the older writers imagined that aqua vitae imbibed from the fire its inflammable, heating, and exhilarating qualities; so in order to increase these qualities to the utmost, they prescribed tedious and repeated warm digestions of the wine before it was put into the alembic, and an exceedingly slow distillation that each drop might come over instinct with fire. In the present article we shall consider distillation solely in reference, to the production of alcohol. The process, when applied to distilled waters, acthers, and oils, belongs to pharmacy, chemistry, perfumery, &c. The subject naturally divides itself into two branches: 1, the formation of the alcohol; 2, its elimination from the ingredients with which it is mixed. The only substances employed in this country in the manufacture of ardent spirits upon the great scale are different kinds of corn, such as barley, rye, wheat, oats, buckwheat, and maize. Peas and beans also have been occasionally used in small quantity. The principles in these grains from which the spirits are indirectly produced are starch and a little sweet mucilage, which, by a peculiar process called mashing, are converted into a species of sugar. It is the sugar so formed which is the immediate generator of alcohol, by the process of fermentation. Hermstädt estimated that two pounds of starch properly treated would yield one quart of whiskey, of specific gravity 0.9427. The following kinds of corn afford of spirits of the said strength the quantities annexed to them in the scale:

* The true etymology of alcohol is uncertain. The Arabic word kohl, with the article al prefixed, signifies' autimony reduced to a fine powder, and used

as a collyrium for the eyes.'

[merged small][ocr errors]

We may therefore conclude, says Hermstädt, that 100 pounds of corn will yield, upon an average, 40 pounds of spirits of the above specific gravity. We shall presently see that 100 pounds or two bushels of corn produce much more alcohol in the British distilleries.

In mashing one or more kinds of corn, a greater or smaller proportion of malt is always mixed with the raw grain, and sometimes majt alone is used, as in the production of malt whiskey.

The process of malting is that incipient growth called germination, in which, by the disengagement of a portion of the carbon of the starch, in the form of carbonic acid, the ultimate vegetable elements become combined in such a proportion as to constitute a species of sugar. Malting is the most effectual method of converting starch into sugar. But it is known from the researches of Saussure, that if starch in solution be digested for some time at summer temperatures with gluten, it will undergo a remarkable change, nearly one-half being converted into a species of

sugar, and one-fifth into gum. A similar change is more rapidly effected upon starch by boiling its pasty solution with one-hundredth part of its weight of sulphuric acid. The recent discovery of diastase by É. and Payen has enabled us to effect this curious conversion with much greater certainty, and to a greater extent than was possible by the gluten or the acid. If 8 or 10 parts of ground malt be mixed with 100 parts by weight of starch previously diffused through 400 parts of water, at 140°Fahr., and if this mixture be kept at a temperature of from 158° to 166° for three or four hours, the nearly insipid pasty liquor will become a limpid syrup, which may be evaporated by a gentle heat into an uncrystallizable sugar, capable of being used as a substitute for ordinary sugar, not only in the vinous fermentation, but in many operations of the confectioner. The same change which takes place upon pure starch in the above experiment is effected in the process of mashing as carried on in breweries and distilleries. A larger or smaller proportion of the secula of the corn is thereby converted into sugar, and thus brought into a state fit for producing alcohol by fermentation. The manufacture of whiskey or ardent spirits consists of three distinct operations: first, mashing; second, fermentation; third, distillation. 1. Mashing.—Either malt alone, or malt mixed with other grains, and coarsely ground, is put into the mash-tun, along with a proper proportion of hot water, and the mixture is subjected to agitation by a mechanical revolving apparatus, exactly similar to that employed in the breweries for the manufacture of beer. When malt alone is used, the water first run into the mash-tun among the meal has usually a temperature of 160° or 165° Fahrenheit, but when a considerable proportion of raw grain is mixed with the malt, the water is let on at a lower temperature, as from 145° to 155°, for fear of making such a pasty magma as would not allow the infusion or worts to drain readily off. The following are the quantities of malt and raw grain mixed which have been found to afford a good product of whiskey in a well-conducted Scotch distillery:

[merged small][ocr errors]

From each bushel of the above mixed meal 2, gallons of proof whiskey (specific gravity 0.921) may be obtained, or 183 gallons per quarter. A few distillers are skilful enough to extract 20 ol. from a quarter of that mixture. Ten imperial gallons may be ... a fair proportion of water to be introduced into the mash-tun for every bushel of meal at the first infusion. After two or three hours' agitation, the whole is left to repose for an hour and a half, and then the worts are drawn off to about one-third the volume of water employed, the rest being entangled in a pasty state among the farina. About two-thirds of the first quantity of water is now let into the tun, but at a temperature somewhat higher, and the mashing motion is renewed for nearly half an hour. A second period of infusion or repose ensues, after which these second worts are drawn off. Both infusions must be cooled as quickly as possible down to the temperature of 80° or 70° Fahr., otherwise they are apt to run into the acetous fermentation by the rapid absorption of atmospheric oxygen. This refrigeration is usually effected by exposing the wort for some time in large shallow cisterns, called coolers, placed near the top of the building, where it may be freely exposed to the aerial currents. But it is sometimes cooled by being passed through serpentine tubes surrounded with cold water, or by the agency of ventilators blowing over its surface in extensive cisterns only three or four inches deep.

After the second wort is drawn off, a third quantity of water, fully as great as the first, but nearly boiling hot, is run into the mash-tun, and well incorporated with the magma by agitation; after repose, this third Wor,” also drawn off, cooled, and either directly mixed wo "o. ceding worts, or after it has been concentrate" "... o: down; in most cases however it is resero" unity of stead of water for the first infusion of * * * meal.

As a revenue of five and a half mill rived from the whiskey distilleries, their op

ions sterling is deerations are sub

jected to a very strict code of regulations, which are administered and enforced by the excise. One of these prescribes the range of specific gravity at which the worts may be lawfully let down into tile fermenting tuns. The distiller must give notice to the excise officer in attendance, before commencing a round, whether he intends to distil from malt alone, or from a mixture of it with raw grain, and of the density he intends his worts to be when introduced into the fermenting backs. He may change this notice at the end of a month or six weeks, when, upon another notice of six days, he may change his specific gravities. In England the law restricts the distiller to the densities between 1.050 and 1.090; in Scotland, between 1.030 and 1.075, which, for brevity's sake, are called 50, 90, 30, and 75, omitting the 1.000 common to them all. At these densities the quantities of solid saccharum contained in one barrel of 36 imperial gallons, are 47.25 lbs., 85 lbs., 28 lbs., and 70.3 lbs. respectively. The mashing and fermentation are jointly called brewing, and the period in which they are carried on is by law kept quite distinct from the distilling period, the one occupying usually one week, and the other another in rotation. About ! 50 gallons of wort or wash are obtained from each quarter of corn employed. The first of the above worts will have generally the density of 1.078 when the grain is good and the mashing is well managed, and the second a density of 1,054, so that the mixture will have a specific gravity somewhat above i:060, and will contain about 60 pounds of extract per barrel. Now, by the excise rules, 100 gallons of such wort ought to yield one gallon of proof spirit for every five degrees of attenuation which its specific gravity undergoes in the fermenting tun, so that if it falls from 1.060 to 1.000, 12 gallons of proof spirit are supposed to be generated, and must be accounted for by the distiller. If he understand his business well, he will be able to produce from 5 to 10 per cent. more than the law requires. Mr. Smith, in his examination before the Molasses Committee of the House of Commons in 1831, states that in one year, reckoning by computation from the above data, he showed produce for 60,000 or 70,000 gallons more than the presumed quantity, and paid duty accordingly; and that in 1830 he was charged for 80,000 gallons of spirits actually produced beyond the presumptive charge, according to the attenuated gravity of the worts. In consequence of an alteration in the excise laws about twelve years ago, the distillers were allowed to ferment worts of less density than they previously could, and have been able to effect a more productive fermentation. They

have been also enabled thereby to reduce the proportion of

malt in the mixed meal. Formerly they were accustomed to use three parts of malt to four parts of barley, or two to three, but they soon diminished the malt to one-fifth, and latterly to one-eighth, or one-tenth, of the whole grain. One principal use of malt, besides its furnishing the saccharine ferment called diastase, is to keep the mash magma porous, and facilitate the drainage of the worts. The cost at which whiskey may be made in England is thus stated by Mr. Smith:-When barley is 38s, per quarter, he reckons that one gallon of proof spirits costs 2s. for corn or meal, 1s. 2d. for the charge of manufacturing, 2d. as the duty on malt employed, and 7s.6d. as the duty on spirit, amounting altogether to 10s. 10d. If we consider that from 18 to 20 gallons of proof spirits may be made from eight bushels or one quarter of mixed grain, we must think this statement of Mr. Smith's somewhat overcharged. Indeed good proof spirits may be bought from some distillers at a considerably less price, which proves either that they can manufacture the article more economically, or that they make a profit at the expense of the revenue. II. Fermentation. This is undoubtedly the most intricate, as it is the most limportant process in distillation, but unfortunately one hitherto studied with too little regard to scientific precision by the distiller. Experiments have proved that the quantity of saccharine matter converted into alcohol is dependent upon the proportion of ferment or yeast introduced into the worts; if too little be used a portion of the sugar will remain undecomposed, and if too much, the spirits will contract a disagreeable taste. In general, the worts are iet down at the specific gravity of 1.050 or 1.060, and at a temperature varying from 60° to 70° Fahr., and for every 100 gallons one gallon of good porter yeast is immediately loured in and thoroughly incorporated by agitation with a

stirrer. When by the attenuation the density is diminished to 1.035 one half gallon more is added, and another half gallon at the density of 1.025, after which the worts usually receive no further addition of yeast. The temperature of the fermenting mass rises soon after the introduction of the yeast 8 or 10 degrees, and sometimes more ; so that it reaches in some cases the 85th or 90th degree of Fahrenheit's scale. From the appearance of the froth or scum the experienced distiller can form a tolerably correct judgment as to the progress and quality of the fermentation. The greatest elevation usually takes place within thirty-six hours after the commencement of the process. The object of the manufacturer of spirits is to push the attenuation as far as possible, which so far differs from that of the beer-brewer, who wishes always to preserve a portion of the saccharine matter undecomposed to give flavour and body to his beverage. The first appearance of fermentation shows itself by a ring of froth round the edge of the vat usually within an hour after the addition of the yeast; and in the course of five hours the extrication of carbonic acid from the particles throughout the whole body!of the liquor causes frothy bubbles to cover its entire surface. The temperature meanwhile rises from 10 to 15 degrees according to circumstances. The greater the mass of liquid, the lower the temperature at which it was let down into the tun, and the colder the surrounding atmosphere, the more slowly will the phenomena of fermentation be developed under a like proportion of ycast and density of the worts. In general large vats afford a better result than small ones, on account of the equality of the process. It is reckoned good work when the specific gravity comes down to 1.000, or that of water; and superior work when it falls 4 or 5 below it, or to 0.995. After thirty-six hours upon the moderate scale the yeasty froth begins to subside, and when the attenuation gets more advanced, the greater part of it falls to the bottom on account of its density relatively to the subjacent fluid. In from forty-eight to sixty hours the liquor begins to grow clear, and becomes comparatively tranquil. It has been deemed advantageous towards the perfection of the fermentation to rouse up the wash occasionally with a proper stirrer, and in some cases to increase its temperature a few degrees by the transmission of steam through a serpentine pipe coiled round the sides of the vat. Some have imagined that a considerable portion of spirit is carried off by the great volume of carbonic acid evolved, and have proposed to save it by covering the vats air tight, and conducting the gas through a pipe in the lids into a vessel containing water. The economy of this apparatus is not worth the expense and trouble which it occasions. The distillers content themselves with enclosing their vats after the first violence of the action under tolerably tight covers. Mr. Octavius Smith, the eminent distiller of Thames Bank, states in his examination before the Molasses Committee, that the acetous fermentation is always proceeding simultaneously with the vinous fermentation; for judging by the usual tests there is always a slight degree of acidity in fermenting wash; that vinegar is in fact forming along with alcohol, or that while the attenuation is increasing, ocetic acid is being formed. This important fact, which agrees with our own experience, serves to show how very fallacious a test the attenuation or diminution of density is of the amount of alcohol generated and existing in a fermented wash. The acetic acid along with the undecomposed mucilaginous starch may, in fact, so far counteract the attenuating effect of the spirits as to produce a specific i.". which shall indicate 10 or 15 per cent, less spirit than is actually present in the wash. Hence the excise officers should be instructed to use test-stills in order to verify upon a small aliquot part the real quantity of distil. lable alcohol contained in each back of wash. After due agitation of the wash three samples should be taken by the dipping cylinder, or sinking-jar, one from the bottom, one from the middle, and one from the top; which being mixed and distilled would denote exactly the whole quantity of spirit that could possibly be extracted. This test-still was clearly described and forcibly pressed upon the attention of the exchequer by Dr. Ure in his several examinations before the said Molasses Committee. The distillers in general, as might have been expected, scouted the idea of the possibility of ascertaining the quantity of spirits in a large back, from the distillation of a quart or a gallon of the wash; but Mr. Steel showed

that by the distillation of 1000 grains in a glass retort

« EelmineJätka »