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- Herausgeber: Edizioni Savine
- Kategorie: Lebensstil
- Sprache: Englisch
- Veröffentlichungsjahr: 2023
In these days when there are few Breweries which do not possess a Microscope, it would seem desirable that the instrument should not fall a prey to the casual or uninstructed observer, but should rather, by the knowledge and skill of those that use it, be made a means of controlling the processes of Malting and Brewing. A Brewer in becoming practically acquainted with the Microscope as a controlling agent in his process, raises, to use a figure of speech, a part of the line of fortification which science provides against the hurtful or injurious influences declaring themselves, when Brewing operations are not conducted with the intelligence and skill that they ever increasingly require.
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The Microscope
IN THE
BREWERY AND MALT-HOUSE.
BY
CHAS. GEO. MATTHEWS, F.C.S., F.I.C., Etc.,
AND
FRANCIS EDW. LOTT, F.I.C., A.R.S.M., Etc.
Illustrated by Steel Engravings Woodcuts, Lithographs, and Chromo-Lithographs.
1889.
[ALL RIGHTS RESERVED.]
THIS BOOK IS INSCRIBED BY THE AUTHORS, IN GRATEFUL APPRECIATION OF THE HIGH SCIENTIFIC AND PRACTICAL VALUE OF THE WELL-KNOWN RESEARCHES IN CONNECTION WITH FERMENTATION UNDERTAKEN BY HIM IN YEARS PAST ; AND IN ADMIRATION OF THE GENIUS DISPLAYED IN THIS AND OTHER BRANCHES OF SCIENTIFIC INVESTIGATION.
September, 1889.
DESCRIPTION OF WOODCUTS.
INTRODUCTORY PREFACE.
IN these days when there are few Breweries which do not possess a Microscope, it would seem desirable that the instrument should not fall a prey to the casual or uninstructed observer, but should rather, by the knowledge and skill of those that use it, be made a means of controlling the processes of Malting and Brewing. A Brewer in becoming practically acquainted with the Microscope as a controlling agent in his process, raises, to use a figure of speech, a part of the line of fortification which science provides against the hurtful or injurious influences declaring themselves, when Brewing operations are not conducted with the intelligence and skill that they ever increasingly require.
The production of a special treatise on the microscope as applied to Brewing, was first contemplated by the authors during the delivery of a course of lectures on this subject to some young brewers. As the lectures were re-delivered to successive groups of students, the impression already gained, namely,—that a real requirement existed amongst Brewers for precise and condensed instruction in the handling of the microscope,—became a very strong one indeed, and the present work was undertaken. As the writing advanced it was deemed desirable, in order to make the work as complete as possible, to cover more ground than the occasion at first seemed to demand. The original lectures, however, constitute the nucleus of the work.
The chief aim of the authors has been to collect within a convenient space and without undue elaboration, matter that appears to them to be of undoubted value in its application to Brewing and Malting; and they believe that a good deal of information has been incorporated at the same time, that has not hitherto been adequately dealt with in print. The fact that a large part of the information is drawn from works of undisputed excellence is fully recognized by the authors; but the works are many—as may be judged from the list of authorities quoted—and the expense involved in their purchase would be very considerable, besides which, the search amongst authorities for required information involves the expenditure of no little time and trouble.
With these explanations, and trusting that their efforts have been attended by a reasonable amount of success, the authors hopefully tender this treatise to the judgment of those who are interested in the Industries with which it seeks to identify itself.
The authors would here express their cordial thanks to the friends in Burton (especially the members of the Chemical Club), and elsewhere, who have materially aided them by useful suggestions, loans of photographs, assistance in corrections of MS., revision of proofs, etc. Where such general kindness has been experienced it seems invidious to make any distinction by name.
The authors also wish to record their thanks to Mr. J. E. Wright for the great care and attention bestowed on the drawings bearing his name.
Bridge Chambers,
Burton-on- Trent.
CHAPTER I.
The Mechanical Arrangements of the Microscope.
BEFORE proceeding to discuss the various uses to which the microscope may be applied by the brewer and maltster, it is essential that a fair understanding of the mechanical construction of an ordinary instrument should be arrived at. Knowledge of the optical principles on which the action of the lenses depends, though a desirable acquisition, must from our point of view be looked upon as a matter of separate study ; and it will therefore be necessary to touch only in the briefest manner on a few purely optical considerations. We will then in this first chapter give a general, followed by a more special, description of the parts of what is known as the Compound microscope. Referring to Fig.1, the entire frame-work there represented, to which various movable accessories of the microscope may be adapted, constitutes the Stand, consisting of the tube A and the part A' immediately supporting it, called respectively the Body and the Limb ; the Stage or object carrier B, and the Foot C, this last carrying the whole weight of the instrument, and being, when well contrived, adjusted so as to secure a maximum of steadiness.
* A single magnifying lens or Simple microscope is of no special use in connection with brewing matters, being used chiefly for the examination and dissection of comparatively large objects under a low magnifying power.
A microscope having a single tube is known as a Monocular—one with a double tube as a Binocular—microscope. Into the tube at the upper end (Fig. I a) slides the Eye-
piece (Fig. 2), generally consisting of two lenses with a diaphragm or stop between them. The lens nearest the eye of the observer is called the eye-lens, the other the field-lens, whilst the screw-threaded socket at the other end of the tube (Fig. 1 b) carries the Object glass or Objective (Fig. 3), the most important of the optical parts of the instrument. The screw-thread as a rule is of such a diameter as to admit of objectives by different makers being used with the same tube and stand.*
The body of the microscope is usually controlled by two movements termed Adjustments. Firstly, the larger milled-headed screws (Fig. 1 D) causing the tube by a rack and
* That is to say, a standard has been agreed upon so as to render objectives of different microscopes interchangeable, but the makers do not seem to exactly work up to it.
pinion to slide through a vertical distance of some two to four inches. Secondly, the smaller milled-headed screw (E) acting either on the whole tube, or on a socket at its lower end, this last having sometimes an extra play of about three-sixteenths of an inch upon a spring independent of either of the adjustments; this is to protect the objective if it should be impelled by accident against a glass slide or other rigid body, such as the stage itself. The movements being imparted by a fine-threaded screw, may be made as small as desired: the arrangement is used for focussing with high powers, and is known as the Fine adjustment, the one first
mentioned being termed, in contradistinction, the Coarse adjustment.
The plane surface with a central opening or Stage for carrying slides may be either of metal or glass, with clips, or a ledge to retain the glass slide. It may be provided with Movements, which are ordinarily rectangular; that is, by the use of milled-headed screws (Fig.1 G) attached to the stage, the slide may be caused to move in directions approaching to or receding from the observer, or from side to side, the two sets of directions being at right angles to each other; or the movements may be compounded into diagonal directions by using both milled-heads simultaneously. A circular movement of the Stage is sometimes provided, but it is not essential to an instrument designed for Brewery purposes; neither, indeed, are the rectangular movements, but they are a great convenience, and are regretfully dispensed with by anyone accustomed to their use. Any receptacle for accessories immediately underlying the Stage is called the Sub-stage (Fig. 1 e). Here, a diaphragm (Fig. 4 aaa), an arrangement to regulate the passage of light to the object under examination is usually found, and is practically indispensable for good definition with high magnifying powers. It consists, generally, of a perforated circular plate, rotating on a centre pin as sketched, the apertures being circles of different diameters ; though for
illumination of special objects, other shaped openings are sometimes included. A very elegant form is Collins’ “Iris ” or graduating diaphragm, in which the aperture may be regulated by a screw, from the smallest circle to a considerable opening. Small perforated discs or “ Stops ” of different apertures are occasionally made to fix underneath the object instead of the movable diaphragm.
To secure the best defining power of the lenses, especially with high powers, a piece of apparatus called a Stage Condenser (Fig. 5)—which is as a rule, Achromatic—is very useful. It fits into the Sub-stage, and consists of an arrangement of lenses contrived to concentrate light on the object under observation. Where this adjunct is employed, the diaphragm is often placed underneath it as in the figure: it then exercises a first control on the amount of light passing to the object.
Another accessory of the Sub-stage is the Nicols prism, which constitutes part of the Polarizing apparatus ; a second Nicol’s prism—the Analyser—fitting into the tube of the microscope just above the Objective. These accessories
are by no means necessary in a Brewery microscope, but might be of some use for special work.
An indispensable adjunct to the microscope stand is the apparatus for reflecting light on to transparent objects placed on the Stage : for this purpose a double mirror, on a jointed arm, is usually provided, occupying the position indicated by H Fig. 1, having one surface plane and the other concave, the action of which reflectors respectively will be explained later.
In the case of Binocular microscopes, two images are
obtained by a portion of the rays of light from the Objective being diverted by a small prism into the second tube of the instrument, which is usually joined at an angle to what may be called the main tube. An image is thus provided for each eye, and the two eye-pieces are moved simultaneously by a rack and pinion like the coarse adjustment.
With a microscope such as that outlined in Fig. 1, the
tube can be lengthened by a sliding piece called the Draw tube, the junction being at d: the object of this is to increase the amplification, the effect being similar to that obtained by using a higher power eye-piece.
Amongst necessary appliances is the Bull’s-eye condenser, which may be on a separate stand as in Fig 12 A, but is more convenient when it can be attached to the Stage (Fig. 6), and should be provided with a universal movement as indicated. Its use is to concentrate the light on to an opaque or semi-opaque object
In absence of sunlight it is desirable to have a good source of artificial light to fall back upon ; any of the following may serve:—Firstly, an Argand gas burner on a vertical stand, which is the more convenient if it has a telescopic slide for raising or lowering the burner, and a blue or neutral tint glass cylinder is to be preferred to the ordinary white glass. Secondly, a Paraffin lamp, with blue or neutral tint glass chimney, or a copper chimney is sometimes employed, having an eye or aperture 1/2 to 1 inch wide, of tinted glass ; or a cylindrical porcelain shade may surround the glass chimney, having a portion cut out to let a certain amount of light issue from the lamp. Amongst more expensive illuminating apparatus, an incandescent electric lamp fitted on a movable arm, is a very neat and effective source of light, and has much to recommend it where the microscope is used intermittently. The new incandescent gas burners of the Clamond and Welsbach pattern yield a very nice steady light.
As regards smaller apparatus. For drawing or sketching with the microscope a Camera Lucida, or Beale’s neutral tint reflector, is often employed attached to the eye-piece ; of the two forms the reflector is" by far the cheaper, and acts almost as well as the Camera Lucida, which last includes a small glass prism in its structure. The mode of employment of these appliances is described under “ Manipulation.” Forceps or pincers contrived to fix on the Stage are sometimes useful for holding an object which it is not convenient to put on a glass slide. A dozen or two of glass slips of the ordinary size, 3 in. by 1 in., and 1/2 oz. of cover glasses from 5/8 to 7/8 in. diameter, may be provided. Circular cover glasses are more conveniently cleansed than squares, as they do not break so easily. With combinations not exceeding 300 to 400 diameters, a cover glass of some strength may be employed, as very fragile ones provide a constant source of annoyance by breakage.
There are, of course, innumerable accessories for special kinds of investigation, but the microscope as used by the brewer does not require them. A convenient Stand, with one good eye-piece and two objectives of low and high power respectively, Stage rectangular movements, an Achromatic condenser, a Bull’s-eye condenser, and a good artificial source of light (should this be required), constitute pretty well the whole of the apparatus necessary or desirable.
We will now enter into some further detail in elucidation of the action of some of the parts of the instrument already referred to, and thus pave the way to manipulation pure and simple. The Mirrors, or reflecting apparatus, call for early
consideration, and in connection with Brewing matters the Concave or hollowed mirror is of the greater importance ; this form of reflector concentrates the light to a certain point or “focus ” some two or three inches from the centre of the mirror, as shown in Fig. 7 A, and is used in conjunction with high power objectives. The best position of,the mirror may be determined, experimentally, by putting a flat piece of .oiled tissue paper or tracing paper on the stage, and moving the mirror vertically till a small disc or spot of light is shown. The action of the Plane or flat mirror is shown in the small sketch B, appended to Fig. 7. Here the light, instead of being concentrated, is reflected in parallel rays, and consequently with small objects and object-glasses, a large portion does not impinge upon them at all. The illumination is, however, quite adequate and satisfactory for objects viewed under low powers of magnification.
We may now deal with the lenses of the microscope as included in the Eyepiece and Objective. Their action is dependent on the optical principle known as Refraction, or the bending that rays of light undergo when entering a medium of different density, a certain amount of the light being at the same time absorbed or lost. The degree of refraction is determined by the curvature of the lens and density of glass, high magnifying power being concurrent with great curvature, high refraction, and short focal length or Working Distance ; this last being the interval between the front lens of an objective and the object examined, when the latter is in proper focus. With high power objectives the object must be very close to the lens, and at a proportionately greater distance as the magnification is less.
Fig. 8 a, b, c shows sections of the Lenses employed in the construction of the microscope, viz., double-convex, plano-convex, and plano-concave, the last-mentioned being used to modify the course of the rays passing through convex lenses to obviate certain imperfections, the nature of which should be understood so as to aid in their detection. One of these imperfections is called Spherical Aberration, and it is rendered obvious by viewing through the microscope a glass slide on which a fine network of squares is ruled. Fig. 9 B represents what is seen with a proper performance of the properly corrected instrument, whilst the distorted appearance of A and C indicate opposite kinds of aberration, caused by lenses imperfectly corrected. The greater the distortion, the more faulty of course are
the lenses. Eye-pieces and objectives thoroughly corrected and free from Spherical aberration are said to be Aplanatic.
Another imperfection of the lenses is that termed Chromatic aberration. It is the cause of the tinting of
colourless objects, and of the coloured fringes so frequently seen surrounding objects viewed through imperfect instruments. Lenses free from this defect are said to be Achromatic.
The Chromatic and Spherical aberration of a lens may be diminished by reducing the aperture with a stop or diaphragm, so that only its central portion is employed, but complete correction is only secured by utilizing different shaped lenses, as already indicated, and lenses of different kinds of glass. Objectives of the cheaper kind and especially those of foreign manufacture, have often only a front lens, but the majority of good objectives are built up in the compound form, each lens consisting of two kinds of glass of different optical properties, cemented together with a transparent medium such as Canada Balsam; and the parting or cracking of the said medium may render an objective practically useless until re-cemented. Fig. 10 shows the arrangement of three pairs of lenses, 1, 2, 3 ; each pair formed of a double convex of crown glass, and a plano-convex of flint glass.
A considerable variety of magnifying power may be obtained by altering the position of lenses in respect to each other and to the object, as shown in the employment of the draw tube ; amplification may be obtained in this way or by using higher power eyepieces, but in the latter case often at the expense of good definition ; for defects of the object glass which are not perceptible when the image it forms is but moderately enlarged, are brought into prominence when the imperfect image is magnified or amplified to a much greater extent ; so that in practice it is found better to vary the power by employing objectives of different magnification.
Eye-pieces are made of various magnifying powers, but always comparatively low ones ; the range is generally indicated by letters A, B, C, etc., or by numerals,1, 2, 3, etc., the power increasing from A and 1 respectively.
Object glasses or Objectives are usually designated by their focal distance from the object, viz., 1 in., 1/4 in., 1/8 in., and so on, but in nearly all cases the distance at which they focus is less than that implied by the figures, which consequently give an imperfect idea of the real magnifying power. Generally speaking, objectives range from 4 in., giving with an A eye-piece some 10 diameters magnification, to 1/50 in. giving 3,000 diameters; but for Brewers’ purposes two objectives, a 1 1/2 in. or 1 in. giving 30 to 50 diameters, and a 1/5 or 1/8 in. yielding 300 to 400 diameters—according to the particular maker—suffice. With these objectives, one good eye-piece a little stronger than an ordinary A, should be provided ; or if expense is not so much an object, both A and B eye-pieces may be included. Many opticians now provide tables in their catalogues giving the magnifying power of the combinations.
We may here remark that a really good combination giving only 200 diameters of magnification, will show Yeast and Bacteria with considerable distinctness of detail as regards the former, and of size and shape as regards the latter ; and it is far preferable to work with excellent lenses magnifying some 200 diameters, than with a poor combination magnifying double as much, for the latter case means constant annoyance and irritation from the imperfect performance.
The amount of light admitted by an Object glass is of considerable importance, and depends in great measure on what is called the Angle of Aperture, which is the angle formed by two lines from opposite sides of the aperture of the Objective with its focus. (See Fig. 10 a, b, c.) Glasses with a high angle of aperture admit much light, but focussing so close to the object they entail considerable inconvenience in general work ; those of medium angle are preferable, combining as they should, Power of Penetration and Brightness of Field. The latter term speaks for itself; by the former, is meant the capability of the glass to give a correct view of an object possessing an appreciable depth. Power of penetration should not be confounded with Resolving power, which is the capability of resolving or dividing the component parts of a minute object, such as the markings on Diatoms, or the closely-ruled lines of a test plate: this resolving power is dependent also on angle of aperture, the higher-angled apertures having a greater resolving power. It will thus be seen that this quality is opposed to that of penetration, which is possessed by glasses of low or moderate aperture, and that the two requisites can only be combined in the same objective by some sacrifice of each. The purpose for which the instrument is required must govern the choice of “powers.”
Another desideratum in an objective is Flatness of Field, which means that the whole of a large flat object should be in correct focus at once, even to the extreme margin of the field of view ; and the same correctness of focus should be exhibited by objects lying in the same plane. This quality is of the most importance in the lower powers with which large objects are usually examined ; in the case of glasses of short focus, as a 1/4 in. or higher power, the object is usually a minute one, and generally placed in the centre of the field ; and if in the margin of it, the slight alteration of focus necessary, causes little trouble.
The varying refraction of the thin glass, covering an object, renders an adjustment of the higher power objectives necessary, and especially so in glasses of high angle of aperture; it is usually effected by altering the distance between the front and second pair of glasses. An engraved line on the brass mount shows the point to which the lens should be set for uncovered objects. Its adjustment for covered objects is effected in the following manner: —
Arrange the objective as if for an uncovered object. Focus any covered object by moving the tube of the microscope ; next move the milled adjustment ring of the objective till particles of dust on the upper surface of the cover-glass are brought into focus. The objective is now corrected for the thickness of the cover-glass, and it only remains to re-focus the object with the tube adjustments.
Many of the high power objectives now in use are worked on the immersion system, which consists in the interposition of a drop of water or oil—generally Cedar oil—between the front lens of the objective, and either the object itself or its cover-glass. It is of course, requisite that the objective should be specially corrected for such use. The advantages gained are a considerable increase of working distance and penetration.
We will conclude this chapter with a few words on the choice of a microscope, first summarizing the qualities of a really good instrument. They are :—
A fairly large and well-illuminated field of view. Freedom from Chromatic and Spherical aberration. Good definition and penetration.
Flatness of field.
Unless the Brewer has had some experience, it is better, in purchasing a microscope, to secure the good offices of someone who knows what a Brewery microscope should be capable of doing, and what is really good value for the amount of money it is purposed to expend ; for with the best intentions on the part of the maker, his want of appreciation of the special purpose to which the instrument is to be applied, may cause him to forward a disappointing or unsuitable article.
There are, at the present time, so many makers of excellent microscopes at a moderate price, such as—Messrs. Baker, Beck, Browning, Crouch, Steward, Swift, and Watson ; and amongst foreign makers, MM. Seibert and Zeiss
—that it would be invidious to make any special selection for recommendation ; suffice it to say that the authors have made the chief part of their observations with the more complete form of Swift’s College microscope, than which, at the price, no more satisfactory instrument has ever been in their hands. With Messrs. Swift & Son’s permission, a drawing of this microscope is given as the frontispiece.
CHAPTER II.
On Manipulation.
IN the first place it is obviously of necessity that the lenses of the microscope should be scrupulously clean. This is best secured by carefully wiping them with a cleansed and softened wash-leather, glass-cloth, or silk handkerchief; some soft fabric that does not “ lint ” is essential. Specks of dust on the glasses of the eye-piece may be detected by turning it round whilst looking through the instrument, as any such specks will be found to move with the eye-piece. In cleaning objectives great care must be exercised, and it is seldom necessary to interfere with their inner glasses.
The same attention should be occasionally bestowed on the Stand, and where the microscope is in frequent use, it may conveniently be kept under a Bell-glass, or glass shade, with chenille edging to exclude dust, in which case there is no objection to the powers remaining attached. The instrument must not stand in a damp place, and on no account let any liquid accidentally taken up by the objective, remain and dry upon it. Especial caution must be exercised in this respect with reagents used in the examination of an object. Ordinary care should obviate any contact at all between the objective and substances under examination. Oil or water immersion lenses should be cleaned after use.*
Glass slips and cover-glasses after use, if not immediately cleaned and dried, may be placed in separate vessels containing water ; this precludes the nuisance of their becoming cemented together by the drying up of liquids contained between them. Two small jam-pots are sufficiently good receptacles, that for the cover-glasses being the smaller, and having preferably a curved bottom ; the water should be renewed frequently, and if slightly acidulated, deposition of Carbonate of Lime is prevented ; or distilled water may be employed. After cleaning and drying, it is a good plan to keep the cover-glasses and slips in a wash-leather case, sewn into separate compartments. (Fig. 11.)
The microscope should stand on a steady table or desk of convenient height, say from 24 to 30 inches, according to the size of the instrument. Should the room be subject to vibrations from machinery, etc., it is well to have the legs of the table on thick India-rubber pads, and the microscope on a sheet of the same material. It is decidedly better to work seated, and a revolving study chair is a great convenience. The instrument should be placed in a good
* A little turpentine may be used if necessary to remove Cedar and other oils.
