Any object which is to be viewed under the microscope must, of course, be supported in some way—this is now usually done by placing it upon a glass slide, which on account of the transparency has a great advantage over other substances. These “slides” are almost always made of one size, viz., three inches long by one broad, generally having the edges ground so as to remove all danger of scratching or cutting any object with which they may come in contact. The glass must be very good, else the surface will always2 present the appearance of uncleanliness and dust. This dusty look is very common amongst the cheaper kinds of slides, because they are usually “sheet” glass; but is seldom found in those of the quality known amongst dealers3 by the name of “patent plate.” This latter is more expensive at first, but in the end there is little difference in the cost, as so many of the cheaper slides cannot be used for delicate work if the mounted object is to be seen in perfection. These slides vary considerably4 in thickness; care should, therefore, be taken to sort them, so that the more delicate objects with which the higher powers are to be used maybe mounted upon the thinnest, as the light employed in the illumination is then less interfered6 with. To aid the microscopist in this work, a metal circle may be procured7, having a number of different sized openings on the outer edge, by which the glass slides can be measured. These openings are numbered, and the slides may be separated according to these numbers; so that when mounting any object there will be no need of a long search for that glass which is best suited to it.
When fresh from the dealer’s hands, these slides are generally covered with dust, &c., which may be removed by well washing in clean rain-water; but if the impurity9 is obstinate10, a little washing soda11 may be added, care being taken, however, that every trace of this is removed by subsequent waters, otherwise the crystals will afterwards form upon the surface. A clean linen12 cloth should be used to dry the slides, after which they may be laid by for use. Immediately, however, before being used for the reception of objects by any of the following processes, all dust must be removed by rubbing the surface with clean wash-leather or a piece of cambric, and, if needful, breathing upon it, and then using the leather or cambric until perfectly dry. Any small particles left upon the surface may generally be removed by blowing gently upon it, taking care to allow no damp to remain.
We have before said, that any object to be viewed in the3 microscope must have its support; but if this object is to be preserved, care must be taken that it is defended from the dust and other impurities13. For this purpose it is necessary to use some transparent14 cover, the most usual at one time being a plate of mica15, on account of its thinness; this substance is now, however, never used, thin glass being substituted, which answers admirably. Sometimes it is required to “take up” as little space as possible, owing to the shortness of focus of the object-glasses. It can be procured of any thickness, from one-fiftieth to one-two-hundred-and-fiftieth of an inch. On account of its want of strength it is difficult to cut, as it is very liable to “fly” from the point of the diamond. To overcome this tendency as much as possible, it must be laid upon a thicker piece, previously16 made wet with water, which causes the thin glass to adhere more firmly, and consequently to bear the pressure required in cutting the covers. The process of cutting being so difficult, especially with the thinner kinds, little or nothing is gained by cutting those which can be got from the dealers, as the loss and breakage is necessarily greater in the hands of an amateur. It is convenient, however, to have on hand a few larger pieces, from which unusual sizes may be cut when required.
If the pieces required are rectangular, no other apparatus17 will be required save a diamond and a flat rule; but if circles are wanted, a machine for that purpose should be used (of which no description is necessary here). There are, however, other contrivances which answer tolerably well. One method is, to cut out from a thick piece of cardboard a circle rather larger than the size wanted. Dr. Carpenter recommends metal rings with a piece of wire soldered18 on either side; and this, perhaps, is the best, as cardboard is apt to become rough at the edge when much used. A friend of mine uses thin brass19 plates with circles of various sizes “turned” through them, and a small raised handle placed at one end. The diamond must be passed round the inner edge, and so managed as to meet4 again in the same line, in order that the circle may be true, after which they may be readily disengaged. The sizes usually kept in stock by the dealers are one-half, five-eighths, and three-quarters inch diameter; but other sizes may be had to order.
For the information of the beginner it may be mentioned here that the price of the circles is a little more than of the squares; but this is modified in some degree by the circle being rather lighter20. If appearance, however, is cared for at all, the circles look much neater upon the slides when not covered with the ornamental21 papers; but if these last are used (as will shortly be described) the squares are equally serviceable.
As before mentioned, the thin glass is made of various thicknesses, and the beginner will wish to know which to use. For objects requiring no higher power than the one-inch object-glass, the thicker kinds serve well enough; for the half-inch the medium thickness will be required; while, for higher powers, the thinnest covers must be used. The “test-objects” for the highest powers require to be brought so near to the object-glass that they admit of the very thinnest covering only, and are usually mounted betwixt glasses which a beginner would not be able to use without frequent breakage; but if these objects were mounted with the common covers, they would be really worthless with the powers which they require to show them satisfactorily.
It may be desirable to know how such small differences as those betwixt the various thin glass covers can be measured. For this purpose there are two or three sorts of apparatus, all, however, depending upon the same principle. The description of one, therefore, will be sufficient. Upon a small stand is a short metal lever (as it may be termed) which returns by a spring to one certain position, where it is in contact with a fixed22 piece of metal. At the other end this lever is connected with a “finger,” which moves round a dial like that of a watch, whereupon are figures at fixed distances. When the lever is separated from the metal5 which is stationary23, the other end being connected with the “finger” of the dial, that “finger” is moved in proportion to the distance of the separation. The thin glass is, therefore, thrust betwixt the end of the lever and fixed metal, and each piece is measured by the figures on the dial in stated and accurate degrees. This kind of apparatus, however, is expensive, and when not at our command, the thin glass may be placed edgewise in the stage forceps, and measured very accurately24 with the micrometer.
Cleanliness with the thin glass is, perhaps, more necessary than with the slides, especially when covering objects which are to be used with a high power; but it is far more difficult to attain25, on account of the liability to breakage. The usual method of cleaning these covers is as follows:—Two discs of wood, about two inches in diameter, are procured, one side of each being perfectly flat and covered with clean wash-leather. To the other side of these a small knob is firmly affixed26 as a handle, or where practicable the whole may be made out of a solid piece. In cleaning thin glass, it should be placed betwixt the covered sides of the discs, and may then be safely rubbed with a sufficient pressure, and so cleaned on both sides by the leather. If, however, the glass be greasy28, as is sometimes the case, it must be first washed with a strong solution of potash, infusion29 of nut-galls, or any of the commonly used grease-removing liquids; and with some impurities water, with the addition of a few drops of strong acid, will be found very useful, but this last is not often required.
The above method of cleaning thin glass should always be used by beginners; but after some experience the hand becomes so sensitive that the above apparatus is often dispensed30 with, and the glasses, however thin, may be safely cleaned betwixt the fingers and thumb with a cambric handkerchief, having first slightly damped the ends of the fingers employed to obtain firm hold. When the dirt is very obstinate, breathing upon the glass greatly facilitates its removal, and the sense of touch becomes so delicate that6 the breakage is inconsiderable; but this method cannot be recommended to novices32, as nothing but time spent in delicate manipulation can give the sensitiveness required.
It was before mentioned that the ordinary glass slides were sometimes worthless, especially for fine objects, from having a rough surface, which presented a dusty appearance under the microscope. This imperfection exists in some thin glass also, and it is irremediable; so that it is useless to attempt to cleanse33 it; nevertheless, care should be taken not to mistake dirty glass for this roughness, lest good glass be laid aside for a fault which does not really belong to it.
When any object which it is desired to mount is of considerable thickness, or will not bear pressure, it is evident that a wall must be raised around it to support the thin glass—this is usually termed a “cell.” There are various descriptions of these, according to the class of objects they are required to protect; and here may be given a description of those which are most generally used in mounting “dry” objects, leaving those required for the preservation34 of liquids until we come to the consideration of that mode of mounting. Many have made use of the following slides. Two pieces of hard wood of the usual size (3 in. by 1 in.), not exceeding one-sixteenth of an inch in thickness, are taken, and a hole is then drilled in the middle of one of these of the size required. The two pieces are then united by glue or other cement, and left under pressure until thoroughly35 dry, when the cell is fit for use. Others substitute cardboard for the lower piece of wood, which is less tedious, and is strong enough for every purpose. This class of “cell” is, of course, fitted for opaque36 objects only where no light is required from below; and as almost all such are better seen when on a dark background, it is usual to fix a small piece of black paper at the bottom of the cell upon which to place them. For very small objects the “grain” which all such paper has when magnified detracts a little from the merit of this background; and lately I have used7 a small piece of thin glass covered on the back with black varnish37, and placed the object upon the smooth untouched side.
Another method of making these cells is as follows:—Two “punches,” similar to those used for cutting “gun-wads,” are procured, of such sizes that with the smaller may be cut out the centre of the larger, leaving a ring whose side is not less than one-eighth of an inch wide. These rings may be readily made, the only difficulty being to keep the sides parallel; but a little care will make this easy enough. For this purpose close-grained cardboard may be conveniently used. It must have a well-glazed surface, else the varnish or cement used in affixing38 the thin glass cover sinks into the substance, and the adherence39 is very imperfect. When this takes place it is easily remedied by brushing over the surface of the cardboard a strong solution of gum or isinglass; and this application, perhaps, closes also the pores of the card, and so serves a double purpose. But, of course, the gum must be perfectly dried before the ring is used.
For cardboard, gutta-percha has been substituted, but cannot be recommended, as it always becomes brittle40 after a certain time, never adheres to the glass with the required firmness, and its shape is altered when worked with even a little heat. Leather is often used, and is very convenient; it should be chosen, however, of a close texture41, and free from oil, grease, and all those substances which are laid upon it by the “dressers.”
Rings of cardboard, &c., have been rejected by persons of great experience, because they are of such a nature that dampness can penetrate42 them. This fault can be almost, if not totally, removed by immersing them in some strong varnish, such as the asphalt varnish hereinafter mentioned; but they must be left long enough when affixed to the glass slide to become perfectly dry, and this will require a much longer time than at first would be supposed.
There has, however, been lately brought out what is8 termed the ivory cell. This is a ring of ivory-like substance, which may be easily and firmly fixed to the glass slide by any of the commonly-used cements, and so forms a beautiful cell for any dry objects. They are made of different sizes, and are not expensive.
Sometimes slides are used which are made by taking a thin slip of wood of the usual size (3 in. by 1 in.), in the centre of which is cut a circular hole large enough to receive the object. A piece of thin glass is fixed underneath43 the slide, forming a cell for the object, which may then be covered and finished like an ordinary slide. This has the advantage of serving for transparent objects for which the before-mentioned wooden slides are unsuitable. A slight modification44 of this plan is often used where the thickness of the objects is inconsiderable, especially with some of the Diatomace?, often termed “test-objects.” The wooden slide is cut with the central opening as above, and two pieces of thin glass are laid upon it, betwixt which the diatoms or other objects are placed, and kept in their proper position by a paper cover. This arrangement is a good one, insomuch as the very small portion of glass through which the light passes on its way to the microscope from the reflector causes the refraction or interference to be reduced to the lowest point.
A novice31 would naturally think the appearance of some of the slides above mentioned very slovenly45 and unfinished; but they are often covered with ornamental papers, which may be procured at almost every optician’s, at a cost little more than nominal46, and of innumerable patterns and colours. How to use these will be described in another place.
It is very probable that a beginner would ask his friend what kind of slides he would advise him to use. Almost all those made of wood are liable to warp47 more or less, even when the two pieces are separate or of different kinds; those of cardboard and wood are generally free from this fault, yet the slides, being opaque, prevent the employment of9 the Lieberkuhn. To some extent glass slides, when covered with ornamental papers, are liable to the same objection, as the light is partly hindered. And sometimes the dampness from the paste, or other substance used to affix27 the papers, penetrates48 to the object, and so spoils it, though this may be rendered less frequent by first attaching the thin glass to the slide by some harder cement. Much time, however, is taken up by the labour of covering the slides, which is a matter of consideration with some. Certainly, the cost of the glass slides was formerly49 great; but now they are reasonable enough in this respect, so that this objection is removed. It is, therefore, well to use glass slides, except where the thin glasses are employed for tests, &c., as above. When the thin glass circles are placed upon the slides, and the edge is varnished50 with black or coloured rings, the appearance of finish is perfect. The trouble is much less than with most of the other methods, and the illumination of the object very slightly interfered with.
To varnish the edges of these covers, make circles of any liquid upon the glass slide, and perform any other “circular” work mentioned hereafter, the little instrument known as “Shadbolt’s turntable” is almost indispensable. It is made as follows:—At one end of a small piece of hard wood is fixed an iron pivot51 about one-eighth inch thick, projecting half an inch from the wood, which serves as a centre upon which a round brass table three inches in diameter revolves53. On the surface of this are two springs, about one and a half inches apart, under which the slide is forced and so kept in position, whilst the central part is left open to be worked upon. The centre is marked, and two circles half an inch and one inch in diameter are usually deeply engraved54 upon the table to serve as guides in placing the slide, that the ring may be drawn55 in the right position. When the slide is placed upon the “table” underneath the springs, a camel-hair pencil is filled with the varnish, or other medium used, and applied56 to the surface of the glass; the10 table is then made to revolve52, and a circle is consequently produced, the diameter of which it is easy to regulate.
Many objects for the microscope may be seriously injured by allowing the fingers to touch them—many more are so minute that they cannot be removed in this way at all, and often it is necessary to take from a mass of small grains, as in sand, some particular particle. To accomplish this, there are two or three contrivances recommended: one by means of split bristles57, many of which will readily be found in any shaving brush when it has been well used. The bristles when pressed upon any hard surface open, and when the pressure is removed close again with a spring; but the use of these is limited. Camel-hair pencils are of great service for this and many other purposes to the microscopist. In very fine work they are sometimes required so small that all the hairs with the exception of one or two finer pointed58 ones are removed. A few of various sizes should always be kept on hand.
Equally necessary are fine pointed needles. They are very readily put up for use by thrusting the “eye” end into a common penholder, so as to be firm. The points may be readily renewed, when injured, on a common whetstone; but when out of use they may be protected by being thrust into a piece of cork59.
Knives of various kinds are required in some branches of microscopic60 work, but these will be described where “dissection,” &c., is treated at some length, as also various forms of scissors. In the most simple objects, however, scissors of the usual kind are necessary. Two or three sizes should always be kept at hand, sharp and in good order.
A set of glass tubes, kept in a case of some sort to prevent breakage, should form part of our “fittings” and be always cleaned immediately after use. These are generally from six to ten inches long and from one-eighth to a quarter of an inch in diameter. One of these should be straight and equal in width at both ends; one should be11 drawn out gradually to a fine point; another should be pointed as the last, but be slightly curved at the compressed end, in order to reach points otherwise unattainable. It is well to have these tubes of various widths at the points, as in some waters the finer would be inevitably61 stopped. For other purposes the fine ones are very useful, especially in the transfer of “preservative62 liquids” which will come under notice in another chapter.
Forceps are required in almost all microscopic manipulations, and consequently are scarcely ever omitted from the microscopic box, even the most meagrely furnished; but of these there are various modifications63, which for certain purposes are more convenient than the usual form. The ordinary metal ones are employed for taking up small objects, thin glass, &c.; but when slides are to be held over a lamp, or in any position where the fingers cannot conveniently be used, a different instrument must be found. Of these there are many kinds; but Mr. Page’s wooden forceps serve the purpose very well. Two pieces of elastic64 wood are strongly bound together at one end, so that they may be easily opened at the other, closing again by their own elasticity65. Through the first of these pieces is loosely passed a brass stud, resembling a small screw, and fastened in the second, and through the second a similar stud is taken and fixed in the first—so that on pressure of the studs the two strips of wood are opened to admit a slide or other object required to be held in position. The wood strips are generally used three or four inches long, one inch wide, and about one-eighth inch thick.
Again, some objects when placed upon the glass slide are of such an elastic nature that no cement will secure the thin glass covering until it becomes hard. This difficulty may be overcome by various methods. The following are as good and simple as any. Take two pieces of wood about two inches long, three-quarters wide, and one-quarter thick; and a small rounded piece one inch long and one-quarter in diameter; place this latter betwixt the two larger pieces.12 Over one end of the two combined pass an india-rubber band. This will give a continual pressure, and may be opened by bringing the two pieces together at the other end; the pressure may be readily made uniform by paring the points at the inner sides, and may be regulated by the strength of the india-rubber band. These bands may be made cheaply, and of any power, by procuring66 a piece of india-rubber tubing of the width required, and cutting off certain breadths. Another very simple method of getting this pressure is mentioned in the “Micrographic Dictionary.” Two pieces of whalebone of the length required are tied together firmly at each end. It is evident that any object placed betwixt them will be subject to continual pressure. The power of this may be regulated by the thickness and length of the whalebone. This simple contrivance is very useful.
Common watch-glasses should always be kept at hand. They are certainly the cheapest, and their transparency makes them very convenient reservoirs in which objects may be steeped in any liquid; as it saves much trouble to examine cursorily67 under the microscope, when the air-bubbles are expelled from insects, &c., &c. They are readily cleaned, and serve very well as covers, when turned upside down, to protect any objects from the dust. For this latter purpose Dr. Carpenter recommends the use of a number of bell-glasses, especially when one object must be left for a time (which often happens) in order that another may be proceeded with. Wine glasses, when the “legs” are broken, may thus be rendered very useful.
As heat is necessary in mounting many objects, a lamp will be required. Where gas is used, the small lamp known as “Bunsen’s” is the most convenient and inexpensive. It gives great heat, is free from smoke, and is readily affixed to the common gas-burner by a few feet of india-rubber tubing. The light from these lamps is small, but this is little or no drawback to their use. Where gas is not13 available, the common spirit-lamps may be used, which are very clean and answer every purpose.
In applying the required heat to the slides, covers, &c., it is necessary in many cases to ensure uniformity, otherwise there is danger of the glass being broken. For this purpose a brass plate at least three inches wide, somewhat longer, and one-eighth of an inch thick, must be procured. It should then be affixed to a stand, so that it may be readily moved higher or lower, in order that the distance from the lamp may be changed at will, and thus the degree of heat more easily regulated. This has also the advantage of enabling the operator to allow his slides, &c., to cool more gradually, which, in some cases, is absolutely necessary,—as in fusing some of the salts, &c.
In order to get rid of air-bubbles, which are frequently disagreeable enemies to the mounter of objects, an air-pump is often very useful. This is made by covering a circular plate of metal with a bell-glass, both of which are ground so finely at the edges that greasing the place of contact renders it air-tight. The pump is then joined to the metal plate underneath, and worked with a small handle like a common syringe. By turning a small milled head the air may be allowed to re-enter when it is required to remove the bell-glass and examine or perform any operation upon the object. The mode of using this instrument will be described hereafter, but it may be here stated that substitutes have been devised for this useful apparatus; but as it is now to be obtained at a low cost, it is hardly worth while to consider them. Much time is, in many instances, certainly saved by its use, as a very long immersion68 in the liquids would be required to expel the bubbles, where the air-pump would remove them in an hour.
The next thing to be considered is what may be termed Cements, some of which are necessary in every method of mounting objects for the microscope. Of these will be given the composition where it is probable the young student can make use of it; but many of them are so universally kept14 as to be obtainable almost anywhere; and when small quantities only are required, economy suffers more from home manufacture than from paying the maker’s profit.
Amongst these, Canada Balsam may, perhaps, be termed the most necessary, as it is generally used for the preservation of many transparent objects. It is a thick liquid resin69 of a light amber70 colour, which on exposure to the atmosphere becomes dry and hard even to brittleness71. For this reason it is seldom used as a cement alone where the surface of contact is small, as it would be apt to be displaced by any sudden shock, especially when old. In the ordinary method of using, however, it serves the double purpose of preserving the object and fixing the thin glass cover; whilst the comparatively large space upon which it lies lessens72 the risk of displacement73. By keeping, this substance becomes thicker; but a very little warmth will render it liquid enough to use even when to some extent this change has taken place. When heated, however, for some time and allowed to cool, it becomes hardened to any degree, which may be readily regulated by the length of time it has been exposed, and the amount of heat to which it has been subjected. On account of this property it is often used with chloroform: the balsam is exposed to heat until, on cooling, it assumes a glassy appearance; it is then dissolved in pure chloroform until it becomes of the consistence of thick varnish. This liquid is very convenient in some cases; as air-bubbles are much more easily got rid of than when undiluted Canada balsam is used. It also dries readily, as the chloroform evaporates very quickly, for which reason it must be preserved in a closely-stoppered bottle. It has been said that this mixture becomes cloudy with long keeping, but I have not found it so in any cases where I have used it. Should it, however, become so, a little heat will readily dispel74 the opacity75. The ordinary balsam, if exposed much to the air whilst being used, becomes thicker, as has been already stated. It may be reduced to the required consistency76 with common turpentine,15 but I have often found this in some degree injurious to the transparency of the balsam, and the amalgamation77 of the two is by no means perfect. (See also Chapter III.) The cheapness of the article renders it no extravagance to use it always undiluted; and when preserved in a bottle with a hollow cover fitting tightly around the neck, both surfaces being finely ground, it remains78 fit for use much longer than in the ordinary jar.
Asphaltum.—This substance is dissolved in linseed oil, turpentine, or naphtha, and is often termed “Brunswick black.” It is easily worked, but is not generally deemed a trustworthy cement, as after a time it is readily loosened from its ground. It is, however, very useful for some purposes (such as “finishing” the slides), as it dries quickly. I shall, however, mention a modification of this cement a little further on.
Marine79 Glue.—No cement is more useful or trustworthy for certain purposes than this. It is made in various proportions; but one really good mixture is—equal parts of india-rubber and gum shellac; these are dissolved in mineral naphtha with heat. It is, however, much better to get it from the opticians or others who keep it. It requires heat in the application, as will be explained in Chapter IV.; but it is soluble80 in few, if any, liquids used by the microscopist, and for that reason is serviceable in the manufacture of cells, &c. Where two pieces of glass are to be firmly cemented together, it is almost always employed; and in all glass troughs, plates with ledges81, &c., the beginner may find examples of its use.
Gold Size.—This substance may always be procured at any colourman’s shop. The process of its preparation is long and tedious. It is, therefore, not necessary to describe it here. Dr. Carpenter says that it is very durable82, and may be used with almost any preservative liquids, as it is acted upon by very few of them, turpentine being its only true solvent83. If too thin, it may be exposed for awhile to the open air, which by evaporation84 gradually thickens it.16 Care must be taken, however, not to render it too thick, as it will then be useless. A small quantity should be kept on hand, as it is much more adhesive85 when old.
Liquid Glue is another of these cements, which is made by dissolving gum shellac in naphtha in such quantity that it may be of the required consistency. This cement appears to me almost worthless in ordinary work, as its adherence can never be relied upon; but it is so often used and recommended that an enumeration86 of cements might be deemed incomplete without it. Even when employed simply for varnishing87 the outside of the glass covers, for appearance’ sake alone, it invariably chips. Where, however, oil is used as a preservative liquid, it serves very well to attach the thin glass; but when this is accomplished88, another varnish less liable to “chip” must always be laid upon it. (See Chapter IV.)
Black Japan.—This is prepared from oil of turpentine, linseed oil, amber, gum anime, and asphalt. It is troublesome to make, and therefore it is much better to procure8 it at the shops. It is a really good cement, and serves very well to make shallow cells for liquids, as will be described in Chapter IV. The finished cell should be exposed for a short time to the heat of what is usually termed a “cool oven.” This renders it very durable, and many very careful manipulators make use of it for their preparations.
Electrical Cement.—This will be found very good for some purposes hereinafter described. To make it, melt together—
5 parts of resin.
1 ” beeswax.
1 ” red ochre.A
A Dr. Griffiths says that the addition of 2 parts of Canada balsam renders this cement much more adhesive to the glass.
It must be used whilst hot, and as long as it retains even slight warmth can be readily moulded into any form. It is17 often employed in making shallow cells for liquids, as before mentioned.
Gum-Water is an article which nobody should ever be without; but labels, or indeed any substance, affixed to glass with common gum, are so liable to leave it spontaneously, especially when kept very dry, that I have lately added five or six drops of glycerine to an ounce of the gum solution. This addition has rendered it very trustworthy even on glass, and now I never use it without. This solution cannot be kept long without undergoing fermentation, to prevent which the addition of a small quantity of any essential oil (as oil of cloves89, &c.), or one-fourth of its volume of alcohol, may be made, which will not interfere5 in any way with its use.
There is what is sometimes termed an extra adhesive gum-water, which is made with the addition of isinglass, thus:—Dissolve two drachms of isinglass in four ounces of distilled90 vinegar; add as much gum arabic as will give it the required consistency. This will keep very well, but is apt to become thinner, when a little more gum may be added.
All these, except one or two, are liquid, and must be kept in stoppered bottles, or, at least, as free from the action of the air as possible.
When any two substances are to be united firmly, I have termed the medium employed “a cement;” but often the appearance of the slides is thought to be improved by drawing a coloured ring upon them, extending partly on the cover and partly on the slide, hiding the junction91 of the two. The medium used in these cases I term a Varnish, and hereinafter mention one or two. Of course, the tenacity92 is not required to be so perfect as in the cements.
Sealing-wax Varnish is prepared by coarsely powdering sealing wax, and adding spirits of wine; it is then digested at a gentle heat to the required thickness. This is very frequently used to “finish” the slides, as before mentioned, and can easily be made of any colour by employing different18 kinds of sealing-wax; but is very liable to “chip” and leave the glass.
Black Varnish is readily prepared by adding a small quantity of lamp-black to gold-size and mixing intimately. Dr. Carpenter recommends this as a good finishing varnish, drying quickly and being free from that brittleness which renders some of the others almost worthless; but it should not be used in the first process when mounting objects in fluid.
Amongst these different cements and varnishes93 I worked a long time without coming to any decision as to their comparative qualities, though making innumerable experiments. The harder kinds were continually cracking, and the softer possessed94 but little adhesive power. To find hardness and adhesiveness95 united was my object, and the following possesses these qualities in a great degree:—
India-rubber ? drachm.
Asphaltum 4 oz.
Mineral naphtha 10 ”
Dissolve the india-rubber in the naphtha, then add the asphaltum—if necessary heat must be employed.
This is often used by photographers as a black varnish for glass, and never cracks, whilst it is very adhesive. Dr. Carpenter, however, states that his experience has not been favourable96 to it; but I have used it in great quantities and have never found it to leave the glass in a single instance when used in the above proportions. The objections to it are, however, I think easily explained, when it is known that there are many kinds of pitch, &c., from coal, sold by the name of asphaltum, some of which are worthless in making a microscopic cement. When used for this purpose, the asphaltum must be genuine and of the best quality that can be bought. The above mixture serves a double purpose—to unite the cell to the slide, and also as a “finishing” varnish. But it is perhaps more convenient to have19 two bottles of this cement, one of which is thicker than common varnish, to use for uniting the cell, &c.; the other liquid enough to flow readily, which may be employed as a surface varnish in finishing the slides.
The brushes or camel-hair pencils should always be cleaned after use; but with the asphalt varnish above mentioned it is sufficient to wipe off as carefully as possible the superfluous97 quantity which adheres to the pencil, as, when again made use of, the varnish will readily soften98 it; but, of course, it will be necessary to keep separate brushes for certain purposes.
Here it may be observed that every object should be labelled with name and any other descriptive item as soon as mounted. There are many little differences in the methods of doing this. Some write with a diamond upon the slide itself; but this has the disadvantage of being not so easily seen. For this reason a small piece of paper is usually affixed to one end of the slide, on which is written what is required. These labels may be bought of different colours and designs; but the most simple are quite as good, and very readily procured. Take a sheet of thin writing paper and brush over one side a strong solution of gum, with the addition of a few drops of glycerine as above recommended; allow this to dry, and then with a common gun-punch stamp out the circles, which may be affixed to the slides by simply damping the gummed surface, taking care to write the required name, &c., upon it before damping it, or else allowing it to become perfectly dry first.
There is one difficulty which a beginner often experiences in sorting and mounting certain specimens99 under the microscope, viz., the inversion100 of the objects; and it is often stated to be almost impossible to work without an erector. But this difficulty soon vanishes, the young student becoming used to working what at first seems in contradiction to his sight.
Let it be understood, that in giving the description of those articles which are usually esteemed101 necessary in the20 various parts of microscopic manipulation, I do not mean to say that without many of these no work of any value can be done. There are, as all will allow, certain forms of apparatus which aid the operator considerably; but the cost may be too great for him. A little thought, however, will frequently overcome this difficulty, by enabling him to make, or get made, for himself, at a comparatively light expense, something which will accomplish all he desires. As an example of this, a friend of mine made what he terms his “universal stand,” to carry various condensers102, &c., &c., in the following way:—Take a steel or brass wire, three-sixteenths or one-quarter inch thick and six or eight inches long; “tap” into a solid, or make rough and fasten with melted lead into a hollow, ball. (The foot of a cabinet or work-box answers the purpose very well.) In the centre of a round piece of tough board, three inches in diameter, make a hemispherical cavity to fit half of the ball, and bore a hole through from the middle of this cavity, to allow the wire to pass. Take another piece of board, about four inches in diameter, either round or square, and one-and-a-half or two inches thick, make a similar cavity in its centre to receive the other half of the ball, but only so deep as to allow the ball to fit tightly when the two pieces of board are screwed together, which last operation must be done with three or four screws. Let the hole for the wire in the upper part be made conical (base upwards), and so large as only to prevent the ball from escaping from its socket103, in order that the shaft104 may move about as freely as possible. Turn a cavity, or make holes, in the bottom of the under piece, and fill with lead to give weight and steadiness. This, painted green bronze and varnished, looks neat; and by having pieces of gutta-percha tubing to fit the shaft, a great variety of apparatus may be attached to it.
Again, a “condenser” is often required for the illumination of opaque objects. My ingenious friend uses an “engraver’s bottle” (price 6d.), fills it with water, and suspends it betwixt the light and the object. Where the21 light is very yellow, he tints105 the water with indigo106, and so removes the objectionable colour.
I merely mention these as examples of what may be done by a little thoughtful contrivance, and to remove the idea that nothing is of much value save that which is the work of professional workmen, and consequently expensive.
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1
perfectly
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| adv.完美地，无可非议地，彻底地 | |
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fully
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| adv.完全地，全部地，彻底地；充分地 | |
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dealers
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| n.商人( dealer的名词复数 )；贩毒者；毒品贩子；发牌者 | |
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considerably
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| adv.极大地；相当大地；在很大程度上 | |
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interfere
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| v.(in)干涉，干预；(with)妨碍，打扰 | |
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interfered
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| v.干预( interfere的过去式和过去分词 )；调停；妨碍；干涉 | |
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7
procured
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| v.（努力）取得， （设法）获得( procure的过去式和过去分词 )；拉皮条 | |
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procure
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| vt.获得，取得，促成；vi.拉皮条 | |
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impurity
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| n.不洁，不纯，杂质 | |
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obstinate
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| adj.顽固的，倔强的，不易屈服的，较难治愈的 | |
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11
soda
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| n.苏打水；汽水 | |
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12
linen
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| n.亚麻布，亚麻线，亚麻制品；adj.亚麻布制的，亚麻的 | |
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impurities
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| 不纯( impurity的名词复数 )； 不洁； 淫秽； 杂质 | |
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14
transparent
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| adj.明显的，无疑的；透明的 | |
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15
mica
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| n.云母 | |
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16
previously
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| adv.以前，先前（地） | |
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17
apparatus
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| n.装置，器械；器具，设备 | |
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18
soldered
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| v.（使）焊接，焊合( solder的过去式和过去分词 ) | |
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19
brass
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| n.黄铜；黄铜器，铜管乐器 | |
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20
lighter
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| n.打火机，点火器；驳船；v.用驳船运送；light的比较级 | |
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21
ornamental
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| adj.装饰的；作装饰用的；n.装饰品；观赏植物 | |
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22
fixed
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| adj.固定的，不变的，准备好的；(计算机)固定的 | |
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23
stationary
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| adj.固定的，静止不动的 | |
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24
accurately
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| adv.准确地，精确地 | |
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25
attain
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| vt.达到，获得，完成 | |
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26
affixed
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| adj.[医]附着的，附着的v.附加( affix的过去式和过去分词 )；粘贴；加以；盖（印章） | |
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27
affix
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| n.附件，附录 vt.附贴，盖(章)，签署 | |
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28
greasy
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| adj. 多脂的，油脂的 | |
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29
infusion
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| n.灌输 | |
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30
dispensed
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| v.分配( dispense的过去式和过去分词 )；施与；配（药） | |
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31
novice
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| adj.新手的，生手的 | |
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novices
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| n.新手( novice的名词复数 )；初学修士（或修女）；（修会等的）初学生；尚未赢过大赛的赛马 | |
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33
cleanse
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| vt.使清洁，使纯洁，清洗 | |
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34
preservation
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| n.保护，维护，保存，保留，保持 | |
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35
thoroughly
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| adv.完全地，彻底地，十足地 | |
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36
opaque
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| adj.不透光的；不反光的，不传导的；晦涩的 | |
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37
varnish
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| n.清漆；v.上清漆；粉饰 | |
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affixing
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| v.附加( affix的现在分词 )；粘贴；加以；盖（印章） | |
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39
adherence
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| n.信奉，依附，坚持，固着 | |
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40
brittle
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| adj.易碎的；脆弱的；冷淡的；(声音)尖利的 | |
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41
texture
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| n.(织物)质地；(材料)构造；结构；肌理 | |
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42
penetrate
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| v.透(渗)入；刺入，刺穿；洞察，了解 | |
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43
underneath
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| adj.在...下面，在...底下；adv.在下面 | |
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44
modification
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| n.修改，改进，缓和，减轻 | |
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45
slovenly
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| adj.懒散的，不整齐的，邋遢的 | |
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46
nominal
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| adj.名义上的；(金额、租金)微不足道的 | |
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47
warp
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| vt.弄歪，使翘曲，使不正常，歪曲，使有偏见 | |
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48
penetrates
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| v.穿过( penetrate的第三人称单数 )；刺入；了解；渗透 | |
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49
formerly
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| adv.从前，以前 | |
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50
varnished
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| 浸渍过的，涂漆的 | |
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51
pivot
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| v.在枢轴上转动；装枢轴，枢轴；adj.枢轴的 | |
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52
revolve
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| vi.(使)旋转；循环出现 | |
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53
revolves
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| v.（使）旋转( revolve的第三人称单数 )；细想 | |
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54
engraved
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| v.在（硬物）上雕刻（字，画等）( engrave的过去式和过去分词 )；将某事物深深印在（记忆或头脑中） | |
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55
drawn
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| v.拖，拉，拔出；adj.憔悴的，紧张的 | |
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56
applied
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| adj.应用的；v.应用，适用 | |
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57
bristles
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| 短而硬的毛发，刷子毛( bristle的名词复数 ) | |
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58
pointed
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| adj.尖的，直截了当的 | |
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59
cork
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| n.软木，软木塞 | |
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60
microscopic
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| adj.微小的，细微的，极小的，显微的 | |
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61
inevitably
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| adv.不可避免地；必然发生地 | |
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62
preservative
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| n.防腐剂；防腐料；保护料；预防药 | |
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63
modifications
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| n.缓和( modification的名词复数 )；限制；更改；改变 | |
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64
elastic
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| n.橡皮圈，松紧带；adj.有弹性的；灵活的 | |
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65
elasticity
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| n.弹性，伸缩力 | |
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66
procuring
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| v.（努力）取得， （设法）获得( procure的现在分词 )；拉皮条 | |
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67
cursorily
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| adv.粗糙地，疏忽地，马虎地 | |
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68
immersion
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| n.沉浸；专心 | |
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69
resin
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| n.树脂，松香，树脂制品；vt.涂树脂 | |
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70
amber
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| n.琥珀；琥珀色；adj.琥珀制的 | |
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71
brittleness
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| n.脆性，脆度，脆弱性 | |
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72
lessens
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| 变少( lessen的第三人称单数 )； 减少（某事物） | |
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73
displacement
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| n.移置，取代，位移，排水量 | |
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74
dispel
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| vt.驱走，驱散，消除 | |
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75
opacity
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| n.不透明；难懂 | |
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76
consistency
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| n.一贯性，前后一致，稳定性；(液体的)浓度 | |
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77
amalgamation
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| n.合并，重组；；汞齐化 | |
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78
remains
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| n.剩余物，残留物；遗体，遗迹 | |
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79
marine
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| adj.海的；海生的；航海的；海事的；n.水兵 | |
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80
soluble
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| adj.可溶的；可以解决的 | |
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81
ledges
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| n.（墙壁，悬崖等）突出的狭长部分( ledge的名词复数 )；（平窄的）壁架；横档；（尤指）窗台 | |
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82
durable
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| adj.持久的，耐久的 | |
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83
solvent
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| n.溶剂；adj.有偿付能力的 | |
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84
evaporation
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| n.蒸发，消失 | |
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85
adhesive
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| n.粘合剂；adj.可粘着的，粘性的 | |
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86
enumeration
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| n.计数，列举；细目；详表；点查 | |
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87
varnishing
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| 在（某物）上涂清漆( varnish的现在分词 ) | |
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88
accomplished
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| adj.有才艺的；有造诣的；达到了的 | |
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89
cloves
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| n.丁香（热带树木的干花，形似小钉子，用作调味品，尤用作甜食的香料）( clove的名词复数 )；蒜瓣(a garlic ~|a ~of garlic) | |
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90
distilled
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| adj.由蒸馏得来的v.蒸馏( distil的过去式和过去分词 )；从…提取精华 | |
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91
junction
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| n.连接，接合；交叉点，接合处，枢纽站 | |
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92
tenacity
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| n.坚韧 | |
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93
varnishes
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| 清漆的面（尤指木器或金属制品上的）( varnish的名词复数 )； 光泽面； 罩光漆 | |
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94
possessed
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| adj.疯狂的；拥有的，占有的 | |
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95
adhesiveness
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| 粘[附着，胶粘]性，粘附[胶粘]度 | |
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96
favourable
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| adj.赞成的，称赞的，有利的，良好的，顺利的 | |
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97
superfluous
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| adj.过多的，过剩的，多余的 | |
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98
soften
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| v.(使)变柔软；(使)变柔和 | |
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99
specimens
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| n.样品( specimen的名词复数 )；范例；（化验的）抽样；某种类型的人 | |
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100
inversion
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| n.反向，倒转，倒置 | |
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101
esteemed
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| adj.受人尊敬的v.尊敬( esteem的过去式和过去分词 )；敬重；认为；以为 | |
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102
condensers
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| n.冷凝器( condenser的名词复数 )；（尤指汽车发动机内的）电容器 | |
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103
socket
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| n.窝，穴，孔，插座，插口 | |
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104
shaft
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| n.(工具的)柄，杆状物 | |
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105
tints
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| 色彩( tint的名词复数 )； 带白的颜色； （淡色）染发剂； 痕迹 | |
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106
indigo
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| n.靛青，靛蓝 | |
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