Photo-micrography

Front matter

No. 54. STAND AND MAHOGANY £2 lls. 6d.

ID AND MAHOGANY CASE, !3 12s. 6d.

irrors. Spread of Jb'eet 7 inches.

Preface

Owing to the more complete knowledge of the subject gained by the experience of years, and perhaps in a measure to the advent of the perfected dry plate, Photography is being rapidly pressed into use to an extent hitherto little dreamed of. In point of fact, it may he said to have started in times past as an interesting amusement, but has now become an absolutely scientific and commercial necessity. Indeed, if we look around, we shall readily recognise this to be true, for there is scarcely any science nowadays that does not in some way seek its aid.

But it is of quite recent years that book illustrations of the highest order have been made by this method. Fine hand drawings of objects as seen in the microscope, for example, used to be all in demand, but now Photo-Micrography has stepped in their place, and pictures are produced with an accuracy hitherto unknown. They leave, too — which is a great advantage — no doubt in the reader’s mind as to the accuracy of the final result, for even the most captious critic is unable to state his belief that some of the details have been produced by the imagination of the artist, or by an exaggerated conception of an over-enthusiastic draughtsman.

But, like almost any art or science which reaches to a high degree of perfection, Photo-Micrography cannot be learnt in a moment, for it requires both knowledge and patience, practice and skill, to carry it out successfully.

It is to help those commencing the subject, and assist others who may be anxious to achieve the highest results, that this little book has been written. It consists, to a certain extent, of a collection of articles written at the request of the Proprietors of the Pharmaceutical Journal, and the Author desires to express his thanks to them, not only for their kindness in allowing him to reproduce the subjectmatter in book form, but also for granting the Publishers of this work a free use of all the blocks and photographs which they had the kindness to reproduce as plates in the articles to which reference has been made.

VI

PREFACE

The work, although entirely original — there being no “ paste and scissors ” in it — does not claim to be an exhaustive treatise on the subject, or pretend to be of classical importance. It has no pretensions of this kind whatever, but purports only to be an account of the experience of the writer, extending over many years, in most if not all departments of the subject. If any novelty can possibly be found it lies in the fact that not only are exact details given as to how most types of test objects can be photographed, but illustrations of the same are actually appended in the Frontispiece and Plates. As so large an amount of space, therefore, is occupied by Photo- Micrography practically considered and explained, so the Author has been compelled to his regret, by the limits of space, to omit all reference to the often better executed work of fellow- workers in the subject, and the reader must excuse, on the same grounds, the entire omission of all matters bibliographical or of an etiological nature.

Being only a book on Photo-Micrography and not on the microscope, so all theory, too, is purposely omitted, save so much as is necessary to render the text the more intelligible.

Notwithstanding the many “ shortcomings ” to be found, it is feared, by the critic, and the expression sometimes of opinion which may be given too dogmatically, perhaps, upon definite topics, the writer hopes the end may justify the means, and that, even if fellow-workers of less experience may not derive the benefit he hopes they may in perusing the chapters of this book, some may perchance be induced thereby to take up this interesting subject, one so particularly of use to the doctor, student, and the advanced chemist.

The reproductions throughout the whole work have been entirely made by Messrs. Dent & Co., art reproducers, Bromell’s Hoad, Clapham, and the Author is desirous of recording his thanks individually to Mr. A. Dent, of the firm, for the amount of care and patience he has so unsparingly bestowed upon them.

This Preface must not be allowed to conclude without the writer adequately expressing his obligations to the several firms who have so liberally allowed him the use of blocks, some taken especially for th is work ; and, not least because last, his thanks to his son, Mr. Harold Spitta, for his very great and continued assistance in all departments of the work, whether in producing the original photo-micrographs or in passing the sheets through the press.

Clapham, S.W Jan. 1899.

EDMUND J. SPITTA:

Contents

CHAP. PAGE

Introduction ........... i

II. Low-Power Work .......... 13

Introduction

By Photo-micrography is meant the art of photographing a magnified image. Seeing this implies reproduction of images of any amplification, so for convenience of description we may divide the subject into three heads :

1. Low-Power Work Tr eating1 with magnitudes from if to about io

diameters ;

2. Medium-Power Work, which deals from io to about 600 diameters ; and

3. High-Power or Critical Work, which, commencing where moderate ends, reaches to about 3000 diameters.

It would seem as if there existed in this arrangement a very unequal division of the subject, especially that low power work should not extend beyond 10 diameters; but it must be at once stated that up to this limit photo-micrography is quite a different matter, and indeed requires in point of fact an entirely different form of apparatus. We should, however, recommend those commencing to begin from the very commencement, inasmuch as the difficulties presented become greater and greater as the initial magnification increases.

Inasmuch as an artificial light is always required for all the three divisions of our subject, we shall first discuss illuminants in general.

A

Chapter I

Oil, incandescent gas, lime-light, and electricity have all been pressed into service. The first is a poor light, and when used necessitates a long exposure even with magnification of 200 to 300 diameters, but may be advantageously employed when using quite low-power work. Double wicks are to be avoided ; one large wick used edgeways, excepting under special circumstances, is found more suitable. Camphor mixed with the oil — the amount seems of but little moment — is used to remove a large amount of the smell, hut the best method really of getting over this trouble is to see that the lamp is scrupulously clean. For that purpose, the wick being removed, the whole lamp should be placed in absolutely boiling water and left- for a few minutes. After submitting it to a repeated washing, it should be well dried and the wick kept away in a stoppered bottle. When the lamp is now used, after these repeated washings, if no oil be spilled over any part of it in filling, there will be but little smell, and what is then left the camphor mostly removes.

Incandescent gas is very good for low-power work, but is objectionable on account of the fact that if “critical light be used, as explained hereafter, on focussing the mantle its uneven appearance is added to the picture, which, save under very exceptional circumstances, spoils its beauty.

But oil as well as incandescent gas are not to be recommended in high-power work for another leason. Both theory and practice demand the use of an illuminant for critical work with as near an approach as possible to a point of light. For the optical student this is easy to understand, but if the reader has any misgivings on the philosophy of the assertion, he can easily satisfy himself as to its correctness by consulting any elementary work on optics, and the formation of the optical image in the microscope.

Electric light on this score, however, offers the exact ideal of the photo-microscopist, as, of course, with the arc form, a point of light may be said to be continually

ILLUM1NANTS existent. One disadvantage, however, putting aside the difficulties of its production, maintenance, let alone its expense, outweighs all the advantages of its use. It arises from the fact that the point of light is always shifting : however slight, still it is frequently changing its position , so that the centring of the light with the optical axis of the microscope is frequently getting out of adjustment, and pictures with unequal illumination may as frequently result. In saying this we are fully aware that some photo-micrographers still champion its use, but we are equally cognisant of the fact that many have relinquished it on this very ground.

Still we feel bound to admit that the steadiness of the arc light has of late been much improved, and many lamps are now in the market of undoubted merit, to wit, one sold by Messrs. Newton & Co., Fleet Street, and another, which is perhaps better suited still, introduced by Pmss & Co. quite recently.

Lime light, however, is that mostly employed. It is used in two forms : the mixed jet, where the gases, oxygen and coal gas (or hydrogen), both under pressure controlled by regulators to be presently described, mix in the jet itself just before ignition ; and the blow -through form, which may often advantageously be employed for low-power work, when the oxygen under pressure blows through and into a stream of house gas issuing from an independent source, such as from the ordinary house tap, from which it is led to the jet by means of a piece of rubber tubing.

The Mixed Jet.— T 'here are several forms of “ mixed gas” jet, but space will not allow us a description of them all ; indeed, it does not seem to be necessary, as the same idea pervades the whole of them, and differences that do exist are those of minute detail rather than those of difference of construction. Jets do differ very much indeed from one another in performance, and we only mention some of those with which we are familiar.

Messrs. Newton & Co., of Fleet Street, the well-known opticians, sell an exceptionally fine jet designed by Mr. Lewis Wright, whose name, as associated with optical projection, is a household word. It has an ingenious means of cutting off the gases, we believe originally suggested by Mr. Pringle, of photo-micrograph ical fame. It is shown in Fig. i , where not only is the jet itself figured, but also an improved form of stand, quite lately introduced, which permits of lateral and up-and-down movement, both governed by milled-headed screws. This is of great service to the photo-micrographer as well as the ordinary lanternist. But the jet we have ourselves mostly used with so much satisfaction is the high-power form designed by Beard. It is shown in Fig. 2 and also in Fig. 3, where it is seen dropped over a pin which is attached to the special stand of our own design which enables the operator to

Fig. i move the light in all directions. The block almost explains itself. The ordinary arrangement for turning the lime is of course present, and in addition a handle for turning both gases down, when not immediately using the light, which is technically known as the “ cut off.” The oxygen is completely stopped by this arrangement, and only an exceedingly small amount of coal gas (regulated by a small additional thumbscrew, also shown in Fig. 3,) is allowed to pass on to the lime to keep it warm.

Underneath the jet is seen in Fig. 3 the stand of which we have spoken. One screw serves to shift the jet from side to side, the other raises it from below upwards, or vice versa, whereas a to-and-fro motion to enable the lime to approach nearer to or farther from the microscope or condenser is obtained by bevelling the wide foot of the stand itself so as it will pass evenly and smoothly through two guides fixed on the base board of whatever apparatus is used. This is a convenience, as the light can easily be shifted from one apparatus to another, as we shall presently show.

We have found this jet by Beard of sufficient intensity for all purposes, but still it is quite possible one of greater power might on special occasions be desirable. In this case we should recommend either the new jet by Gwyer (about which we shall very shortly speak), or the latest pattern quite recently introduced by Beard, or a still more modern jet by Boss & Co. to which our attention has been drawn whilst these pages were passing through the press. It is needless to ])oint out that these high-power jets use an enormous amount of gas, sometimes up to as much as 10 feet an hour of oxygen as well as of coal gas. In our experience we have compared most carefully the high power of Beard and the most intense form by Gwyer, and we have found that there is but a small difference in intensity of light between them ; but what exists, shows that the latter is a trifle the more powerful. Beard’s, however, has a much smaller bore, and we think burns less gas.

Messrs. Boss & Co.’s latest jet, to which we have just referred, is shown in Fig. 3a. The stand has several movements, and the jet is exceedingly powerful. We are informed that critical tests endorse the extreme power of this jet.

The Gwyer Jet, Fig. 4, is another form of mixed gas illuminant and one of great power. Although it has not been very long for sale, it has already won many warm adherents. It is exceedingly well made, and has in our hands, when dealing with it experimentally, produced the most admirable results of the greatest intensity. It is manufactured by Messrs. Will way & Sons, who are a guarantee for its perfection. The firm issue a very neat pamphlet of instructions for working it, and their remarks are so neatly compiled that with their permission we repeat them at length, as they apply almost equally well to any other form of mixed jet.

“ i. Always work up the light by increasing the hydrogen side first, then increasing the oxygen until the best light is obtained for that amount of hydrogen, and repeating this until the jet very slightly roars. Then reduce by turning the oxygen down first very slightly, then the hydrogen until the light is at its best and perfectly silent.

2. — Always work the taps very slowly and steadily when it is important to get the highest results.

3. — Attend carefully to the distance of the lime from the nipple of the jet, and do not forget that the more gas you turn on the greater the distance must be between the lime and the nipple, or you will get a black spot on the centre of the lime instead of a bright one. This is done after you have adjusted your taps by working the lime backwards and forwards until you have the light at its best. Roughly speaking, for a low pressure about inch will not be far oft’, gradually increasing the distance to § or \ inch, as you open the jet taps more and more to increase the light.

4. — For the most powerful light, rack the lime up until the jet plays almost upon the bottom of the lime cylinder, which should be rendered incandescent right up to the top, and where it is imperative to maintain light for a long time at the utmost power, it will be preferable to remove lime with the tongs and invert it rather than lower the level very much, so that no portion of its incandescent spot may be sacrificed.

5. — For the greatest light use large limes of medium hardness, but when only a moderate light with extreme economy of gas is required, it will be far better to use a medium-size lime ; very large hard limes do not yield such a rich light with a very low pressure of gas as a moderately hard medium-size lime ; on the other hand, such limes must be turned frequently when used with full pressure of gas, and when working the jet at its utmost power. The smaller the bore of the nipple the quicker the pitting of the lime.

6. — Do not forget to rime out the hole in the lime until it will drop easily upon pin ; if limes are forced down slightly upon the jet pin the expansion of the pin when heated must crack or burst the lime.

7. — If the jet becomes unduly hot by firing back it is probably leaking somewhere. Test the tap and front tube carefully : a very slight leak will cause trouble with a tV bore nipple.

8. — The Gwyer Jets will dissolve perfectly with a nipple even up to bore if the i dissolver is in good order. Never jerk the dissolver when using large bore nipples or jets with large mixing-chambers. Always move the handle slowly at first, but as quickly as you like after.

9. — Remember that you do not always get a strong light by turning on a large quantity of the gases. The mixture must be correct to get a perfect white light. There should be no hydrogen flame round the lime as with a blow-through. It is this flame that gives trouble with the heat.

The Gwyer Jet does not give a strong light by a larger consumption of gas, but through the more perfect mixture and adjustment of the gases.

10. — Keep the jet nipple clean and bright, and if your jet has a tendency to roar or hiss send it to the works to be tested. A very small accident will sometimes prevent the smooth working of a jet, and which generally takes only a few minutes to remedy. It is very rarely that any charge is made for repairs of this sort.

11. — The No. 1 and 2 jets are generally sent out with a TV inch bore nipple, but when not working to the full power a At inch bore may be used with advantage, and a lime of \ inch diameter.

1 2. — The size bore of the nipple should be in proportion to the light required if the jet is to be worked to the best advantage. A whiter light will be obtained with a Ar inch bore at full pressure than a TV inch at half pressure, each consuming approximately the same quantity of oxygen. The lime also should be proportional to the amount of light : a small lime will give the best result with a small bore nipple.”

Fig. 4a

The Blow-through Jet (Fig. 4a). — This form is the easier one to work, and to those commencing the safest. It consists of two tubes to which the oxygen and coal gas are respectively attached by india-rubber tubing. The coal gas is lighted first and the oxygen then turned on, which “ blows through ” the stream of coal gas, and then is made to impinge on the lime. Too much oxygen will blow out the coal gas, too little will give but a feeble light.

Whichever jet be used the oxygen must always be under pressure, and if the mixed form of jet be employed, the coal gas must be so as well. The compressed gas, whether oxygen or coal gas, is contained and stored in steel bottles, and as these receptacles have to be of sufficient strength to sustain enormous pressure — which, as a matter of fact, in a full-charged bottle is about eight times the amount employed in a modern locomotive — it is necessary to say a few words about them. We strongly advise every purchaser of one of these cylinders to go to the headquarters of the leading gas compressors in England — we refer to Messrs. Brin’s, of Horseferry Road, Westminster. Their cylinders may be considered absolutely safe, both for carriage and use, because the company have made the most careful and exhaustive tests and elaborate and costly experiments that can possibly be designed to ensure perfect workmanship, perfect material, and perfect testing. No expense has been spared in this department, and whether the customer orders it or not his cylinder is periodically overhauled and tested, being destroyed if showing the least signs of weakness.

We regret to say that one London firm apparently does not feel bound by the recommendation following the careful and rigorous investigations of the Board of Trade, and has been known to send out cylinders made of metal which is positively and absolutely condemned by the Board in question. This is a subject which should occupy the attention of every lanternist and user of the limelight, and they should avoid having anything to do with cylinders badly made. The only advice that can be given in the matter, seeing it is impossible for a customer to analyse the steel of the cylinder sent to him, is to have no compressed gas except from those who not only conform with the regulations of the Board of Trade in question, but who mainly were the investigators in the whole subject from the first. We refer to Brin’s Oxygen Co., of whom we have already spoken ; and in saying this it must be distinctly understood the writer has no interest directly or indirectly in the company, but merely makes this statement as a guide to those he is attempting by these remarks to assist.

One more point also should not be overlooked : seeing that the greatest danger is caused by mixing oxygen and hydrogen unless in a properly appointed jet, so it is exceedingly dangerous to have interchangeable cylinders, that is to say, those that can be filled to-day with oxygen and to-morrow with hydrogen, for it is very obvious that an explosive mixture may thereby be readily formed which, the instant the unfortunate operator applies a light, causes an explosion hardly less terrific than that of dynamite or gunpowder.

Brin’s Oxygen Co. have now for some years instituted a plan which utterly prevents any possible accident of this description, for the oxygen cylinders have a right-handed thread, and those for coal-gas a left handed one. It is, therefore, impossible for any employe accidentally to fill a cylinder used for one gas with the other, for the screws will not fit, and cannot be made to do so. In closing these remarks we regret to further add that firms still exist in London who sell both gases cheaper, and as a matter of fact not so pure, who still refuse to adopt these ingenious precautions, which leads us once more very obviously to select the same firm that we have already named, even if it were for this reason alone.

To resume, no accident can possibly happen when using the “ blow-through ” jet,

Fig- 5

Fig. 6 for, as before stated, using too much oxygen simply causes the light to go out, which is of no serious consequence.

In all cases regulators must be fitted to the gas bottles. When employed for mixed jets these can be “ matched,” but even that is not absolutely necessary. The regulator which we have used with never-failing satisfaction is also made by Mr. Beard, who has rendered it after numerous experiments and long experience almost perfection ; we cannot find any fault with it after several years of constant use. A cut is given in Fig. 5 which shows its internal mechanism to depend upon an ingenious arrangement of a “ lazy-tongs ” design. In Fig. 6 the regulator is shown attached to what is known as a gauge. The object of this additional piece of apparatus is to indicate how much gas is contained in a bottle. It must be stated here that no gas “ regulator ” or “ gauge ” once used for coal-gas should ever be employed for oxygen ; there are chemical reasons which forbid interchange of this description.

B

Mr. Beard now makes right and left-handed regulators and gauges so that they fit the right and left-handed nozzles of the oxygen and coal-gas cylinders ; hence there is no danger of an interchange being made in a moment of forgetfulness. For a full and detailed description of gas bottles, regulators and gauges, the reader is referred to an excellent brochure on the subject by Mr. K. S. Murray, M.I.M.E., engineer of the Messrs. Brin’s works, Horseferry Road, Westminster.

To use the mixed jet is somewhat of an art, but one that may quickly be learnt. On the brass tube of each “ regulator,” where the india-rubber tube is attached (P in Fig 5), it is a great convenience to have fixed, in addition, a common tap, for there are times when one may want to shut off the gas temporarily, or even suddenly as in the case of an emergency, and this can be done with far greater speed and ease by these common gas taps than by shutting off the cylinders themselves. A common tap suffices, as there is no pressure worth noting in this situation.

To start the light, having placed the lime upon the pin made for its support, the screws which regulate the amount of gas passing into each pipe of the jet are screwed completely down, both gases being gently turned on at the cylinder, and if gauges are used as shown in the diagram, they can be watched to see when the valves are sufficiently opened. The “cut off” handle is then placed horizontal, which means both gases, if not controlled by the screw-down valves in the tube of the jet to which reference has been made, would rush on towards the lime. We undo first the red one, which permits the hydrogen or coal-gas to pass to the jet and thus impinge on the lime.

It is then lighted. Still leaving the “cut off” untouched, slowly turn on the oxygen screw-down-tap on the jet until the light is quite bright. These two screws must now be slowly opened one against the other till the best light is obtained, always remembering that it is better to turn the hydrogen on first, as suggested in the Gwyer pamphlet. If too much oxygen be put on, the light will fade and require more hydrogen, but we recommend any one using the mixed light having a few lessons before attempting it. With Beard’s jet very little “snapping” occurs, but in some forms made by other makers the slightest misproportion of oxygen will produce it. There is no danger in this snap in , a well-appointed jet, but we venture to suggest to any reader who is contemplating buying this form of illumination only to go to best makers. Cheap jets are always to be avoided for they are often dangerous.

Before quitting the subject it should be again noted that the gases should always be turned on gently, especially when using a gauge, as accidents have been known to occur from a too sudden “jerking on” of the oxygen. To avoid the possibility of this accident, Mr. Beard (and others, we believe) have arranged a “ check ” which is placed in the mouth of the gauge, which only allows the oxygen to pass very slowly no matter how much the gas bottle valve is turned on. That is to say, even if by accident this latter valve is violently opened an undue amount, the gas only enters the gauge quite slowly. It is an invention which can be added at the small expense of five shillings and is well worth the money.

So far as relates to limes, the very best “hard” Nottingham variety is always to be bought for the mixed jet, but the “soft lime” does quite well for the blow-through

Fig. 7

Fig. 8 and is cheaper. Messrs. Zeiss have introduced a small lime which is some compound of Zirconium. We have tried it and like it very much. Ordinary limes rapidly wear away under the intense heat of the mixed jet, and require frequent turning, but these of which we have just spoken are extremely hard and do not apparently require any attention for some protracted interval. Their only fault seems to be their price and that a special arrangement of the jet is required for their use.

So far as to the use of artificial lights. Another illuminant exists, however, which is almost a necesssity for a few picked specimens — we refer to the sun. This, when employed, requires some form of special arrangement, owing to the rotation of the earth, for it is never still for more (apparently of course) than a few seconds together. That is to say, when employing it just as the light is made central in a manner to be hereafter explained, the sun apparently moves and does not retain its position in the field of view long enough to enable a photograph to be taken with its use. The special form of apparatus to keep it so is called a heliostat and is shown in Figs. 7 and 8. We believe the form (Fig. 7) which is sold by Baker, of Holborn, answers the purpose very well indeed. Other forms are made, notably one after Prazmowski, by Messrs. Besu, Hauser & Co. of Paris, and by Hartnack in Potsdam. Messrs. Watson & Son of Holborn also supply an ingenious arrangement devised by Dr. Johnson Stoney, shown in Fig. 8 ; neither of these two are personally known to us, but by repute they are generally acknowledged to be exceedingly good although rather costly. Any kind of heliostat must be made for the latitude of the place, and as full directions for their setting up and use are issued by each maker a detailed description need not be here given.