The lens being removed from an ordinary 1/4-plate camera, a mahogany cone, blackened inside, and about 2 in. deep, is substituted, made to fit tightly into the flange of the camera, and having an opening at the apex through which the tube of the microscope can just pass freely, and only just, and to which a rubber band very slightly smaller than the tube of the microscope should be glued, to prevent light entering between the microscope and the cone. The microscope is then placed in a horizontal position, and the eye-piece having been taken out, the tube is passed through the cone and the eye-piece is replaced. The object to be photographed, which should be as transparent as possible, is then secured on the 6tage of the micrpscope, the manner of doing which, when the stage is vertical, varies with the construction of the microscope. This may be done with two email slips of wood 3 1/2 in. by 1/4 in. under the stage, one on each side of the opening, and two small rubber bands slipped over the ends, of both wood and slide. The object can then be focused on the ground-glass screen, but as the. microscope is not specially constructed for the purpose, the chemical and visual foci do not coincide, and the chemical focus must be found by experiment.

A few trials, using the fine adjustment, will give the requisite difference between the two foci, which, once found, is constant. A strong light must be employed, but not direct sunlight. The light from a white cloud on a bright day is the best illuminator. No special collodion or developer need be used, beyond being of the best, a necessary point in every photographic operation. The exposure will, of course, vary with the intensity of the light, quality of the lenses of the microscope, sensitiveness of the plate, etc. It should, however, be short, as the image is very bright with a good microscope. If there are many to do, it will be found advantageous to contrive an arrangement of both microscope and camera on a board which can be screwed to the camera stand. Some operators prefer to work without the eye-piece of the microscope, but there is then sometimes an objectionable flare in the centre of the picture. The eye-piece occasions some little loss of light, and therefore it would be preferable to work without it if possible.

Photo-Micrographs On Gelatine Plates

For the negative, a plate of extreme sensitiveness and fine texture, developing with sharp contrasts and great density, is required, and development with pyrogallic acid has given better results than ferrous oxalate. With such plates, powers ranging from 4 diameters to 2000 may be successfully employed with the light obtainable from a good lamp, while a simple and inexpensive camera, and which can be adapted to any microscope, is all sufficient for the production of the most perfect negatives by any process between the above extremes.

The gelatine plates for making the positives are of quite a different character from those used for negatives, being much less sensitive to light, and requiring a development which shall produce clear glass in the highlights, transparency in the shadows, and full detail in all portions. Two distinct kinds are now made, the one with a silver bromide base, the other with a chloride. The latter is much slower than the former, requiring many times 'the length of exposure, but the transparency of the shadows is much greater.

Possessed of a good negative (no other should be used since it is not possible to make a good positive from a bad one), two methods of producing the latter are open to us - by contact printing or by the camera. The latter is undoubtedly the more perfect, and enables us to utilise a negative of any dimensions, enlarging or reducing it to the proper lantern slide. A deep printing frame with plate glass front must be employed, on which is laid the negative, film side up; upon which - film side down, so that the two shall be in contact - is placed the slow plate which is to form the positive. Of course this must be done in the dark room, by ruby light. A piece of dead black velvet, to prevent halation or any reflection from the back of the plate, must now be placed over the same, and the back of the printing frame secured in position. The exposure is made to the light of a lamp or gas jet, at a distance of about 15 in. If a bromide plate be employed, the length of exposure may vary from 5 to 20 seconds, according to density of the negative: if a chloride plate, however, be used, the time required may be as many minutes. No rule can be given, experience alone will enable one to determine with an, certainty the length of time require.

For negative making, the "diamond" plates by Richardson are eminently satisfactory, while Carbutt's transparency plates, both bromide and chloride, leave little or nothing to be desired. They are cut from extremely thin and flat glass, so that when covered with a slip of the same thickness, and the edges neatly bound with needle paper, they present an exceedingly attractive appearance, and are very light in weight, fitting readily the cavities of any lantern in common use.

The development of the plate is of the utmost importance, since upon its success depend the beauty and perfection of the resulting transparency. The image should be sharp, clear, and transparent in the deepest shadows. Where clear glass appears, it must be absolutely so; the least smokiness or muddiness will spoil the brilliancy of the image upon the screen. The ferrous oxalate, made in the following simple manner, is entirely satisfactory when used with the Carbutt plates: -

No. 1. Saturated solution neutral potash oxalate.

No. 2. Saturated solution iron pro-tosulphate. To the latter add a few drops of a saturated solution of citric acid.

To make the developer, add 1 part of No. 2 to 6 of No. 1, and have ready a solution of ammonium bromide for use in case of over-exposure. This developer will be found to act very promptly, and to bring out all the details with proper density before those portions of the plate which have not been acted upon by light, and which should be clear glass, begin to show any signs of fog. If the plate we are using be one of the bromides, it will be well to continue the development until rather more density than is desired has been obtained, as it will lose somewhat in the subsequent fixing. If, on the contrary, we are using a chloride plate, the development must be stopped as soon as requisite density is reached, as it will lose nothing in fixing. The usual washing and fixing in the hypo bath, followed by an alum one, and prolonged washing to remove all traces of the soda hyposulphite, must follow as a matter of course. Should the image flash up too suddenly, from overexposure, add a few drops of the bromide solution to prevent flatness and want of contrast in the image.

If the negative image be of larger dimensions than the lantern plate, and it be desired to place the whole thereof upon the latter, it will be necessary to employ some kind of copying camera. One especially constituted for this purpose, with a double shifting front, capable of carrying one sized plate, will of course be found the best. In the absence of such,* we may successfully use the same camera with which the negative was made, by removing the cone front and putting the negative in its place; which can readily be done by any one possessing a little patience and ingenuity. Then a board carrying a rectilinear lens of moderate focal length must be inserted in the central division of the bellows, and the front elevated toward the sky. An image of the exact size required may now be thrown upon the forming screen by withdrawing the front section of the bellows, carrying the lens to the proper distance, when it must be clamped, and the forming effected by the back bellows which carry ground glass screen. The plate holder containing one of the slow lantern plates is now to be substituted for the groun4 glass, and an exposure of 5-20 seconds made, governed by the density of the negative.

The subsequent operations of development and fixing are precisely the same as those given for contact printing.

Should the resultant positive be lacking in density, or of a slaty hue and without crispness, it may frequently be greatly improved by the following method: -

After thorough washing to remove all traces of hypo, place it in a bath composed of Mercury bichloride .. 96 gr. Potassium bromide .. 90 „ Distilled water .. .. 12 oz.

This bath, it may be observed, should be returned to a well-stoppered bottle for future use, as it will retain its qualities for a very long period.

Its effect upon the gelatine film of the plate will be to bleach the same, but care must be exercised not to carry the bleaching too far, lest over density be the final result. Removed from this bath and well washed, it must be plunged into another consisting of a 12 per cent, solution of soda sulphate, until the desired tone is reached. Almost any gradation of colour from a light yellow-brown to black, may be thus obtained, varied by the length of time immersion in the soda bath is continued. Final washing and drying must follow as in the original development.

When dry, the film is to be protected from injury by covering it with a thin plate of glass of the same dimensions as the slide, with a mat of paper cut out in suitable shape placed between the two, and the edges bound around with a strip of needle paper. - (W. H. Walmsley.)

Simple Apparatus For Photo-Micrography

This apparatus is for use on an ordinary camera, its chief advantage over the use of a microscope with the camera being that the ordinary use of the microscope is not interfered with, so that objects can be examined in the latter, and selected parts be immediately photographed. A brass disc or adapter, a, shown in section in Fig, 96, screws into a flange on the camera, and has a screw-threaded aperture to receive ordinary object-glasses. The disc carries a triangular rod, 6, about 3 1/2 in. long, on which a square stage, c. slides, or can be clamped in any position by a screw, d. The stage has a central opening for light, and springs for holding a slide. The back of the camera is movable to a distance of 20 in. by a screw; but an ordinary quarter-plate camera, with a rack and pinion, serves almost as well, the magnification then obtainable being less, owing to the shortness of such cameras. Focusing is effected by clamping the stage so that the object is approximately in focus, and then moving the back of the camera as found necessary.

This apparatus has been found to work very well with low powers, the illumination being effected by a paraffin lamp with one wick, the flame of which is focused on the object by stand condensers, with a blue cell interposed. - (T. H. Muras.)

Fig. 96.

Simple Apparatus For Photo Micrography 10079