It has been presumed in commencing these notes that most would-be experimenters already possess a camera, or will at least shortly do so. Thus the greater number of experiments are such as would interest a camera fiend more deeply than the ordinary reader, although the latter might still derive much enjoyment from conducting them so far as the lack of a “dark box” will allow him.

It will perhaps be as well to spend a paragraph at the outset in describing simply and noting a few peculiarities about the commonplace camera. Photography means drawing by the agency of light. Now light is reflected from an illuminated object in straight lines or rays, of which a proportion may be collected by a lens and thrown in points upon a surface behind. (See Fig. 1, A, illuminated object; B, lens; C, surface behind lens; D, rays of light thrown upon surface C.)

The front of a camera contains the lens, and is provided with a movable shutter, so that light may be only allowed to enter the dark box when a picture is to be taken on one of the sensitive plates inside. According to Fig. 2—which represents a camera in position to photograph the object A—the light is reflected in rays, which are collected in myriads of groups and cast pointed upon the surface of the sensitized plate B. Such ray groups—being parallel when they leave the object and pointed after passing the lens—are termed pencils of light, a most applicable name when they are employed in “sketching” a portrait on the photographic plate.

It will be seen that the action of the lens causes the base of the object to be registered upon the top of the plate, and vice versa—i.e. the picture is taken upside down. Another noticeable feature about the magazine box camera, which does not, however, apply to the focussing camera with bellows, is that it may not be placed nearer than a certain distance (usually 10 feet or thereabouts) to the object photographed, or else the picture obtained will be blurred. The remembrance of this simple fact will save the loss of many plates to the tyro.

Finally a last note remains to be taken of the “stops.” These are really various sized holes in a metal screen, any one of which may be placed at will before the lens, and by the use of which the sharpness or distinctness of the photograph may be improved. Thus a lens at full aperture will not give such a sharp picture as would be obtained if a small hole were used, but, as the amount of light permitted to pass in the latter case is much diminished, a longer exposure must be given. Consequently when a short-timed snapshot is being secured, the largest practicable aperture or stop should be employed, even though the sharpness of the picture be thereby to some extent sacrificed.

Having thus briefly reviewed the essential features of a camera, arrangements may be made for conducting our first experiment.

Experiment A.—A Fireside Photo

Probably no souvenir can give greater pleasure to the amateur photographer, or prove more acceptable to his bosom chums, than their portrait, as a fireside group, lighted by the glow from a genial fire. Nor is this difficult of attainment.

First the figures should be grouped seated on chairs—and perhaps some standing behind, if many faces are to be included—in a quarter circle from one chimney-corner, whilst the camera may be securely placed some 9 or 10 feet away, about the position shown at X in Fig. 3.

Next some shade like a small fire-screen must be placed between the blaze and the camera, in order to protect the sensitized plate from the full glare of the firelight. Now of course the photograph is not actually secured by the coal flame illumination, which would not be bright enough to give proper exposure, so recourse is had to dropping some material into the fire which will burn rapidly with a bright white flame. Magnesium powder is generally used for this purpose.

Supposing the group to have been arranged and the camera firmly in position, the person (B, in Fig. 3) seated next the grate should hold a tablespoonful of saltpeter and also a square inch or so of sheet zinc. Then, all being so far ready, let the outside member of the group (marked A in Fig. 3) open the camera shutter and slip back to his seat, whilst the flashlight operator drops the saltpeter and zinc successively among the glowing coals. The flame of dazzling brilliancy which results records the sitters’ figures on the plate, so that directly it is over, the person (A) may again visit the camera and close the shutter. His movements will not be noticeable, since they are made before and after the flashlight.

The operation of development may be proceeded with at once and should go fairly easily, but flashlight exposures are difficult to estimate accurately, and therefore, although a square inch of zinc has sufficed for a small group with stop and an extra rapid plate, this amount may have to be increased if the group be large or if other conditions be changed.

One last hint as to behavior of the sitters. Let them sit as naturally and quietly as possible, but be advised to blink their eyes as much as the bright light prompts them rather than keep them staring wide open, when their faces must wear a most inane expression in the finished photo.

Experiments B.—“Photo-Chemical”

Salts of silver form the basis of most modern photographic processes. Thus in order to perform chemical experiments of a photographic nature, some solution of silver must be available, the nitrate salt being usually employed.

It is best procured at the druggist’s in solution or as crystals, in which latter case it must be dissolved for use in clean rain or distilled water. The solution need be only weak, but must be kept in a dark bottle screened from daylight. Chemical test-tubes, if they can be obtained, will be found best for the experiments.

(1) Prepare a weak solution of table salt, and add it drop by drop to a little of the silver nitrate in a test tube (or wine-glass as a makeshift). A white sediment is precipitated, which, by shading part of the tube with a band of paper and exposing to daylight, may be shown to be sensitive to light, inasmuch as the unscreened part will rapidly turn purple. This precipitate consists of silver chloride, which, in combination with unaltered nitrate, forms the essential ingredient of printing paper. In Fig. 4, A is Solution; B, Precipitate; C, Band of Paper.

(2) Photographic plates are coated with bromide of silver, a yellow substance, which may be prepared similarly to the previous precipitate by adding potassium bromide solution (instead of table salt) to the nitrate of silver. Its appearance does not change rapidly under the influence of light, but if first exposed and then treated with a developing solution the yellow color very soon changes to black—finely divided metallic silver being, in fact, produced. Actually, light more readily alters the constitution of the bromide than that of the white chloride, but the former knows better how to preserve an outward appearance of composure.

(3) Suppose, now, another solution be made, this time of the fixing salt known familiarly to every camera knight as “Hypo.” When this is added to either the white chloride or yellow bromide precipitates above noticed, they gradually dissolve away, except such portions as have changed color under the influence of light.

Such action constitutes the process of fixing a photograph, whereby the sensitive silver compound is removed from those parts of the paper or plate which have more or less escaped the influence of light.

(4) This experiment is an aquatic performance in which one actor only—our old acquaintance Hypo—takes part. Provided proper care be taken in the preparatory stages, it will afford at the climax as excellent a spectacle as many another more complex.

A tumbler glass full of saturated solution has first to be prepared, and this is best done by tying about ¹/₂ lb. of Hypo in a piece of muslin, so that it may be held against the rim of the glass and allowed to hang in hot water after the manner of Fig. 5. When an appreciable quantity of the salt has dissolved, the liquid being but lukewarm, the muslin bag may be removed and the solution stirred gently. Then it must be stood somewhere firm, and allowed to remain absolutely undisturbed until cold. There should then be a glass full of clear liquid, and the phenomenon is at hand.

Let the smallest crystal of solid Hypo be dropped in this liquid, or let it but be disturbed, and behold! a wonderful transformation proceeds, until the glass interior becomes a shimmering mass of sparkling crystals. The reason of this curious behavior is not far to seek. Hypo, in common with most chemicals, dissolves to a greater extent in hot water than in cold, but is different, inasmuch as the excess of salt does not settle out as the solution becomes cold. Cold solution is therefore really over-saturated, and to such an extent that only an extra crystal or the least disturbance is sufficient to upset the delicate balance, upon which climax the great excess of Hypo soon settles out.

(5) This is another reaction in which Hypo takes part, but one other substance is required as well, viz. permanganate of potash. Condy’s fluid is equally suitable, and in either case the solution need only be weak—just a transparent deep pink color. The vessel containing this permanganate may be about half full. When Hypo solution is gradually dripped into this and the mixture stirred, the color is immediately dispelled, leaving the liquid clear as water.

Inasmuch as every photographer knows the necessity for washing his prints until all fixing salt is removed, this decoloring action may be fully employed in testing the washing water occasionally. When it no longer affects the tint of a pink permanganate solution he may rest assured that the deleterious Hypo—like some friends in being welcome so they stop not too long—has really departed. For the ready performance of this experiment it may be noted that any solution can most easily be “dropped in drips” from a bottle whose cork is cut grooved at both sides (Fig. 6).

Experiment C.—Blue Print Paper

Engineers’ drawings have for many years past been copied upon ferro-prussiate, or “blue print” paper. The original design being made in opaque ink upon tracing linen, a sheet of the sensitive paper is held against this in strong daylight until blue coloration has advanced everywhere except beneath the ink lines of the drawing. These remain yellow, or rather white, when finished, as the excess of sensitive salt is removed by washing.

Since this last operation is in itself all-sufficient to insure permanency, the simplicity is unique. In fact, the impossibilty of securing other colors than blue has been the only factor to exclude this process from far wider use.

The preparation of the sensitive surface presents no great difficulties, provided a drawing-paper of good quality be used. It should be cut into strips about 6 inches wide, which are passed one by one up and down (see Fig. 7) through a dish containing the following solution: 1 oz. ferri-cyanide of potash + 4 oz. water, added to 1 oz. ammonio-citrate of iron + 4 oz. water. (Note—4 oz. water = nearly ¹/₄ pint.) This must be done in very dull light—candle or paraffin oil by preference—and the wet paper pinned up to dry in a dark cupboard, hanging from the edge of a shelf or other projecting support. Then it may be cut into pieces of the required size and stored with a wrapping of tissue and brown paper in a handy box.

All manner of designs may be produced on this paper, such for example as fern leaves, lace, and embroidery. Actual sea-view photos or imitation moonlight views also look very well indeed. Another notion is to secure the copy of some picture printed in black on thin paper, which has been oiled and dried in order to render it translucent for quicker printing. The final washings should be thorough, and then the blue print will last its maker as long as the latter cares to keep it.

Experiment D.—To Show the Constituents of White Light

Few physicists to-day doubt that light consists of waves set up in an all-pervading medium called ether; that, moreover, white light is composed of different tinted rays—to be seen reflected from the bevel edge of a looking-glass, or indeed from the more natural rainbow—which further are caused by the different lengths of waves whereby the colored lights are propagated.

Now we may produce these phenomena for ourselves by cutting a slit 1¹/₂ inches long in a temporary window-shutter, or, more conveniently, in the end of a large wooden box (A, Fig. 8). Near this a glass prism, such as once adorned gas-pendants so profusely, must be supported (B, Fig. 8) on a block of wood, and at the opposite end of the box a sheet of paper pinned to the inside (C, Fig. 8). The arrangement is shown in the diagram.

Now notice, if you regard this screen from the open top—a large cloth covering head and box in order to keep out superfluous light—a band of color is depicted thereon, gradating gently like a rainbow from violet through blue and yellow to red. Thus the white light which entered through the slit has been separated into its component parts. So far, gorgeous enough! But for the photographer much greater interest is at hand, will he proceed as follows. Place the box so that bright sunshine enters through the slit, and after fastening a piece of blue print paper instead of the white on the box interior, allow this to print, at the same time excluding extraneous light by a dark cloth overspread. When this piece of paper has been washed and fixed, the colored band should have registered itself in various shades of blue, from which it will be noticeable that the purple and blue lights have darkened the paper most, whilst red and yellow hardly affect it at all. If ordinary printing paper, or still better, a photographic plate (in which latter case a considerably shorter exposure will suffice, and outside light must be rigorously excluded) be used, instead of the blue print paper, the result is still more striking.

Fig. 8.—The refraction of white light into its constituent colors.