The Boy's Playbook of Science / Including the Various Manipulations and Arrangements of Chemical and Philosophical Apparatus Required for the Successful Performance of Scientific Experiments in Illustration of the Elementary Branches of Chemistry and Natural Philosophy

by John Henry Pepper

Fourth Experiment. The Wax-paper Process.

This mode of taking negative photographs begins where the talbotype ends—viz., by first waxing the paper perfectly and evenly, as already explained, Cansan's negative paper being preferred. The wax paper is now well soaked in a bath, made by dissolving one hundred grains of iodide of potassium, six grains of cyanide of potassium, four grains of fluoride of potassium, ten grains of bromide of potassium, ten grains of chloride of sodium, in one pint of fresh whey, with the addition of a little alcohol and a few grains of iodine. When soaked in this solution for about one hour, the paper is taken out and hung up to dry.

N.B. With respect to iodizing the wax paper, it is almost better to obtain it ready prepared, and then every sheet may be relied on. Mr. Melhuish, of Blackheath and Holborn, supplies it in any quantity, and his paper never fails; the operator has then only to perform the sensitizing and developing processes. To render the iodized paper sensitive it is immersed for about six minutes in a bath containing a solution of nitrate of silver (thirty-five grains to the ounce of water, with forty drops of glacial acetic acid); the paper is now removed, and washed in two trays of common clear rain-water or distilled water, and is then dried on between folds of blotting-paper.

This process may be performed on the previous evening by the light of a candle, or by day in a room lit by one window covered with four thicknesses of yellow calico, and after the paper is dry it will keep for three weeks or a month, and may be exposed in a camera with a three-inch lens of eighteen-inch focus, with the inch diaphragm, on a bright day from five to fifteen minutes; in bad weather the exposure must be longer. The picture may be carried home and rendered visible or developed by immersion in a bath containing a saturated solution of gallic acid, and as the developing continues, a few drops of the sensitizing solution of nitrate of silver and glacial acetic acid may be added. Finally, the picture is fixed by immersion for a quarter of an hour in a solution of hyposulphite of soda (four ounces of the crystal to one pint of water, or one part of the saturated solution to eight of water), and being well washed, is then dried, hung before the fire to melt the wax, and is now ready to print from.

Fifth Experiment. Albumen on Glass Process.

Albumen is the scientific name for the white of egg, of which four ounces by measure are mixed with one ounce and a half of distilled water, and after being whisked to a froth, are removed by a spoon into another basin or a beaker glass, and allowed to stand for several hours and then filtered. Mr. Crookes has recommended a very ingenious, simple, and useful filter. (Fig. 139.) He says: "This simple and inexpensive piece of apparatus, which any instrument maker or glass-blower can supply at a few hours' notice, will be found invaluable in almost every photographic process on glass. The sponge has this great advantage over all other kinds of filters, that thick gelatinous liquids—e.g., honey, albumen, gelatine, meta-gelatine, or the various preservative syrups—flow through it with the utmost readiness; whilst at the same time dust, air bubbles, or froth, and dried particles floating in the liquid, are effectually kept back, and if fitted with stoppers, collodion might be filtered in it; or if the ends were fitted together with a bit of flexible pipe, the stoppers might be dispensed with altogether.

Fig. 139.

a b. Glass tube, bent as in picture. c. Piece of damp sponge squeezed into the head of the tube. Any liquid poured in at b will flow through the sponge until it has attained the same level in a.

Having poured the albumen on a perfectly clean glass plate, taking care to have sufficient to run freely over the surface of the glass, the excess is then gently drained off and the plate turned so as to have the coated side downwards; it is then fixed in a sling made by taking a stout bit of string about three feet long, which is doubled and knotted at the fold, leaving the two ends free; two small triangles or stirrups of silver wire looped at one corner are now tied on to the ends of the string, and these form a support for the opposite edges of the glass plate to rest on; the two strings are knotted together at a convenient distance from the stirrups to prevent the glass slipping out, and the plate is now rotated rapidly over a heated metallic surface, such as an iron box containing some burning charcoal or the warming pan, care being taken to avoid dust as much as possible, and to use only the whites of new-laid eggs. (Fig. 140.) The glass plate, covered with dry albumen, is now iodized to a straw colour by exposure over a box containing iodine, as in the Daguerreotype process, and is sensitized by immersion for three or four minutes in a bath containing a solution of nitrate of silver (twenty-five grains to an ounce of water); the plate is afterwards washed in distilled water and left to dry spontaneously, of course in a darkened room. The plates may then be placed ready for use in a very ingenious tin box devised by Mr. Crookes, which keeps them perfectly light-tight even in the sun, and at the same time is less bulky than the ordinary wooden ones. It is made of tin plate, the cover sliding tight over the top, and more than half way down the sides; light is further excluded by means of an outer jacket of tin, which is soldered to the box a little below the centre. The cover thus slides between the case and the jacket, and renders injury to the plates by the entrance of light an impossibility. (Fig. 141.)