(11) Dr. Eder has for a considerable time directed especial attention to the soda and potash developers, either of which seems to offer certain advantages over the ammoniacal pyrogallol. This advantage becomes particularly apparent with emulsions prepared with ammonia, which frequently show with ammoniacal developer green or red fog, or a fog of clayish colour by reflected, and of pale purple by transmitted light. Ferrous oxalate works quite well with plates of that kind; so do soda and potash developers.
For soda developers, Eder uses a solution of 10 parts pure crystallised soda in 100 of water. For use, 100 gr. of this solution are mixed with 6 gr. of a pyrogallic solution of 1:10, without the addition of any bromide.
(12) More pleasant to work with is Dr. Stolze's potash developer. (a) Water, 200 c. c.; potassium carbonate, 90 gr.; sodium sulphite, 25 gr.; (6) Water, 100 c. c.; citric acid, 11/2 gr.; sodium sulphite, 25 gr.; pyrogallol, 12 gr. Solution (6) is for its better keeping qualities preferable to Dr. Stolze's solution.* The solutions when in well-stoppered bottles keep well for some time. To develop, mix 100 c. c. of water with 40 min. of (a) and 50 min. of (6). The picture appears quickly and more vigor-ously than with iron oxalate. If it is desirable to decrease the density of the negatives, double the quantity of water. The negatives have a greenish-brown to olive-green tone. A very fine greyish-black can be obtained by using a strong alum bath between developing and fixing. The same bath after fixing does not act as effectually in producing the desired tone. A bath of equal volumes of saturated solutions of alum and ferrous sulphate gives the negative a deep olive-brown colour and an extraordinary intensity, which excludes all possible necessities of an after intensification.
The sensitiveness with this developer is at least equal to that when iron developer is used, frequently even greater.
The addition of bromides is superfluous, sometimes injurious. Bromides in quantities, as added to ammoniacal pyro, would reduce the sensitiveness to 1/10 or 1/20 will even retard the developing power almost entirely.
* 100 c.c. water; 10 cc. alconol; 10 gr. pyrogallol; l gr. salicylic acid.
Must a restrainer be resorted to, 1 to 3 min. of a 1:10 solution of potassium bromide is quite sufficient.
(13) H. J. Newton communicates a formula for an improved developer for gelatine plates which he has found by experiment to be particularly valuable in the development of. instantaneously exposed plates, and to produce negatives of a superior colour and quick printing quality. He makes 2 stock solutions in the following proportions: -
(a) Water ...... 1 oz.
Anhydrous soda carbonate ...... 48 gr.
Potash carbonate .. 48 gr.
(b) Water ...... 1 oz.
Soda sulphite .. .. 48 gr.
To develop a 5 X 8 plate with a drop-shutter exposure he pours in the graduate 6 dr. each of (a) and (6), and then adds 11 1/2 oz. water and 6 gr. dry pyro-gallic acid. It may be mixed 1/2 hour before use if desired. The soda sulphite keeps the solution clear.
If the exposure has not been too long, the developer will rapidly bring out the image; the development should be carried on until the whites of the shadows have turned a steel grey colour. If the plate has been over-exposed, the developer should be diluted with water and restrained with 2-3 gr. sodium bromide to each oz. of developer, which may be in the form of a 10 per cent. solution. If the plate has been known to have been greatly over-exposed, development should be commenced with 1 dr. each of (a) and (6) to 2 3/4 oz. water and 3 gr. dry pyro, adding a little of each at a time should the picture develop too slowly.
(14) The following developer, containing ammonia and ammonium sulphite, has proved excellent with almost all kinds of commercial plates.
(a) Dissolve 10 parts pyrogallol, and 25-30 of ammonium sulphite, in 100 of water.
(6) Dissolve 5 parts ammonium bromide in 150 of water, and add 50 of liquid ammonia.
The working developer is made by mixing 100 gr. water, 4 gr. of the pyrogallic solution (a), and 4 gr. of the alkaline solution (6). Development takes place very quickly, and if it is desired to make the reaction slower, more water (50 gr. extra) is added. This leads to the production of softer pictures. If, on the other hand, more vigorous images are required, a few drops of a 10 per cent. solution of ammonium bromide must be added. The ammonium sulphite developer gives very well-modelled, brilliant negatives, in which the high lights are well rendered, and the deep shadows are full of modelling, while the negatives have an agreeable dark-brownish tint. The am-monium sulphite makes the aqueous solution of pyrogallol more permanent than when the sodium sulphite is used, and there is but little liability to fog with it.
(15) A Developer With Lime Water
Pyrogallic acid and lime water were first recommended by Davanne for col-lodio-bromide emulsion, and this developer can also be used with gelatine emulsion plates. As lime is but slightly soluble in water, it is convenient to make a 10 per cent. solution of sugar in water, and to saturate this with slaked lime. The pyro-lime developer becomes violet and brown in use, also becomes turbid; while the developed images produced are very thin.
(16) By Col. Dawson. Pyrogallic Solution. - Remove the cork from a 1-oz. bottle of pyrogallic acid, and pour into it 30 gr. citric acid dissolved in 6 oz. water; shake up, and then add to the contents in the bottle 4 oz. powdered neutral recrystallised soda sulphite. Fill the bottle with cold water up to' the bottom of the neck, shake up until the crystals are dissolved; transfer to a stoppered bottle The contents will be about 10 oz., and will keep a year at least; every 10 minims represent about 1 gr. pyro and 4 gr. sulphite. (N.B. - Ordinary commercial sulphite is useless for the purpose). * This solution is to be used with the two forms of developer.