(1) For the development of gelatino-bromide plates, Egli & Spiller recommend the following solutions: -

(a) Hydroxylamine hydrochloride...... 32 gr.

Citric acid...... 15 gr.

Potassium bromide .. 20 gr.

Water ...... 1 oz.

(b) Caustic soda .. .. 1 dr.

Water ...... 1 oz.

(c) Potassium bromide .. 20 gr.

Water ...... 1 oz.

For a 7} by 5 plate, the film is first soaked for about 1 minute in 3 1/2 oz. water containing 1 dr. of (a), about 20 drops of (b) are then added, and, if necessary, an extra 10 or so. Should the image show signs of over-exposure, or if the plate is one of the specially sensitive kind, a few drops of (c) must be used to restrain the action still more. The advantages resulting from the use of this developer are that the image is of a wet-plate tone, perfectly free from stain or deposits; a great variation of exposure is permissible; and the solution is not acted on by the atmosphere, and therefore does not deteriorate during development from external causes. (2) By J. Edwards: -

(a) Neutral potash oxalate 2 oz.

Ammonium chloride 40 gr.

Citric acid...... 2 dr.

Distilled water .. .. 20 oz.

(6) Iron sulphate .. .. 4 dr.

Alum........ 90 gr.

Distilled water .. .. 20 oz.

Add 1 part of (b) to an equal part of (a), but do not reverse this by adding (a) to (6), or the result will not be so good. If the plate is properly exposed, the result will be a fine purple-black tone in the transparency. If you like a warm brown tone, expose double the time, and add an equal bulk of water to the developer. The development in this case will be much slower. To fix the picture, use 1 part of hypo to 8 of water. After fixing and washing, put the plates for 1/2 minute in the following: -

Alum........ 1 oz.

Sulphuric acid...... 1 oz.

Water ........ 20 oz.

This will dissolve the opalescence caused by the oxalate. The plate must now be well washed, dried, and varnished in the usual way.

(3) H. J. Newton gives the following formula for a developer well adapted to bring out fully the details in a plate which has had a very short exposure: -

(a) Water ...... 1 oz.

Soda carbonate .. .. 15 gr.

Potash yellow prussiate 15 gr.

Soda sulphite .. .. 5 gr.

(6) Water ...... 1 oz.

Ammonia chloride .. 7 gr.

Pyro (dry) .. .. 6 gr.

(a) and (6) are mixed, and the whole is poured over the plate. Development commences within a minute, and is usually finished at the end of 3-4 minutes. The proportions named above are correct for an ordinary drop-shutter exposure, but they are not arbitrary; they may be varied to suit different cases, as, for example, should the plate have been greatly under-exposed, equal parts of (a) and (b) (with the pyro left out of the latter) may be added, a little at a time, to 3-4 times the strength stated, until all the details in the shadows are brought out, without danger of producing green fog, which frequently appears from the excessive amount of ammonia sometimes used in the ordinary ammonia and pyro developer. In case of over-exposure, 1/2 gr. to the ounce of developer of sodium bromide is added, and the solution is diluted with water.

The (a) and (6) solutions may be kept in a more concentrated form, and diluted for use. The following are the right proportions for 10 per cent. solutions: -

(a) Water ...... 9 1/2 oz.

Soda carbonate .. 480 gr. Potash yellow prussiate...... 480 gr.

Soda sulphite .. .. 160 gr.

(6) Water ...... 9 oz.

Ammonia chloride .. 510 gr. Solution of 1 drop sulphuric acid in 1 oz. water.. .. 1 drop Pyro(l oz.) .. .. 437 gr.

If (b) does not change from purple to a clear yellow colour within an hour after mixing, 1 or 2 drops more of the sulphuric acid solution may be added.

To prepare a developer of the proper strength with the above solutions for the development of a 5 x 8 plate which has had a drop-shutter exposure, take:

Water ........ 5 1/2 dr.

(a) solution ...... 2 3//4 „


Water .. 7 "

(6) solution ...... 1 "

Mix the two, and develop in the usual way. The proportions given will be equivalent in grains to those stated in the first formula.

Newton has described some interesting experiments, which substantiate very forcibly the value of the developer for instantaneous work. Two plates exposed precisely the same time, on the same object, were developed side by side, one with the developer as prescribed in the directions of the manufacturer of the plate, and the other with the above developer. With the ferrocyanide, there was 1/3-1/2 more detail brought out in the shadows, and development was completed sooner than with the prescribed developer; the negatives being more brilliant and vigorous. For photo-micrography, the process is admirable. The exposure appears shortened by fully 1/3, and negatives abounding in detail, strength, and density are easily obtained. The colour of the negatives is not the nice black-and-white given by potash, but is of a strong olive brown, and very non-actinic. Owing to this fact, care must be taken not to push the development too far, or unduly dense negatives will result. The ferrocyanide developer has advantages in cleanliness and freedom from green fog, as compared with ordinary pyro and ammonia, and is more powerful, requiring much less exposure of the plate.

During cold winter weather it works exceedingly well, and uniformly brings out brilliant and plucky images.

One word of warning: there are some makes of plates that will not stand this developer without fogging, unless bromide be used. The same may be said of plates that have received an excessive exposure. It is best with every plate to start with 2 drops of a 10-gr. per oz. solution of potassium bromide, increasing the dose to 6-8 drops if necessary. Using the bromide, you can count on every plate turning out a success with a much shorter exposure than usual, say 1/3-1/2, which is a decided advantage when working with artificial light.