Ammonia Solution.

Ammonia, 880 .. .. 2 dr. Water ........ 1 oz.

Keep in stoppered bottles.

To develop, give the plate the ordinary soaking in water, and pour over it:

Pyro solution...... 1 dr.

Water ........ 3 oz.

Allow this to act on the film for at least 2 minutes. Then put 1/2 dr. of ammonia solution into the developing cup, pour the pyro from the dish into it, and back again to the plate in the usual way. On the appearance of the image, add another 1/2 dr. of ammonia solution gradually, and more if required. (H. Man-field.).

(9) Hydroquinone or quinol will bring out a fully developed picture with at least half the exposure necessary when pyro is employed. This appears strange, when it is observed how much more powerfully pyro absorbs oxygen; but the explanation probably is in the fact that hydroquinone is more gradual it its action, and has a more "selective" power than pyro. With a collo-dio-bromide film, for instance, which is not so much protected from chemical action as a gelatine one, pyrogallic acts with such energy, when mixed with an alkali, that the whole film is reduced immediately, and no image, or only a faint one enveloped in fog, appears; hence there must be used a powerful restrainer to keep this action within bounds. A soluble bromide, which is usually used, has this effect; but, unfortunately, at the same time, partially undoes the work which the light has done, rendering it necessary to give longer exposure. But with hydroquinone no restrainer is necessary unless a great error in exposure has been made. It does its work rapidly and clean, in this resembling the ferrous oxalate; it does not discolour during development so much as pyro, and consequently does not stain the film so much, while full printing vigour is very easily obtained without having to resort to intensification.

The colour and general appearance of the negative are more like the wet-plate process, since the shadows remain so clear and free from fog. It seems almost impossible to fog a plate with it.

A collodio-bromide, or even a collodio-chloride, plate exposed in the camera will develop clean and rapidly without any restrainer. This property of developing a chloride is surprising, and will probably be very important; 1 gr. to the oz. is strong enough for most purposes. With some samples of hard gelatine, it is advisable to use 2 gr.; but with most kinds, and with collodion, 1 gr. is quite sufficient. Banks prefers using it with a saturated solution of washing soda as an alkali: 2-3 drops of this to the oz. of solution of hydroquinone rapidly develops the image, and the addition of a few drops more to complete development is all that is needed. A soluble bromide acts very powerfully as a retarder and re-strainer. With a mere trace added, development is very much slower. Although its cost is greater than pyro, 1 oz. of it will go as far as 2 oz. of pyro, so the difference is not so much as it appears. No doubt, if a demand sprang up for it, the price would also be reduced considerably. Another useful property of this developer is its suitability for developing on paper either a bromide or a chloride film, whether it be produced by an emulsion, or by the older method of first brushing over the paper the haloid, and afterward the silver.

The clearness with which it works renders it very suitable for this purpose, and for enlargement or printing enables pictures to be obtained with very short exposures.

(10) Experiments with the soda developer in all of its different forms have resulted in G. H. Monroe adopting the following formula as being the simplest and giving the finest negatives. The sal soda developer has been objectionable, both on account of the slowness of its action and the green colour given to the films. These objections have now been overcome. All possible variation in the plate can be secured, from thin clear negatives to any amount of contrast and density.

(a) Soda sulphite (cryst.) .. 4 oz. Hot water...... 11 oz.

When dissolved and cool, acidify with 3-4 oz. sulphurous acid. Add 1 oz. dry pyro. Filter.

(b) Sal soda ...... 3 1/2 oz.

Soda sulphite .. .. 3/4 oz. Water .. .. .. 64 oz.

To develop, use 1 dr. of (a) to each oz. of (6). By using more or less of (a), any change in density may be secured, more pyro producing greater contrast, and vice versa. If, upon the first appearance of the image, a negative is found to be over-exposed, lift the plate out of the developer and pour over it from a bottle a solution of potassium or ammonium bromide (5 gr. bromide, 1 oz. water), letting it run off the plate into the tray containing the developer without draining off too much; place the plate in the tray and proceed with development. The above operation can be repeated with the same plate in extreme cases.

This developer has the valuable property of not becoming discoloured in use; it also imparts to the film the very desirable grey colour, and the whole operation of development is complete in 2-3 minutes. Sufficient may be made in the morning for the day's use, and it can be used over and over again without in any way deteriorating, provided it has not been necessary to add restraining bromide, which changes the condition of a normal developer. The developer should be returned to a wide-mouthed bottle with a rubber stopper after each use of it, and the tray rinsed out and set up to drain. Should this formula not give strong enough contrast, add 1-3 gr. of dry pyro. This will hasten and produce the desired result.

The development should be carried to about the point desired in the finished negative.

It sometimes happens that the washing of the finished negative changes the grey colour to a greenish cast, which can be instantly removed by immersing the plate in the following solution: -

Common alum .. .. .. 8 oz.

Citric acid ...... 1 oz.

Water ........ 32 oz.

Should the plates show any signs of softness in warm weather, immerse them in a strong alum solution after development and before fixing. The sal soda developer, unlike the ammonia, has a persistence of action, and in instantaneous exposures, interiors, and portraits does not give any hardness. The time of exposure is also decreased by 1/3, as there are no restraining Bromides present.