A. Metol....................... 1/4 oz.

Sodium Sulphite........2 1/2 "

Water .........25 ,,

B. Sodium Carbonate . . . . . . 2 oz.

Water..........20 „

Metol is generally preferable as an addition to hydro-quinone or pyro, when it acts as a useful corrective. For an example we will give the Imperial Dry Plate Company's developer of this class (single solution):

Metol.......... 50 gr.

Hydroquinone . . . . . . . . 40 ,,

Sodium Sulphite...... 500 ,,

Potassium Bromide....... 25 ,,

Sodium Carbonate . .... 500 „ Water......... 20 oz.

Or for two solutions (Metol Pyro):

A. Metol......... 45 gr.

Potass. Metabisulphite...... 120 ,,

Pyro.......... 55 "

Potass. Bromide....... 20 ,,

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

B Sodium Carbonate....... 4 oz.

Water ......... 20 „

Hydroquiuone (C6H4(OH)2)

Negatives from this developer tend to rather harsh contrasts, detail in the shadows not appearing until the high lights have acquired considerable thickness. Its chief value, especially in solutions with bromide, is for the necessary contrasts when copying prints and drawings, and for some of the photo-engraving processes. When hard negatives are desired, try:

A. Hydroquinone . . . . . . . . 40 gr.

Metabisulphite of Potash...... 40 „

Bromide of Potassium...... 5 „

Water......... 10 oz.

B. Caustic Potash....... 100 gr.

Water......... 10 oz.

Amidol (C6H3OHNH2HCL)

This developer is slightly acid in solution and acts very energetically without any alkali. The image appears almost at once in full detail, but requires long development. It produces good black negatives, and is often recommended for instantaneous work. Amidol does not keep well in solution but a stock solution consisting of-

Amidol........ 80 gr.

Sodium Sulphite ...... 800 ,,

Water . . . . . . . . 8 oz.

Will keep for a few weeks if well corked. For use dilute 1 part with 4 parts of water. Old amidol developer sometimes leaves serious stains behind it. The best way of all is to make a stock solution of:

Sodium Sulphite ...... 1 oz.

Potassium Metabisulphite .... 1/8 „

Water........ 20 ,, and with a horn spoon measure out 5 gr. of dry amidol for every two ounces immediately before using. A very weak solution of citric or acetic acid is a better restrainer for this developer than bromide of potassium.

Diamidophenol (C6H3OH(NH2)2)

A variation of that previously described, as will be seen by the symbol. It will give an excellent black image with good gradations, and is not so likely as amidol to produce stains, but it does sometimes cause inflammation on delicate skins.

Diamidophenol........ 40 gr.

Metabisulphite of Potash . . . . . . 1/2 oz.

Sodium Sulphite ....... 2 ,,

Water......... 20 „

Or it may be substituted for amidol in the previous formula. Ortol - A composite developer introduced by Dr. Hauff, which consists of a mixture of hydroquinone with methyl-ortho-amido-phenol. It acts in a very similar way to pyro but is stainless; the negative produced is somewhat less dense.

A. Ortol.......... 70 gr.

Potassium Metabisulphite...... 35 ,,

Water......... 10 oz.

B. Sodium Carbonate....... 1 oz.

Potassium Bromide....... 5 gr.

Sodium Sulphite . . . . . . 1 oz.

Water......... 10 ,,

Pyrocatechin (CTiH4(OH)2)

This developing agent, first introduced by M. Benoist, is the same in its components as hydroquinone, but behaves very differently. It acts energetically at a low temperature, giving a brown, fairly printing negative. On the other hand it is equally useful in hot weather, as the tanning action which it exercises upon the gelatine diminishes the risk of blisters and frilling in the film. The formula given for pyro soda will serve for pyrocatechin with the addition of more water, if required.

A. Pyrocatechin........ 1/4 oz.

Sodium Sulphite....... 1 "

Water......... 20 „

B. Sodium Carbonate....... 1 oz.

Water..... 10 "

The acid fixing bath is said to be unsuitable for negatives developed with Pyrocatechin.

Eikonogen is not very widely used for plates, but gives clear negatives, full of detail without great density in the high lights, and therefore suitable when bromide enlargements are needed rather than direct printing.

A. Eikonogen . . . . . . . 80 gr.

Sodium Sulphite....... 160 „

Water......... 5 oz.

B. Sodium Carbonate....... 1 oz.

Water......... 10 „

Eikonogen is often used in conjunction with hydroquinone, the presence of the latter increasing vigour and contrast. The following formula we have used with great success and especially for the development of Kodak films:

A. Sodium Sulphite . . . . . 2 oz.

Eikonogen......... 180 gr.

Hydroquinone........ 120 „

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

B. Potassium Carbonate ..... 1 oz.

Water . ...... 20 „

Take A 1 part, B 2 parts.

Kachin

The chief recommendation of this developer is its cleanliness and its success for the development of stale plates, on which it does not produce the usual iridescent markings.

A. Kachin......... 1/4 oz.

Sodium Sulphite..... 1 „

Citric Acid........ 20 gr.

Water......... 10 oz.

B. Sodium Carbonate....... 360 gr.

Water......... 10 oz.

For use take 1 part of A and 1 part of B, with from one to two parts of water according to the nature of the exposure. No bromide is required.

There are many other developers of this kind. We may mention adurol, the action of which is very similar to hydroquinone; edinol, sometimes recommended as a clean substitute for pyro and equal to it in range of densities; glycin, slow in action, but very sure and specially adapted for tank development; azol, synthol, imogen sulphite, diphenol, etc., etc.

Those who wish to experiment will find suitable formulae provided in the ounce packages supplied by the manufacturers.

Ferrous Oxalate, once a great favourite, is now very little used for plates. It gives a very brilliant, sparkling negative, but the resulting prints have often a deadly dull look on most modern papers. The old formula was :

A. Saturated solution of Ferrous Sulphate.

B. Saturated solution of Potassium Oxalate.

Take I part of A and 3 parts of B.

Before fixing the plate must pass through three changes of water, to which a few drops of citric-acid solution have been added to remove the otherwise insoluble iron salt. From the peculiarity of its chemical reaction ferrous oxalate is the one chosen for standard tests. We subjoin the formula used by Messrs. Hurter and Driffield:

A. Potassium oxalate..... 1 part.

Water....... 4 parts.

B. Ferrous Sulphate ...... 1 part.

Citric Acid ....... 0.01 part.

Water....... 3 parts.

C Potassium Bromide..... 1 part.

Water........ 100 parts.

For use, take A 100 parts, B 25 parts, C 10 parts.

Daylight Development

In the British Journal of Photography, August 27, 1909, a method was described for desensitising plates after exposure by immersion for a minute or two in a 4 per cent. solution of potassium iodide. They may then be brought out into daylight and developed in a metol-hydroquinone developer fully restrained with bromide. As an interesting experiment at the lecture table the process may have its value. But the results will not bear very critical examination, although the solution is said to be sold for the purpose in Germany.

We do not know whether the following combined developing and fixing bath for daylight use, described in the same journal, is permissible by the patent laws. Picrate of soda or of magnesia forms the colouring agent, the first-named being the more soluble.

Magnesium Picrate . . . . 81 parts.

Sodium Sulphite (anhydrous) .... 544 parts.

Sodium Hyposulphite (hypo) .... 250 parts.

Diamidophenol....... 125 parts.

This powdered mixture is dissolved in water to the extent of about 20 gr. per ounce, and the exposed plate or print having been placed in it in the dark, the further operation may be continued in daylight or other actinic light. The credit of the proposal is due to MM. F. Jeannot and M. R. Bremner.