One further advantage of this process is that it actually reduces the chemical fog on the negative, which is a very great assistance in practical work; for thus, in common parlance, it enables us to obtain more details in the shadows. It also completely alters the character of the normal hydrochinon developer which, as every practical worker knows, has a tendency to give hard, contrasty negatives, whereas with the addition of phenosafranin it works more like metol or paramidophenol, giving soft results. A suitable formula for this modification is:

A. Hydrochinon 12 g.

Sodium sulphite, dry 50 g.

Potassium bromide 1 g.

Water to 1000 ccm.

B. Potassium carbonate 50 g.

Phenosafranin, 1: 2000 solution 200 ccm Water to 1000 ccm.

Mix in equal volumes just before use.

As stated, the phenosafranin stains the gelatine rather deeply and this is not readily washed out with water, but it can be removed by treatment with either an acid alum solution or a nitrite bath. The former is made by adding 10 per cent of hydrochloric acid to a 2 per cent solution of ordinary alum, and the nitrite bath is made as follows:

Sodium nitrite 1 g.

Hydrochloric acid 10 ccm.

Water 1000 ccm.

The best way of using this bath is to make up a 10 per cent solution of the nitrite; just before it is required for use add 1 part to 99 parts of water and then add the acid; the mixed solution cannot be kept in stock. It should be noted that the salt is nitrite and not nitrate of soda. The latter is useless, for the efficiency of this bath depends on the evolution of nitrous acid, which converts the dye into a nitrous compound, or diazotizes it. The rather deep red stain is thus converted into a bluish-violet compound which washes out from the gelatine more readily. Naturally, as probably everyone knows, an acid bath should not be used immediately after fixing or the hypo is decomposed, giving rise to various sulphur compounds, with the possible deposition of sulphur in the gelatine. Therefore, the above baths should only be used after the negatives have been washed. The one disadvantage of the nitrite bath is the evolution of nitrous acid, which has a rather unpleasant smell and in any quantity causes coughing and irritation of the eyes. As the negatives have already been fixed, the bath can easily be used in full daylight, so that one need not be cooped up in a small dark room with it.

This desensitizing process is an extremely valuable one and is applicable to all sensitive silver materials. With bromide or development papers, aurantia is the only dye that should be used, as the phenosafranin stains the paper very deeply, while the aurantia can be readily washed out.

It may be as well to add that for the bright light not more than an 8-candle power lamp should be used, though of course if the work is carried out at some distance from the lamp or an opaque screen be temporarily interposed between the developing dish and the light, the power of the lamp may be increased.

As regards developers for panchromatic plates in general, it is probable that every worker has his own pet formula, and there is no reason to alter it or adopt a new one. The two points to be kept in view in the selection of a developer are that the negatives should be what are usually called "soft," that is, without extreme contrasts, and that they should as far as possible be free from fog. Metol-hydrochinon appears to be the favorite and the following is a standard formula:

Metol 4 g.

Sodium sulphite, dry 50 g.

Sodium carbonate, dry 20 g.

Hydrochinon 2 g.

Potassium bromide 0.1 g.

Distilled water to 1000 ccm.

For use mix 1 part with an equal volume of water. The temperature of the developer should be 180 C. (650 F.), and the duration of development three to four minutes. The author's favorite developer is the following:

A. Paramidophenol hydrochloride 30 g.

Sodium sulphite, dry 90 g.

Distilled water to 1000 ccm.

B. Potassium carbonate 140 g.

Distilled water to 1000 ccm.

For use mix in equal volumes. Temperature 180 C. (650 F.), and duration of development three and one half minutes.

Presumably everyone knows that the correct method of mixing the first formula, or any metol developer, is to dissolve the metol in the water and then add the other ingredients in the order named. In making the second developer, the paramidophenol should be dissolved in some of the water, the sulphite in the remainder, and the two solutions mixed. The paramidophenol base is thereby thrown out of solution, therefore it is essential to thoroughly shake the bottle before measuring a quantity for use. The suspended base immediately dissolves on the addition of the alkali. It will be noted that there is no bromide in this formula, and none is required, as the hydrochloride combines with some of the potash, forming potassium chloride, which is a mild restrainer and fog preventer. Should the paramidophenol base itself be used instead of the hydrochloride, and it can be, of course, with equally good results, 0.05 per cent of potassium bromide should be added. Too much should not be used, as it actually slows the plate with normal time of development, that is, it holds back the shadow detail, the most important part of the negative; if development be prolonged sufficiently to bring this out, the negatives are, as a rule, too hard. It may be said that if the pure paramidophenol base be chosen, one fourth less should be used, that is, seventy-five parts of paramidophenol will do as much work as one hundred of the hydrochloride.

The temperature given above for the developer is important and should be strictly adhered to. If the solution is cold, the development is prolonged and, conversely, if it is too warm the duration is curtailed and there is a much greater chance of chemical fog. Also with strict adherence to a given temperature and time of development, the character of all negatives will be alike.

Other developers may be used, but enough has been said to enable the reader to adapt his own pet formula to the work. There is one very important point, which must be rigidly observed, and that is that the developer must not be used a second time. If the plates are so large that they cannot be developed together, which is the ideal method, then fresh solution should be used for each plate; obviously there are more possibilities of variation in the negatives by separate development than by developing all together.

The reason why great stress is laid upon this matter of fresh solution for each batch or each plate, is that in development the bromine set free from the silver salt by the reducing agent combines with the alkali and forms a bromide, and this, naturally, in quantities varying with the amount of metallic silver deposited to form the image; so that one has, after development, a solution of unknown and variable bromide content, and constancy of results is impossible. This may seem a wasteful and expensive method of working; but when one considers the importance of perfect results, the cost of the fresh developer becomes negligible.

But little need be said about the fixing bath. Any formula may be adopted, though an acid chrome bath of the following constitution gives excellent results; it fixes very rapidly in about five minutes, and hardens the gelatine:

Sodium sulphite, dry 45 g.

Water 100 ccm.

Stir well and add:

Glacial acetic acid 20 ccm.

Then add to the following, when the hypo is dissolved:

Hypo 400 g.

Hot water 600 ccm.

Finally add:

Chrome alum 20 g.

Hot water 50 g and make the total bulk up to 1000 ccm.

The washing of the negatives follows the usual course. It is unnecessary to deal with intensification and reduction, as these also can be carried out as usual; but these operations should be avoided as far as possible by correct exposure and development, as the gradations are apt to be altered by them, with consequent false color-rendering.