Although there is a great variety of developers, they all consist essentially of three elements—(1) The developer proper or reagent; (2) an alkali, the addition of which sets the reagent going, and as the quantity is increased quickens its action, and is hence called the accelerator; and (3) bromide of potassium or bromide of ammonium, which retards action, and is called the restrainer. These may be made up in three separate solutions, and by using a little of this and a little of that development may be accelerated or retarded as the progress of affairs may suggest as desirable. But perhaps we are not experienced enough to profit by this opportunity of controlling the development, and hence it will be best to use a formula in which due proportions of all three are mixed together, thus giving only one solution.

Here is one such formula, which is easily made up, or if preferred a ready-made one solution metol-hydroquinone developer, may be procured :—

Metol .... 200 grains, or 6 grammes Water .... 80 ounces, or 1,000 c.c. Sodium sulphite . . 6 ,, or 75 grammes.

Hydroquinone . . 150 grains, or 4 ,,

Potassium bromide . 50 „ or iy Potassium carbonate . 2 ounces, or 25 „

The ingredients had better be dissolved in turn in the order given, using hot water to begin with, but using the mixed developer only when quite cold.

Although we have now made a " one-solution " developer, yet it is a good plan to have always ready in addition a ten per cent, solution of potassium bromide—that is, one ounce of potassium bromide dissolved in ten ounces of water. This should be a stock item, always ready on a shelf, close at hand to the developing table.

It need not, of course, be said that, our solutions being ready, white light is excluded from the room, and the darkroom lamp, of whatever form that may be, is alone used.

Placing the plate in a suitable developing dish, having previously lightly wiped the surface with a silk handkerchief or the soft part of the hand, provided the hand is dry and clean—this being done in order to remove any particles of dust on the surface—sufficient developer is taken in a glass measure or similar vessel to cover the plate when poured over it.

And here I am going to make a suggestion which is the outcome of experience, and it is this, that, if we take four fluid ounces of developer, we add thereto one to two ounces of plain water, thus diluting it in strength. The formula given above is a standard stock solution, but it is very energetic and it may be found safer to weaken it a little. The same suggestion applies to ready-made developers, the instructions with which tell you to take, say, one part to four parts of water, in which case I should take five or six parts of water. The reason for this dilution may appear presently.

Now pour the contents of the glass measure over the plate in one even continuous wave, and—here let it be said that to take too little of the solution is a false economy—there should be enough of it to well cover the plate when at rest, and a sharp look-out must be kept that after flowing no corner or edge of the plate remains uncovered, also that no bubbles have formed; a touch with the finger will disperse the latter, and then the dish is gently rocked so as to keep the developer slightly moving. The result of an uncovered patch may not and probably will not be revealed until the negative is finished, and then appears as an irregular thin area which nothing can rectify; similarly, a bubble prevents the developer acting on the plate by interposing a tiny dome of air, and this will produce a semi-transparent circular spot.

Rocking the dish and watching the plate during the first half minute or so will be an anxious period, and if exposure has been correct and no error unwittingly committed there will presently appear a darkening of the film here and there in more or less well-defined areas. These represent those portions of the scene where the light has been strongest and has affected the plate most. These should rapidly blacken ; meanwhile other parts in turn darken, not in very quick succession but with due precision. We know now that exposure has been correct, and each part of the view has duly impressed the plate according to its relative lightness; but suppose we find that very soon after the developer is flowed on, the whole of the plate darkens, or after the first dark area appears the other parts follow very rapidly, then it is evident that the plate is over-exposed.

After a little experience has been gained at this sort of thing, such a plate may perhaps be saved by at once pouring off" the developer back into the measure, instantly flooding the plate with water to stop further action, adding a few drops of the bromide solution to the developer and beginning over again ; the bromide restraining the developer's action, and giving what will eventually be the densest parts of the negative time to gather density before the others With the developer made up as above, this course is not perhaps to be recommended, because it will be seen that the formula already includes bromide, and we may easily get an excess of it; but the addition of bromide to retard the action is mentioned here to illustrate a principle which applies more particularly with some other developers to be given later.

If, on the other hand, after the first darkening, the remainder of the film shows no sign of following on, and the first dark area, probably representing the sky, grows black with a well-defined edge to it, then we may recognise the evidence of under-exposure. The sky, always so luminous as to impress a plate in a fraction of a second, has had its effect, but the terrestrial objects, reflecting much less light, have not had sufficient time, and for an under-exposed plate there is practically no salvation.

Supposing, however, that the exposure has been approximately correct, we shall next want to know when to stop development. Perhaps the most practical course at first will be to procure, if possible, a good or fairly good finished negative, and cover it with two or three thicknesses of fine tracing-paper. As soon as that portion of your plate which has darkened has assumed a fairly deep tint, lift it out and hold it so that you can look through it towards the dark-room lamp, and hold the paper-covered pattern negative by its side. With a fully-exposed and fully-developed plate there still remains a certain thickness of film which is unaffected and deprives the plate of a certain degree of transparency, and I have suggested the tracing-paper addition to the clear finished model negative as something like an equivalent; but you have not to compare the general transparency of the two so much as the relative intensities of the various parts. If the darkest part of your plate seems less dense than the darkest part of the model, return it to the developer, being careful that no bubbles are formed, and that the solution thoroughly covers the surface. After a minute or so examine it again, and if you are uncertain perhaps this plate had better be used purely experimentally, so rinse it in water and place it in the fixing-bath made as follows :—

Hyposulphite of soda ... 6 ounces.

Water ..... 12 ,,

To which when dissolved add —

Metabisulphite of potassium . . I ounce.

Water ..... io ounces.

Or an alternative is—

Hyposulphite of soda ... 6 ounces.

Water ..... 12

When dissolved add to it —

Sulphite of soda .... 2\ ounces.

Tartaric acid . . . . 2 ,,

Water ... . 8 „

Both these are what are known as acid fixing-baths, and are much pleasanter to use than the old-fashioned and still largely employed plain hypo bath, consisting of 4 ounces hyposulphite of soda in 20 ounces water.

After a few minutes' immersion the opalescent appearance at the back of the negative will have disappeared; leave the plate therein for yet another five minutes, and then wash in water.

You have now your finished negative, and it may be examined by daylight and compared with your model with its tracing-paper removed. If it is too dense it has been developed too long ; if too thin, not long enough. Try now and recall its appearance when examined by the dark-room lamp, and, remembering this, try and profit by the experience in future.

A much simpler but not less important operation remains. The finished negative must be left in running water for not less than an hour and a half to two hours, or, if the water supply be limited, it should receive ten changes of water with an interval of five minutes' soaking between the changes, and then set on end to dry in an airy place free from dust.