The pyro., as we have already observed, is the true developer, and the density of the negative will depend, to a certain extent, upon the amount present in the mixed solution. The ammonia, or accelerator, as its name im plies, hastens or accelerates the action of the developer, and the bromide solution restrains or retards it. It requires but slight consideration, therefore, to appreciate the general principles which govern the operation of deve lopment. In our first experiment we found upon applying the normal developer that the plate was somewhat under exposed, we therefore accelerated the action of the developer by adding more ammonia, and by increasing the developing energy of the solution, forced more detail to appear in the negative, and gained an increase of deposit. When it becomes necessary to force development in this way, the ammonia should be added cautiously in small quantities at a, time, as to add the full amount at once would spoil the negative by causing fog ; a defect we shall have something to say about hereafter. The second negative having deve loped with the normal strength of solution, and having required only the addition of a small quantity of accelerator to complete development, proved that the exposure was as nearly as possible correct. The flashing out of the imaEre, in the case of the third negative, immediately upon the application of the normal developer, conclusively proved that the plate had been over-exposed, and to remedy this, development was arrested by washing off the developer, a new one being applied in which the proportion of restraining bromide Ivas greatly increased, with the view of retarding the action of the solution, and giving the plate time to acquire the necessary amount of density. Indeed, if WO were to add a sufficient amount of the latter salt, he developing action would entirely cease. And it should also be noted that when frequent additions of ammonia Lave to be made, certain proportion of bromide should be added also, say in the proportion of 1 to 4, or general fog may result.
The foregoing instructions, if carefully followed, although they constitute merely a tithe of what might be written upon the subject, should be sufficient to enable the reader to grasp the general principles involved, and enable him to turn out a satisfactory negative.
Although I have recommended the reader to use for his early experiment the pyre. developer, it should be mentioned here that there are several other alternative methods which may be employed. The oldest of these is that known as the ferrous oxalate method. I do not, however, propose to describe it in detail here, as it does not, in the hands of a beginner, allow so much latitude in exposure as some other methods do, and it will, moreover, be necessary to fully deal with it when we learn how to print upon bromide paper.
The hydroquinone developer has become a great favomite with amateurs, probably owing to the fact that all the chemicals of which it is compounded may be dissolved together and used in one solution, and because it is a very cleanly developer to use, in that it does not cause the hands to become stained. The last-named property is, to some extent, an advantage, particularly if the oprator be inclined to be careless in his manipulations ; but to make it a practice to use a "one-solution developer" is a system which cannot be too strongly condemned. Having referred to the advan tages of hydroquinone, it is only right to point out its chief defect, which is an almost unavoidable tendency, at any rate in the hands of beginners, to produce negatives of such a character that hard prints result. It is, in fact, difficult to avoid getting undue contrast in negatives so developed, and it is for this reason that I do not recommend its use for ordinary negative work, although for other purposes, such as the production of transparencies, the making of lantern slides, and for copying engravings where density an& clear ness are essential conditions, it probably has no equal. I
have condemned the very general practice of making it up in one solution, for the reason that so doing greatly lessens the control which the user would otherwise have over its action ; but there is no necessity to so use it, and in the formula which has been given we shall employ two solutions. No. 1, containing the hydroquinone, is the true developer, and No. 2 the accelerator. For correct exposure, equal parts of 1 and 2 are taken, further additions of No. 2 being made in the event of the plate being under-exposed. If, on the other hand, the plate is found to be over-exposed, the normal developer is simply diluted with an equal bulk of water, and more time allowed. Full exposure always gives the best results with hydroquinone. Under-exposure gene rally results in negatives of a character which is spoken of among photographers as " soot and whitewash." There will be found very little tendency to fog when using hydro quinone, unless the plate has been very considerably over exposed, and the fact should also be borne in mind that it acts more slowly than does pyre., and the time occupied in development is usually longer.
A developer of still more recent origin, the application of which to photographic purposes is due to Dr. Andresen, is the substance which has been called eikonogen, and although up to the time of writing it has not been very generally adopted, yet the results obtained from it are exceedingly promising, and it would seem to have a great future before it. The chief drawback to its employment lies in its comparative insolubility, this property rendering it a matter of impossibility to prepare the developer in a concentrated form. Like hydroquinone, it acts somewhat slowly on the plate, but there the resemblance ceases, for, instead of producing strong, vigorous negatives, with a tendency to hardness, the characteristics of negatives developed with eikonogen are a remarkable amount of fine detail, combined with great softness and an even gradation. It has been suggested to utilise the markedly different tendencies of the two developers by combining the two substances in one solution, so that the advantages of each may be obtained. The following formula, due to Mr. W. H. Walmsley (Philadelphia), will be found to give good results : Solution No. 1, sulphite of soda 240 gr., soda carbonate 120 gr., distilled water 6 oz. Solution No. 2, eikonogen 100 gr., hydroquinone 80 gr., distilled water 6 oz. To make a developer of normal strength equal parts of these solutions are mixed together, 6 parts of water being added. In cases of over-exposure the proportion of No. 1 may be reduced with advantage.
The following is a good formula for an eikonogen developer : Dissolve in 15 oz. of distilled water 4 oz. of eikonogen, 1 oz. of sulphite of soda, and 4 gr. of bromide of potassium ; label this No. 1. In 10 oz. of distilled water dissolve 1 oz. of carbonate of potassium ; label No. 2. For a normal developer mix the solutions in equal proportions. The detail-giving properties of this developer are very great, and it is most valuable for developing under-exposed plates.
In concluding this chapter upon development I cannot, perhaps, do better than warn the reader against the com mon practice of trying the plates of first one maker and then of another. If this be done, success will seldom be attained, for if it be imagined that one dry plate is very much like another the assumption is an erroneous one; the fact being that, although nearly all commercial dry plates are of good quality and thoroughly reliable, each particular make possesses characteristics entirely its own, a knowledge of, and mastery over, which the photographer can only acquire by the experience gained by long use. Therefore, having chosen a good make of plate, the reader should studiously avoid all temptation to try rival makes until he can, with reasonable certainty, produce a good negative.