Before entering on the subject of development, it is necessary to tell the student that if he does not already understand the principles of chemistry, he should lose no time in doing so, and as aids to such understanding he cannot do better than get Roscoe's "Lessons in Elementary Chemistry," 1 and Abney's "Photography with Emulsions," and master the chapters mentioned in the footnote, ignoring the rest for the time. Also let him buy Bloxham's "Laboratory Teaching," For a few shillings he can purchase apparatus enough to do qualitative analysis. This he will be able to do by following Mr. Bloxham's directions, omitting, perhaps, testing with the blow-pipe. If he has the time and means, he will do well to do some quantitative analysis, working, say with water, since it is of such immense importance to the photographer. He will find a knowledge of chemistry as interesting as useful, and the power of observation and accuracy acquired by the study will be invaluable in subsequent stages of his work. We refer the student to works on chemistry by specialists, because we think it is a mistake to swell the bulk of our book by an exposition of chemical principles. We caution the student, however, who intends to take up photography as an art, to have nothing to do with plate-making. That manufacture can only be done satisfactorily by experts constantly employed at it, and it is as reasonable to expect a painter to prepare his own colours, and make his own canvas, as to insist upon a photographer making his own plates. Some people have tried to propagate the false idea that a picture taken on a plate of the exhibitor's own making has a special kind of merit, but obviously this is only true when the object is an "Emulsion process competition." In judging of the merits of a picture, no facts should be taken into consideration, save the art expressed by the picture. Still the student should know the methods by which his plates are prepared, and that his chemistry will teach him, and when he has found plates which suit him, let him keep to them. We have worked with fourteen different kinds of plates, and have found most of them good, though each requires different treatment. One piece of advice is, however, necessary, always buy your plates direct from the makers, unless you can rely upon your dealer. Some plates are, of course, much quicker than others, and this point the beginner must carefully bear in mind, making his exposures accordingly. He must not forget, however, that there are brands of plates which are " starved" of silver; these he should avoid, and it would be well if a vigilance committee were appointed in every society to test batches of plates occasionally, and report on them in the photographic journals, thus showing up the fraudulent manufacturers. Assuming, then, that the student has carefully studied the chemistry of development and has fixed on a satisfactory brand of plates, we will proceed to give him a few practical hints, but before we do so we must get rid of an obstacle in his path, and that is the wet-plate process.

Roscoe's Chemistry: -

Lessons 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,12, 13,14, 15, 16,17, 18, and potassium, sodium, and ammonium in lessons 19, 22, 23; chromium and uranium in lesson 25; mercury, silver, and platinum in lessons 26, 27, and 28. "Photography with Emulsions:" - Caps. 1, 2, 3, 5, 6, 7, 8, 9, 22, 24, and 31.