This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Preparing A Bromide Solution. Into a bottle pour 9 ozs. of water, and to this add 1 oz. bromide of potassium. Shake until dissolved. With a pocket knife, cut a thin notch the entire length of the cork stopper and insert the cork tightly. When you want to add a few drops of bromide turn the bottle upside down and the notch in the cork stopper will permit the solution to drop, one drop at a time. Any time that a negative flashes up too quickly, indicating over-exposure, a few drops of bromide should at once be added, as the bromide acts as a restrainer and prevents the shadows from developing, thus enabling the highlights to build up and thereby supply the necessary contrast. Negatives that are treated in this way, or rather negatives that are over-timed and treated in this way, should be developed farther (thicker) than normal exposures; and after thorough fixing they can be reduced. (See instruction for Reducing.)
Over-Development. Over-developed negatives are those which have been left in the developer too long. This may be caused by accident, lack of knowing when the plate is fully developed, or it may be caused by over-exposure where you purposely over-developed in order to obtain detail, snap, and contrast. In any of these cases you can improve the printing quality of the negative by reducing.
304. (See Illustration 31.) Here we illustrate the advantage of reducing strong, thick negatives - plates that would require hours for printing if printing-out paper were used. By reducing, the plate is made to print in a few minutes. Note the contrast between the half of the plate that has been reduced and that which has not. This illustration should serve to show the advantage of altering negatives improperly developed.