A Manual Of Photography

210 PRACTICE OF PHOTOGRAPHY. The finest kind of paper being chosen, it should he pinned by its four corners to a board, and carefully washed over with a solution of six grains of the nitrate of silver to half an ounce of water: when this is dry, it is to he washed with a solution of iodide of potassium, five grains in the same quantity of water, and dried by, hut at some little distance from, the fire; then, some short period before the paper is required for use, it must he again washed with the silver solution, and quickly dried, witli the same precaution as before. If this paper is warmed too much in drying, it changes from its delicate primrose colour to a bright pink or a rosy brown, which, although still sensitive, is not so much so as the parts which are not so altered. The pe- culiar property of this salt to change thus readily by calorific influence, and some other very remarkable effects produced on already darkened paper when washed witli a hydriodic salt, and exposed to artificial heat, or the pure calorificrays of the spectrum, which will be hereafter noticed, appears to promise a process of drawing of a new and peculiar character. The few simple directions here given will be sufficient to guide the young experimentalist in his earliest essays; and it is particularly recommended that the first experiments should be confined to the salts named in this chapter. The minute details required for the more highly sensitive processes are described in immediate connection with the process to which they refer.