SLIDE CASE.
They searched through their books, and at last found a good diagram which gave Jim the hints he needed for his work. He first built a frame which fitted to the slide in the back of his camera box. This frame was provided with a hinged door at the back, and a sliding door in front. In order to receive plates of different sizes, Jim also made several plate frames with larger or smaller openings. The plate frame fitted tightly inside the slide frame, and was held firm by a spring fastened in the centre of the hinged door, which pressed against the plate when the door was shut. Another frame, exactly the same size as the plate frame, had to be made to hold the ground glass upon which to obtain the focus for the pictures. When the focus was regulated, the ground glass was to be carefully withdrawn, and the sensitive plate placed in exactly the same position.
Perseverance and school-boy grit having conquered the slide difficulty, the perplexing question of the lenses came up. Fred's father, who was watching the boys' undertaking with considerable interest, now came to the rescue, and presented the young photographers with a fine set of mounted Dallemeyer lenses with diaphragms, which he bought of a dealer in photographic apparatus.
THE CAMERA.
The camera being in readiness, Fred and Jim now went to work to mix their baths. They began with the sensitive bath, but to their astonishment, when they placed nitrate of silver in ordinary water, a white cloud instantly formed. The text-book was at once consulted, and Fred discovered that distilled water must be used. As the boys had no long-necked retort with which to distill the water, they agreed to suspend all operations until they could see their teacher on the following day, and ask his advice.
The next afternoon, when school was over, the boys marched up to the door of Professor Drood's class-room, and timidly knocked. "Come in," said a hearty, kindly voice. Fred, who was the most courageous, went in first, and clearly stated the case, while Jim stood hesitating in the doorway. "If you take rain-water, and filter it to remove the dust," said the Professor, "it will answer your purpose as well as distilled water."
The boys thanked him, and were going away, when he called them back. "I like to see you taking interest in things of this kind," said he, "and if you will stop, I will give you the whole story as clearly as I can." Fred and Jim were delighted to listen, and when the Professor told them to take a pencil and note-book, and write down the proportions in which the different baths were to be mixed, they were eagerly attentive at once.
"The sensitive bath," said the Professor, "is prepared in this manner: dissolve in two ounces of rain-water one ounce of nitrate of silver in crystals. Then add two to five grains of iodide of potassium. You must now add eight ounces of rain-water, and let the mixture stand two hours to saturate. It must be kept in a dark chamber, where no rays of sunlight can penetrate. You must always work by the light of a candle, and it is a good plan to have a screen of yellow paper around the flame, so that no direct light may fall on your sensitized plate.