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To Prepare the Sensitizing Solution

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TO PREP.A.RE THE SENSITIZING SOLUTION.

For this purpose we should have two glass graduates perfectly clean; into one pour one-half ounce of water and add to this sixty grains nitrate silver crystals. They will dissolve in a few minutes by stirring them with a glass rod. When dissolved we add, drop by drop, concentrated ammonia; a dark brown precipi tate will be formed. Keep adding the ammonia, drop by drop, and after about thirty drops begin stirring with the glass rod; after awhile, the dropping and stirring being continued, the am monia will redissolve the dark precipitate, and the solution will begin to grow clear. When it is perfectly clear pour one-half of the solution into the other empty graduate; then, to either one of these solutions, add drop by drop strong nitric acid, stirring the solution with the glass rod. Continue adding the acid until the solution turns blue litmus paper red; then pour the acid solution into the solution in the other graduate and add water to make up to one ounce. This is the solution required for our sensitizing. If made in the day time these operations should be carried on in the dark-room, or it can be made in the evening by gas or lamp light. The solution should be poured into a bottle covered with dark paper, and will keep indefinitely in a dark place.

We will now proceed to sensitize the paper, which can be done in the evening by gas light. We lay a sheet of clean paper, larger than the paper we wish to sensitize, on a smooth board, and to this we pin a sheet of the salted paper with the salted side up. The pins should be placed in the four corners of the paper, and as near to the edge as possible.

We now have to describe how to make the brush for applying the solution. For this purpose we need a glass tube three or four inches long, and about one-half inch in diameter inside. In case we do not have this we can break a hole through the bottom of a four-ounce bottle, and use that in the place of the tube. We pass the loop of a doubled string—clean white cord is the best to use for this purpose--we pass this loop through the tube and run through it, that is through the loop, a wad of fine cotton wool. We then, by pulling on the two ends of the string, pull a portion of this wad into the tube, the greater part of it forming a sort of ball or brush at the end. The ends of the string are then fastened securely around the tube, and then the wad is trimmed neatly with scissors, cutting off all the loose ends. This sensitizing brush should be from one inch to one and a half inches in diame ter, the size depending somewhat upon the size of the paper which we wish to sensitize. If we wish to prepare a sheet of 5 a 8 paper

only, a very small brush will answer for that purpose. Every thing being ready, we pour a few drams of the silver solution into a four-ounce graduate, and in this we place the brush, allow ing it to soak up as much of the solution as it will. Then with the paper before us on the board as described, and inclined towards us, we take the brush and swab the paper, beginning at the upper left hand corner and brushing across the paper to the right until all the paper has been covered. With the first sheet of paper, if it is a large sheet, it may be necessary once or twice to take up a little more solution on the brush. As soon as we have thus finished the paper we turn the board at right angles to its former position, so that one end will incline towards us, and immediately, without adding any more solution to the brush, swab the paper across, beginning at the top and working down to the bottom of the paper. This cross brushing prevents the formation of any streaks which might make their appearance if the paper were brushed one way only. Also, care must be taken, in laying on the solution, always to brush right to the edge of the paper.

The board should now be laid flat, and after a few minutes, or as soon as it becomes partly or surface dried, the paper should be hung up by two corners to dry. As this is done in the evening it is not necessary, of course, to hang the paper in the dark-room. When a sufficient quantity of paper has been sensitized and allowed to dry thoroughly, which it will do in fifteen minutes, it can be cut to the required size, and the clippings preserved with the clippings from ordinary silver paper. The sheet of paper on which the paper has been sensitized should also be kept for sub sequent use. Any silver solution remaining in the graduate should be returned to the dark bottle, and the brush, when dry, can be added to the clippings of silver paper, as it is quite rich in silver. This brush should never be used a second time. This silver paper which we have now made should be printed on the next day or two after being made, or it can be preserved for several weeks by keeping it in a dark box between sheets of blot ting paper that have been saturated with a solution of carbonate soda and afterwards thoroughly dried. The solution of carbo nate soda for this purpose should be in the proportion of two ounces carbonate soda to twelve ounces water.

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