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 for each, it will be found possible to secure more complete control over the character of the prints, and a more perfect uniformity of result than is possible in ordinary silver printing.

The tissue should be kept in a cool, dry place, packed flat, and kept under a weight. If suffered to be exposed to the atmosphere, it will be apt, in hot weather, to curl up and become unmanageably horny; whilst in damp weather it would, being a hygroscopic substance, absorb moisture.

This and other subsequent operations will of course be conducted in the "dark-room." A nearly saturated solution of bichromate of potash is employed. As the strength of a saturated solution varies with temperature, Mr. Swan prefers to make a solution of definite strength, by dissolving such a quantity of bichromate of potash as will not, during cold weather, crystallize. Such a solution is formed by dissolving one pound of bichromate of potash in twelve pounds of water.

The tissue is immersed by drawing it (face up) under the solution (contained in a dish two or three inches deep), care being taken to avoid the formation of air-bubbles. After immersion the sheet is turned, and a flat camel's-hair pencil is employed to remove the bubbles that form on the back, which, being apt to repel the aqueous solution in small points, should be brushed over until all parts absorb properly. After the displacement of the bubbles from the back of the tissue, it is