A Manual Of Photography

CHLORIDE OE SILVER. 125 Experiment 2.—Place a stick of charcoal in pure water con- taining nitrate of silver, and expose to sunshine. Under the radiant influence, most beautiful crystals of silver will form around the charcoal, until all the metal is separated from the solution. We here see that carbonaceous matter has the power, under the influence of the solar rays, to effect the decomposition of the silver salt. In the first example, we have the metal pre- cipitated as a black powder—oxide of silver ; in the last, it is revived as a pure white metal, the crystals being of exceeding brilliancy. Thus we learn that the organic matter of the paper or the size is necessary to determine the change on which the photographic phenomena depend. For the formation of the chloride of silver, any of the follow- ing salts may be employed; but the resulting colour varies curiously witli each change, as will be noticed more fully presently. 2. Muriate of Soda (Common Salt). 3. of Baryta.\ 4. of Strontia. These salts have very 5. of Ammonia. - remarkable colorific 6. of Peroxide of Iron. properties. 7. ■ ----of Lime. ' 8. Chloride of Potasium. 9. Chloride of Sodium. 10. Hydrochloric Acid (Spirits of Salts). 11. Solution of Chlorine in water. 12. Hydrochloric Ether. All the above salts are necessary only for the purpose of giving a variety of colour to the artist’s productions. This is a point of much interest, as the result of using these different mate- rials as the mordant base determining the tone of the finished picture enables us to produce effects which are in accordance with the subject which we desire to represent. A few experiments of an easy character will be instructive, as pointing out the character of those changes which sensitive sur- faces undergo. Experiment 3.—Pour some of the solution of common salt into the solution of nitrate of silver ; immediately, a very copious white precipitate takes place. Pour off the supernatant liquor, and well wash it, by the dim light of a candle, with pure dis- tilled water; then expose it to daylight: it will change colour very slowly, passing from white to grey. Drop a little nitrate of silver upon the white precipitate, it will darken much more rapidly than before ; add a little organic matter, and the change occurs still quicker; and the degree of darkness