A.—PREPARATION OF PAPER WITH SALTS OF SILVER.

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■—tho increased sensitiveness given to paper, by alternate ablutions ofsaline and argentine washes—the striking differences of effect producedby accidental variations of the proportions in which tho chemical ingre-dients are applied—and the spontaneous change which takes place, evenin the dark, on the more sensitive varieties of tho paper, are all sub-jects of great interest, which demand yet further investigation, andwhich, if followed out, promise some most important explanations ofchemical phenomena at present involved in uncertainty, particularlyof some which appear to show the influence of time-—an element notsufficiently taken into account—in overcoming the weaker affinities.A few particulars of remarkable changes, as observed in photographicpapers, will have a place in this volume.

The proportions in which the muriate of soda has been used, areexceedingly various; in general, the solution has been mado too strong;but several respectable chemists have recommended a wash as muchtoo -weak. For different uses, papers of various qualities should beemployed. It will be found w T ell in practice to keep papers of tlireoorders of sensitiveness prepared; the proportions of salt and silver foreach being as follows:—

Sensitive Paper for the Camera Ohscura.

Muriate of soda, fifty grains to an ounco of water.

Nitrate of silver, one hundred and twenty grains to an ounce ofdistilled water.

The paper is first soaked in the saline solution, and after being care-fully wiped with linen, or pressed between folds of blotting paper anddried, it is to bo washed twice with the solution of silver, drying it bya warm fire between each washing. This paper is very liable to becomebrown in the dark.

Less Sensitive Paper for copies of Engravings—Botanical or Entomo­ logical specimens,

Muriato of soda, twenty-five grains to an ounco of water.

Nitrate of silver, ninety grains to an ounce of distilled water.

Applied as above directed.

Common Sensitive Paper, for Copying Lace-work, Feathers, Patternsof Watch-icorh, §c.

Muriate of soda, twenty grains to an ounce of water.

Nitrate of silver, forty grains to an ounce of distilled water.

Applied as above directed.

This paper keeps tolerably well, but we cannot always depend uponits darkening equally in all parts.

The irregularities discoverable in the texture of the finest kinds ofpaper have before been mentioned. These give rise, however carefullythe successive washes may have been applied, to irregular patches withsharply defined outlines, exhibiting a much lower degree of sensibility