PAPER incombustible, and the writing on it, of course, indestructible by fire. Of all the substances which he tried, he found the liquor of flints the most proper to secure paper from destruction by fire. He dipped a sheet of paper several times in the above liquor freshly made, or daubed it several times over the whole paper with a hair brush, and dried it in the sun or in an oven. Paper prepared in this manner lost some of its softness, became a little rougher than before, and acquired a lixivious caustic taste. In other respects it was not different from common white paper. When this paper was laid upon glowing coals, it did not burn like common paper, but became red, and was converted to a coal, which however did not fall into ashes like the coal of common paper, so that it might therefore be considered as petrified paper. This coal, however, is exceedingly friable; for when it is taken between the fingers, or pressed together in any manner whatever, it drops to pieces. Still the discovery must be a valuable one, if there be any kind of ink of such a nature as that the characters written with it continue visible on this coal. Such an ink M. Brugnatelli made by combining dissolved nitrite of zinc with common ink; and found, that the colour of this mixture, though it appeared somewhat pale on common paper, became so dark on prepared paper, that words written with it appeared more conspicuous than words written with common ink. When the paper was burnt, or reduced to a coal, those characters were so visible, in a clear white colour on a dark ground, that they could be read with as much ease as characters written with the best ink on white
white paper. If the ingenious author succeed in his attempts to discover a method of rendering his prepared paper less friable when burnt, his discovery will be one of the most important of the present age.