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blacked, by using colourless fluids for writing with; it isplain, that the inks thus produced must be in greaterdanger of fading than those made in the common man-ner, as the proportions of the ingredients, which formthe ink, cannot be ascertained, and will be different ondifferent parts of the paper. The preparation beforerecommended depends on a different principle, in regardboth to the intention and the means : for here the pre-paration is only superficial, while there it is diffusedthrough the substance of the paper : the intention hereis only the producing of a black colour on the surface,by applying a fluid which has no blackness, while therethe paper is impregnated with the material which is mostperishable in ink, in order to continue the blackness be-yond the period in which that of the ink itself woulddecay.

IV. Attempts to prepare an ink from more durable materials..

To introduce into writing the ink whose permanencewe fee daily in printed books, appeared so desirable an ob-ject, that though there were small hopes of attaining it, itsimportance seemed to deserve some trials.

Printers ink, as we have seen in the foregoing section,is a thick mixture of lamp black and oil; and such a mix-ture, though diluted with more oil, is evidently unfit forwriting. Instead of oil, I mixed both lamp black andivory black with solution of gum arabic, made of suchconsistence as just to flow sufficiently from the pen. Theliquors wrote of a fine black colour, but when dry, part ofthe colour could be rubbed off, especially in moist wea-ther, and a pencil dipt in water washed it away entirely.

I tried solutions of the animal glues, with the fameevent. Isinglass or fiih-glue being the most difficultly dis-soluble of these kinds of bodies, I made a decoction of it

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