the Ink of ancient Writings. 455 
latter way preferable. For the principal inconvenience which 
occurs in the propofed method of reftoring MSS. is, that the 
colour frequently Ipreads, and fo much blots the parchment, 
as to detract greatly from the legibility ; now this appears to 
happen in a lefs degree when the alkali is put on firh, and the 
dilute acid is added upon it. The method 1 have hitherto 
found to anfwer beft has been, to fpread the alkali thin with 
a feather over the traces of the letters, and then to touch it 
gently, as nearly upon or over the letters as can be done, with 
the diluted acid, by means of a feather, or a bit of hick cut 
to a blunt point. Though the alkali has occalioned no fenfible 
change of colour, yet the moment that the acid comes upon 
it, every trace of a letter turns at once to a fine blue*, 
which foon acquires its full intenfity, and is beyond compari- 
fon ftronger than the colour of the original trace had been. 
If now the corner of a bit of blotting paper be carefully and 
dexteroufly applied near the letters, fo as to fuck up the 
fuperfluous liquor, the ftaining of the parchment may be in 
great meafure avoided: for it is this -fuperfluous liquor, which, 
abforbing part of the colouring matter from the letters, be- 
comes a dye to whatever it touches. Care mufl be taken not 
* The phlogijlicated alkali (which is to be conftdered Amply as a name) appears 
to confift of a peculiar acid, in the prefent extenlive acceptation of that term, 
joined to the alkali. Now the theory of the above-mentioned procefs I take to 
be, that the mineral acid, by its ftronger attraction for the alkali, diflodges the 
colouring (Pruflian) acid, which then immediately feizes on the calx of iron, and 
converts it into Pruftian blue, without moving it from its place. But if the 
mineral acid be put upon the writing firft, the calx of iron is partly diflblvedand 
diffufed by that liquor before the Pruflian acid combines with it ; whence the 
edpes of the letters are rendered more indiftintt, and the parchment is more 
tinged. The fudden evolution of fo aline colour, upon the mere traces of letters, 
affords an amufirig fpe&acle. 
Vo l. LXXVII. 
S f f 
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