14 On the Composition of Writing Ink , 
4, Finally, the discovery of an ink which should re- 
sist all chemical agents. 
We shall now give an abridgement of these four ar 
tides : 
ARTICLE I. 
Processes for Discharging Writing . 
The art of discharging writing is very ancient, and 
the means employed are very simple. In fact, we know 
that it is sufficient to moisten a written paper with any 
acid, when the writing will gradually disappear. But 
all the acids cannot be employed with equal success. 
Some leave a stain on the paper which is not easily re 
moved : others corrode and render the paper unservice- 
able. The way to avoid these inconveniences is to make 
choice of an acid which shall act on the writing only, 
without injuring the paper or giving it a colour dif- 
ferent from that which it had before it was written upon. 
In order to discover such of the acids as are best 
suited for the operation in question, the author deter- 
mined to submit common writing ink to the action of 
different acids, and to observe carefully the phenomena 
which these bodies present at the time of their mixture, 
According to him, the sulphuric acid easily takes out 
writing, but at the same time it gives an oily tint to the 
paper. 
The acid oxalate of potash produces more certain 
and more prompt effects. The oxygenized muriatic 
acid, if it be newly made, seems to be preferable to 
the above two acids, because at the same time that it 
takes out the writing it bleaches the paper without alter- 
ing it. 
It is not the same case with the nitric acid, which 
always takes out the ink, hut soon penetrates the pa- 
