Gn the Composition of JlYiting Ink, 35 



easilv removed : others corro-le and render tlie paper unser- 

 viceable. The way to avoid th^se inconveniences is to make 

 ttioice of an acid which shall acton the writing only, wiih- 

 oul injuring the paper or giving it a colour dillcrent ironi 

 that whicli it had before it was written upon. 



In order to uiacover such, of the acids as are best suited 

 for the optration ni question, the author determnied to sub- 

 mit eoninion writing ink to the action of diflerenl acids, and 

 to observe carefully the phcenomena which these bodies pre- 

 sent at the truie of tiieir mixture. Accordnig to hiu), the 

 sulphuric acid easily lakes out writing, but at the same tiiiie 

 it givts an odv tiiit to the paper. 



'Ihe acid oxalate of poiajh produces more certain and 

 more prompt effecis. The oxygenized muriatic acid, if it 

 be newly made, seems to be preferable to the above two 

 acids, liecat'se at the same time that it takes out the writing 

 it bleaches the paper without al'ering it. 



It is not the same case wiih the nitric acid, which al- 

 ways takes out the mk, but soon penetrates the paper and 

 forms above it undulated lines of a yellow colour. 



We may succeed, however, in softening both these effects, 

 by taking the precaution to dilute the nitric acid with a 

 sufficient (juantity of water, or to wash the paper imme- 

 diately after the writing has been taken out. 



A mixture of the muriatic and nitric acids has but a slow 

 action upon writing. It bleaches the paper and does not 

 oppose its desiccation, as when we employ the nitric acid 

 alone. 



In eeneral, whatever be the kind of acid employed to 

 discharge writing, it is always proper when the ojieratiou 

 is performed to clip the paper in water, in order to dissolve 

 ihe new combmations which the acids have formed with 

 the particles of ink which have been discharged. 



M. Tarry, at the conclusion of this article, does not fail to 

 ()bserve that China ink does not act like common ii.k with 

 the acids, as iis composition is quite different from that 

 which we use f<)r wilting of all kinds. So far from the 

 acids attacking China ink, they make it, on the contrary, of 

 a deep black: it cannot be discharged therefore witliout 

 erasing it. 



ARTICLE II. 



processes for ascertaining what Jfiiling has been snhstitulcd 

 Jor something taken out, and Meihods (f leviiing the 

 U'liltng which has disa/jpeaud. 



All ihfc nitlhods wh.ch have been given fur discharging 

 C -2 writinjr 



