INDELIBLE WRITING INK. 339 



V. 



On the Processes emnloi/ed to cause Writing to disappear 

 from Paper f to delect the Writing that has. been iuhstU 

 iutedj and to revive that which has been made to disap- 

 pear ; Improvement of common Ink; a Notice of a new 

 Inky that resists the Action of chemical Agents: by B. 

 H. Tarry, M, D. *. 



W RITING is removed either by scraping with a knifcj Indications of 

 or by means of acids. When writing has been scratched ^^^^^"1.^^^^ ' 

 out, commonly pounce, or size, is applied to the paper, out. 

 that the ink afterward used may not run. If pouncevhave 

 been employed, the strokes of the same pen will app^r 

 more slender, if size more fuU, than on other parts of the ^ 

 paper. Immersion in warm water for a few minutes will 

 dissolve and wash away size: alcohol will have the same 

 effect on pounce. After the paper is taken out, it should 

 be dried slowly; at first in the shade, till three parts dry, 

 and afterward between the leaves of a book, or a quire of 

 paper. While it is drying the ink last used will spread and v 



sink into the paper more or less. Generally indeed close 

 inspection with a good lens will show where any writing has 

 been scratched out, by the appearance of some loose or 

 torn filaments. 



If the means employed to obliterate Writing have been If all the iron 

 such as to remove the whole of the iron from the P^P^r, ^^^^^ ,^t" '^^^ 

 every attempt to restore the writing must be vain. If some writing cannot 

 ferruginous compound remain, the characters maybe re-^^'^^^^° 

 produced in their original form; though the colour, will 

 vary, according^ to the nature of the compound in which 

 the iron is concealed, and of the reagent employed. 



In some cases the gallic acid is capable of recomposing Sometimes it 

 the writing, that has been made to disappear by chemical ^^^^1^,^^^.^'^® 

 means; but its attraction for the oxide of iron is not so 

 f> strong as is commonly supposed. The red or brown oxide 

 of iron, obtained from the sulphate or nitrate hy means ©f 



• Abridged from the Ann. de Chim. vol. Ixxiv, p. 153; and 

 from the report made to the Institute by BerthoUet, Vauquelin> 

 and Deyeux, ib, vol. Ixxv, p. 194. 



Z 2 . alkaline 



