189 



Transactions of the Canabridge Philosophical Society. Vol. 6, 



Part ii. — By the Society. 

 Bulletin de la Societc de Geographic. 2nie Serie, Tome 8. — By the 



Society. 



The following Communications were read : 

 1. On the Composition of a new Ink, which, by resisting 

 chemical deletion, promises to diminish the chances of 

 the successful falsification of bills, deeds, and other do- 

 cuments. By Professor Traill. 

 The author was led to the investigation of this subject by its 

 connection with that branch of Medical Jurisprudence which treats 

 of the prevention and detection of forgery. 



It is well known that common writing-ink may be totally effaced 

 from paper by certain chemical agents, and that several others so 

 impair its colour, that the characters traced with it become illegi- 

 ble. To the first class of chemical agents belong chlorine, and 

 substances containing it, as well as oxalic acid : to the second diluted 

 solutions, or the vapours of the mineral acids, and of the caustic 

 alkalis. These agents were applied to written specimens of a great 

 number of different inks, and the degree of resistance to their ef- 

 fects was considered as the criterion of the durability of each. 



These views engaged the author in an extensive series of expe- 

 riments on coloured metallic preparations, suspended in different 

 vehicles, the results of which were laid before the Society. In one 

 series, the colouring matter was precipitated on paper previously 

 imbued with various chemical substances, capable of effecting the 

 decomposition of the solutions applied ; but no advantage was de- 

 rived from this method. No useful results were obtained from the 

 use of any of the metallic sulphurets or iodides, either alone or 

 mixed with common ink ; nor from preparations of indigo or other 

 * vegetable colours. Among the metallic preparations which resisted 

 chlorine was a fine blue substance obtained by precipitating chlo- 

 ride of antimony by ferro-cyanide of potassium : but it was imme- 

 diately destroyed by ammonia. The rich yellow substance formed 

 by adding nitrate of cobalt to ferro-cyanide of potassium resists al- 

 kalis well ; but it is effaced by acids. An ink composed of both 

 these last-mentioned metallic salts was effaced by immersion, first in 

 chlorine, and then in an alkali. 



These failures to produce a durable ink from metallic combina- 

 tions induced the author to attempt the composition of a carbona- 

 ceous liquid which should possess the qualities of good writing-ink 



