36 On the Composition of Writing Ink. 



writing consist, as abovementioned, in decomposing th6 

 ink and in forcing its conotituent parts to form other com- 

 binations. These combinations, being decomposed in their 

 turn by different agents, may regain a tint, which, if it be 

 not that of ink, at least exhibits a shade which becomes 

 perceptible enough for ascertaining the letters and words 

 which had been traced on the paper before it was touched 

 by the acids. 



The gallic acid is, according to the author, one of those 

 ageuls, which in this case succeeds very well. 



The liquid prussiate of lime also produces a good effect. 



It is the same case with the alkaline hydrogenatcd sul- 

 phurets. But it is very certain that we never obtain any 

 success from the employment of these agents, when we have 

 left any acid long in contact with the writing, and particu- 

 larly if we have washed the paper afterwards. 



In short, we may easily conceive, that in this case the 

 constituent parts of the ink which were combined with the 

 acid, and had formed with it compounds soluble in water, 

 having been taken up bv this fluid, ought not to leave any 

 trace of their existence longer; and consequently it is im- 

 possible that the agents employed for discovering them can 

 render them visible. 



It is also for this reason that the gallic acid, the liquid 

 prussiate of lime, the alkaline hydrogenated sulphurets, and 

 so many other reaejents w hich have been so much praised, 

 can no longer be regarded as infallible methods for reviving 

 writing. 



ARTICLE III. 



Improvement of Common Ink, 



Most of the inks now in use are of a bad quality. Some 

 are spontaneously destroyed; others imperceptibly lose their 

 black colour, and assume a yellow one; several, after a length 

 of time, enter into the paper, and spoil it : lastly, there are 

 some which are tirst pale and then become very black. 



All these differences arise from the nature of the sub- 

 stances which have been emploved in the roakiiio; of the 

 ink. 



Convinced of the advantage of having a good article of 

 this kind, the author commenced a series of experiments, 

 but is forced to admit that he has not discovered any recipe 

 superior to that which has been published by Lewis. This 

 ink, according to our author, combines every advantage : but 

 we must observe that it is no more exempt than the rest 

 from being dissolved in the acids, and in this rasped it has 



an 



