254 ANNUAL OF SCIENTIFIC DISCOVERT. 



ancient deeds, written on stamped paper, and a few words of which had 

 been removed by us with chemical agents, to recognize the places where 

 their action was exerted, to see and to measure the extent which they 

 occupied on the surface of the paper. 



The testing of a paper with the vapor of iodine will present this double 

 advantage over the methods hitherto practised for detecting falsifications in 

 writings, that it points out at once the place in the paper in which any 

 alteration may be suspected, and that, on the other hand, it enables us to 

 act afterwards with the reagents proper for causing the reappearance of 

 traces of ink, when that is possible. If the means which we now propose 

 cannot always make the former writing appear, they demonstrate the 

 places where the alterations must have been made, when, however, the 

 want of uniformity presented by the surface of the paper is not explained 

 by any circumstance. This proof becomes, therefore, a weapon which the 

 guilty person cannot avoid. But might not the presence of a stain, or several 

 stains, developed by the vapor of iodine, in different parts of a public or 

 private deed, give rise to a suspicion, where these stains have, perhaps, been 

 occasioned by the spilling of some liquid on the surface of the paper ? and 

 would it not be rash and unjust to raise an accusation from such a fact ? 

 There would indeed be great temerity in drawing such a conclusion from 

 a fortuitous circumstance ; but the inference which may be drawn from the 

 place occupied by these stains on the surface of the paper, from the more 

 or less significant words found in those places, would not permit an accu- 

 sation to be so lightly brought, where simple reasoning would be sufficient 

 to destroy its basis. Besides, the subsequent reactions which would be 

 made would certainly never revive words formerly written and effaced ; 

 whilst the latter effects may be often produced, more or less visibly, on 

 those parts of the paper on which falsification has been practised, figures 

 or words being substituted for other figures or words. 



2d. The applications made to the surface of a sheet of paper, with a 

 view of covering it again at certain parts with a fine layer of gum, gela- 

 tine, starch, or flour paste, or in other places to cause other sheets of paper 

 to adhere, may be recognized not only by the reflection of light falling upon 

 the paper inclined as a certain degree of obliquity, and by the transmis- 

 sion of light through the paper, but also by the varying action which the 

 vapor of iodine exerts on the surface which is not homogeneoiis. Papers 

 containing starch and resin are more powerfully acted upon by this vapor 

 than papers of a less complex composition. Both in the parts covered 

 with starch, or flour paste, are colored in a few minutes of a violet blue ; 

 but with starched papers alone a more intense coloration is manifest oil 

 the places covered again with a thin layer of gum arabic, size, or gelatine. 

 By looking, then, at the surface of the paper, held somewhat obliquely to 

 incidental light, we distinguish clearly, by their different aspect, the parts 

 on which these various substances have been applied. The vapor of iodine, 

 in condensing at the ordinary temperature on the surface of the papers to 



