o 
162 i: 
The method which I have adopted in applying these re- 
agents is to moisten one or more strokes or letters of the 
writing with each reagent, and then to absorb by blotting 
paper the excess of fluid, a few seconds afterwards. 
By thus treating the ink on different envelopes lately sent 
to me I find they give very diverse results ; with sulphuric 
acid, for instance, the black colours of the different inks are 
changed, in some to bright crimson, in others to deep red, 
whilst some become blue, green, violet, and grey of different 
shades, and some remain practically unaltered ; and when, 
as sometimes happens, the same or nearly the same colours 
are produced in two different inks by one reagent, the 
colours produced by another are very different, thus show- 
ing clearly that the letters were not written by the same 
inks. 
The same kind of ink, sold by the same maker, but made 
at different times, also varies more or less in its behaviour 
with the reagents, as shown by the comparisons of three 
samples of Lyon’s inks, sold in small penny bottles, which 
were bought at different places. 
Differences between inks which give nearly the same re- 
actions may sometimes be observed by noticing the lengths 
of time which the reagents require to bring about the ulti- 
mate changes and by the shades of colour through which 
the ink passes after applying each reagent. Changes also 
continue to go on gradually for days and weeks after the 
reagents have been applied. The colours and shades of the 
same colour can be much more distinctly seen by the aid of 
a good pocket lens. 
It is evident that if two persons use ink made by the 
same maker at the same time the reactions would be pre- 
cisely similar, but it is easy to understand that after such 
ink has been in use for some time, owing to the different 
habits of the users, each may acquire a distinct individuality. 
One, for instance, may have been more exposed to the air 
