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means are usually employed. Seldom however is it sup- 
posed that a common substance such as the ink used in 
writing a letter or document, has any special individuality 
about it. All ordinary inks are black or nearly so, yet it is 
conceivable that the name and address of the writer of an 
anonymous letter may, under a given combination of cir- 
cumstances, be contained within the black fluid with which 
the letter was written. If then a murderer has left his trace 
behind him in the shape of paper and ink, it seems to me 
not improbable that by a judicious use of the latter, some 
important information may be obtained respecting him 
which may ultimately lead to his capture. Some years ago 
the information obtainable by the examination of the ink on 
papers or documents would probably have been compara- 
tively insignificant, owing to the fact that the number of 
different kinds of ink in the market at that time would be 
small, and the modes of preparation of the ink simple, and 
the materials used not specially subject to variation. At 
the present day however a large number of different articles, 
many of which are subject to variation, are employed in the 
manufacture of ink, and a large number of different inks 
are in general use, and from these reasons the testimony 
capable of being obtained by the chemical examination of 
the ink on letters or documents at the present time may, in 
some cases, prove to be of the greatest importance. 
The reagents which I have found to act best in the test- 
ing of the ink on papers are nine, viz. 
1. Dilute sulphuric acid. 
2. Strong hydrochloric acid. 
3. Slightly diluted nitric acid. 
4. Sulphurous acid solution. 
5. Caustic soda solution. 
6. Cold saturated solution of oxalic acid. 
7. Solution of bleaching powder. 
8. Solution of protochloride of t’’n. 
9. Solution of perchloride of tin 
