Altogether, though the work is interesting, and even fascinating in a way, the responsibilities are so great that the effect on the nerves is often very trying at times.  One thing we are particular about, and that is to take no chances.  If we have the slightest doubt about the genuineness of a check we at once communicate, either by telegraph, special messenger, or telephone, with the supposed drawer of the check, and in this way turn doubt into certainty.  During the last three years not a single wrong check has passed our vigilant optics, and, though I say it who should not, I do not believe there is a cleverer set of experts any where than those who compose my staff.

CHAPTER XIII

HOW TO DETERMINE AGE OF ANY WRITING

The Different Kinds of Ink Met With—­Inks That Darken by Exposure to Sunlight and Air—­Introduction of Aniline Colors to Determine the Age of Writings—­An Almost Infallible Rule to Follow—­To Determine Approximate Age of Ink Possible—­The Ammonia System a Sure One—­A Question of Great Interest to Bankers and Bank Employes—­Thick Inks and Thin Inks—­So-called Safety Inks That Are Not Safe—­How to Restore Faded Inks—­An Infallible Rule—­Restoring Faded Writing—­Restored by the Silk and Cotton System That Anyone Can Arrange—­Danger of Exposing Restored Writing to the Sun.

The inks in common use over the United States at the present time, and for some years past, are not as numerous as one might be led to conclude.  They are probably fifteen or at most twenty in all, including the most popular blue, red, magenta, and green inks.  But among these there is a notable difference in character.  Some are thick, heavy, and glossy, in character, and flow sluggishly from the pen.  Few of these become much darker by standing.  In this class will be found the copying inks and those in which a large quantity of gums or similar thickening agents are used.

Other inks are pale, limpid, and flow easily from the pen, and this class usually shows a notable darkening by exposure to sunlight and air.  It will be unnecessary here to refer more particularly to the intermediate varieties or to discuss their various composition.

It should be, remembered here that in the last twenty years, or since the introduction into general commerce of aniline colors, which Hofmann discovered in 1856, these latter have been employed more and more in writing fluids; not only in mixtures of which they are the principal ingredients, but to a greater or less degree in all inks.  Their presence, even in small quantity, in the gallo-tannate of iron and logwood inks can be generally detected by an iridescent and semi-metallic luster.