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influence of the vapor of iodine； and the parts
which have received superficially a layer of another
agglutinative body resist this action for a certain
time； and are distinguished from the parts of the
paper which are not covered with it。〃
My own investigations confirm to a great extent
the value of these experiments and the accuracy of
the deductions； in so far as they relate to 〃linen〃
paper； but they do not always obtain when made in
connection with paper of inferior grades。
It is also true that dry paper is affected differently
under the influence of the vapor of iodine； as would
be paper which had been moistened and then dried；
but the part which had been moist assumes the color
of blue…violet； while unaltered paper assumes a yellow…
brown color。 Even when the paper thus treated is
moistened all over with water； there will be a difference；
for those parts which had been before moistened；
will appear a dark violet…blue； while the other parts
will show a plain blue coloration。
In cases where pencil writing has been removed
with a soft rubber or fresh bread； the parts thus
erased will assume； when subjected to iodine fumes； a
brown color trending towards violet and much darker
than the undisturbed portions of the paper。 Lines
impressed upon paper with a 〃stylus；〃 a glass or
ordinary dry pen； can be made visible by the fumes of
iodine； the lines showing with a stronger coloration
than the surrounding paper。
CHAPTER XX。
FUGITIVE INK。
SOME OBSERVATIONS ABOUT 〃ADDED〃 COLOR TO INK
INVENTION OF COAL TAR COLORSCHRONOLOGICAL HISTORY
OF THE 〃ANILINES〃 EMPLOYED AS INKOTHER
SUBSTANCES USED FOR THE SAME PURPOSE。
THE term 〃added color；〃 as applied to ink； is the
popular phraseology for a multitude of materials
which have been more or less utilized for a period of
centuries； in adulterating and coloring ink。 In olden
times they were introduced into ink with an honest
belief that it would also improve and ensure its lasting
qualities； but latterly more often to cheapen the
cost of its manufacture。 Reference has been made
to a large variety of these substances used for this
purpose and the story told of the effect of the test of
time upon them as indicative of their supposed value。
Attention has also been directed to the discovery
during the nineteenth century of the colors which
owe their origin to by…products of coal tar。
Generically these colors are classified as 〃anilines。〃
They have worked a revolution in all the arts in
which colors are used。 Employed without a mordant；
with few exceptions； they are measurably affected by
both light； heat； moisture； or other changes and as
made into inks are never permanent。 Hence they
should not be used for records； because if obliterated
from any cause whatever； there are no known means
to render them again legible。
The origin and history of the 〃anilines〃 are
known。 Viewed from an ink standpoint they are of
vast interest。 So extended in number are the 〃anilines〃
（they run into the thousands） that they include
every shade of black and all possible tints or hues of
the colors of the rainbow。
The chronological history of such of these artificial
colors which appertain to ink or its manufacture is
important as locating the dates of their invention
and commercial use。
The first discovery of 〃aniline〃 is credited to
Helot in 1750。 In 1825 Faraday in rectifying naphtha
discovered benzole； which by the action of strong
nitric acid be converted into nitro…benzole； and this
latter； when agitated with water； acetic acid and iron
filings produced aniline。 Unverdorben in 1826 discovered
an analogous material in products obtained
by the destructive distillation of indigo。 Runge in
1834 claims to have detected it in coal tar and called
it kyanol； which after oxidation became an insoluble
black pigment and known as aniline black。 It could
not； however； be used as an ink。 Zinan in 1840；
experimenting along the same lines； produced another
compound terming it benzidam。 Fritsche in the same
year by the distillation of indigo with caustic potash
developed a product which he also called aniline； the
name being derived from the Portuguese word anil；
meaning indigo。 Shortly afterwards A。 W。 Hoffman
established the identity of these substances。
Aniline when pure is a colorless liquid； possessing
a rather ammoniacal odor。 It soon becomes yellow
and yellow…brown under the influence of light and air。
It does not affect litmus paper。
In 1856 Perkins accidentally discovered the violet
dye called mauve； which acquired considerable commercial
importance besides its utility for ink purposes。
Nicholson in 1862 succeeded in producing the first
of the soluble blue anilines。
The discovery of induline； one of the modifications
of aniline black； was made known in 1864。
Nigrosine； produced by the action of concentrated
sulphuric acid on the insoluble indulines； was discovered
in 1868。
The soluble indulines and nigrosines differentiate in
appearance； the first a bronzy powder and the latter a
black lustrous powder。 When made into ink they
possess about equal color values。
In 1870 the German chemists； Graebe and Liebermann；
announced that they had succeeded in producing
artificial alizarin；the coloring matter of the
madder root。 Commercial value was not given to
this discovery until it was put on the market in 1873；
although it did not meet all the requirements。
Springmuhl in 1873 obtained an accessory product
in the artificial manufacture of alizarin out of anthracene；
from which a beautiful blue was made； superior
in many respect to the aniline blues。 It differed from
aniline in having the same color in solution。 Alkalis
destroyed the color but acids restored it。 The process
was kept a secret for a long time。 This product was
originally sold as high as 1；500 for a single pound。
Caro； a German chemist； invented in 1874 the red
color known as eosine； which was brought to this
country in the following year and sold for 125 per
pound。 Its color is destroyed by acids。
Orchil or archil （the red color） was discovered in
1879。 The commercial use of the so…called 〃orchil
substitutes〃 （purples） began； however； in the years
1885 and 1887。
Artificial indigo； as the result of many years of
experimenting； came into commercial use under the
name of 〃indigo pure〃 only in 1897。 It had previously
been produced synthetically in a variety of
ways； but the cost of the production was far above
that of the natural product。 Baeyer and Emmerling
in 1870； Suida in 1878； Baeyer in 1878； Baeyer and
Drewsen in 1882； and Heumann in 1890； can be said
to have been the pioneers in the production of artificial
indigo。
The intensity of some of the aniline colors may be
indicated by the fact that a single grain of eosine in
ten millions of water exhibits a defin