IMPROVEMENTS IN MEANS FOR DETECTING THE OPENING OF ADHESIVE ENVELOPES OR THE REMOVAL OF ADHESIVE LABELS, APPLICABLE ALSO IN SYMPATHETIC WRITING
Year: 1877

page_text: LETTERS PATENT to Theodore Kroner, of Freiburg, in the German Empire, but
at present of No. 20, Southampton Buildings, in the County of Middlesex, for
'the Invention of "IMPROVEMENTS IN MEANS FOR DETECTING THE OPENING OF
ADHESIVE ENVELOPES OR THE REMOVAL OF ADHESIVE LABELS, APPLICABLE
ALSO IN SYMPATHETIC WRITING." Partly a communication from abroad
by William Kromer, of Freiburg, in the German Empire.
PROVISIONAL SPECIFICATION left by the said Theodore Kromer at the
Office of the Commissioners of Patents on the 20th June 1877.
THEODORE KRONER, of Freiburg, in the German Empire, but at present of No. 20,
Southampton Buildings, in the County of Middlesex. "IMPROVEMENTS IN MEANS
FOR DETECTING THE OPENING OF ADHESIVE ENVELOPES OR THE REMOVAL OF
ADHESIVE LABELS, APPLICABLE ALSO IN SYMPATHETIC WRITING." [Partly a com-
munication from abroad by William Kromer, of Freiburg, in the German.
Empire.]
.
My Invention relates to means of readily detecting the tampering with adhesive
envelopes or labels for the purpose of opening or removing the same, and the means
which I employ for this purpose are also applicable in sympathetic writing, that is
to say, in producing writing on post cards, open circulars, and the like, in such a
manner as to be illegible until it is treated as I will describe. For this purpose I
employ known substances which on being moistened react chemically on one
another, producing colour or change of colour in the following manner :-On
the adhesive edge of an envelope or on a label I apply as a line or mark one of the
said substances on the inside of the paper, and after the adhesive matter has dried
I apply the other substance outside. When moisture is afterwards applied to the
outside of the paper for the purpose of again dissolving the adhesive matter so that
the envelope may be opened or the label removed, the moisture soaking through the
[Price 4d1

page_text: paper causes the substances to react on each other, producing such a change as
renders the line or mark visible.
As an example of substances applicable in this manner I may mention sulphate
of iron and infusion of galls, the one of which I employ to mark the inside of the
paper, and the other to mark the outside. Other substances may however be employed
which produce colour or change of colour by mutual reaction when they are
moistened.
•
In like manner I apply this method to sympathetic writing, as for post cards,
open circulars, and the like, in the following manner :-I prepare the post card or
sheet to be written on with a margin of the one substance, and then write on the
body of the card or sheet with the other substance, such writing being then
invisible or nearly so.
When it is desired to read the writing, a moistened cloth or sponge is passed over
the card or sheet, so as to bring the marginal matter into contact with the written
matter, which will thereupon become visible.
In order the better to disguise the writing before it is thus rendered visible, I
prefer to print or impress the body of the card or sheet with water marks or faint
lines of colour corresponding with that of the writing material employed, such lines
of colour being of such a nature that they undergo no change when moisture is
afterwards applied.
I have above described the use of two substances which chemically react on each
other when moistened. A single substance of hygroscopic character may however
be employed in a similar manner. For example, I mark the edge of an envelope
inside with such hygroscopic material, and protect the mark so made by a coating
of varnish against the moisture employed in applying the adhesive matter. When
the paper is afterwards moistened on the outside, the moisture soaking through the
paper affects the hygroscopic substance within, and causes such a change as to render
the mark more or less visible through the paper.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Theodore Kromer in the Great Seal Patent Office on the 14th December
1877.
THEODORE KROMER, of Freiburg, in the German Empire, but at present of No. 20,
Southampton Buildings, in the County of Middlesex. "IMPROVEMENTS IN MEANS
FOR DETECTING THE OPENING OF ADHESIVE ENVELOPES OR THE REMOVAL OF AD-
HESIVE LABELS, APPLICABLE ALSO IN SYMPATHETIC WRITING." Partly a communi-
cation from abroad by William Kromer, of Freiburg, in the German Empire.
This Invention relates to means of readily detecting the tampering with adhesive
envelopes of labels for the purpose of opening or removing the same; and the means
which I einploy for this purpose are also applicable in sympathetic writing, that is
to say, in producing writing on post cards, open circulars, and the like, in such a
manner as to be illegible until it is treated as I will describe. For this purpose I
employ known substances which on being moistened react chemically on one
another, producing colour or change of colour in the following manner:-On the
adhesive edge of an envelope or on a label I apply as a line or mark one of the said
substances on the inside of the paper, and after the adhesive inatter has dried I
apply the other substance outside. When moisture is äfterwards applied to the
outside of the paper for the purpose of again dissolving the adhesive matter, so that
the envelope may be opened or the label removed, the moisture soaking through the
paper causes the substances to react on each other, producing such a change as
renders the line or mark visible.
As an example of substances applicable in this manner I may mention sulphate
of iron and infusion of galls, the one of which I employ to mark the inside of the
paper, and the other to mark the outside. Other substances may however be
employed which produce colour or change of colour by mutual reaction when they
are moistened.
In like manner I apply this method to sympathetic writing, as for post cards,
open circulars, and the like, in the following manner:-I prepare the post card or
sheet to be written on with a margin of the one substance, and then write on the
body of the card or sheet with the other substance, such writing being then
invisible or nearly so.
When it is desired to read the writing, a moistened cloth or sponge is passed over
the card or sheet, so as to bring the marginal matter into contact with the written
matter, which will thereupon become visible.
In order the better to disguise the writing before it is thus rendered visible, I
prefer to print or impress the body of the card or sheet with water marks or faint
lines of colour corresponding with that of the writing material employed, such lines
of colour being of such a nature that they undergo no change when moisture is
afterwards applied.
I have above described the use of two substances which chemically react on each
other when moistened. A single substance of hygroscopic character may however
be employed in a similar manner. For example, I mark the edge of an envelope
inside with such hygroscopic material, and protect the mark so made by a coating
of varnish against the moisture employed in applying the adhesive matter. When
the paper is afterwards moistened on the outside, the moisture soaking through the
paper affects the hygroscopic substance within, and causes such a change as to render
the mark more or less visible through tho-paper.
The hygroscopic material may also be applied outside the envelope. If this be
done before closing the envelope, a thin coat of varnish should first be applied
outside, so as to protect the hygroscopic material from the moisture within used in
causing adhesion. Otherwise after the envelope is closed and the adhesive portion
is dried, the hygroscopic material may be applied outside by a brush or otherwise.
A substanco suitable for use in this manner may be prepared as follows:-Crys-

page_text: tallised sulphate of iron, about 140 parts, and tannic acid, about 600 parts, are
separately dried, all water of crystallisation being expelled, and being separately
reduced to fine powder are intimately mixed together. The mixture is then made
up into a thin paste with rectified benzoline quite free from water, and a small
quantity of varnish or caoutchouc solution is added. The paste thus prepared being
laid as a colourless paint on the paper and allowed to dry, will afterwards on
moisture being applied shew a dark stain.
Paper treated with the mixture above described may be written or drawn on by
a pen or brush charged with water, the parts thus moistened becoming visible as if
they had been marked with ink.
Also the mixture above described may be employed as a sympathetic ink to be
written or otherwise applied to plain paper, remaining invisible thereon until
moisture is applied.
Having thus described the nature of the said Invention, and in what manner the
same is to be performed, I claim the method, substantially as herein described, of
treating paper so that on its being moistened with water it will shew a stain for
the purposes set forth..
In witness. whereof, I the said Theodore Kromer, have hereunto set my hand
and seal, this Seventh day of December, in the year of our Lord One thou-
sand eight-hundred and seventy-seven..