"Alternately wash the paper with a camel"s- hair brush dipped in a solution of cyanide of pota.s.sium and oxalic acid; then when the ink has disappeared wash the paper with pure water."
Inks of the tanno-gallate of iron family, whether containing "added" color or not, can be more or less "erased" by chlorinate of lime or soda, in the presence of a weak acid. These chemicals do not, however, materially affect the prussian blue inks, which require solutions of hydrate of potash or soda.
Real indigo can be removed by chloroform, morphine or an aniline salt (indigo and aniline both owe their names to the same Portuguese source), which possess the rare property of dissolving pure indigo. Such combination, if refractory in the presence of permanganate of potash with sulphuric acid, must be followed by an application of sulphurous acid. In like manner, inks composed of by-products of coal tar, can be effectively treated, when irradicable with plain water or soap and water.
The erasure and removal of most inks from paper can be accomplished by the application of the chemicals heretofore enumerated. The requirements in this direction of some inks, however, though of rare occurrence, are to be met by the employment of other and particular reagents.
Many of the tests specified in the Allen citation to determine the character of ink const.i.tuents, if made alone are practically valueless, because the same behavior occurs with different materials employed in the admixture of ink. To avoid error in judgment the operator should verify if possible by confirmatory tests. Thus, in the one for logwood, sulphurous acid will cause a logwood ink mark to turn yellow; mercuric chloride, orange; tartar-emetic, red; and if the marks are faded ones, solutions of sulphate of iron or bichromate of potash will restore them respectively to a violet or blue-black color.
Prussian blue, aniline blue and indigo blue are to be tested as follows: Solution of chloride of lime, no change of color for prussian blue; decoloration or faint yellow for aniline blue or indigo. To discriminate between the two latter, test with solution of caustic soda, when decoloration or change of color will indicate aniline blue and permanence will indicate presence of indigo blue.
In the manufacture of the blue-black inks, a variety of violets have been and are still employed. Among them are aniline violet, iodine violet, madder, alkanet, orchil and logwood.
(a) Apply chloride of lime solution: 1. No change of color indicates alkanet. 2. Any change, one of the other five.
(b) Apply lemon juice: 1. The violet becomes brighter if it is one of the aniline violets, to be distinguished from each other by applying one part of hydrochloric acid to three parts of water, when it will become violet-blue, changing to red if it is common aniline-violet, but blue changing to a green hue and upon adding plain water to a lilac or pearl gray if it is iodine-violet (Hoffman"s). It will also turn from red to yellow in lemon juice. To test for the other three violets: (a) Apply chloride of lime, to be followed by a solution of yellow prussiate of potash: absence of a blue coloration leaves orchil and logwood to be considered. To distinguish between them apply solution of hydrate of lime, whereby a change to gray, followed by complete decoloration indicates logwood, and a change to violet-blue, orchil.
The substances utilized with but few exceptions for red ink are the "eosins," possessing different names like erythrosine, as well as different hues. Antecedent to about thirty-five years ago, cochineal (known as "carmine"), madder, Brazil wood and saffron formed the basis of most of the red inks.
Make a soap solution adding a small quant.i.ty of ammonia, lemon juice, muriate of tin, all in water: 1. No change upon application indicates madder.
2. Any change, the presence of one of the three other reds: (a) thus a complete decoloration with a return of the color indicates saffron; (b) reappearance of the red color though weaker, aniline-red: (c) production of a yellowish red or light yellow color, cochineal or Brazil wood, to be distinguished from each other by the application of concentrated sulphuric acid, when Brazil wood will at once give a bright cherry-red, and cochineal a yellowish orange.
No yellow inks are in commercial use. Doc.u.ments do, however, often contain yellow marks about which information is required as to their origin. As a rule they are iron rust, picric acid, turmeric, fustic, weld, Persian berries or quercitron. In order to recognize the different colors, the presence or absence of iron rust and picric acid must first be determined.
Apply a warm sample of a slightly acid solution of yellow prussiate of potash; iron rust will be indicated by a blue coloration.
Apply a weak solution of cyanide of pota.s.sium; picric acid will yield a blood-red coloration.
If picric acid and iron rust are both absent, apply a bit of ordinary wetted soap: 1. It turns reddish-brown and becomes yellow again with hydrochloric acid-- turmeric; 2. It turns quite dark--fustic; 3. It is unaffected--weld, Persian berries or quercitron. To distinguish between these three, apply sulphuric acid, the color of weld will disappear, and of the others remaining apply tin-salt solution, when a change to orange indicates Persian berries, and no change or a very slight one, quercitron.
Inks containing also logwood, fustic, Brazil wood, or madder, were all of them more or less employed some years ago. Their color phenomena, following long periods of time, is much the same. Tests as prescribed in the accompanying table for such inks will serve to cla.s.sify them preliminary to subsequent and more certain ones.
LOGWOOD. FUSTIC.
Concentrated Hydrochloric Acid Red-yellow Red Dilute " " Reddish Yellow-Brown
Concentrated and dilute Nitric Acid Red Red-Yellow " Sulphuric Acid . . Black Dark Purple Dilute " " Red Brown Purple Pota.s.sium Chromate . . . . Black Stannous Chloride Violet Yellow Tartaric Acid . . . . . Gray-Brown Yellow Sulphate of Copper . . . . Dark Gray Tannin . . . . . . Yellow-Red Yellow Potash Dark Red Yellow Pota.s.sium Permanganate Light-Brown Yellow " Iodide . . . . . Red-Yellow Pyrogallic Acid . . . . Yellow-Brown Yellow Chrome-yellow . . . . . Dark Violet Sodium (Salt) Violet Red Sulphate of Iron Gray to Black Alum . . . . . . . Violet Red,Brown. Faint Red
BRAZIL WOOD. MADDER.
Concentrated Hydrochloric Acid Light Red Pale Yellow Dilute " " Light Red Pale Yellow
Concentrated and dilute Nitric Acid Dark Purple Pale Yellow " Sulphuric Acid . . Red Pale Yellow Dilute " " Purple Pale Yellow Pota.s.sium Chromate . . . . - - Stannous Chloride Light Red Light Red Tartaric Acid . . . . . Red Yellow Pale Yellow Sulphate of Copper . . . . - - Tannin . . . . . . No Change Pale Yellow Potash Crimson Light Red Pota.s.sium Permanganate - - Iodide . . . . . - - Pyrogallic Acid . . . . - - Chrome-yellow . . . . . - - Sodium (Salt) - Red Sulphate of Iron Dark Violet - Alum . . . . . . . - Faint Red
CHAPTER XIX.
FRAUDULENT INK BACK GROUNDS.
DETECTION OF ALTERATIONS IN DOc.u.mENTS BY CHEMICAL TESTS WHICH APPLY SOLELY TO THE PAPER--ACCURACY OF RESULTS OBTAINED BY USE OF IODINE EXCELS THAT OF ALL OTHER CHEMICALS--IT APPLIES BEST TO LINEN PAPER--MODERN HARD PAPER DOES NOT GIVE COMPLETE INFORMATION--EFFECT OF IODINE ON MARKS MADE BY A STYLUS OR GLa.s.s PEN.
FIFTY years ago and long before the employment of the fugitive "anilines" for ink uses, and "wood pulp" as a material for paper, two French chemists, Chevallier and La.s.siagne, published in the Journal de Chimie Medical, an article "On the Means to be Employed for Detecting and Rendering Perceptible Fraudulent Alterations in Public and Private Doc.u.ments,"
which as translated is valuable enough to quote in full:
"The numerous experiments which have been already tried at various times, have made known the processes which may frequently be put in practice for causing the reappearance of traces of writing effaced by chemical reactions, and for throwing light on the work of the guilty. But there are cases in which all the means proposed for this purpose fail, and then the criminal may escape justice from the want of conclusive material proofs. If, as has already been proved, it is not always possible to cause the reappearance of the effaced writing, for which written words have with a fraudulent intent been subst.i.tuted, at least, as our experiments demonstrates, we may recognize, by some effects which are manifest on the surface of the altered paper, the places where the criminal act has been performed, circ.u.mscribe them by a simple chemical reaction visible to the least practiced eye, and even measure their extent. In a word, the visible alterations produced on a deed are susceptible, owing to the partial modifications which the surface of the paper has undergone, of being differently affected by certain chemical actions, and of being rendered visible. The following experiments, made in a judicial investigation, furnish us with the following facts:
"1st. The surface of paper sized in the ordinary way, or letter paper, no longer presents with certain reactions, the same uniformity where it has been either accidently moistened in several places by various liquids, or left in contact for a certain time with agents capable of removing or destroying the characters which have been traced on it with ink.
"2d. The application of a thin layer of gum, of starch, or farina, of gelatine, or fish-glue, with a view of sizing certain parts of the paper, or of causing certain bodies to adhere to it momentarily, is detected by an action similar to that which shows paper to have lately been wetted by the contact of liquids.
"3d. The heterogeneousness of the pulp of the papers, and the kind of size with which they are impregnated, lead to differences in the results which are observed with the same chemical reagents.
We shall now examine each of these propositions, and describe the means which we have employed in endeavoring to solve questions of so high a degree of interest.
"1st. The h.o.m.ogeneousness of sized paper not partially altered by the contact of liquids (water, alcohol, salt-water, vinegar, saliva, tears, urine, acid salts, and alkaline salts) is demonstrated by the uniform coloration which this surface takes on being exposed, if not wholly, at least in various parts, to the action of the vapor of iodine disengaged at the ordinary temperature from a flask containing a portion of the metalloid. When the surface of paper not stained by any of the above mentioned liquids is exposed to the action of this vapor for three or four minutes in a room the temperature of which is about 60 degrees F., a uniform yellowish, or light-brownish yellow, coloration is noticed on the whole extent exposed to the vapor of iodine; in the contrary case, the surface which has been moistened, and afterwards dried in the open air, is perfectly distinguished by a different and well circ.u.mscribed tint. On the papers into which paste starch and resin have been introduced, the stains present such delicate reactions that we may sometimes distinguish by their color the portion of paper which has been moistened with alcohol from that which has been moistened with water. The stain produced by alcohol takes a bistre-yellow tint; that formed by water is colored of a more or less deep violet blue, the desiccation having been effected at the ordinary temperature. For the stains occasioned on these same papers by other aqueous liquids, the tint, apart from its intensity, resembles that of the stains of pure water. The feeble or dilute acids act like water on the surface of the same paper containing starch in its paste; but the concentrated mineral acids, by altering more or less the substances which enter into the composition of the latter, give test to the stains which present differences. We are always able to recognize by the action of the vapor of iodine the parts of the paper which have been put in contact with chemical agents, the energy of which has been arrested by washing in cold water. We are able, on several ancient deeds, written on stamped paper, and a few words of which had been removed by us with chemical agents, to recognize the places where their action was exerted, to see and to measure the extent which they occupied on the surface of the paper.
"The testing of a paper with the vapor of iodine will present this double advantage over the methods. .h.i.therto practiced for detecting falsifications in writings, that it points out at once the place in the paper in which any alteration may be suspected, and that, on the other hand, it enables us to act afterwards with the reagents proper for causing the reappearance of the traces of ink, when that is possible. If the means which we now propose cannot always make the former writing appear, they demonstrate the places where the alterations must have been made, when, however, the want of uniformity presented by the surface of the paper is not explained by any circ.u.mstance.
This proof becomes, therefore, a weapon which the guilty person cannot avoid. But might not the presence of a stain, or several stains, developed by the vapor of iodine, in different parts of a public or private deed, give rise to a suspicion, where these stains have, perhaps, been occasioned by the spilling of some liquid on the surface of the paper?
and would it not be rash and unjust to raise an accusation from such a fact? There would indeed be great temerity in drawing such a conclusion from a fortuitous circ.u.mstance; but the inference which may be drawn from the place occupied by these stains on the surface of the paper, from the more or less significant words found in those places, would not permit an accusation to be so lightly brought, where simple reasoning would be sufficient to destroy its basis. Besides, the subsequent reactions which would be made would certainly never revive words formerly written and effaced; whilst the latter effects may be often produced, more or less visibly, on those parts of the paper on which falsification has been practiced, figures or words being subst.i.tuted for other figures or words.
"2d. The applications made to the surface of a sheet of paper, with a view of covering it again at certain parts with a fine layer of gum, gelatine, starch or flour paste, or in other places to cause other sheets of paper to adhere, may be recognized not only by the reflection of light falling upon the paper inclined at a certain degree of obliquity, and by the transmission of light through the paper, but also by the varying action which the vapor of iodine exerts on the surface which is not h.o.m.ogeneous.
Papers containing starch and resin are more powerfully acted upon by this vapor than papers of a less complex composition. Both in the parts covered with starch, or paste flour, are colored in a few minutes of a violet blue; but with starched papers alone a more intense coloration is manifest on the places covered again with a thin layer of gum arabic, size or gelatine. By looking, then, on the surface of the paper, held somewhat obliquely to incidental light, we distinguish clearly, by their different aspects, the parts on which these various substances have been applied. The vapor of iodine, in condensing at the ordinary temperature on the surface of the papers to which any kind of size has been applied in various places, produces differences which are most commonly well recognized by the greater or less transparence of the paste of the paper.
3d. The heterogeneousness of the pulp of the various papers of commerce, and the nature of the size with which they are penetrated, cause differences, either in the coloration which the surface of these papers takes when exposed to the vapor of iodine, or in the tint which is manifested in the portions of the size deposited in certain portions of that surface; thus, papers with starched pulp generally turn brown, or blue, according to the amount of water that remains in their interstices; other papers turn yellow only under the 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 a.s.sumes the color of blue-violet, while unaltered paper a.s.sumes 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 a.s.sume, 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 gla.s.s 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 COLORS--CHRONOLOGICAL HISTORY OF THE "ANILINES" EMPLOYED AS INK--OTHER SUBSTANCES USED FOR THE SAME PURPOSE.
THE term "added color," as applied to ink, is the popular phraseology for a mult.i.tude 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 cla.s.sified 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.