SYMPATHETIC INKS The so-called sympathetic inks, by which is understood inks that give a writing that is invisible, or nearly so, until it has been acted upon by the air or treated with a special reagent, have been put to many ingenious uses by the criminal. Some five years ago an innocent-looking individual called at the laboratory of one of the leading consulting chemists in London, and asked whether he could be supplied with a writing fluid that would give writing which would fade away in a short time, and also with another ink that would produce words that would be invisible for some time and then appear. He gave as his reason for requiring these that he wanted to amuse a small boy. The sequel was seen a few weeks later when the same plausible individual was arrested for swindling on the race-course. He had made tempting bets on certain horses, the names of which he had written on slips of paper, and had handed these slips to those who had accepted his wagers. In a short time the name of the horse on each slip of paper gradually faded away while the name of another horse slowly appeared in its place. One man to whom one of these slips had been given, having been warned by another victim, hurried away to the police station, and was in time to let the superintendent see the name of an “outsider” replace that This appears to have been the last detected attempt to use a sympathetic ink upon the race-course. A disappearing ink frequently used for this purpose is a weak solution of starch containing a slight trace of iodine, the effect of which is to produce a faint blue colour. On exposure to the air the colour of writing done with such a fluid soon fades away. Fugitive dye-stuffs have also been employed as disappearing inks, and some of these, such as quinoline blue, give characters that rapidly disappear when exposed to sunlight. An ink that is invisible for some time is a solution of silver nitrate in ammonia, which gradually becomes black when acted upon by air and light. Or certain dye-stuffs such as magenta, that have been treated with a bleaching reagent in just sufficient quantity to decolorise them fulfil the same purpose, the original colour gradually reappearing as the oxygen of the air acts upon the pigment. The earliest inks that were rendered visible by chemical reagents were believed to act by magnetism. Thus in a medical book of the seventeenth century, written by Brossonius, a “magnetic fluid” is described made from “arseniated liver of sulphur,” which only became visible when looked at with the “eyes of affection.” This appears to have been nothing more mysterious than an ink of lead acetate, the characters written with which could be rendered visible by exposing them to the vapour of sulphuretted hydrogen. Inks of this kind were also mentioned, in 1669, by The best known sympathetic inks consist of solutions of cobalt salts, the writing done with which changes on heating from a nearly invisible pink to blue. This peculiarity of cobalt to form two series of salts containing different amounts of water was discovered in 1715 by Waiz. Other compounds that may be used as sympathetic writing fluids include tannin, which forms ordinary ink on the addition of iron sulphate; cobalt nitrate which becomes blue on adding oxalic acid, and gold chloride which gives a purple colour with tin chloride. Some thirty years ago a patent was taken out by Kromer for the use of a sympathetic ink in detecting any tampering with envelopes. The two dried constituents of the ink, say tannin and iron sulphate, are separated by the adhesive gum upon the envelope, so that should steam be applied to open the letter, the two substances come into contact, and form an ink, which leaves a stain upon the paper. Printing inks based upon these principles are used in preparing the groundwork of cheques, so that any attempt to remove the writing from the cheque by means of chemical agents will be betrayed by the change of colour upon the body of the paper. The value of sympathetic inks in detecting an offender was strikingly shown in the recent Sutton The story is a very remarkable one. For many months during 1908 and the early part of 1909, there was an epidemic of anonymous post cards in Sutton, many people receiving them and no one being able to trace their origin. Among other people who received these cards was a Mrs. Tugwell, and in some of them it was stated that she and another woman were “not fit members” of a certain congregation. Suspicion fell upon the housekeeper of the Roman Catholic priest, Annie Dewey, and mainly on the evidence of a handwriting expert, she was committed for trial at the Assizes. The writing on the libellous cards was undoubtedly extremely like that of Miss Dewey, and, as events subsequently proved, was a very skilful imitation of it by someone who wished to throw suspicion upon her. When the Assizes came on, no evidence was offered by the prosecution and the case was dismissed. The libels still continued, however, and Mrs. Tugwell having received more libellous cards, her husband again took the matter up, and Miss Dewey was once more committed for trial in March, 1910. The trial was a very exhaustive one, but no convincing evidence was brought against the accused, who was therefore acquitted. In the meantime a number of suspicious circumstances pointed to the conclusion that Mrs. Tugwell herself was the author of the libellous cards and letters, and that she had also apparently written those that she had received through the post. Instructions were given to the postmaster that these marked stamps were to be supplied to none but members of the Tugwell family. In April two more libellous post cards were sent to Canon Cafferata, a Roman Catholic priest, and the stamps upon these cards were two of those marked with the invisible ink. The house of the Tugwells was now watched by the police, and one evening when Mrs. Tugwell was seen coming out, the pillar-box close at hand was immediately cleared of all its letters by an official. Mrs. Tugwell then put two letters in the box, both of which contained foul libels. One of these was addressed to a friend of hers and the other to herself. The handwriting on both these letters was an imitation of that of Miss Dewey. A warrant was now issued for the arrest of Mrs. Tugwell, and when her house was searched, envelopes having the same watermark as that of the envelopes containing the libellous letters were discovered. There were also found some French books containing the French phrases used in the letters, and several pieces of blotting paper upon which were words and phrases occurring in libellous letters. |