In what trial upon a charge of murder has there ever been witnessed the sight of the prisoner, whose life was hanging in the balance, laughing and chatting with his friends, and making sketches of the judge, the counsel, and the witnesses? Even at the most crucial moment of the trial, when the jury had withdrawn to consider their verdict he exhibited no trace of anxiety, but until called below sat calmly sketching, while he waited for their return. And thus Mr. Hall Caine wondered, as he got the prisoner to sign his name upon the back of a copy of the charred fragments of the letter, whether "with all his mental alertness, his intellectual activity, his temperamental composure, this was not one of those men, the rare and mysterious men, who lack some necessary quality on the moral side of their nature." CHAPTER X 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 of one of the favourites upon which he had laid his money. 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.