FullReads

“I want you to examine the letters in this case with me,” continued Kennedy. “Take the letter which I read from Miss Lytton, which was found following the strange disappearance of the note from Thurston.”

He dipped a pen into a little bottle, and wrote on a piece of paper:

What is your opinion about Cross’s Headache Cure? Would you recommend it for a nervous headache?

BURGESS THURSTON,
c/o Mrs. S. BONCOUR.

Craig held up the writing so that we could all see that he had written what Dixon declared Thurston wrote in the note that had disappeared. Then he dipped another pen into a second bottle, and for some time he scrawled on another sheet of paper. He held it up, but it was still perfectly blank.

“Now,” he added, “I am going to give a little demonstration which I expect to be successful only in a measure. Here in the open sunshine by this window I am going to place these two sheets of paper side by side. It will take longer than I care to wait to make my demonstration complete, but I can do enough to convince you.”

For a quarter of an hour we sat in silence, wondering what he would do next. At last he beckoned us over to the window. As we approached he said, “On sheet number one I have written with quinoline; on sheet number two I wrote with a solution of nitrate of silver.”

We bent over. The writing signed “Thurston” on sheet number one was faint, almost imperceptible, but on paper number two, in black letters, appeared what Kennedy had written: ” Dear Harris: Since we agreed to disagree we have at least been good friends.”

“It is like the start of the substituted letter, and the other is like the missing note,” gasped Leland in a daze.

“Yes,” said Kennedy quickly. “Leland, no one entered your office. No one stole the Thurston note. No one substituted the Lytton letter. According to your own story, you took them out of the safe and left them in the sunlight all day. The process that had been started earlier in ordinary light, slowly, was now quickly completed. In other words, there was writing which would soon fade away on one side of the paper and writing which was invisible but would soon appear on the other.

“For instance, quinoline rapidly disappears in sunlight. Starch with a slight trace of iodine writes a light blue, which disappears in air. It was something like that used in the Thurston letter. Then, too, silver nitrate dissolved in ammonia gradually turns black as it is acted on by light and air. Or magenta treated with a bleaching-agent in just sufficient quantity to decolourise it is invisible when used for writing. But the original colour reappears as the oxygen of the air acts upon the pigment. I haven’t a doubt but that my analyses of the inks are correct and on one side quinoline was used and on the other nitrate of silver. This explains the inexplicable disappearance of evidence incriminating one person, Thurston, and the sudden appearance of evidence incriminating another, Dr. Dixon. Sympathetic ink also accounts for the curious circumstance that the Lytton letter was folded up with the writing apparently outside. It was outside and unseen until the sunlight brought it out and destroyed the other, inside, writing – a change, I suspect, that was intended for the police to see after it was completed, not for the defence to witness as it was taking place.”

We looked at each other aghast. Thurston was nervously opening and shutting his lips and moistening them as if he wanted to say something but could not find the words.

“Lastly,” went on Craig, utterly regardless of Thurston’s frantic efforts to speak, “we come to the note that was discovered so queerly crumpled up in the jar of ammonia on Vera Lytton’s dressing-table. I have here a cylindrical glass jar in which I place some sal-ammoniac and quicklime. I will wet it and heat it a little. That produces the pungent gas of ammonia.