“I take a soup plate and I put boiling water in it and let it stand for about a quarter of an hour, after which I throw away the water. The plate being warm, I place one of these collars in it. I pour over the collar one hundred grams of boiling water and let it stand for half an hour. Then I wring out the collar, and the water that remains is my invisible ink. They call it ‘pyrogram.’ It looks like water, it is not poisonous and it can be drunk. “I wash my hands, since they are wet with this ink, and take the paper and fold it crosswise and begin the letter, writing two fingers from the edge. I let it dry, and then take a glass of water and put about one teaspoonful of ammonia in it. With a piece of wadding dipped in this solution of ammonia and water, I rub the paper both ways, and thus prepare it on both sides. After this I place the paper in this wet condition between blotting paper and under heavy books or a trunk for three hours. You will not be able to recognize the paper any more. It looks like foreign writing paper, very thin and glazed. I can write anything I choose on this letter now. When they get the letter and develop it the writing appears positively black. I head the letter ‘Dear Bob’ and they know it is a code letter. When I am through with the letter I use the word ‘Schluss,’ because in developing it, they want to know if they have the entire letter, and that word ends it up.” This passenger also told the examining officials that in carrying addresses without an address book, the German agents usually take a bone button of an overcoat or a large button of some sort and on the reverse side scratch the address with a diamond, sometimes also scratching instructions which they cannot carry in their heads. After this they treat the button with shellac, or, as they call it in Germany, “spitituslak.” That fills the crevices and dries rapidly. On reaching the destination, they use pure alcohol to wash off the shellac. They also write addresses on this paper and work them into leather buttons. Cipher and code are part of the education of certain intelligence officers, but into a discussion of these matters we may not go, as they are secrets of the American Government. Our own experts were able to decipher and decode all the secret messages bearing on the great German plots in this country, but this was not usually A. P. L. work. Of course, the lay reader, or more especially the A. P. L. member, may know that a cipher means the substitution of some symbol, or some number, or another letter, for each letter of the alphabet. Or the real letters may be transposed, one to stand for another, in such a way that only the sender and receiver may understand. That looks hard to read? Not at all. It is easier than code. It is said that any cipher message can be unriddled in time.