Outwardly it was a book, but between the covers there were no leaves except dummy edges. In the recess thus formed was four pounds of very high explosive, sufficient to blow a hole completely through the steel plating of a merchant-ship's hold. The explosive without a primer was comparatively innocuous. It could be subjected to a severe blow without detonating; fire had no effect upon it, except that it would smoulder without bursting into flame. But when mixed with a solution of potash the latent power was instantly and terrifically released.
Until the bomb was prepared for action Schoeffer kept the glass tube containing the potash separate from the main explosive. If necessary he could easily explain the potash by saying it was medicine.
The detonation of the infernal machine was actuated by a fairly simple device. It was only necessary to smash the glass tube of potash; but the point was: how could Schoeffer break the glass when he was away from the ship?
If anyone had had an opportunity of inspecting Mr. Porter's watch he would certainly have been interested; for, in addition to the hours, minutes, and seconds hands, the dial sported a hand that indicated the days up to seven. But in place of numbers on the day circle there were seven black dots. Each of these dots proved to be a small insulated metal peg, capable of being raised until it projected a fraction of an inch from the dial, yet sufficiently to hold up the hand.
To complete the outfit there was a small eight-volt battery, which, on a circuit being formed, would detonate a minute charge of explosive, enough to smash the glass tube, liberate the potash, and cause the desired catastrophe. By means of the watch Schoeffer could delay the explosion from one to seven days after he had set the bomb in position.
Mr. Porter made rapid strides in forming acquaintances on board. He was affable without being obtrusive; communicative up to a certain point, without volunteering information; a good conversationalist without boring his listeners. He took a keen interest in the officers, the stewards, and even the lascars, but, in the course of conversation with them, he rarely if ever asked questions concerning their professional duties.
One person in particular he cultivated. That was Wilkins, the Captain's steward. Wilkins was a professional postage-stamp agent; he bought large quantities of stamps in foreign parts on behalf of a London firm. Mr. Porter was a keen amateur collector, and so a bond of interest was formed.
Since the facilities for encouraging conversation between passengers and stewards are limited, Schoeffer found a convenient opportunity to confer with Wilkins on the subject of postage stamps. The opportunity occurred just before "lights out", the venue being the pantry.
Schoeffer found that the subject of stamps afforded him a splendid chance of gaining information concerning the Old Man. He knew that the skipper kept the code-books in his cabin. Two of them—the ABC and the Telegraph Code—were practically public property, but the third was the private code of the Blue Crescent Line, by which the owners telegraphed orders to their various ships.
The German agent made no attempt to suborn the steward to "borrow" the code-book. He preferred to work single-handed. It was infinitely safer. But he soon discovered that Captain Bullock was a light sleeper and that he was practically an abstainer from strong drink, except for his regular "night-cap".