OFF FOR THE AMAZON.

Motor Matt considered himself personally responsible for the safety of the Grampus. The boat had been placed in his charge by Captain Nemo, Jr., her owner, and the captain's faith in the king of the motor boys was unlimited. Matt was to take the submarine to Mare Island Navy Yard and collect one hundred thousand dollars for her from the government. Those were his instructions, and the captain not only expected them to be carried out to the letter, but he also expected to pay Motor Matt well for doing it.

All this responsibility, it may be, had got on Matt's nerves a little, so that he was apt to shy at imaginary dangers. But this fact in no wise interfered with his coolness and courage.

The whole under part of the submarine's hull was filled with smoke—a smoke that had the acrid smell of burned gas. On hands and knees, Matt groped his way through the haze, pulled a switch, and set an electric ventilator fan at work. The fan soon cleared the ship, and the first figure Matt saw was that of the gasping Chinaman. He was on his knees in the tank room. In front of him lay a twisted and broken gasolene tank—a small reserve reservoir sometimes used to help out the larger tank when the fuel in it was running low. This auxiliary tank had not been used for a month, but had hung empty from a rack in the tank room.

At the Chinaman's side lay a cigarette and a half-burned match.

"What the deuce happened?" cried Glennie, creeping after Matt.

"Your Chinaman tried to light a cigarette," answered the young motorist, quick to reason out the cause of what had happened. "He was under an auxiliary gasolene reservoir, and the match set it off."

"Thunder, Matt!" exclaimed Gaines, who had dropped down below after Glennie, "there hasn't been any gasolene in that tank for a month."

"The vapor was there, all the same."

"Nonsense!" exclaimed Glennie. "Vapor wouldn't stay in that tank for a month. It would escape and find its way out."

"Gasolene vapor is heavier than air," said Matt; "and it would remain indefinitely at the bottom of the reservoir. A little of it probably leaked through the bottom of the feed pipe, so that the match set it off. Luckily for the Chink there wasn't very much of it."

"Gee, klismus!" babbled Ah Sin. "Me tly smokee, something go boom! No likee devil-boat!"

"Have you any more cigarettes?" demanded Matt sharply.

Ah Sin dug a handful out of the breast of his blouse.

"Is that all?" demanded Matt.

"No gottee allee mo'."

"Don't strike any more matches," went on Matt sternly. "You're going with us to Para, and you're going to do the cooking. Take him in hand, Speake," he added to Speake, who had dropped down behind Gaines, "and show him how we do that part of our work on the Grampus. Keep an eye on him, and see that he doesn't blow up the boat."

"Never did like a bloomin' chink, nohow," grumbled Speake. "If he gits too blame' troublesome, I'll break his scrawny neck. Come on here, yaller mug!"

Speake made off forward, toward the torpedo room, and Ah Sin meekly followed. Just then a thump on the deck, and a loud hail, announced that Dick had arrived with the gasolene.

"Rig the hose, Gaines," called Matt. "Clackett, get the pump on deck. We've got to get the fuel into the tank in short order and then slant away for the Amazon and Para."

While Gaines and Clackett busied themselves, Matt and Glennie went up to the periscope room. Carl was just climbing the ladder to help Dick. Glennie, without further talk, picked up his suit case and went on to the room that had been set apart for his use.

"Dot ploomin' shink vill ged us all indo some hot vater," grunted Carl.

"I guess not," returned Matt. "Speake is looking after him."

"Vat iss a shink anyvay," went on Carl, "but some monkies mit der tails in der wrong blace?"

Clackett came with the pump and passed it to Dick, who was in the boat with the barrel of gasolene. The pump was rigged, the end of the hose clamped on, and Clackett and Dick got busy pouring the fuel through the hose and into the big tank below.

While they worked, Clackett explained to Dick that they were to make a quick departure for the Amazon. Dick was disappointed, for he had hoped for a night's shore-leave in Port-of-Spain, where he had some friends. When he learned that business of Glennie's had all to do with their short stay in port, Dick was inclined to be resentful.

The ensign had not made much of a hit with Ferral—nor with any of the rest of the submarine's complement, for that matter. Dick, however, did no more than grumble. If Motor Matt thought it necessary to pull out for the Amazon in such short order, then there was nothing more to be said. Matt knew what he was about.

Dick alone, of all the submarine's crew, had been the only one to set foot on shore. As soon as the gasolene was transferred, and the boatman paid for his services, the anchor was taken in and the Grampus laid her course for the Serpent's Mouth and began her long voyage toward the Amazon. Dick took the wheel. Matt, studying the charts, gave him the course. Glennie came out of his room and watched the two lads while they were at work.

Everything was going well, and the rhythmical hum of the motor echoed through the boat from the engine room. Glennie walked over and took a look at the periscope. In the mirror were reflected the slowly receding shore line and the distant mountains that arose behind the town.

"You fellows seem to know your business," remarked Glennie.

"Aye," growled Dick, "and we mind it, Mr. Glennie."

The ensign turned from the periscope and went up on deck.

"Why are you keeping the boat so high in the water?" he called down.

"He knows so much, matey," said Dick to Matt, "why not let him figure that out for himself?"

"Because," Matt answered, shaking his head at Dick, "we can make better speed when we're riding light. Once out of the Gulf of Paria, though, the sea will probably be so rough we'll have to submerge."

The ensign continued to ask questions and Matt continued to answer them until Speake announced dinner. The meal was served to the crew at their different stations, Ah Sin carrying the plates and the steaming cups of coffee.

After the meal Matt went up on deck with Glennie, and Dick did the steering from the top of the conning tower. The Gulf of Paria was a great watery plain, over which the waters of the Orinoco spread themselves before mingling with the sea.

The ensign, feeling that he was disliked, drew back into his shell and bore himself with a chilly reserve. Along toward three o'clock Matt relieved Dick and sent him below to sleep. Directly after supper Dick would have to relieve Gaines and stand his trick at the motor, and it was necessary for him to get a little rest. Carl would also have to relieve Clackett, and, in order to be fit for his duties, the Dutch boy had turned in immediately after dinner. He was sleeping on the floor of the periscope room, and Dick curled up on the locker.

The afternoon saw the Grampus well across the gulf, and by five o'clock she changed her course to south by east, leaving the densely wooded hills of Trinidad far behind with the coast of Venezuela in plain view to starboard.

Ah Sin, having been duly instructed as to his duties, prepared the supper on the electric stove, and served it. Speake relieved Matt at the steering gear, and when Dick went below to take Gaines' place at the motor, Matt sprawled out on the locker to catch his own forty winks. A stiff sea was running, and the Grampus was submerged to a depth that merely left the periscope ball clear of the combers.

As the darkness deepened, Speake had Carl put the turbines at work, throwing out sufficient water ballast to lift the conning-tower lunettes clear of the waves. The electric projector was then turned on, and a ray of light shot through the forward lunette and marked the submarine's path through the tumbling sea.

For some hours everything went well. Then abruptly the motor began to sputter and misfire, lessening the speed of the boat and throwing her—now that she was riding higher and with the top of the conning tower awash—more at the mercy of the waves.

Loose furniture began to slam around the periscope room. Matt was thrown from the locker, and sat up, wondering what had gone wrong with the motor.

"What's the matter down there, Dick?" he called through the motor-room tube.

"I'm a Feejee if I know," Dick answered. "You'd better come down, old ship, and take a look."

Matt was soon at his chum's side. His keenly trained ear was usually able to locate any ordinary trouble, but this time he was puzzled. The ignition was all right, and the supply pipe from the tank was clear. Nevertheless the motor sputtered and jabbered with a wheezy but unsuccessful attempt to do its full duty. The platinum, in the blade or spring of the commutator, will, in rare cases, get loose and cause misfiring, but that was not the cause of the present trouble. Another rare cause, resulting in similar symptoms, lay in the loosening of the carbon pole in the cell of a battery. But, just now, the batteries were not at fault.

Finally, as a last resort, Matt examined the gasolene that was being fed into the carburetor. A few drops in the palm of his hand aroused his suspicions. The next moment the hydrometer test was made and water was found in the gasolene.

"How did it get there?" demanded Dick. "The gasolene has worked well enough all afternoon and so far during the night."

"None of the gasolene you bought in Port-of-Spain has been used as yet?"

"Not a drop."

"Well, connect up the carburetor with the storage reservoir. If there is a little water in the carburetor, it will soon work out. After that, empty this tank, strain the gasolene through chamoiskin, and then give the tank a compressed-air treatment. I'll send Clackett to help you."

"But how, in the name of sin, did water get in that tank?" cried the perplexed Dick.

As Matt turned to crawl away, he picked up a six-inch ebony cylinder, about the size of a lead-pencil, from near the tank. It was a chopstick!

"Has the Chinaman been here?" he asked.

"Not that I know of," answered Dick. "Why?"

"Nothing," said Matt, but he was doing some tall thinking as he stepped into the torpedo room, aroused Clackett, and sent him aft to lend Dick a hand.