Constantio turned white, fighting was not in his line, but the sailor stepped to his side and whispered something, at the same time pressing his revolver to the Spaniard's head, and the wretch, trembling in every limb, followed the others back. But the attacking party was doomed not to get any more treasure that night. As they approached the camp Frank called out in a clear voice:

"We don't want to do you any harm, but don't come any closer or we shall fire."

For reply Wells let fly a bullet at the boy's head, which, if the sailor had not been an indifferent shot, would have inflicted a serious wound. As it was, it flew wide and went whistling out to sea.

Before Frank could check him, old Ben in a furious rage stood up and fired straight at Wells. He shattered the man's wrist and with a howl of pain he dropped his revolver.

"Come on, men," shouted Constantio, as he saw the mainstay of the attackers rendered helpless; "we've got enough loot in that one sack to secure us all a good sum when we get ash.o.r.e. Come on--I'm for the boat!"

So saying he turned and ran at top speed for the boat, the others after him. The sh.o.r.e gained, they leaped to the sides of the craft, having first thrown in the wounded sailor Wells, and then shoved the boat off till they were waist-deep in water.

The boys and Ben reached the spot just as they were clambering in and getting out the oars.

"Shall I tell 'em to come back, or have a hole shot in their boat?"

asked Ben.

"No," decided Frank, "let them go. We are cheaply rid of the rascals at the cost of only one sack of valuables."

The men fell to the oars with a will, and were soon out of sight in the darkness. Nothing more was ever heard of them by the boys, but as some time ago a sailor was arrested on the Bowery trying to p.a.w.n a candlestick of solid gold marked Buena Ventura, it is reasonable to suppose the men eventually got ash.o.r.e. The prisoner gave the name of Jones, but as he had red hair it is not unreasonable to a.s.sume that he was none other than Wells. As n.o.body claimed the candlestick and the police had received no word of such an article being stolen, it was given back to the man and he was released.

CHAPTER XXVI.

THE BOYS WIN OUT.

"Now," said Frank briskly the next morning, "as that scoundrel Constantio tried to steal a march on us we shall have to try to discover his powder and make the gas by ourselves."

"What," exclaimed Harry, "do you mean to say that you think it would be possible to do it?"

"If he can, I don't see why we can't," rejoined the other. "The first thing to do is to find his powder. Then to mix it with equal parts of water and sand in the cylinders and screw the caps on."

"Sounds easy," commented Harry.

"I guess the hardest part will be to find the powder," put in Ben.

"How are we to tell whether it's hydrogen gas powder or Seidlitz powder, I'd like to know."

After a hasty breakfast a thorough rummaging of the cabin occupied by Constantio was begun.

"Say, Frank," suddenly cried Ben, who was bending over a locker, "is this the stuff?"

Frank hastened to his side and saw, ranged side by side, a number of wooden boxes about a foot square labeled "Dangerous."

"I guess that's the stuff all right, Ben," he said, "bear a hand and we'll drag it out. Only be very careful of it. It is probably a high explosive if not handled delicately."

One by one the boxes were transferred until two dozen of them stood on the beach, set in soft sand. Then a sudden difficulty flashed into Frank's mind. Constantio had said "equal parts of sand, water and the powder," but he had not said how much these equal parts were to be.

The only thing to do was to experiment.

Fortunately the ma.s.sive steel cylinders, in which the gas was to be generated, were provided with gauges to register the pressure. One thousand pounds were marked as top measure, so Frank a.s.sumed that somewhere about 800 pounds would be enough.

The first mixture they tried only registered three hundred pounds, but by gradually increasing the amount of powder they at last hit upon the required strength, and were ready to start on the work of inflation.

They had six cylinders full of the gas. Not enough to fully inflate the bag, but enough, Frank calculated, to render it sufficiently buoyant to carry the reduced weight it would be called upon to convey now that the crew was gone.

The inflation nozzle was connected with cylinder after cylinder, till the bag became so buoyant that it was necessary to weight the machine down with heavy stones. At last the cylinders were emptied and the great bag, expanded by the warm sun, swelled up till it seemed it must burst. The expansion of gas by the sun was one of the things Frank had counted on when filling the bag, and he was glad to see his theories work out right. The treasure bags were hastily laden on to the craft and then the boys, standing on the lower framework, one on each side, while Ben stood in the pilot-house, started to kick off the weights that restrained the ship from rising.

They had not cast off more than half a dozen before the ship gave a mighty bound upward that threatened to throw them off her frames and before they could catch their breath they had shot up 1,200 feet or more. Hastily clambering aboard and laughing at the sudden jump, the boys got the engine going and shaped a course that would bring them over the spot where they had left the Bolo.

They held steadily on their course that day and the next. Early in the morning of the second they encountered a surprising incident. Frank, who was on lookout, hailed "Air-ship ahead."

And there, sure enough, heading northward, was a big red dirigible coming toward them like the wind.

As they drew near, a man with a megaphone appeared on her bridge and signaled that he wanted to hail them. Frank shut down the engine and the two air-ships drew alongside.

"What ship is that?" hailed the man on the bridge of the red air-ship, who wore yachting flannels as did his three companions.

"The Luther Barr of New York," responded Frank for lack of a better name.

"We are the Dos Hermanos, five days out from Cuba, bound for Jacksonville, Florida," was the response, "can you spare us any bread?"

"Come alongside," responded Frank in a hearty tone, "and we'll give you some tins of pilot bread."

"Bully for you," responded the red air-ship man.

The two dirigibles drifted together and the boys handed over some tins of pilot bread or ship biscuit with which the larder of the Luther Barr, as Frank had called her, was well provided.

"Thank-you," shouted the men on the red dirigible, as the lines were cast off, "good-bye and good luck."

"Same to you," hailed the boys, as the engines were started. An hour later the red dirigible had vanished on its voyage to the north.

"Well," said Frank, "that's the first time I've ever heard of 'ships that pa.s.s in air and speak to each other in pa.s.sing.' I'm glad we were able to help a fellow voyager out."

Frank's observations that day showed that they could not be far from the spot from where the Bolo had been left, but eager scrutiny failed to reveal her till almost sundown, when Ben's sharp eyes spied her--little more than a tiny black object on the horizon.

"There she is," he hailed.

Frank's binoculars soon confirmed the good tidings.

But as they neared the Bolo an astonishing thing happened.

Through the gla.s.ses they saw a form they recognized as Bluewater Bill's come out on the deck and gaze at them in amazement, to judge from the way he threw his arms about.

Presently he was joined by two other figures that the boys recognized as Billy Barnes and Lathrop.

Harry impetuously rushed to the rail, oblivious of the fact that at that distance the boys could not hear him, and shouted at the top of his voice.