They knew it could not last long. Even the professor seemed to have given up hope. The engine was not going to free the ship in time to save the lives of those on board. Washington crawled to the engine room, as some of the bearings needed oiling. The professor seemed in despair. He opened one of the slides that covered the glass bulls eye windows. Then he turned off the electric lights. The opening was black, showing that the sea of grass still surrounded them. With a groan Mr. Henderson turned aside. The last hope was gone. He sank down on the floor of the darkened cabin. Just then Mark happened to look at the bull's-eye. He saw a glimmer of light. Then he noticed several fishes swimming about. The water was clear. The grass had disappeared from the vicinity of the window. "Look!" cried Mark to the professor. The inventor peered forth. As he did so he uttered a cry. Then he staggered rather than ran to the engine room. "What are you doing?" he called to Washington. "I jest let some ob de sulphuric acid out ob de storage battery tank," replied the colored man. "That's it! That's it!" exclaimed the professor. "Quick, let some more out, Washington. Let out all there is in that tank. It will save our lives." Wonderingly Washington obeyed. The air in the ship was growing more foul every second. It was hard to breathe even on the floor, and all were gasping for breath. A few minutes more and they would all become unconscious and death would come in a little while if the air was not freshened. The professor staggered back to the main cabin. He looked out of the bull's-eye windows. Then he exclaimed: "See, it is getting lighter! Thank Heaven we are saved!" The next instant the ship began to move backward. Then with increasing speed it pulled out of the grip of the long grass, and in another minute was floating on top of the water, at the edge of the Sargasso Sea. "Quick! Open the man hole cover!" said Amos Henderson. Washington threw back the lever cams, and in rushed the fresh air. It was a blessed relief from the terrible oppressiveness of the foul atmosphere of the boat. They all breathed deeply, and, in a few minutes the effects of their long imprisonment had passed off. They went out on the small deck. It was getting dusk, and the reflection of the red sunset shone brightly on the heaving water. "I 'spected I'd neber see dis again," said Washington. "Thought suah I was a gone chicken!" "We had a most fortunate escape," said the professor. "You did the trick for us when you let the acid run from that tank into the sea. It mingled with the water and burned or ate through the stems of the grass so they no longer held the ship. I saw what had happened as soon as I looked out of the bull's-eye, and that's why I had you turn out all the acid you could. It was just as if liquid fire had touched the sea weed and burnt it off." "Golly!" exclaimed Washington. "Fust I know I'll be a perfessor myself!"