Word: oxygen
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...except for some further gestures of rescue. Diver George Crocker slid down a grapnel line to 370 feet, found that his special mixture of helium and oxygen (to keep nitrogen out of the blood stream, thus forestall bends) was failing him. Later, two divers did reach the bottom, in the subterranean dark and pressure could see nothing, do nothing. On the third day, the Chief of Naval Operations (Admiral Stark) in Washington announced: "The decision must be to accept the situation as loss of naval personnel at sea, who can best be honored as men still at their station...
Green plants take water, carbon dioxide (from the air) and energy (from light), transform them with the help of chlorophyll into carbohydrates and free oxygen. The chemical form for this reaction...
...achieved. The classic explanation, commonly accepted until recently, was proposed in 1870 by Johann Friedrich Wilhelm Adolf von Baeyer, and amplified by Nobel Prizeman Richard Willstütter of Munich: Under the influence of chlorophyll, carbon dioxide and water combine to form formaldehyde (CH 2 O) and free oxygen. Then, under the influence of light, six formaldehyde molecules somehow assemble into one glucose molecule...
Unimpressed with this explanation was Biochemist Cornelis Bernardus van Niel of Stanford. "Forget about sugar," he told his students. "Consider the other end-product-oxygen. Where does it come from? Discover that and you will be closer to the whole solution." Dr. Ruben at California took this line...
Hitch was that both the raw materials of photosynthesis, H 2 O and CO 2 , contain identical oxygen atoms. There was no way of telling them apart. So Ruben obtained heavy oxygen-a rare isotope which has a mass of 18 instead of the normal atomic weight of 16-and made from it heavy-oxygen water. This was fed to a green plant, together with ordinary, light-oxygen carbon dioxide. As photosynthesis proceeded, the scientists caught the freed oxygen, found it was the heavy variety. Next they fed the plant light-oxygen water and heavy-oxygen carbon dioxide...