A Wonderful, Terrible Liquid

Its atom contains only one proton and one electron, which makes it the lightest element known to science. It is completely colorless, completely odorless. And it is that ultimate simplicity that has earned for hydrogen some of the most sophisticated jobs in modern science. Refrigerated into a liquid state, hydrogen is helping physicists to peer into the heart of the atom, to trace the fleeting histories of the smallest building blocks of matter. Space scientists are depending on it to launch the Apollo spacecraft that will take the first U.S. astronauts to the moon.

Simplicity, however, is not hydrogen's only attribute. In its liquid state, it is one of the most intractable and unforgiving substances on earth. It is given to violent explosions on the slightest opportunity. It was only natural that the very presence of a tank of liquid hydrogen was immediately blamed last week for the blasts that rocked the Harvard-M.I.T. electron accelerator laboratory at Cambridge and injured eight young scientists.

Investigators are still trying to determine the exact cause of the blast. The accelerator, buried 16 ft. below ground, was not damaged, and there was no danger of radioactivity. Still, the laboratory's new bubble chamber for the study of subnuclear particles lay twisted and scorched in the $1,000,000 wreckage. When all the evidence has been studied, the deceptively simple element may yet be exonerated. But significantly, when the accident occurred, the scientists were cautiously handling hydrogen, piping it into the 100-gal. bubble chamber.

Vicious Problem. Although a British scientist, Sir James Dewar, first liquefied hydrogen in 1898, it remained a mere curiosity until after World War II. Then it was enlisted as a tool in the modern specialty of cryogenics (the science and technology of very low temperatures), which has been instrumental in developments ranging from exotic new metals to important new discoveries in superconductivity. Liquid hydrogen came into its own when it was put to use in bubble chambers for experiments in high-energy physics. In such studies, accelerators smash the nucleus of a hydrogen atom, scattering subnuclear debris through the bubble chamber, where scientists can follow and photograph the paths of the tiny charged particles by their tracks of small bubbles. This technique, which was to have been used at Cambridge, has led to the discovery and identification of many new particles.

Valuable as liquid hydrogen is in the lab, though, the men who use it can never forget its dangerous characteristics. The trouble is, it really does not want to be a liquid. Forced into a fluid state by powerful refrigeration machines, it must be sealed in a double-walled vacuum container and kept constantly below its boiling point (-423DEG F.) to control vaporization. As a liquid, it is not readily flammable. It is when it vaporizes and comes in contact with oxygen that hydrogen becomes explosive. Which makes for a vicious problem: how to let off the inevitable vapors and avoid rupture of the tank as a result of the pressure of expanding gas, without running the risk of a fire outside the tank. Surprisingly, there have been few serious accidents in handling the stuff.

Explosive Energy. The same property that makes liquid hydrogen so intractable makes it a powerful and efficient rocket fuel. For use in rockets, liquid hydrogen is changed to its gaseous state, mixed with an oxydizing agent and ignited. Its explosive energy is greater per unit of weight than that of any other fuel now in use: one-third more thrust for each pound of liquid hydrogen than for the same weight of kerosene-oxygen fuels. "The difference in performance of liquid hydrogen over any other rocket fuel," says Norman C. Reuel of North American Aviation's Rocketdyne division, "represents the difference between man orbiting the earth and getting to the moon."

Liquid hydrogen is the fuel for two important U.S. rocket engines--Pratt & Whitney's RL-10 and Rocketdyne's J2. The RL-10 powers the second stage of Saturn 1, scheduled for early Apollo flights; two RL-10s combine to form the Centaur stage of the Atlas-Centaur system built to soft-land Surveyor spacecraft on the moon. J-2 forms the second and third stages of the Saturn V designed for Apollo's man-carrying lunar missions. In the near future, violent but versatile liquid hydrogen may become still more familiar as a fuel for supersonic aircraft.

This file is automatically generated by a robot program, so reader's discretion is required.