Page 143 - James Rodger Fleming - Fixing the sky

high-pressure stream of liquid through the overhead pipe. Its nozzles hissed, and
jets of Mr. Houghton’s chemical cut into the fog like rapiers. The white sea seemed
to divide, roll back like the Red Sea before Moses. Soon the watchers were looking
through a half-mile tunnel of clear air, 30 feet high, 100 feet wide.” 34
Houghton’s research supported the goals of military chemists who were seek-
ing effective smoke screen agents and possible chemical neutralizing agents for
use during poison gas attacks. He learned that titanium or zinc chloride could be
used in generating smoke screens, but calcium chloride (CaCl ) acted as a hygro-
2
scopic drying agent, or desiccant. Calcium chloride is a non-toxic exothermic
compound that lowers the freezing point of water. It is used as a water softener,
to suppress dust on dirt roads, to melt ice, and as a drying agent in concrete. It
can be used as a food preservative, but can also be a powerful abrasive irritant on
moist skin tissue and in the eyes, nose, mouth, throat, and lungs. When burned,
it produces toxic and corrosive fumes. It attacks zinc in the presence of water to
form highly flammable hydrogen gas, and it corrodes steel rebar. Experiments
conducted in a laboratory cloud chamber indicated that 1 gram of calcium chlo-
ride could clear 3 cubic meters of foggy air, possibly by lowering the vapor pres-
sure of water. Houghton hoped his chemical sprays might be used to clear fog
at airports and to add a margin of safety for ocean liners using it to sweep their
paths clear. He had basically designed a huge chemical dehumidifier. 35
Working against the practical adoption of this technique was the enormous
amount of chemical needed to keep open even a moderate-sized hole in the fog.
Since the ocean fog kept rolling in and re-forming, a constant chemical spray
of about 400 pounds a second (!) would have been needed to maintain a half
mile opening during the Round Hill experiment. Moreover, as the researchers
admitted, “Apparatus of the type described cannot readily be made portable
and its size makes it a rather serious obstruction for some applications, nota-
bly at airports.” As mentioned, the electrified, high-pressure calcium chloride
spray was corrosive to metals. It tended to clog the spray nozzles and had to be
washed off any metal objects it contacted, especially electrical systems, but also
the piping and even the airplanes and ships it was designed to serve. It was also
dangerous to personnel, producing skin rashes if not rinsed off, and it killed
vegetation (it was sold as a weed killer). The navy had some unfortunate expe-
riences with the chemical and ultimately decided not to use it on its air-
plane carriers. 36
Reminiscent of the later distinction between cloud physics and weather mod-
ification—perhaps also between basic research and practical applications—MIT
researchers were quick to point out that fog research, not fog control, was their
ultimate aim: “The end result, whatever the practical application of local fog

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