There were two choices now. He could close the cover and wait for the freezer itself to lower the air temperature, or he could make the process occur faster by adding dry ice, a gas in solid form that is very, very cold. He chose the latter plan. He decided to try a container of dry ice.
As he dropped the steaming white dry ice into the freezer, he happened to breathe out a large amount of air. And there, before his eyes, it happened! He had made ice crystals, not by adding centers to the moisture but by cooling the breath so much that the liquid had to form crystals ! Schaefer called to his helpers to come and watch. Then he began to blow his breath into the freezer and drop large pieces of dry ice through it to create crystals which became a tiny snowstorm falling slowly to the floor of his laboratory.
If he could make snow in a freezer, Schaefer thought, why couldnt he do so in a real cloud? He decided to try it in an airplane with a machine to blow dry ice out into the clouds.
On a cold day in November, Schaefer and Langmuir saw clouds in the sky, and Schaefer climbed into the airplane. He realized he would have to fly some distance before finding the right kind of cloud a big gray one that must be filled with moisture. Seeing one, Schaefer told the pilot of the plane to fly above the cloud. At the proper time, he started the machine, and dry ice began to fall from the airplane into the cloud below. When half the load of dry ice was gone, the motor stopped because it had become too cold. Schaefer had to think quickly. He merely threw the remaining dry ice out of the window of the plane 80
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