Laboratory Studies -27- 



A significant fact resulting from the Mt. Washington studies was 

 the rarity of relatively high concentrations of active ice -forming nuclei 

 in the atmosphere.^ ' If the observed results are a true representation 

 of the average mean condition of the atmosphere, it is obvious that, by 

 the artificial introduction of sublimation nuclei into the atmosphere, man 

 possesses a powerful method of modifying many cloud systems. 



One prolific source of ice -forming nuclei might be the Great Plains 

 and the more arid regions immediately adjacent to the Continental Divide. 

 Wind storms, dust devils, and strong convective activity could easily ac- 

 count for the formation of ice -forming nuclei aerosols. H7) 



It seems probable that the smoke produced by forest fires is a 

 poor source of such nuclei.^ 4 '' An attempt was made to determine the^ 

 role that bacteria and the spores of fungi might play in this respect^?;! 

 and to evaluate the role of industrial smokes of various kinds J59) 



Adiabatic Expansion of Gas . An important contribution to the early 

 knowledge of meteorological phenomena was made through Vonnegut's 

 observations that, when gas is cooled to below -39°C by adiabatic expan- 

 sion, very large numbers of ice crystals are formed. (°0) For example, 

 the low temperature produced at airplane propeller tips and wings can 

 seed supersaturated air or supercooled clouds, resulting in persistent 

 vapor trails or cloud modification. Cwilong had reported' ^' that ice 

 crystals could be produced by this method, but he apparently had not 

 appreciated the enormous numbers which are so produced. 



It was found that the adiabatic expansion resulting from the bursting 

 of a rubber balloon a millimeter in diameter produced over 10,000,000 

 ice crystals. Schaefer made a popgun which did the same thing, lending 

 itself to careful control of temperature, pressure, and humidity. 



This provided corroboration of conclusions already reached with 

 dry ice and furnished additional quantitative data which were found very 

 useful. 



Chemical Effects . An interesting effect noticed by Vonnegut while 

 carrying out some studies of ice crystals in a cold chamber was that 

 the presence of normal butyl alcohol caused the crystals to form as hex- 

 agonal columns instead of hexagonal plates. '5°) The phenomenon was 

 studied by Schaefer in some detail, but no practical application of the 

 findings was developed. 



