Laboratory Studies -29- 



A very interesting fact discovered as the result of one of Vonnegut's 

 studies is that silver-iodide particles do not react immediately as ice- 

 forming nuclei when introduced into a supercooled cloud of water droplets. 

 Even 50 minutes after introducing a smoke sample into the cold chamber, 

 ice crystals could be seen to form at a measurable rate. The general 

 conclusion reached as a result of this study was that the rate of reaction 

 at -13°C is 30 to 40 times faster than at 10°c/ 61) 



The first unambiguous results in cloud seeding using silver -iodide 

 generators were obtained in 1948. Silver-iodide nuclei produced by one 

 of Vonnegut's generators installed in an airplane resulted in cloud mod- 

 ification similar to that produced by dry ice. (69) 



Experiments were conducted to determine whether the burning of 

 charcoal particles used in silver -iodide seeding from an airplane would 

 be seriously affected by the moisture in clouds. It was concluded that 

 the burning is not seriously affected if the charcoal is thoroughly ig- 

 nited.^ 57) 



Some experiments were conducted to discover the value of a turbo- 

 jet burner as a silver-iodide smoke generator. It was decided that such 

 a method might be of value if larger generators were needed than those 

 already in use„^ 8 ^ 



Experiments were also made in tracing silver-iodide smokes after 

 their release by seeding generators .(69) 



The nature of silver iodide is such as to suggest the possibility 

 that its effectiveness as a seeding agent might be reduced by the action 

 of ultraviolet and near -ultraviolet radiation from the sun. Accordingly, 

 an investigation was made to determine its rate of decay under expected 

 conditions of radiation in the free atmosphere. The results of work in 

 this field not only by Project Cirrus, but also the New Mexico School 

 of Mining and Technology, suggested that far greater quantities of silver- 

 iodide particles might be required for seeding operations under conditions 

 of bright sunlight than would be needed at night or under conditions of 

 cloud cover. But later work and observations indicated that the effect 

 of sunlight might not be as bad as was forecast. '51> '2) 



Experimental work showed that it is possible to convert super- 

 cooled ground fogs to ice crystals by releasing silver-iodide smokes/ ' 



