n - EARLY HISTORY 



It would be difficult, if not impossible, to trace the complete lineage 

 of everything leading up to Project Cirrus. General Electric scientists were 

 not the only ones who studied many of the problems involved. And even when 

 restricting consideration to General Electric research projects, the situa- 

 tion is complicated. 



The following material is confined as much as possible to work which 

 has a relatively direct bearing on Project Cirrus research. 



GAS MASKS & SMOKE FILTERS 



The earliest activity leading directly to Project Cirrus was the study, 

 beginning in 1940, of the fundamental nature of filtration in gas masks. This 

 work was undertaken by Dr Irving Langmuir and Dr. Vincent J. Schaefer at 

 the request of the Chemical Warfare Service.'-^) 



Gas masks normally use charcoal to absorb poison gases, but even in 

 World War I the possibility arose that the enemy might use toxic smokes 

 which could not be absorbed by charcoal and thus would have to be removed 

 by -a filter somewhat like filter paper. 



The first step in attacking the problem was to make some smokes of 

 the type for which the filters would be used. In doing so, the scientists stud- 

 ied the particles which composed the smokes. They investigated such things 

 as particle stability, concentration, and measurement. They obtained fairly 

 successful theoretical results and a better understanding of how to build a 

 good filter. And incidentally, they acquired a great deat of detailed know- 

 ledge as to how to make a smoke which would be non-volatile and would con- 

 sist of particles far smaller than those of ordinary smokes, and they learned 

 much about optical properties. 



This work was done under a National Defense Research Committee 

 contract. As Langmuir and Schaefer neared the end of the work, a form 

 letter was received in August, 1941, asking if anyone could think of a way 

 to make a white screening smoke that could be used over large areas to 

 cut down the hazard from aerial bombardment. 



SMOKE GENERATORS 



Langmuir and Schaefer wondered whether they couldn't do this by 

 using the methods they had adopted for making smokes for testing filters. 

 They decided to try. 



They had found that the easiest way to make smokes and control the 

 particle size was to take some oil and put it into a volatile condition. They 



