DDT Formulations 81 



if they happened to be hiding at the time, the mist floated 

 in on them and spoiled their plans for an evening meal. 



Some years ago the late Thomas Midgley, of General 

 Motors Corp., developed a new refrigerant for use in domes- 

 tic and commercial refrigerators and in air-conditioning units. 

 This substance — dichlorodifluoromethane — known as Freon- 

 12, is a non-toxic gas at ordinary temperatures. To liquefy 

 it at atmospheric pressure, you must cool it to about 22 deg. 

 F. below zero. To liquefy it at room temperature, you must 

 put it under considerable pressure. To make an aerosol 

 bomb, all you have to do is dissolve 3 % DDT and 2 % py- 

 rethrum extract in Freon-12 under pressure and charge the 

 mixture into a metal container which is strong enough to 

 withstand the pressure. When the valve is opened, the 

 mixture under pressure rushes out at high velocity through a 

 very small opening. This breaks the stream up into an ex- 

 ceedingly fine mist — the particles of which are very much 

 smaller than the particles from an ordinary spray gun. 

 Furthermore, with the release of the pressure, the solvent 

 evaporates almost instantaneously, leaving the minute 

 particles of DDT and pyrethrum suspended in the air. Be- 

 cause they are so fine, these particles do not readily settle out 

 of the air; instead, they are carried around by the air cur- 

 rents, reaching practically all parts of the room. 



Although developed primarily for killing mosquitoes in 

 army and navy barracks and tents, the aerosol bomb is equal- 

 ly effective on other household insects, such as flies, sandflies, 

 and moths in the flying stage. Their convenience of use and 

 the rapid effectiveness of aerosols as space sprays led to con- 

 siderable civilian demand for the bombs, and it was an easy 

 matter for the manufacturers to turn from wartime to peace- 

 time production. 



