Laserfiche WebLink
<br />VARIATIONS OF SILVER IODIDE <br /> <br />Research in weather modification began in 1949. Numerous <br />materials have been studied as possible cloud seeding agents. <br />Silver iodide has almost always been used because equip- <br />ment to disperse it is compact and lightweight for aircraft <br />and small amounts of it are adequate to treat several clouds. <br /> <br />From 1950 to 1970 the most common method of dispensing silver <br />iodide was to burn a solution of silver iodide and sodium <br />iodide in acetone. The sodium iodide was needed only to <br />help the silver iodide dissolve in the acetone. <br /> <br />In the late 1960's, it was determined that the long used <br />acetone solution really wasn't producing pure silver iodide. <br />Rather, it was producing a water soluble complex chemical. <br /> <br />In 1968 it was found that if ammonium iodide were substi- <br />tuted for sodium iodide in'the solution, pure silver iodide <br />was, indeed, produced. <br /> <br />, I <br /> <br />In the 1960's, the Navy developed a variety of pyrotechnic <br />devices for producing silver iodide. These devices have <br />been extensively used since their development. <br /> <br />Since, 1970, all major research and operational weather mod- <br />ification projects have used the new acetone solution and the <br />pyrotechnic devices. <br /> <br />As might be expected, more recent cloud seeding programs <br />have produced more positive results than were previously <br />obtainable. The experiments conducted in the 50's and <br />60's showed that the then used formulation of acetone <br />solution does not work as well when released below cloud <br />base as it does when released in cloud at temperatures <br />colder than freezing. Many times the material was released <br />into the warm portion of the clouds where it dissolved in <br />cloud water drops, reducing its effectiveness at the colder <br />temperatures. However, the 1968 findings concerning the <br />acetone solution made it possible to release the silver <br />iodide below cloud base and still obtain predictable, pos- <br />itive results. <br /> <br />42 <br />