(225 ILCS 705/24.06) (from Ch. 96 1/2, par. 2406)
Sec. 24.06. All rock dust used shall meet the following specifications:
1. All of the dust shall pass through a 20 mesh sieve, and at least 70% shall pass through a 200 mesh sieve.
2. The dust shall not contain more than 5% combustible matter, nor more than 5% free silica. The rock dust should be as light in color as possible.
(Source: Laws 1953, p. 701.)