The instrumental difference and collection efficiency of Jet Dust Counters (Roken Dust Covnter and Funken Konimeter) were studied, and the conclusions are as follows:
(1) There is a significant difference between dust collecting capacity of each instrument.
(2) There is an insinificant difference between 400X and 600X at a microscopic examination of dust collected on the cover glass.
(3) The differences of dust kind have some significant effect on dust collection, and the humidity of atmosphere has some effect on dust collection.
(4) There is an interrelation between the efficiency of dust collection and free silica content of dust.