Document aJmN9jGzQ1eV0YLXwob7MyBXy

Preliminary Dust Survey for Asbestos Tcxtllo Inatitutc, Juno, 1947, zk 2. Secondly -- since the limit of resolution of the microscope lenses used in dust counting does not permit seeing particloe very much smaller then one nicron, one raj esk if there are many fibers of great length, but of such small vidth that they are invisible? Samples of atmospheric dust vere obtained for examination by the electron rdcroscope, by mounting the small specimen slide U9ed vith this instrument, in the dust collecting zone of the electric precipitator. In order to eliminate very large fibers, the air being sampled vao caused, to pass first through a glass spiral coated vith adhesive on its interior. This subjected the dust particles to centrifugal force and the largest ones vould be pre cipitated out, much as they might be in the nasal passages of man. Studies vith other industrial dusts employing this spiral Indicate that very rarely do cubical particles larger than three to five microns suc ceed in passing through the several turns of the spiral. ' In saeplco obtainedwith thio apparatus in a card room having a good dust control, ve obtained pictures, oome of uhich are reproduced in the attached Figure. They demonstrate first, that the cubical particles seen by a low pever light-microscope are in fact bundles of fiber resembling a life- size handful of partially opened fibers. . The picture further demonstrated that there are many fibers of con siderable length, some fully 50 microns, vhose other dimension is only a fraction of a micron; the fiber is therefore invisible in the dust counting microscope. MTS 007915