Document 0Jganb7qMgvnQELezVQReKMeV

12through a moistening chamber which has at its lower end a narrow slit. The dust is deposited through this slit on to the circular speoimen slide in the form of a ribbon. The slide can be rotated until the sample comes into proper position for viewing with the miarosoope, or a nwHimrm of twelve samples can be collected on the slide and then viewed. The slides are quickly removable and replaceable. This dust counter is not designed for accurate dust determination but rather as an inexpensive device for roughly checking dust conditions. It has not been available long enough for a thorough test in actual practioe. i The principal objection to instruments like the Bausch & Lamb Dust Counter and the Owens jet dust sampler for determining number concentration is that their dust oolleoting efficiency decreases with an increase in the atmospheric dust concentra tion and the fact that they take grab samples. Since the major portion of dust present in industrial atmospheres is small enough to gain entrance to the lungs, very little attention need be given to determina tions of the exact sites of particles. E KO 01502