Document 82gJey3qGjLzR5N2p0Z4dNzja

es Holmes: Developments in Sampling 295 lh comment* above concerning the possibility of drawing fibers right through the "Otlway" sampler. Opaque filter* possess une disadvantage in that they tend to distort whoh mounted, particularly in warm weather and therefore become rather difficult to count. Further work was therefore undertaken on cleared mem branes, glycerol triacetate ("Trlacetin") being chosen as the clearing liquid. The samples were, counted under phase contrast conditions at a tots] magnification of 480 x;.using'a 4mm.'achromatic objective, later in- ' creased to MO x using a 3.75mm. fluorite oil immersion objective. It may be argued that phaae contrast illumination should not be necessary when using a liquid such as "TrUcetin" with" a.very different refractive index.;.-' u shown in F1GUKE 6 where,'the correlaUop efflcient;i*^0.9B. Based on yV this work, a standard inetliod bT sampling an^ eouhtm'g haknow been" " adopted by the members of the Asbestos)* Research Council. This is set out in detail in Appendix 1 .0........../ -- `-'J> counts on clears/' mbrane. This Is s in the progress ng a sample of it care must b* efTVlva indax.,; rn. trimethyl ;r, .idshyde (1.62);`;: .ring membrane': pose. . .. .erienced with' <h sampling by ark ground re>er of different vn in noun* 8, to the 46' lint, and "Ottway" slightly higher eted in view of i * fr i Opaque Uembsake Dun Concextsatiok (Ftms its tx) . PjOtmz 6. Cotnpsrlson of opaque end "Trisectin'* cleared membrane sample*. Cteued sample* counted in phase contrast illumination (640 x ). Opaque sam ples counted In dark ground reflected light (640 X). PRODUCED BY FORD