Document LgQQMZajxYbDOgQ7EmebV1Bv7

the sample* TMa dovioo takes advantage of tho phenonona that a body warmer than the gas about It is surrounded by a dust froc sono* This tone le lnterooptod by the surfaces of tho covcr-glaesea whloh oro kopt oool by tnossos of metal In olose oontaet* Also sinoe portioulato tanttor in warm gasos toads to deposit upon oool surfaocs wo have two foroos whloh act * to doposlt tho dust from the sample upon tho two disos of glass* The sanplo appoars as a narrow strip on occh glass parallol with tho wire* These samples nay bo used for count or partiolc size determination after thoy aro suitably nounted upon a elide* Tho Thermal Pro'oipltator is usod t In England and South Africa for ohcoking other methods end to some extent for routino sampling* It is high in eollcotion officleney exoopt possibly for the larger particles* Its main disadvantages are the difficulty in properIns Qod mounting tho cover glasses and tho snail sampling rate poseiblo for this Instrument, about 6 nl per ninuto* Tho most rccont development, tho Eloctroatatio Proolpitator, whieh will bo described In dotail later by Barnes, is without quostion tho cost eatisfaotory dovioo for oonplcto separation of solid dispersions from gases* It collects a large samnio In a short time and if properly constructed and oporatod has cn cffioicncy of 100 por eont* '.To coco now to tho nost v/ldcly used class of dust collecting instruments, tho devices which operato upon the impingement principle. Three typos of inpingers aro fairly well known; The "IConinctcr"^ tho "0won8-Jct dust sampler, and tho "Grocnburg*Snith Impinger*" Thu Sanloeter was developed in South Afrioa about 1916 and is widely used both thcro and In Canada today* It oonsista of a snail pump with a spring operated piston v/hioh when roltasod draws a 2^ or 5 oo sample of air through a small circular orlfieo that faces and is closo to a glass plate which is propared with an adhesive film* Tho dust in tho air sample is impinged upon tho odhesivo film and sticks thoro*