Palmer Tube

PALMER TUBE (Palmer), a device for collecting dust samples from air, proposed by Palmer in 1916 and widely adopted for professional-hygienic studies of air dustiness in workrooms. The apparatus consists of a glass vessel (see figure), the inlet opening of which through a short tube leads into a U-shaped tube about 2.5 cm in diameter. The latter directly communicates with the narrowed end of the pear-shaped expansion of the apparatus, which terminates in a coil. From the bottom of the vessel extends a branch equipped with a rubber tube with a clamp. Distilled water serves as the dust-capturing medium. About 40 cm³ of it is poured into the U-shaped tube, the coil is connected to a measuring instrument (rheometer) and then to an air-sucking device (electric vacuum cleaner, motor). Under the influence of suction, water, mixing with the drawn air, boils and rushes from the U-shaped tube into the expanded part, which is accompanied by its intense splashing. In this process, air passing through water is washed by it and freed from the dust suspended in it, the particles of which come into close contact with the boiling and finely splashed water. The design of the apparatus—the pear-shaped expansion and the coil that prevents water from being sucked in—makes it possible to draw air at high speed and thereby enhance the splashing of water, and consequently the wetting of dust particles. According to Palmer and other authors, the optimal air suction speeds range from 140-100 l/min. Lower speeds, by reducing the intensity of splashing, thereby decrease the surface area of contact between dust particles and water, weakening the dust-capturing power of the apparatus. The sampling usually lasts 15-30 minutes, depending on the degree of dustiness of the air being examined. The resulting dust suspension is drained through tube e into an Erlenmeyer flask, the water is also drained here after thoroughly washing the apparatus from dust trapped in it, and the sample is ready for analysis. For gravimetric determination, the liquid is evaporated in a platinum or porcelain dish, the dry residue is weighed, and the result is calculated per 1 m³ of air. Another method of weight analysis—passing the liquid through a filter and determining the difference in its weight before and after filtration—has not found application due to the cumbersome nature of the method and the inaccuracy of the results obtained. For konimetric analysis, i.e., for determining the number of dust particles in 1 cm³ of drawn air and the morphological properties of dust, the suspension obtained after sampling is brought to a certain volume, 0.1 cm³ of suspension is taken with a micropipette and examined in a counting chamber; the number of dust particles is then calculated per 1 cm³ of drawn air. P. t., having water as the dust-capturing medium, is applicable only for certain types of dust: metallic, silicate, coal, etc., dusts insoluble in water and not changing their physicochemical properties under the influence of wetting (in individual cases, however, water can be replaced with oil, alcohol, or another suitable liquid medium). The main advantages of P. t.: a) it allows determining dust both gravimetrically and konimetrically; b) it passes large volumes of air in a short time; c) it permits relatively rapid determination of dustiness at low concentrations. The main disadvantages: a) the fragility and breakability of the apparatus; b) applicability exclusively for insoluble dusts; c) impossibility of long-term preservation of dust samples in water. The effectiveness of the apparatus in the initial period of its introduction into professional-hygienic practice was assessed very highly. In 1917, the American Public Health Association recommended it as the best device for determining airborne dust. According to Palmer's own data (1916), the effectiveness of the apparatus was 71% of the actual dustiness of the air being examined, according to Bill's data (1919)—63%, Smith's (1919)—82%. But as early as 1920, Katz with co-authors showed that the useful effect of the apparatus is extremely insignificant with respect to fine-dispersed dust, giving better results only for larger particles, e.g., for tobacco smoke the efficiency turned out to be 13-15%, for fine silicate dust—20-30% (in both cases the tyndallmeter served as the standard), and for larger dust—45-48% (the standard was the electro-precipitator). The apparatus also received a restrained assessment in the work of a special commission of the USA, which in 1925 studied the comparative effectiveness of a number of methods for studying industrial dust. Nevertheless, P. t. still belongs to the relatively widely distributed devices for dust research both abroad and in the USSR.