VACUUM INTERLOCK and LINEAR MOTION DEVICES Now available, a complete line : vacuum interlock loading systems for surface analysis, vacuum preparation of surfaces, or introduction of samples into other devices such as accelerators. These intruments can cool, heat, manipulate, or fracture samples under UHV conditions. Moves samples up to a few meters under vacuum. Programmable linear motion devices are also available.
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UHV INSTRUMENTS 901 Fuhrmann Blvd., Buffalo, N.Y., 14203
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Solve your materials problems by
N E W Automatic Particle Size Analysis By new wet-sieving Analyzer: 500 to 38 /urn diameter (35 to 400 mesh) Micromeritics' AutoSieve is the first automatic wet-sieving particle size analyzer. Its microcomputer controls sieving, collection, weighing and data reduction. An operator simply introduces sample, starts the analysis and returns in 20 minutes for a complete printout of results. Accuracy and reproducibility are superior to manual sieving methods. By sedimentation: 100 to 0.1 /urn diameter: Micromeritics' SediGraph is automatic, fast and accurate. It is simple to operate with no calibration required. Results are given as a direct plot of cumulative mass percent versus equivalent spherical diameter. For more information, contact Micromeritics Instrument Corp, 5680 Goshen Springs Road, Norcross, Georgia 30093 U.S.A. (404) 448-8282 TELEX: 70-7450.
micromeritics
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CIRCLE 140 ON READER SERVICE CARD 100 A ·
ANALYTICAL CHEMISTRY, VOL. 52, NO. 1, JANUARY
1980
pressures of 500 psi were required to eliminate leakage of reagents during the push cycle. T h e mixing cell is shown in greater detail in Figure 4 and is similar to the design of Gerisoher and Holzwarth (25). Reagents enter the cell separately through the two inlets and flood the circular reagent channels which lie ahout the circumference of the cylindrical cell body. T h e solutions flow through feed tubes which connect the reagent channels to 14 slits arranged in a radial fashion on the top face of the cell. T h e reagent channels and feed tubes supply reagents to the slits in an alternating fashion. Reagents proceed through the slits across the top face of the cell and mix just as they enter the 2-cm long, 2 mm in diameter observation tube. T h e mixture flows down the observation tube and into the receiving syringe via the outlet. T h e windows on either end of the observation tube are polished quartz, and the remainder of the cell is constructed of Kel-f or PVC. Seven o-ring seals are positioned throughout the cell to prevent leakage during the push cycle. If the solution flow velocity in the observation tube reaches 9 m/s, as shown in Figure 3, then the flow velocity through each of the 0.25 X 0.25 m m slits is 31 m/s (from the ratio of the cross-sectional areas). With such high flow velocities and the accompanying hydrostatic pressures, two questions had to be addressed. First, is the pressure inside the observation tube large enough to affect the value of the rate constant or the refractive index of the solution? Second, is the large quartz window remaining flush against the front face of the cell during the push cycle? Since the pressure at the outlet of the cell drops to atmospheric, the pressure at various points inside the cell can be calculated by applying the appropriate fluid dynamic relationships (26) and working backwards from the outlet. Thus, for a flow velocity of 10 m/s a pressure of only 60-80 psi is expected in the flow tube. Hence, effects due to pressure on the chemical process or the solvent properties can be neglected. T h e second question was resolved by positioning two three-quarter inch steel bars as a clamp on the mixing cell. This held the large quartz window firmly against the face of the cell body. Imposition of the clamp was attended by improved mixing efficiency and mechanical measurements indicated negligible movement of the cell faces during the push cycle. T h e optical system consists of a feedback stabilized (27) photometer utilizing photodiode detectors. A Hewlett-Packard 2100A minicomputer with several peripheral devices is
