Stick, gauging

The simplest instrument for the measurement of the volume of a liquid in a vessel is the dipstick or gauge stick. The dipstick is a straight rod, calibrated along its length, which is immersed vertically in the liquid so that its lower end touches the lowest point in the vessel On raising the dipstick the volume of liquid in the vessel may be read from the mark coinciding with the liquid level. A dipstick can only be used in the vessel for which it has been calibrated. 

Another adsorption characteristic which can be deduced from the primary experiments described above is the evaporation rate E. This i.s the number of molecules of nitrogen which leave the surface per square centimeter per second and which previously were chemisorbed as atoms. That nitrogen leaves the surface as molecules rather than as atoms follows from the experimental fact that the flash-off experiments yield the same values as the pressure-time curves. If the nitrogen came off as atoms, it would stick to glass walls and would not reach the ion gauge bulb to be recorded as a sudden increase in pressure. Only at very high flash-off temperatures is the evaporation rate of atoms comparable with the evaporation rate of molecules. 

When the mouth of the piece Is too narrow to admit the insertion cf the hand, as is often the case with a jug, it is either made in two halves, afterwards cemented together, or shaped out by means of a wet sponge attached to the end of a crooked stick. In order to insure uniformity in the sizes of the piece, a gauge is used, consisting of a small rule, a—Fig. 475—sliding up and down a rod, h, and fixed to any required height by the marker, c, the whole being attached to the stand, d. 

Once depth is established with a depth gauge, measurement can be read directly, or the device is removed and laid onto a meter stick to determine depth measurement. 

The difference in level of the mercury surfaces in the limbs, as measured with a metre stick, gives the pressure in the limb attached to the apparatus. The open limb is exposed to atmospheric pressure, which must be measured on the laboratory barometer and allowed for. A good standard of accuracy in measuring pressures is possible with this type of gauge if the mercury and the inside surface of the glass U-tube are clean and the levels are measured with a cathetometer. 

Filter Stick. A typical filter stick for solution filtration is shown in Figure 4. A section of teflon tubing (2-3 ft) is pushed over the Luer fitting of an observation port (Popper Sons), and conventional filter paper is then attached to the end of the observation port as shown. Half inch teflon sealing tape (Aldrich - this may also be available from a local plumbers supplier as pipe dope) is first wrapped around the base of the observation port, filter paper is then wrapped around the outside of the teflon tape, and one or two loops of nichrome wire (20 gauge, 32 thou) are used to secure the filter paper in place. The teflon tape provides a bed into which the wire can bite and seal the system. Any filter paper may be used, but we have found water resistant fine filter papers such as Whatman s 50 to be most satisfactory, except for gummy solids which may require a faster paper. 

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