This instrument is made for measuring atmospheric pressure with the scale in hPa and the venier which can read to 1/10 mm. Since this precision fortin. INTRODUCTION. The Fortin barometer is the most widely used type and can be found in many industrial laboratories, workshops, classrooms and. A wooden wall plaque supports a brass outer casing which protects the glass barometer tube and wood and leather cistern. A brass screw provides the means .
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How do I use a Fortin or Kew Pattern mercury barometer? In order to read the prevailing atmospheric pressure, the Screw W is rotated until the tip of the ivory pin S, just touches the Mercury surface. The barometer tube itself should not be lifted at all at this stage, but should be secured by the lower clamp vacated by the brass housing.
The reading of a Fortin Barometer is straight-forward.
This process can be repeated until the barometer tube is empty. If the barometer is being used in an application where particular measurement uncertainties are needed the barometer should be re-conditioned.
Kew Pattern barometers should have their scale edge made vertical. For a 6mm diameter tube the capillary correction is about 0. The emptying of the barometer tube can be accomplished by carefully removing some mercury from the cistern using a hypodermic syringe, and then lowering the mercury baromter using screw W to a point just below the opening of the barometer tube T. Restoring and Using a Fortin Barometer The Fortin Barometer is the most widely used, and generally most accurate of mercury barometers and while the use of mercury is still permissible, will remain the primary absolute instrument for calibration purposes and in all circumstances where a dependable, precise measurement of atmospheric pressure is required.
Correct setting is achieved when the mercury surface is raised to the fiducial point but not lowered – if the mercury surface overshoots the point it should be lowered and then raised again. Tube T is some mm in length and is supported by the top plate of the cistern C, by corks B, and bxrometer a slot not shown in the top of the brass scale housing D.
When the glass barometer tube is secure, the brass housing can be removed completely. Simple device used for filling barometers using a vacuum pump. Users without a subscription are not able to see the full content. With all the mercury removed, the components of the barrometer can be carefully cleaned. A Fortin barometer is usually also provided with a gimbal mount to that it may be maintained vertical.
It should then be washed and dried. An ivory pin, S, is provided as an index visible through the cistern glass. A thermometer Q is located half way along the brass casing.
Figure 1 shows the essential features of the instrument. The trap fills with mercury during this process.
Please note that the information will not be divulged to third parties, or used without your permission. Normally distillation is not necessary.
The Fortin barometer makes no correction for changes in temperature, which affect the volume of mercury, or for capillarity, which introduces inaccuracies. Ecology and Conservation GO. dortin
: Repairing and using a Fortin Barometer
At the upper end of the instrument, the barometer tube T passes into the brass scale housing D. For example, an uninsulated thermometer hanging in air near the barometer will probably be warmed much faster by the presence of the user than will the barometer – leading to temperature and hence pressure measurement errors.
The instrument is nevertheless sufficiently accurate for most purposes. The accuracy of the scale is important also, but can easily be checked with a cathetometer. In the Fortin barometer the bottom of the reservoir is flexible originally it was made from leather and can be raised or lowered by means of a screw, allowing the surface of the mercury to be adjusted to a predetermined level.
Mercury barometers have a temperature coefficient of nearly 0. The pressure is then read from scale D using the Vernier. This particular Fortin Barometer was in use in the second year laboratory until V is the total volume of mercury in the barometer and A is the effective area of cross section of the cistern.
Restored recently, it would still be operational, however it contains no mercury. Conceptually, it is a simple matter: