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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The wheel Y is then turned so that the lower edge of vernier Barometwr is exactly level with the top of the Mercury column M.
If the surface is bright and the setting correct, the tip of the point will appear to coincide with its reflected image in the mercury surface. A mercury thermometer attached to the casing gives the temperature of fotin barometer, and baromeher corrections to be made. The pressure is then read from scale D using the Vernier. The Pattern Greensand Casting: Before the days of high performance vacuum pumps, barometer makers would boil the mercury throughout the entire length of the tube for 5 hours to remove air and moisture, before inverting it over the cistern.
Users without a subscription are not able to see the full content. An ivory pin, S, is provided as an index visible through the cistern glass.
The leather lining to the cistern should be treated with particular respect forrin the surface is relatively easily damaged. Calculation of pressure from Fortin barometer readings where: Here you can find out more about the interesting things we do, science outreach activities you can get involved in or take a look at some of our educational resources. After thorough pumping, the tube is sealed off in the flame and the instrument reassembled. Commercial Services NPL’s commercial services are built on years of leadership in accuracy, innovation and scientific research.
Mercury transferred from the bottle on left to that on the right, leaving the dross behind. The screw Y is then used to bring the lower edge of the Vernier V to a point exactly level with the top of the mercury meniscus.
Fortin barometer – oi
When the clamps are in place, the three long bolts P are slackened and removed. The space above the mercury in T contains a Torricellian vacuum. The availability of a good vacuum pump makes other methods possible.
A thermometer Q is located half way along the brass casing. Air pressure on the free surface of the mercury in the cistern supports the column of mercury, the length of which is read by a vernier operated by a rack and pinion over a graduated scale marked on the casing. Ecology and Conservation GO. All All Title Author Keyword.
The instrument is clamped vertical using a clamp on the lower part of the cistern and two other clamps at top and bottom of the barometer tube housing.
In use the vertical tube T and the cistern C are filled with mercury. A vernier scale on the side of the barometer tube is then lowered until its base touches the top of the mercury in the reservoir and a reading is taken from the fixed scale marked on the tube.
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.
The correct sequence for measuring pressure with a Fortin or Kew Pattern barometer is: Recently viewed 1 Fortin barometer. Related Overviews Kew barometer fiducial point. Mercury barometers have a temperature coefficient of nearly 0.
The cistern C has a lower brass section containing a leather bag, the capacity of which can be adjusted by the screw W. Arrangement used for filling barometer with a vacuum pump. User Account Sign in. An Improved Fortin Barometer.
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 level using screw W to a point just below the opening of the barometer tube T. If the mercury is to be reused is should be cleaned. This, of course, is especially important in marine instruments. This process can be repeated until the barometer tube is empty. The whole is arranged so that it is possible to read the vertical distance between the tip of the ivory pin S and the lower edge of the vernier V.
Simple device used for filling barometers using a vacuum pump.
The cistern and lower section of the barometer tube after removal of the barometer tube housing. For a 6mm diameter tube the capillary correction is about 0. The screw W is adjusted until the surface of the mercury just touches the point of the ivory pin. Parallax error in reading the position of V is avoided by means of a plate level with and attached to V running vertically at the rear of D.
A portable mercury barometer that was invented in by the French instrument maker Jean Nicholas Fortin — Mercury barometers must be firmly supported, made vertical and given time to adopt ambient temperature before attempting to use them. The stopcock is then opened and the barometer pumped down for an hour.