Do you know the correct way to use the glass gauge?

[China Glass Network] 1. General Principles

When higher accuracy is required, the calibration conditions should be used as much as possible, and calibration values ​​for the indexing error are required. The meter should be cleaned before use. If there is a deviation in the indication capacity during calibration, it should be corrected.

2, the volume bottle

If a volumetric flask is used to prepare an aqueous solution, it may not need to be dried after washing with distilled water. The method of diluting the aqueous solution is recommended as follows: the substance to be dissolved is added to an appropriate amount of water, and if necessary, it may be appropriately heated and shaken to dissolve. Then add water to raise the liquid level to a few centimeters below the mark. After capping the bottle stopper, rinse with a bottle of water to raise the liquid level to 1 cm below the mark line, open the capacity bottle stopper, let stand for 2 min, let the bottleneck liquid drain, and make the solution reach the room temperature again to cover the bottle. Sedido waits for a certain amount of time. Later, a certain amount of water flows down the bottle neck from a point within 1 cm below the scale line, so that the lower point of the meniscus is set on the scale line. Cover the stopper and shake the volume bottle to make the solution even.

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3. Measuring cylinder and measuring cup

After the cylinder is cleaned and dried, it is filled with the liquid to be tested to the nominal capacity line or a few millimeters of the desired line, and then the excess liquid is sucked out by a pipette.

4, burette

The burette (including the plug valve and the flow port) is washed with distilled water and then rinsed three times with the test solution to be used. If the burette is not large enough, the top of the burette cannot be inserted into the thermometer for observing the temperature of the liquid. A normal glass test tube sufficient to hold the thermometer can be placed next to the burette.

Fill the burette clamped in the vertical position to a few millimeters above the zero line. If the pipe wall is wet, there should be sufficient draining time before setting the zero line. In order to eliminate the bubble between the plug valve and the liquid port, adjust Before the zero line is removed, some liquid should be discharged from the liquid outlet to refill.

The outflow time is the time it takes for the liquid to flow freely from the neutral to the nominal capacity when the plug valve is fully open. In order to get better accuracy, the index correction value should be used. The plug valve should be fully open during draining, and the fluid port must not be in contact with the receiving container and the liquid surface. Therefore, for the burette, it is better to estimate how many milliliters of solution the sample needs to reach the end point. If there are enough samples, a pre-titration can be performed to get this. If this is not possible, as long as the titration time does not exceed the specified outflow time of 60 s, the error produced is generally less than ± tm L when the capacity tolerance is ± tmL. If the waiting time is specified, then the time between the closing of the plug valve and the time before the reading is taken, it is usually not necessary to observe the waiting time while the titration is in progress, since the time to reach the end of the titration is generally longer than the specified waiting time.

The above conditions apply to transparent liquids with similar viscosity to water. Particularly viscous liquids cannot be used accurately and conveniently because they leave a lot of mucus on the tube wall and the flow rate is very slow, but it is usually used for capacity analysis. A dilute aqueous solution is suitable and there is no significant error. For example, a 1 mol/L solution produces an error that is less than the tolerance of Class A. The 0.1 mol/L solution produces a smaller error. Accuracy is also reduced when using non-aqueous liquids because their surface tension differs greatly from the surface tension of water. Liquids with poor visibility at the bottom of the meniscus can be read at the edge of the meniscus, but less accurate than at the lower point of the meniscus.

5, measuring pipette

After the pipette is washed with distilled water, it is rinsed with the liquid to be used. The pipette draws liquid above the zero mark or a few millimeters above the desired mark. It is recommended to use a suction device that can freely flow the liquid to be tested, such as sucking the ball.

In order to obtain the correct volumetric capacity, the pipette should be operated as described in the relevant capacity definitions in its product standard. The specified waiting time should be observed before the pipette is disconnected from the receiving container. Usually, the waiting time of the pipette wall liquid to the liquid port is 3s, and it is not necessary to accurately measure. Once it is determined that the meniscus reaches the flow port and tends to be stationary, the pipette can be out of contact with the receiving container. The remaining liquid remaining in the flow port shall not be discharged, and the "blow-out" type pipette shall blow out the remaining liquid as part of the measured capacity. As with burettes, very viscous liquids cannot be easily and accurately absorbed. Dilute aqueous solutions commonly used for capacity analysis are suitable without significant errors.

6, the metered pipette

After washing with distilled water, it is dried or washed three times with the solution to be tested. Draw liquid above the zero mark or above the desired mark. In order to obtain the correct metering capacity, the pipette should be operated as described in the relevant capacity definition.

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