Here are two methods for adjusting the temperature range:
First, the constant temperature bath mediation method
1. First determine the temperature range used. For example, to measure the lowering of the freezing point of an aqueous solution, it is necessary to be able to read a temperature reading between 1 ° C and -5 ° C; to measure the increase in the boiling point of an aqueous solution, it is desirable to be able to read a temperature reading between 99 ° C and 105 ° C; At room temperature, the mercury column value is most suitable between 2 to 3 ℃.
2. According to the application range, estimate the temperature value when the mercury column rises to the elbow at the end of the capillary. In general Beckman thermometers, the mercury column rises from the highest point of the scale to the end of the capillary, and it needs to be increased by about 2 ° C. Adjust the amount of mercury in the mercury ball according to this estimate. For example, when it is determined that the freezing point of water is lowered, the maximum temperature reading is to be adjusted to 1 ℃, then the temperature at the elbow of the capillary end should be equivalent to 3 ℃.
4. Use another thermostatic bath to adjust it to the temperature that the elbow at the end of the capillary should reach, and place the Beckman thermometer in the thermostatic bath at a constant temperature above 5 ℃.
5. Take out the thermometer, hold the middle of it with your right hand so that it is almost vertical, and lightly tap the right arm with your left hand, as shown in Figure 3-3. The mercury can now be disconnected at the elbow. After the thermometer is taken out of the constant temperature bath, the mercury volume will change rapidly due to the temperature difference. Therefore, this adjustment step requires quick and light, but there is no need to panic to avoid mistakes.
6. Place the adjusted thermometer in a constant temperature bath with a predicted temperature, observe its reading, and estimate whether the range meets the requirements. For example, in the measurement of the molar amount of the freezing point reduction method in experiment 2, it can be checked with an ice water bath of 0 ° C. If the temperature value falls at 3 to 5 ° C, it means that the range is suitable. If the deviation is too large, you should readjust according to the above steps.
Second, the ruler reading method
This method can be used by people who are more skilled in operation. The method is to directly use the temperature scale on the upper part of the Beckman thermometer without having to use a constant temperature bath to adjust it. The operation steps are as follows:
1. First estimate the maximum operating temperature value.
2. Invert the thermometer so that the mercury ball and the mercury in the capillary are slowly injected into the ball at the end of the capillary, and then slowly tilt the thermometer to connect the mercury in the storage tank to it.
3. If the estimated value is higher than room temperature, use warm water or an inverted thermometer to use gravity to allow mercury to flow into the mercury storage tank. When the mercury surface at the temperature scale reaches the desired temperature, tap gently as shown in Figure 3-3. Disconnect the mercury column at the elbow; if the estimated value is lower than room temperature, the thermometer can be immersed in a lower constant temperature bath to allow the mercury surface to drop to the reading on the temperature gauge just to reach the estimated value of the desired temperature, the same method Disconnect the mercury column.
4. Same as the above method, whether the amount of mercury adjusted by the experiment is appropriate.
Precautions
1. The Beckman thermometer is made of thin glass, which is much longer than the general mercury thermometer and is susceptible to damage. Therefore, it should generally be placed in a thermometer box, or installed on the instrument stand, or held in the hand. It should not be placed arbitrarily.
2. When adjusting, be careful not to let it get hot or cold, but also avoid heavy hits.
3. The adjusted thermometer, take care not to connect the mercury column in the capillary tube with the mercury in the storage tank.
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