PH meter
Acidity meter is a precision instrument for measuring pH value, and it can also be used to measure electromotive force.
1. Usage (1) Installation â‘ The voltage and frequency of the power supply must conform to the data indicated on the instrument nameplate, and must be well grounded, otherwise the pointer may be unstable during measurement.
â‘¡The instrument is equipped with glass electrode and calomel electrode. Clip the bakelite cap of the glass electrode to the small clip of the electrode clip. Clip the metal cap of the calomel electrode onto the large clip of the electrode clip. The height of the two electrodes can be adjusted using the head screws on the electrode clip.
â‘¢Before using the glass electrode for the first time, it must be soaked in distilled water for more than 24 hours. It should also be soaked in distilled water when not in use.
â‘£Before the first use of calomel electrode, it should be immersed in saturated potassium chloride solution, and should not be soaked in distilled water with the glass electrode. When not in use, soak in saturated potassium chloride solution or cover the lower capillary hole of calomel electrode with a rubber cap.
(2) Correction â‘ Turn the "pH-mv" switch to the pH position.
â‘¡ When the power is turned on, the indicator light is on, and it is warmed up for 30 minutes.
â‘¢Remove the small beaker with distilled water, and gently absorb excess water beads on the glass electrode with filter paper. Place the selected standard buffer solution with known pH in a small beaker. Immerse the electrode. Pay attention to immerse the capillary pores of the glass electrode tip and calomel electrode in the solution. Gently shake the small beaker to make the solution in contact with the electrode even.
â‘£ According to the pH of the standard buffer, turn the range switch to 0 ~ 7 or 7 ~ 14.
⑤ Adjust the temperature control knob so that the temperature indicated by the knob is the same as the room temperature.
â‘¥ Adjust the zero point so that the pointer is at pH7.
⑦ Press lightly or turn the reading switch slightly to make the switch stuck. Adjust the positioning knob so that the pointer is exactly at the pH value of the standard buffer. Release the reading switch and repeat the operation until the value is stable.
⑧ After adjustment, do not turn the positioning knob again, otherwise it will be adjusted again. Remove the standard beaker and rinse the electrode with distilled water.
(3) Measurement â‘ Absorb excess water on the electrode or rinse it twice with the test solution, then immerse the electrode in the test solution, and gently turn or shake the beaker to make the solution evenly contact the electrode.
â‘¡ The temperature of the tested solution should be the same as that of the standard buffer solution.
â‘¢ Correct the zero position, press the reading switch, the value indicated by the pointer is the pH of the liquid to be measured. If the pointer reading exceeds the scale when measuring in the range of pH 0 ~ 7, the range switch should be placed at pH 7 ~ 14 and then measured.
â‘£After the measurement, after releasing the reading switch, the pointer must point to pH7, otherwise readjust.
⑤Turn off the power, rinse the electrode, and soak according to the aforementioned method.
2. Notes (1) Prevent the instrument from contacting with humid gas. The immersion of moisture will reduce the insulation of the instrument, reducing its sensitivity, accuracy and stability.
(2) The glass film of the glass electrode ball is extremely thin and easily damaged. Avoid contact with hard objects.
(3) The glass film of the glass electrode should not be stained with oil. If it is accidentally stained with oil, it can be washed with carbon tetrachloride or ether, then with alcohol, and finally with distilled water.
(4) No bubbles are allowed in the potassium chloride solution of the calomel electrode, and there are very few crystals in it to maintain the saturation state. If there is too much crystallization and the capillary pores are clogged, it is best to refill with a new saturated potassium chloride solution.
(5) If the pointer of the acidity meter shakes seriously, the glass electrode should be replaced.
3. Standard Buffer Preparation The standard buffer reagent used in the acidity meter is easy to purify and stable. Commonly used preparation methods are as follows:
(1) Standard buffer solution with pH = 4.00 Weigh 5.07g of potassium hydrogen phthalate dried at 105 ℃ for 1 hour, add distilled water to dissolve, and bring the volume to 500ml.
(2) Standard buffer solution with pH = 6.88 Weigh 3.401g of potassium dihydrogen phosphate (KH2PO4), 8.95g of disodium hydrogen phosphate (Na2HPO · 12H2O) or anhydrous disodium hydrogen phosphate (Na2HPO4) dried at 130 ℃ for 2 hours 3.549g, add distilled water to dissolve and dilute to 500ml.
(3) Standard buffer solution with pH = 9.18 Weigh 3.8144g of sodium borate (Na2B4O7 · 10H2O) or anhydrous sodium borate (Na2B4O7) 2.02, add distilled water to dissolve and dilute to 100ml.
Drying oven and thermostat
The drying box is used for drying and heat sterilizing items, and the constant temperature box is used for the cultivation of microorganisms and biological materials. The structure and use method of these two instruments are similar. The use temperature range of the drying oven is 50 ~ 250 ℃, and the blast type electric heating is commonly used to accelerate the temperature rise. The maximum operating temperature of the thermostat is 60 ° C.
1. How to use (1) Insert the thermometer into the seat (in the middle of the top vent regulator).
(2) Insert the power plug into the power socket.
(3) Turn the head of the heating wire group to the 1 or 2 position (depending on the required temperature), at this time, the blower can be turned on to promote the hot air convection. After the heating wire group starts, the red indicator light is on.
(4) Observe the thermometer. When the temperature of the thermometer is about to reach the required temperature, adjust the automatic temperature control knob to make the green indicator light illuminate. Observe the thermometer and indicator light after ten minutes. Turn the automatic temperature control knob slightly counterclockwise until the temperature is constant at the required temperature, and the indicator turns red and green. The automatic thermostat knob is on the upper left of the front of the cabinet. Its scale plate can not be used as a standard temperature indicator, but only as a mark for adjustment.
(5) In the process of constant temperature, if three sets of heating wires are not required to generate heat at the same time, only one set of heating wires can be turned on. The more the number of open groups, the faster the temperature rises.
(6) After working for a certain period of time, the deflation regulator at the top of the top can be turned on to discharge the moisture, and the blower can also be turned on.
(7) After use, turn off the grouping switches of the heating wire, and turn the knob of the automatic thermostat to the zero position in the counterclockwise direction.
(8) Unplug the power plug.
2. Matters needing attention (1) Check the power supply before use, there must be a good ground.
(2) There is no explosion-proof equipment in the drying oven. Never put flammable and volatile materials in the oven for heating. No flammable items should be placed near the cabinet.
(3) The inside of the box should be kept clean, and the net should not be rusted, otherwise it will affect the cleanliness of the glassware.
(4) During use, regular monitoring should be conducted to avoid temperature rise and fall affecting the use effect or accidents.
(5) The motor bearings of the blower should be refueled every six months.
(6) Do not twist the temperature sensor in the box, and avoid collision with the temperature sensor when placing items, otherwise the temperature will be unstable.
(7) The power supply should be cut off during maintenance.
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