BS EN ISO 4787:2021 pdf free download – Laboratory glass and plastic ware一 Volumetric instruments – – Methods for testing of capacity and for use.
Determine the delivery time while the tip of the jet is in contact with the inner surface of the receiving vessel, above the level of any collected liquid, but without movement of one against the other throughout the delivery period. The delivery time thus determined should be within the limits specified in the corresponding International Standard (ISO 648 or ISO 835) for the particular pipette.
A waiting time, if specified, shall he observed before making the final setting of the meniscus for delivery of a given volume, lithe setting after delivery is done at a lower graduation line, the liquid flow shall be nearly stopped a few millimetres above the graduation line. After observation of the waiting time, the final setting shall he completed quickly.
9.3.3 Pipettes adjusted to contain
Fill the pipette by suction slowly and carefully, stopping when the meniscus reaches the graduation line. Carefully wipe off any residual water from the end of the pipette.
The filled pipette shall be weighted in the balance using the appropriated means in order to measure its contained volume.
9.3.4 Burettes adjusted to deliver
Burettes adjusted to deliver in accordance with the specifications given in ISO 385 shall be clamped in a vertical position and filled to a few millimetres above the graduation line to he tested. The stopcock and jet shall be free from air bubbles. Any liquid remaining on the outside of the jet shall be removed. The b final setting of the meniscus shall then be made by running out the surplus water through the jet. Any drop of liquid adhering to the jet shall be removed by bringing a ground glass surface into contact with the tip of the jet at an angle of about 300. Draw this ground glass surface downwards through a distance of about 10 mm.
9.3.5 Pycnometers
The filling of a pycnometer shall be performed in accordance with the specifications given in ISO 3507 and the manufacturer’s instructions.
9.4 Weighing
The volumetric instrument or the receiving vessel (see fzA) shall be tared and weighed using a balance in accordance with &1 and the temperature of the water shall be measured to ± 0,1 °C.
Alternatively, two weighings can be performed (empty and loaded vessel). The corresponding balance indications are !L referring to the loaded vessel, and IE referring to the empty vessel. Usually. IE and IL are observed under the same conditions, hence a precise zero adjustment of the balance is not necessary. Both of the required weighings shall be carried out in a short time interval as convenient to ensure that they have been made at the same temperature. This air temperature, the humidity and the barometric pressure shall be recorded for use in the subsequent calculations.
The manufacturer’s instructions shall he followed in making the required measurements. Weighings shall be made with care and made expeditiously to minimize evaporation losses which would constitute a source of error.
To perform repeated tests in flasks and cylinders two options may be used:
a) Option 1 — The flask or cylinder is dried after each run. Obtaining an initial dry weight will allow the operator to determine when the flask or cylinder is sufficiently dry.
b) Option 2 — After the first run, for the subsequent runs, a sufficient amount of liquid is removed, the temperature of the water inside the flask or cylinder is measured, the inner walls of the volumetric instrument above the graduation line to be calibrated are dried and finally the meniscus is set again. The initial value of the dried flask or cylinder (tare) is used in all repetitions.