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A number in parentheses indicates the year of last reapproval. A superscript epsilon e indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the Department of Defense. Scope 1. Terminology 3. NOTE 1—The unit of electrical conductivity is siemens per centimetre. The actual resistance of the cell, Rx, is measured in ohms.
It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Referenced Documents 2. NOTE 2—The unit of electrical resistivity is ohm-centimetre.
Current edition approved April 1, Published April Originally approved in Last previous edition approved in as D — 95 The resistance measured between opposite faces of a centimetre cube, R, is called resistivity. See 7. These tabulated conductivity values are in international units. When using measuring instruments calibrated in absolute units, multiply the tabular values by 0. B From Glasstone These include dissolved electrolytes in natural and treated waters, such as boiler water, boiler feedwater, cooling water, and saline and brackish water.
These test methods may also be used for checking the correctness of water analyses 4. Interferences 5. This is extremely important in the case of very pure waters with low concentrations of dissolved ionized materials. The carbon dioxide, normally present in the air, can drastically increase the conductivity of pure waters by approximately 1? Contact with air should be avoided by using? Chemically pure inert gases, such as nitrogen or helium, may be used to blanket the surface of samples.
For example, biofouling of the cell or a build-up of? In most cases these problems can be eliminated by washing the cells with appropriate solvents. For this reason it is recommended that conductivity cells for this application be of coaxial shielded type or equivalent, and that the cables and instrument also be shielded.
Apparatus 6. Instruments shall energize the conductivity cell with alternating current and, together with the cell and any extension leadwire, shall be designed to reduce errors from the following sources: 6. Leadwire resistance can add signi? Temperature compensation errors can be signi? Calibration may be in either conductivity or resistivity units. See Section Reagents 7. Unless otherwise indicated, it is intended that all reagents shall conform to the speci?
In making up the potassium chloride solutions for cell constant determinations, use water of conductivity not greater than 1. If necessary, stabilize to the laboratory atmosphere by aspirating air through the water from a fritted glass or stainless steel gas dispersion tube.
The equilibrium point is reached when the conductivity remains constant but not greater than 1. The equilibrium conductivity must be added to Table 1. Alternatively, use isopropyl alcohol or methyl alcohol. This reagent should be used immediately after its preparation.
However, samples with conductivity greater than 10? In all other cases, pipet-type or dip cells can also be used. Pipet or dip cells may be used to measure samples in the range of 1 to 10?
For laboratory bridges, Table 2 provides conservative guidelines. The cell shall retain calibration under conditions of pressure,? The chamber or cell shall be equipped with means for accurate measurement of the temperature. Note that these electrodes may require special surface preparation. Titanium and monel electrodes are especially suitable for high resistance solutions such as ultrapure water, but may introduce a small surface resistance which limits their accuracy when the measured resistance is less than a few thousand ohms 1.
Thermometers, thermistors, and resistance temperature detectors with accuracies of Pharmaceutical Convention, Inc. Store the solution in a glass-stoppered bottle of chemically resistant glass which has only been used for storage of this solution. The values for electrical conductivities for the solutions are those of G. Jones and B. Bradshaw 5 , con? The data of T. Shedlovsky 8 are used for Solution D. Solutions A, B, and C were prepared by Jones and Bradshaw using the molal or demal basis by dissolving The densities of 1.
The deposit should present a black, velvety appearance and should adhere well to the electrode surface. The procedure for platinizing is not critical. Good platinized coatings are obtained using from 1. For example, for an electrode having a total area both sides of 10 cm2, the plating time at a current of 20 mA would be from ?
Plate the electrodes one at a time with the aid of an extra electrode. During the plating, agitate the solution gently, or use ultrasonic bath.
When not in use, platinized cells should be? For a? Calibration Alternatively, standard resistors with certi? Some instruments may be factory calibrated, taking into account the resistance of the cable wire attached to the conductivity cell; this may be indicated by a warning to avoid cutting or extending the cable length.
When lead wires between the instrument and the cell are long, check the installation at least once by connecting the calibrating resistor at the far end of the lead wire and noting the difference, if any, in reading with the long lead wire in the circuit. Check portable or manually operated instruments in a similar manner with one or several calibrating resistors.
Note errors of signi? Calibration checks should be made at values as close as possible to the conductivity values expected in samples. Instruments subjected to? For direct reading instruments, the conductivity check resistance in ohms equals the cell constant cm? Sampling 8. Protect the sample to avoid gain or loss of dissolved gases, particularly if there is some delay before the conductivity measurements are made.
Preferably, use a? For waters in the range of 5 to 10? Preparation of Electrodes 9. In general, no mechanical cleaning should be attempted. In high purity water measurements, where the presence of? On the other hand, clean and well-platinized electrodes are increasingly important in testing water of higher conductivities, particularly above ? After cleaning, thoroughly?
If the old platinum black coating is to be removed, judicious application of aqua regia to the electrodes, or electrolysis in HCl sp gr 1. Make sure that the conductivity readings are uncompensated. Scope Summary of Test Method Temperature control and correction methods are also provided. Determination of Cell Constant If the conductivity cell has been in service for a period subsequent to this certi?
Control the solution temperature to 25 6 0. Measure the resistance of the cell. Repeat the measurement on additional portions of the KCl reference solution until the value obtained remains constant to within the limits of precision in accordance with Section Resistivity-reading instruments will indicate in direct proportion to the cell constant, while conductivity reading instruments will indicate in inverse proportion to cell constant. Conductivity cells may be calibrated with reference solutions in accordance with Section
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