LaMotte Multi-Range Conductivity Meter 1704 DA-LR User Manual

Page 6

SAM PLE MEA SURE MENT - METHOD B
MAX I MUM AC CU RACY WITH TEM PER A TURE COR REC TION
5.

Use the thermometer (1066) to measure the sample water temperature.
Record this temperature. The “TEMP” knob should be still set at 25°C.

Immerse the probe into sufficient solution to at least cover the end slots of
the probe. Make sure all bubbles are removed from the probe.

Switch the control knob to the “ON” position and the range selector to
either “X.1", ”X1", “X10", or ”X100". Select the range which gives readings
as close to the middle of the scale as possible. Record the reading. During
this test the probe should not touch any surface of the sample container.

Calculate result:

Conductivity, micromhos/cm at 25°C =

Meter Reading x Range Factor x [1.0 + 0.02 (T-25)]

T = Temperature of Sample in °C

After the measurement, switch the meter to “OFF”. Rinse probe thoroughly
with water, preferably deionized water, and air dry.
NOTE:

Reference solutions which have known conductivities may be

prepared by consulting the latest edition of Standard Methods for the
Examination of Water and Wastewater

, American Public Health Association,

1015 East Eighteenth Street, NW, Washington, DC 20036. A series of
accurately prepared reference solutions in both the high range and low
range allow the operator to check on the manipulative procedure as well as
the verification of results.

DETERMINATION OF
CONDUCTIVITY & TDS IN BOILER WATER
In boiler water where high concentrations of hydroxides may be evident, it is
necessary to neutralize the sample solution with gallic acid or lactic acid.
Otherwise false high conductivity readings will be noted. For a 100 mL sample
add 0.4 grams of gallic acid or lactic acid. This will neutralize approximately
1300 ppm hydroxide alkalinity. If a small amount of gallic acid or lactic acid
does not dissolve within the sample solution, the conductivity reading will not
be affected. On some highly alkaline waters higher concentrations of gallic acid
or lactic acid may be required.
The determination of conductivity for boiler water is made by following the
General Operating Procedure given on Page 4. To convert the conductivity
reading to Parts Per Million Total Dissolved Solids (ppm TDS), multiply the
reading by 0.7.
EXAMPLE:

Conductivity reading is 3500 micromhos/cm.

3500 x 0.7 = 2450 ppm TDS

DETERMINATION OF SOIL
CONDUCTIVITY & TOTAL DISSOLVED SALTS
An approximation of the Total Dissolved Salts in soil is obtained by making a
soil extraction with distilled water and measuring the conductivity of the soil
extract. For purposes of comparison, all conductivity values are recorded at
25°C.
NOTE:

For determination of Soluble Salts in greenhouse soils, see below.

PRO CE DURE
1.

Fill a 50 mL beaker full with the soil to be tested. Tap it lightly to eliminate
any air trapped. Strike the excess soil off the surface.

Empty the contents of the beaker into a 250 mL widemouth flask and add
100 mL of distilled water.

Stopper and shake vigorously. Allow to stand for thirty minutes. During the
thirty minutes waiting period the sample should be shaken vigorously three
or four times.

Filter the contents of the flask and collect filtrate in suitable conductivity
chamber.

Take conductivity reading according to method given for General
Operating Procedure on page 4.

To convert to Total Dissolved Salts use the following formula:

micromhos/cm @ 25°C x 0.7 = ppm Total Dissolved Salts

If the Soluble Salts as determined above are greater than 1000 ppm, the
chlorides and sulfates should be determined in order to learn whether the
Soluble Salts are chlorides or sulfates.
Usually in calcareous soils, the sulfates represent gypsum and cause little injury
to plants, while high concentrations of chlorides might result in damage to the
plants. Greenhouse and sensitive plants may be damaged if the Souble Salts are
over 500 ppm of chlorides.

DETERMINATION OF SOLUBLE SALTS FOR GREENHOUSE SOILS
The LaMotte Multi-Range Conductivity Meter may be used to read
conductivity in the limited volume of soil extract obtained through the soil
extraction procedure employed in the LaMotte Model GS-01 Greenhouse
Outfit. Follow the extraction procedure in the GS-01 manual. Take
conductivity reading according to method given for General Operating
Procedure on Page 5. Use the following formula to convert the conductivity
reading to parts per million Soluble Salts:

Conductivity Reading (micromhos/cm) x 0.7 = ppm Soluble Salts