Field Determination of Water (Moisture) Content of Soil by the Calcium Carbide Gas Pressure Tester - Soil Properties: Testing, Measurement, and Evaluation - page 190

be used.) A calcium carbide gas pressure tester can also be used to
determine moisture content quickly with fairly good results. The latter
method is described in this chapter.
This test method (using a calcium carbide gas pressure tester)
determines the water (moisture) content of soil by chemical reaction us-
ing calcium carbide as a reagent to react with the available water in the
soil, producing a gas. A measurement is made of the gas pressure pro-
duced when a specified mass of wet or moist soil is placed in a testing
device with an appropriate volume of reagent and mixed. [1]
This method is applicable for most soils. Calcium carbide, used as a
reagent, reacts with water as it is mixed with the soil by shaking and ag-
itating with the aid of steel balls in the apparatus. To produce accurate
results, the reagent must react with all the water that is not chemically
hydrated with soil minerals or compounds in the soil. Some highly plas-
tic clay soils or other soils not friable enough to break up may not pro-
duce representative results because some of the water may be trapped
inside soil clods or clumps that cannot come in contact with the reagent.
There may be some soils containing certain compounds or chemicals that
will react unpredictably with the reagent and give erroneous results.
Any such problem will become evident as calibration or check tests with
ASTM Test Method D 2216 (Chapter 4) are made. Some soils containing
compounds or minerals that dehydrate with heat (such as gypsum) that
are to have special temperature control with Test Method D 2216 may
not be affected (dehydrated) in this test method. [1]
This test method is limited to using calcium carbide moisture test
equipment made for 20 g or larger soil specimens and to testing soil that
contains particles no larger than the No. 4 Standard sieve size. [1]

Calcium carbide pressure moisture tester (see “Speedy Moisture
Tester” in Figure 13-1)
Tared scale
Two 1 1 ⁄ 4 -in. steel balls
Cleaning brush and cloth
Scoop for measuring calcium carbide reagent
Calcium carbide reagent
Sieve No. 4 (4.75 mm)

APPARATUS
AND SUPPLIES

(1) When combined with water, the calcium carbide reagent pro-
duces a highly flammable or explosive acetylene gas. Testing should
not be carried out in confined spaces or in the vicinity of an open
flame, embers, or other source of heat that can cause combustion.
Care should be exercised when releasing the gas from the appara-
tus to direct it away from the body. Lighted cigarettes, hot objects,
or open flames are extremely dangerous in the area of testing.

SAFETY
HAZARDS [1]

(2) As an added precaution, the operator should use a dust mask,
clothing with long sleeves, gloves, and goggles to keep the reagent
from irritating the eyes, respiratory system, or hands and arms.