Method 2:
(for this method, use the sample holder)
Here, use a liquid for causing buoyancy with lower density than that of the solid
for which the specific gravity is to be determined. We have had good results with
ethanol (up to a density of approx. 0.8 g/cm
3
).
The density
ρ
(fl) of ethanol (with regard to its temperature) can be found in the table
in the supplement.
The negative effect of the liquid’s surface tension on the results is less noticeable
when ethanol is used than when distilled water is employed. Therefore, it is not
necessary to add tensides.
When working with ethanol, you must observe the valid safety precautions.
Use method 2 if the density of the solid varies only slightly from that of distilled
water. Since the sample is suspended in water, measuring errors may occur if the
first method is used.
It also makes sense to use the second method when determining the specific
gravity of a granulated substance, since it would be difficult to get the entire sample
under the sieve as required when performing the first method.
Do not use ethanol if the sample could be attacked or dissolved by it.
Preparation (for Method 1 only)
(Distilled water is used in the description.)
– Center the large-diameter beaker (76 mm Ø) on the metal platform
– Fill it so that the distilled water is approximately 5 mm below the rim
– Add three drops of tenside to the distilled water
– Attach the thermometer to the rim of the beaker using the retainer clip
– Clean the sieve with a solvent (especially the wires that will be immersed) and
hang it from the frame
19
