Sensor Sensor Range (kPa) Osmometer Osmometer
0~40 Earth pressure gauge Earth pressure gauge 0~600 Matric suction sensor Matric suction sensor 1~1500 Sensor Precision Osmometer
[+ or-]0.05%F x S Earth pressure gauge [+ or-]0.05%F x S Matric suction sensor [+ or-]5%F x S Table 2: Particle composition of soil.
By doing so (using a perfect osmometer instead of a tensiometer), one determines the 'minimum' water availability as far as salinity is concerned.
Whether the water comes and goes in the form of the equilibrium soil solution (as found in a tensiometer), or as the chemical compound [H.sub.2]O (as found in a perfect osmometer), or anything in between (as found in the xylem of a plant), depends on the properties of the wall separating the soil solution from the receiving or delivering vessel.
If salinity exerts its full osmotic power ([sigma] = 1), as it probably does for extremely salt-sensitive species (glycophytes) or as it is experienced by a perfect osmometer, one finds from Eqn 19:
For [h.sub.os] = 8 m (E[C.sub.s] = 2.2 dS/m), only 32% of the unimpeded value remains available to the osmometer (hypothetical plant with [sigma] = 1).
After 12 hours, the pressure in the osmometers containing 2.0 and 3.0 M solutions exceeded the maximum pressure (220 kPa) that could be measured by the transducer (data not shown).
In an effort to determine if temperature played a significant role in osmosis, we measured the changes in pressure in osmometers containing 1 M sucrose solution at three temperatures (10, 20, and 30[degrees]C).
To introduce the concept of osmotic pressure, a teacher will often show students a traditional osmometer that he/she has assembled, or more likely, a diagram of an osmometer from the textbook.
What the teachers lack is a simple, inexpensive osmometer that can be attached to that existing equipment.
* Membrane Osmometer Design & General Procedure
A membrane osmometer is a closed osmometer that uses a pressure transducer to directly measure the osmotic pressure generated by a solution; they are used in laboratories and industry to measure osmolality of solutions and molecular weights of macromolecules (Grattoni et al., 2008).
To assemble the osmometer cap, place a 1 1/8" disk, cut from a sheet of 0.05" aluminum, perforated with 5/32" holes, inside the Gatorade(R) cap and glue the smaller water bottle cap in place using Loctite 496(R) adhesive (Figure 2).