Lab. equipment

This section lists a number of useful items which I have had to source for my laboratory.

1. Synthetic soil mixes - for use as contact materials, or when minimal chemical reaction is needed from a porous material. Includes how to make a silicate powder tension plate.

2. Moisture Cans - polypropylene and metal. Needed for measuring the water content of soils at 105C

3. Tension Plates - for bringing soils to a set moisture suction potential.

3a How to set up a suction plate system

4. Saran Resin (or alternatives !!) - for coating soil aggregates to measure their volume

5. Pot water controller - to maintain the water content of pots at a fixed suction or water content

6. Transparent Adhesive Scales - for sticking onto glass or clear plastic tubes to convert them to ‘measuring cylinders’

7. Vacuum grade laboratory taps: These taps are plastic - so they dont corrode. They have 1/4 inch barb fittings for laboratory tubing sizes, and they do not leak - even under 200kPa pressure or suction.

‘Synthetic soil’ mixes. Sometimes a soil-like porous material is needed for experimental work. Soil Water Solutions stocks (or can get) a large range of glass bead, clay mineral, or silicate based powders which can be mixed to produce specific properties.

Price depends on the components of the mix - typically $10/kg

Examples : (call with your needs!)

a. Soil water sensor calibration mix. This material can be wet up to anywhere from 0 to 0.45 cc/cc water content and still remain non-sticky, friable and easily repacked around a sensor.

b. Tension plate mix. If you need to make a tension plate to wet soils or drain them to 9 kPa (approx field capacity) then all you need is some tubing a plastic box and some of our tension plate mix.

Moisture cans : Small containers with fitted lids which can be placed in an oven at 105 degree C for soil moisture measurement

Polypropylene tubs. The lids do not jam (unlike aluminium lids). The lids are a firm, but not vapour tight fit. In the field, the lids should be taped up with PVC tape or similar to prevent vapour loss under extreme conditions. They are, however, ‘vapour tight’ under conditions where temperature is reasonably constant - eg in a laboratory.

small 43mm diam x 28mm high (holds 40g dry soil) 50c each

large 43mm diam x 50 mm high (hold 70g dry soil) 70c each

These tubs usually have similar weights within a batch - an order of twice as many as you need will probably yield a set with the same weight within 0.02g . Hence the actual weight of the tub within a batch can be considered constant. These tubs absorb a small amount of water 0.1% in air which is lost on drying - for high precision work they should be pre-dried or kept in a desiccator.

Can they be used in hotter ovens than 105C ? - NO! Polypropylene does not actually melt until 200C but it becomes soft at 120C - NOT recommended for use over 105C. But use at 105C will allow some 1000 uses before they become brittle.

Aluminium tubs - these are made to order there is a set up charge of approx $600 then about $8 each.

WARNING: If wet alkaline soil is put in these cans, they can corrode in a few days. We recommend that they be sprayed with enamel inside to prevent corrosion

New tension plates: Soil Water Solutions can now source ceramic plates with air entry 40kPa (400cm water suction). These plates have good flow rates and are suitable for all suction plate operations up to 40kPa. ie good for 10 kPa field capacity measurements.

The ceramics are available in a range of sizes and shapes - and the final dimensions of the Soil Water Solutions plates will depend on what is available at the time at the time of order. As a guide, rectangular plates 35 x 38cm $550 GST incl (see photo right) or round plates 33cm diam ($450 incl GST)

Tension plate refurbishment: many of the plates circulating in CSIRO or universities are very high flow rate 80-90kPa air entry plates. The technology for making this ceramic seems to have been lost. If you have old, clogged or leaking tension plates we can refurbish the ceramic to as-new condition and (if necessary) fit it to a new base Price approx $500 I will need to see the plate to give a better quote

NOTE: Refurbishing tension plates or is done on an ‘every care but no responsibility’ basis - ie if we break your plate we won’t charge you, but we will not replace the plate either.

Pressure plates: Soil Water Solutions Do not sell pressure plates or the rubber backed ceramic inserts for them.

Try www.ictinternational.com.au

But if you have plates which need new rubber backing - we can replace the backing for $150 per plate

NOTE: this is done on an ‘every care but no responsibility basis’ - we sometimes break a plate ! if that happens we wont charge you, but we will not replace the plate either.

Saran Resin : to water proof soil aggregates so their density can be measured.

The bad news : SARAN is no longer made by Dow Chemical and is hard to get. However, a google search will locate fireworks manufacturers who may supply it. (it is used as fuel in fireworks).

Ordinary PVA house paint is a good substitute for non swelling soil. Soil Water Solutions has found several good substitutes for difficult soils - call or email for the latest findings



Pot water controller: Watering experimental pots is an onerous and exacting task - especially if the pot must be held close to a fixed water content. Our answer is to fix the pot at a particular soil water tension. Just place our pot water controller device in your pot connect it to a water reservoir below the level of the pot and the water content will be kept constant, drawing water from the reservoir as needed. Controllers are $15 each and operate best with the reservoir 0.5 m below the pot.



			Transparent Plastic adhesive scales: 0-80cm We use these to put these waterproof scales on the permeameters we sell. They can be applied to glass or plastic to provide a measurable scale of water levels etc. These are bumper sticker technology and will last a long time even in wet dirty conditions. If you only want 20cm lengths, we can supply offcuts numbered from 60-80cm for $1 each Price 0-80cm (full length scales) $10 each incl GST

Laboratory grade plastic taps

These taps are plastic , so they don’t corrode. They are high grade seals and do not leak when connected to pressure or suction systems.

The connection is a 1/4” (6mm) barb to fit common sizes of laboratory tubing

Price $30 each incl GST

How to set up a suction plate system

To drive suction plates at 100 cm (or less) Connect a bottle as in the picture to the right. The bottle is a regular 500 ml reagent bottle with the addition of an O ring to help the seal the lid. Holes in the lid are drilled slightly undersize to ensure a seal. (Nylex PVC tube works OK for a while but gets hard and leaks eventually- silicon tube works better - we can supply this if needed - $15/m).

Set up a shelf 100-150 cm from the floor and put the plate on it. Put the bottle up next to the plate to wet the samples, and move it to 100cm below the plate to drain them at 100cm (field capacity) suction. Leave them until they no longer lose water - usually a few days

NOTE It is not possible to take these plates apart for cleaning - build up of algae can be minimised by putting a few drops of algaecide in the water in the bottle. Algaecide is readily available from swimming pool suppliers.

To drive suction plates at 300 cm, you could use a bench 300 cm from the floor and a hanging column 300cm long (as above) - but this is rather difficult in most buildings, so you need a means of regulating the suction provided by a pump - this can be a vacuum pump with a vacuum regulator or (my choice) a 'folded water column'. The pump can be an (expensive) vacuum pump designed for the purpose , an aquarium air pump (for small suctions only) or a compressor from a defunct refrigerator or air conditioner (do the right thing and get it removed by a refrigeration tech to avoid the gas being released) These are not designed for pumping wet air but will give good service for a year or so and cost around $20

See the diagram (right) for folded column design. This is a set of (preferably transparent) tubes interconnected and connected to a vacuum pump such that air enters the first column is sucked down the first tube and bubbles up through 1m of water. The air at the top of the first column is therefore regulated at 100cm suction. This air can then be connected to the second column and sucked through a further 100cm of water - so the air at the top of the second column is regulated at 200cm suction. A third column gives air at 300 cm etc.

If the air at the top of the relevant column is connected to the air in the bottle (attached to the suction plate) AND THE BOTTLE KEPT AT THE SAME HEIGHT AS THE PLATE Then the suction plate will be at the same suction as the air in the column.

NOTE if the bottle is lower than the plate then the plate suction will be the sum of the air suction from the column and the suction head created by the difference in plate and bottle height