SPAC demonstration

dh321 at excite.com dh321 at excite.com
Mon Dec 10 21:52:01 EST 2001


The Soil Moisture Equipment Company -
http://www.soilmoisture.com/ceramics.htm - sells a variety of porous ceramic
products for tensiometers and other uses.

I looked back through a bunch of old plant physiology lab manuals on use of
atmometers. They all used mercury which may not be acceptable to some today.
However, without the mercury a major aspect of the demonstration is lost.
With modern materials such as narrow-bore plastic tubing, perhaps it would
be possible to create a much taller atmometer demonstration with water
instead of mercury.

Oels (1894) early atmometer used a thistle tube with a pig bladder or ox
bladder stretched over the opening instead of an porous clay cup. He could
raise mercury 20 cm with a pig bladder and 30 cm with an ox bladder. 

MacDougal (1895) reported that active coniferous shoots, in place of a
porous clay cup, could raise mercury 76 cm high.

Lemon (1958) noted that the atmometer is a "a classic experiment
...difficult to carry out" and noted the importance of recently boiled
distilled water, super clean glassware, and eliminating all air bubbles. He
mentioned that this was Askenasy's experiment. The porous clay cups he also
called Livingston atmometers. Lemon (1958) also has an exercise
demonstrating capillary rise with panes of glass and capillary tubes
0.05 to
3 mm in diameter.

Meyer et al. (1955) gave a detailed description of the atmometer setup
saying a 1 meter-plus length of 1 mm bore glass capillary tube should be
used with a porous porcelain cylinder. Their drawing of the porous porcelain
cylinder looked like a tensiometer tip. They suggested coating the porous
cylinder with a hot 20% gelatin sol "to permit attainment of satisfactory
results with cups which otherwise could not be used."

Witham et al (1971) adapted the experiment of Meyer et al. (1955) but cited
Askenasy's 1896 papers in German. They also gave the source for the porous
clay cups as Mrs. Burton E. Livingston, Sherwood Ave., Riverwood, Baltimore,
MD. but I doubt that source is still valid.

The latest three manuals all cite Thut (1932) but I have not seen that
article.  

References

Lemon, C. Paul. 1958. Laboratory Exercises Plant Physiology. Dubuque, IA.
Wm. C. Brown.

MacDougal, Daniel T. 1895. Practical Text-book of Plant Physiology. New
York: Longmans Green.

Meyer, Bernard S., Anderson, Donald B., and Swanson, Carroll A. 1955.
Laboratory Plant Physiology. Princeton, NJ: D. Van Nostrand. 

Oels, Walter. 1894. Experimental Plant Physiology. Mineapolis: Morris and
Wilson.  

Thut, H.F. 1932. Demonstrating the lifting power of transpiration. Amer. J.
Botany 19:358-364. 

Witham, Francis H., Blaydes, D.F. and Devlin R.M. 1971. Experiments in Plant
Physiology. New York: Van Nostrand Reinhold.





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