wet weight versus dry weight

Søren Laurentius Nielsen nielsen at virgil.ruc.dk
Wed Dec 1 02:54:44 EST 1999


You could try to weigh your samples repeatedly - ie. after, say, 18
hrs, 24 hrs,  30 hrs etc.  in the oven to check that 24 hrs. at 60
degrees is really enough to remove all water.
Additionally, I think that it is a standard procedure to let your
samples cool to room temperature in a closed container containing
silica gel or some other water vapour absorping material to prevent
the dry samples to take up water from the sourrounding atmosphere

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>I am doing research on the duckweed growth and competition. To measure =
>the growth rates of the 2 duckweed species I work with - Lemna obscura =
>and Wolffia globosa -
>I need to relate their wet and dry weights respectively. Thus far I heat =
>both species in a drying oven at 60-70 degrees C for 24 hours. After a =
>day has elapsed I turn off the oven and weigh my Lemna and Wolffia =
>samples at room temperatures (the samples having cooled in the oven to =
>room temperature). From the difference in wet and dry weights I =
>calculate the percentage moisture, etc.
>
>Can anyone suggest a better way to dry my duckweed samples? How can I =
>test to see if the method described above gives reliable results? Both =
>Lemna and Wolffia are more than 90% water in their fresh state and Lemna =
>is hydroscopic when dry. However I have observed that dry Lemna stays at =
>about the same weight in the dry Texas climate after it is fully dried.
>
>Reply to Louis at lxl7392 at louisiana.edu
>
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Søren Laurentius Nielsen
Department of Life Sciences and Chemistry
Roskilde University, Denmark
nielsen at virgil.ruc.dk
http://virgil.ruc.dk/~nielsen
ICQ: 11355525



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