By
this apparatus I have learned that all things vegetable arise directly and
in a material sense from the element of water alone.
I took an earthen pot and in it placed 200 pounds of earth which
had been dried out in an oven.
This I moistened with rain water, and in it planted a shoot of
willow which weighed five pounds.
When five years had passed the tree which grew from it weighed 169
pounds and about three ounces.
The earthen pot was wetted whenever it was necessary with rain or
distilled water only.
It was very large, and was sunk
in the ground, and had a tin plated iron lid with many holes
punched in it, which covered the edge of the pot to keep air-borne dust
from mixing with the earth.
I did not keep track of the weight of the leaves which fell in each
of the four autumns.
Finally, I dried out the earth in the pot once more, and found the
same 200 pounds, less about 2 ounces.
Thus, 164 pounds of wood, bark, and roots had arisen from water
alone."
(Howe 1965)
-
What
was van Helmont's reason for conducting the experiment?
In other words, what question did he set out to answer?
-
What
was van Helmont's hypothesis?
-
Briefly
restate in your own words the experiment performed by van Helmont.
-
List
at least five variables that might affect this experiment.
Which variable(s) is(are) controlled?
Which is the experimental variable(s)?
-
Identify
the experimental group and control group in this experiment.
-
If
van Helmont had tested his hypothesis correctly, his experiment would have
failed miserably (i.e., the plants would not grow).
What experiment should he have done?
(Hint: rain water
lacks essential minerals for growth)
-
van
Helmont did not describe his methods in sufficient detail.
For example, how did he actually remove the soil from the roots
without destroying or loosing too many?
Can you think of any other methods that need to be clarified?
-
Calculate
how much weight the soil should have lost during the growth of the willow.
To do this you will need to make some assumptions:
20% of the fresh (or wet) weight of the plant is dry matter, and 5%
of the dry matter is minerals (that the plant extracts from the soil).
-
Scientific
papers should always include the identity, source and method of the
preparation of any living materials used.
What information are we missing?
-
The
plant van Helmont selected was an excellent choice.
Why?
-
How
big was the pot that van Helmont used in his experiment?
Was it the size of a gallon ice cream pail, a five gallon bucket, a
20 gallon garbage can or a 30 gallon garbage can?
Calculate the size of the pot using the following assumptions:
1 pound of soil weighs about 0.5 kg; there is one kg of soil per
liter.
-
Why
did van Helmont sink the pot in the ground?
-
The
accuracy of commercial balances can vary greatly.
For example a good quality 1000 pound capacity balance has an
accuracy of +- 0.5 pounds. Let's assume you use this balance to weigh a pumpkin and you
get a reading of 120 pounds (a hefty pumpkin!).
Thus the true weight of the pumpkin falls somewhere in the range
from _____ to _____.
-
How
much weight did the soil loose by the end of the experiment (____ oz)?
Convert this value to pounds (____ lbs).
Is the soil weight loss within the accuracy limits of a decent
quality, contemporary balance? Explain.
