Van Helmont decided that plants gain mass by taking in water:
In 1648 Van Helmont set up the following experiment:
Dried soil, weighed it, and placed it into a pot.
Planted a 2.2kg willow tree in to the pot with soil.
He then added rainwater to the pot whenever it was dry.
5 years later Helmont removed the tree from the pot:
The tree now weighed 76.7kg; therefore the willow tree had gained a mass of 74.4kg.
He then had dried the soil, and the mass of the soil had very little change, (60g less)]
He concluded that because the weight of the soil had changed not by much, the tree must have gained mass from another source. The reason for this theory is because Helmont had only added water to the willow tree. Therefore he concluded that the tree must have gained mass by taking in water. Scientist now have come to know that plants can also gain mass by using co2 from the air- however Helmont’s experiment was very important to our research today because we found out that plants don’t just gain mass by taking in minerals from the soil.
Priestley’s experiments showed that plants produce oxygen:
In early 1770s Priestly did the following experiment:
Priestley placed a burning candle in a sealed container and found out that the flame would go out after a short period of time. In comparison to this, the candle was unable to be re-lit while in the sealed container. Priestley decided that the burning candle used up something in the container. After indentifying this Priestly placed the burning candle back into the container with a living plant. The flame again went out after a short time, but after a few weeks the candle coul be re-lit.
Priestly then decided that another source use up something in the container. He a;lso found out that the living plant restored the air so the candle would burn again.
Priestley experiment 2:
Filled a sealed container with exhale air. He put a mouse in the air, and found out that the mouse only survived for a few seconds.
He filled a second container with exhale air. He put another mouse into the container and it survived for a few minutes.
From these two experiments Joseph concluded that plants restore something to the air that burning and breathing take out. We now know that this is called oxygen - used in photosynthesis.
