It will weigh about ten thousand pounds less.
How much less, when filled with coal gas than when filled with air?
About two thousand pounds less.
How much force then is necessary to hold the balloon filled with coal gas to the earth?
A force of two thousand pounds, because the balloon is two thousand pounds lighter than the same bulk of air.
If a weight of only one thousand pounds were fastened to the balloon, what would result?
The balloon would rise in the air and carry the weight of one thousand pounds with it.
How high will the balloon ascend?
It will ascend until the air displaced is of the same weight as the balloon.
What will then become of the balloon?