John Dalton was fascinated by Earth’s atmosphere.
He called air “elastic fluid” and made his own weather instruments, barometers, thermometers, and rain gauges, to study it.
Dalton made daily readings of the air for 57 years and recorded his findings in notebooks. In all, he recorded over 200,000 observations on the weather in these notebooks, the last one on the day he died.
By Dalton’s time, scientists knew that the air consisted of oxygen and nitrogen along with very small amounts of carbon dioxide and water vapor.
Dalton collected hundreds of samples of air from all over England, from mountaintops, valleys, and cities.
He analyzed the samples and found that the composition was the same in every case. He wondered why the heavier gas, carbon dioxide, didn’t settle to the lower elevations.
Dalton conducted experiments in which he separated the lighter and heavier gases and placed them in flasks.
He then upended the flask with the lighter gas and placed it on top of the flask with the heavier gas so that the openings met. In each case, the heavier gas did not remain on the bottom; the gases mixed very quickly.
This led to Dalton’s theory of partial pressures. This theory states that the particles of one gas combine easily with the particles of another gas, but the particles of the same gas do not combine easily.
Dalton’s theory confirmed his belief in the atom, but he wanted more. He wanted to prove the existence of atoms by weighing them.