In the early 1800s, chemists started experimenting with different chemicals. They had the ability to measure the temperature, pressure, and mass of a sample of gas. In 1911, a chemist named Amadeo Avogadro published an observation that came to be known as Avogadro's law. This law states that any two gasses that are held under the same pressure, temperature, and volume will contain the same number of molecules (measured in moles) regardless of the identity of the gasses. Table 11.1 shows data collected from various gas samples at 1 atm and 0°C.