TABLE OF CONTENTS The Schilling specific gravity analyzer for gasesisbased onthe principle that less dense gas molecules move with greater velocity than do heavier molecules at the same temperature and pressure. Therefore, a gas with the lowest specific gravity escaping from a container through a small orifice will escape in the shortest time.
The Schilling instrument is a glass tube (1 inch in diameter and 10 inches long) with the bottom end open and suspended in a tube about 4 inches in diameter. The smaller tube has a mark just below its midpoint. Water is added to the larger tube to within about 1 inch from the top.
Air pressure is applied at the top of the water in the larger tube, forcing water to rise into the smaller tube until it reaches the mark. The gas entry valve is then closed.
A valve connected to a small platinum orifice is opened, and the time required for the water level in the inside tube to return to its original level is recorded.
Gas, the specific gravity of which is to be determined, is introduced into the instrument, filling the smaller inner tube and the top of the larger tube. The gas should be allowed to bubble through the water for a short period to remove dissolved air from the water. The experiment is then repeated for the gas, and the specific gravity of the gas is calculated as follows:
where: SG = specific gravity.
t gas = effusion...
