Gas Bubblers Information
Gas bubblers are laboratory equipment used to exclude air from a system carrying out chemical reactions by functioning as a one-way valve. They also serve as a pressure relief mechanism for the reaction. Eliminating atmospheric gas from a reaction is desirable when conducting air sensitive chemistry in which the compounds being investigated could react with elements in the air such as oxygen or water vapor. Gas bubblers are used in laboratory and educational applications, often attached to condensers or Schlenk lines to prevent air from reaching reaction vessels.
Gas bubblers function by allowing reaction gases to escape while atmospheric gas is prevented from reaching the reaction location. When the pressure at the gas bubbler inlet from the reaction system is higher than atmospheric pressure, excess gas will bubble out through the bubbler fluid before being vented to the atmosphere. If the pressure in the reaction system drops below atmospheric, the fluid in the bubbler will be displaced up the gas bubbler tube, preventing air inflow into the system. If the pressure of the reaction system is too low, however, the oil or mercury in the gas bubbler will be forced into the reaction system, in addition to air. This can occur if the inert gas flow into the system is not increased when the heat is removed from a reaction, or if a vacuum is pulled on the reaction system when it is open to the bubbler.
The fluid filling the glass bulb is usually mineral oil, silicone oil, or mercury.
Mercury is less common due to its safety and health issues. Hazardous reactions can occur if mercury comes into contact with chemicals like ammonia and acetylene. Mercury exposure is harmful to human health, and spills can be difficult and expensive to clean up. Mercury bubblers often have a sintered glass disc at the inlet connection to prevent mercury from contaminating the inert gas system when refilling an evacuated vessel. In addition, the body is typically elongated to reduce the chance of mercury escaping from the outlet.
The main advantage of mercury is the higher pressure that can be created in the inert gas system due to mercury’s relatively high density. This allows elevated temperatures for chemical reactions due to the higher boiling points enabled by high pressures. Cannula transfers are also facilitated by higher pressures in the inert gas system, pushing the fluid from one vessel to another via cannulae.
Compared to mercury, silicone and mineral oil are nontoxic, chemically resistant, and inexpensive. The downside is that they have a lower density, and so the higher pressures that can be created in the inert gas system with a mercury bubbler are not attainable. Instead, inert gas pressures remain close to atmospheric.