A gas bubbler is a piece of

laboratory glassware Laboratory glassware refers to a variety of equipment used in scientific work, and traditionally made of glass. Glass can be blown, bent, cut, molded, and formed into many sizes and shapes, and is therefore common in chemistry, biology, and anal ...

which consists of a glass bulb filled with a small amount of fluid — usually

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

or silicone oil, less commonly mercury. The inlet to the bulb is connected to a

ground glass joint Ground glass joints are used in laboratories to quickly and easily fit leak-tight apparatus together from interchangeable commonly available parts. For example, a round bottom flask, Liebig condenser, and oil bubbler with ground glass joints may ...

, while the outlet is vented to the air. Gas bubblers are used to exclude air from a reaction or a system. In the former case, the gas bubbler is fitted on the condenser of the reaction set-up. In the latter case, an oil bubbler is usually installed at the end of the

inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...

manifold on a Schlenk line to prevent contamination by atmospheric

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

and

water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

. A gas bubbler acts as a one-way valve — gases (hot air, evolved gases, solvent vapors) from the inlet will bubble through the fluid before being vented to the atmosphere. If there were an underpressure in the reaction vessel (such as when heat is removed, and the gases within contract), some fluid is sucked into a sump to equalize the pressure, instead of air. Wherever possible, such "suck back" should be avoided by filling the reaction apparatus with inert gas because an excessively low pressure will cause oil to be sucked into the reaction vessel, contaminating it. The bubbles allow the worker to visibly confirm that the system is being flushed with inert gas; the rate at which bubbles form allow the worker to adjust the inlet pressure.

Oil bubblers

Oil bubblers are filled with

or silicone oil. These are both quite resistant to chemical attack. Oil bubblers are predominantly used; the oil is inexpensive and not toxic. A drawback is that due to oil's lower density, in event of underpressure in the reaction vessel, enough oil may be sucked through the sump into the inert gas system to contaminate it. Due to the same reason, the pressure within the inert gas system will always remain close to atmospheric. This is a disadvantage when attempting

cannula transfer Cannula transfer or cannulation is a set of air-free techniques used with a Schlenk line, in transferring liquid or solution samples between reaction vessels via cannulae, avoiding atmospheric contamination. While the syringes are not the same as ...

s using inert gas pressure to force a liquid reagent into another using a cannula.

Mercury bubbler

Mercury bubblers are largely similar in construction to oil bubblers. They usually have a longer body to prevent mercury from splashing out through the bubbler outlet, and the inlet connection usually has a

sintered glass Fritted glass is finely porous glass through which gas or liquid may pass. It is made by sintering together glass particles into a solid but porous body. This porous glass body can also be called a frit. Applications in laboratory glasswar ...

disc to prevent mercury from being sucked back into the inert gas system when refilling an evacuated vessel. The most important advantage of mercury over oil, is that a fair amount of pressure can be maintained within the inert gas system (equivalent to the height of the mercury column). Tall columns may be used to exploit this further. By increasing the pressure within the inert gas system, boiling points are increased, allowing reactions under reflux to be carried out at a higher temperature. Also,

s are accomplished more easily due to the greater gas pressure available to push a liquid reagent from a vessel, through a cannula, into another vessel. Mercury bubblers are avoided where possible, due to the difficulty and expense in dealing with mercury spills. In addition, mercury can react with various chemicals, such as

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...

and

acetylenes \ce \ce Acetylene \ce \ce \ce Propyne \ce \ce \ce \ce 1-Butyne In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and no ...

, with potentially hazardous results. {{cite web , publisher = J. T. Baker , title = Mercury MSDS , url = http://hazard.com/msds/mf/baker/baker/files/m1599.htm In the context of cannula transfer, mercury bubblers may be avoided by pulling (instead of pushing) liquids through the cannula by vacuum. Alternatively, the oil bubbler may be closed off from the inert gas line with a stopcock, allowing inert gas to push the reagent through the cannula. Excess pressure is bled off from a bubbler fitted directly over the receiving vessel.

References

Laboratory glassware

Oil bubblers

Mercury bubbler

See also

References