A filter funnel is a laboratory funnel used for separating solids from liquids via the laboratory process of filtering

Filter (chemistry)

In chemistry and common usage, a filter is a device that is designed to physically block certain objects or substances while letting others through. Filters are often used to remove solid substances suspended in fluids, for example to remove air pollution, to make water drinkable, and to prepare...

.

In order to achieve this, a disk shaped piece of filter paper

Filter paper

Filter paper is a semi-permeable paper barrier placed perpendicular to a liquid or air flow. It is used to separate fine solids from liquids or air.-Properties:Filter paper comes in various porosities and grades depending on the applications it is meant for...

 is usually folded into a cone and placed within the funnel. The suspension

Suspension (chemistry)

In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase is dispersed throughout the external phase through mechanical agitation, with the use of certain...

 of solid

Solid

Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...

 and liquid

Liquid

Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

 is then poured through the funnel. The solid particles are too large to pass through the filter paper and are left on the paper, while the much smaller liquid molecules pass through the paper to a vessel positioned below the funnel, producing a filtrate. The filter paper is used only once. If only the liquid is of interest, the paper is discarded; if the suspension is of interest, both the solid residue on the paper and the filtrate are kept for further analysis.

If the filter paper has small pores, long chained non polar liquids such as oil may clog the filter paper.

Filter funnels vary in size depending on the volume of suspension required to be filtered. They are usually constructed out of plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

, except where the filtering of certain solvent

Solvent

A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

s requires the use of glass

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

.

Cruder versions, made of polyethylene

Polyethylene

Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

 or galvanized

Galvanization

Galvanization is the process of applying a protective zinc coating to steel or iron, in order to prevent rusting. The term is derived from the name of Italian scientist Luigi Galvani....

 steel and using a brass

Brass

Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...

 or plastic mesh filter, are typically for automotive

Automobile

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

 and workshop

Workshop

A workshop is a room or building which provides both the area and tools that may be required for the manufacture or repair of manufactured goods...

use, to filter debris from fuel, lubricating oil and coolant. The screen is reusable, and may be cleaned by inverting the funnel and tapping it on a hard surface, or popping it out and washing it separately. This helps to avoid spilling any liquids.

Legal issues

Like many other common pieces of glassware, filter funnels could potentially be used in the production of illegal narcotics. In an effort to restrict such production, some U.S. states (including Texas) have begun requiring permits to purchase such glassware, including filter funnels, as well as chemicals identified as common starting materials. Memorandum of Understanding between the Texas Department of Public Safety and the Texas Higher Education Coordinating Board (PDF)