A dasymeter was meant initially as a device to demonstrate the buoyant effect of gases like air; as shown in the pictures on the right. A dasymeter which allows weighing acts as a densimeter used to measure the density

Density

The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 of gas

Gas

Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

es.

Principle

The Principle of Archimedes

Archimedes' principle

Archimedes' principle relates buoyancy to displacement. It is named after its discoverer, Archimedes of Syracuse.-Principle:Archimedes' treatise On floating bodies, proposition 5, states that...

 permits to derive a formula which does not rely on any information of volume:
A sample, the big sphere in the images on the right, of known mass-density is weighed in vacuum and then immersed into the gas and weighed again.
From the known mass density of the sample (sphere) and its two weight-values can be calculated the mass-density of the gas:
(The formula was taken from the article buoyancy

Buoyancy

In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

 and still has to be solved for the density of the gas.)

Construction and Use

It consists of a thin sphere

Sphere

A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...

 made 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...

, ideally with an average density close to that of the gas to be investigated. This sphere is immersed in the gas and weighed

Weight

In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...

.

History of the dasymeter

Was invented in 1650 by Otto von Guericke

Otto von Guericke

Otto von Guericke was a German scientist, inventor, and politician...

. Archimedes

Archimedes

Archimedes of Syracuse was a Greek mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity. Among his advances in physics are the foundations of hydrostatics, statics and an...

used a pair of scales which he immersed into water to demonstrate the buoyant effect of water. A dasymeter can be seen as a variant of that pair of scales, only immersed into gas.