Dasymeter

Dasymeter at standard pressure

Dasymeter at reduced pressure

Historical drawing of a dasymeter (in German: "Fig. 109. Baroscope. (Apparatus for proving the buoyancy of air)" )

Adasymeterwas meant initially as a device to demonstrate the buoyant effect of gases like air (as shown in the adjacent pictures). Adasymeterwhich allows weighing acts as adensimeterused to measure thedensityofgases.

Principle

ThePrinciple of Archimedespermits to derive a formula which does not rely on any information of volume: a sample, the big sphere in the adjacent images, of known mass-density is weighed in vacuum and then immersed into the gas and weighed again.

${\frac {\text{density of sphere}}{\text{density of gas}}}={\frac {\text{weight of sphere}}{{\text{weight of sphere}}-{\text{weight of immersed sphere}}}}\,$

(The above formula was taken from the articlebuoyancyand still has to be solved for the density of the gas.)

From the known mass density of the sample (sphere) and its two weight-values,the mass-density of the gascan be calculated as:

${\text{density of gas}}={\frac {{\text{weight of sphere}}-{\text{weight of immersed sphere}}}{\text{weight of sphere}}}\times {\text{density of sphere}}$

Construction and use

It consists of a thinspheremade ofglass,ideally with an average density close to that of the gas to be investigated. This sphere is immersed in the gas andweighed.

History of the dasymeter

The dasymeter was invented in 1650 byOtto von Guericke.Archimedesused 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.

External links

• Volume Conversion