# 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)")

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 of gases.

## Principle

The Principle of Archimedes 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:

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

(The formula was taken from the article buoyancy and still has to be solved for the density of the gas.)

## Construction and Use

It consists of a thin sphere made of glass, ideally with an average density close to that of the gas to be investigated. This sphere is immersed in the gas and weighed.

## History of the dasymeter

Was invented in 1650 by Otto von Guericke. Archimedes 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.