Victor Meyer's vapour density apparatus, 1878.
© Science Museum / Science & Society Picture Library
Designed by the German chemist Victor Meyer (1848-1897), this apparatus consisted of a long narrow corked tube blown into a cylindrical bulb at its lower end and fitted with a short side arm about 5cm from the top. This tube was supported in an outer jacket of glas or copper in which water was boiled. The sample was introduced in a small weighing tube, and the cork quickly replaced. On reaching the heated zone, the sample boiled, blew out the stopper, and pushed an equal volume of air through the side arm that lead to a measuring tube.