The Oxford vaporiser was originally conceived by the British anaesthetists Robert W. Macintosh and H.G. Epstein.
The object of the device was to produce a constant and reliable concentration of ether. To do this it was necessary to ensure that the ether was always kept at a constant temperature below its boiling point. The vaporiser consisted of three concentric chambers. The central one held hot water, the middle anhydrous calcium chloride and the outer the ether. Hot water poured into the central chamber fed through to the calcium chloride which dissolved producing the constant source of latent heat needed for the vaporisation of ether in the outer chamber for about one hour. After refilling the water chamber the heat source could rapidly be restored.
Conceived in 1941 for use in war conditions, the Oxford inhaler was an extremely practical device requiring only the addition of hot water. Being extremely portable and compact, it was used by the British Army throughout the Second World War.