Historical information

When Hewitt introduced his regulating stopcock in 1887, attempts were made to dilute the nitrous oxide with air and so obviate the element of asphyxiation. The method was to be seen in London, mainly in dentistry and minor surgery, so late as 1930. It was not very successful. To give even 10% of oxygen (which is not enough) the gas-mixture must contain 55% of air and 45% of nitrous oxide. The latter is thus so diluted by atmospheric nitrogen as to be incapable of producing anaesthesia except by asphyxiation. "Gas-air" was confined to analgesia, for example in midwifery. (Source: Penn catalogue)

Physical description

Brown leather facemask attached to metal inhaler and stopcock device that has been sectioned to reveal its inner workings. The various exposed channels have been painted either green, red, blue or purple.

Inscriptions & markings

Engraved into side of stopcock: HEWITT'S / N20-02 / 1895 / G. Kaye sect. 1952.
•Stamped into other side of stopcock: [indecipherable] BARTH & CO. / SOLE MAKERS / 54. POLAND STREET LONDON.W.