This instrument was the part of an anaesthesia machine that mixed oxygen and nitrous-oxide, commonly referred to as 'laughing gas'. Nitrous-oxide is not used alone as a general anaesthetic as it is too weak to make someone completely unconscious. When mixed with oxygen in a 50-50 ratio, however, nitrous-oxide provides an excellent analgesic, dulling pain whilst leaving the patient conscious if perhaps a little dizzy. It is used most frequently in childbirth and in emergency medicine.