Note 9 — Chapter IV · THE VARIOUS STATES OF MATTER
Reading edition
Professor Soddy, in a paper read before the Royal Society on the 15th November 1906, warns experimenters against vacua created by charcoal cooled in liquid air (the method referred-to in the text), unless as much of the air as possible is first removed with a pump and replaced by some argon-free gas. According to him, neither helium nor argon is absorbed by charcoal. By the use of electrically-heated calcium, he claims to have produced an almost perfect vacuum.—ED.