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“Joseph Black (1728—1799), a doctor of medicine and 
professor of natural philosophy at Glasgow and Edinburgh, 
discovered carbonic acid gas—fixed air, as he called it, and 
pointed out that it was altogether distinct from common air.” 
«Dr. Joseph Priestley (17833—1804), a Nonconformist minister, 
who in August, 1774, succeeded in obtaining a new air of 
exceptional goodness, which was afterwards named Oxygen.”’ 
«¢ Antoine Laurent Lavoisier (1743—1794), an eminent French 
chemist, who went a step further than Priestley, and showed that 
the Oxygen, discovered by the latter, was a constituent of the 
air, and was one-fifth of it by volume; the other four-fifths which 
would not support combustion (that part was discovered one 
hundred years earlier by Mayow) was called Nitrogen.” 
“The Hon. Henry Cavendish (1731—1810), aristocrat, 
millionaire, chemist, the most exact worker of his time, deter- 
mined most accurately the percentage of Oxygen and Nitrogen 
in air, and pointed out the possibility of the presence of another 
gas, which was discovered a century later by Rayleigh and 
Ramsay.” 
“Experience has taught us that to liquefy certain gases 
intense cold is absolutely necessary. The contemplation of the 
production of great cold dates back to the ancient history of 
Science.” 
‘«« Fyancis Bacon, in ‘ Sylva Silvarum,’ says ‘ The production 
of cold is a thing very worthy of inquisition, both for the use and 
the disclosure of causes.’ ”’ 
‘«‘ Fahrenheit, in 1714, thought that a mixture of ice and salt 
produced the lowest temperature obtainable, and this, on his scale, 
was marked zero, and the freezing point of water 32°; although 
Amontons, twelve years earlier, had contemplated almost the 
modern scientific view of zero temperature.” 
“The lowest temperatures obtained naturally, of which we 
have record, appear to be those in parts of Siberia, where 
122 degrees of frost have been registered. It is not always 
convenient to go to Siberia when low temperatures are required, 
and this has led to considerable research in their artificial 
production. There are three well-known methods of doing this : 
(1) By mixture of chemicals, such as snow and nitric acid, 
ammonium nitrate and water; (2) By rapid evaporation of 
liquids, such as ether, eau de Cologne, ammonia, &c.; (3) By 
sudden expansion of compressed gases. The last method is only 
one example of the many cases in which a piece of pure scientific 
research, having apparently no practical use whatever, has turned 
