154 ESSAYS BIOGRAPHICAL AND CHEMICAL 



could be collected separately; while any 'heavier' gases 

 would be the last to distil over*. The hope was not dis- 

 appointed at all events as regards the first expectation ; 

 for the first part of the gas which evaporated was consider- 

 ably lighter than argon and had a much lower boiling- 

 point. After a few redistillations, however, it was found 

 that liquid air was not sufficiently cold to condense this 

 light gas to liquid. But Dr. Travers was equal to the 

 emergency. He constructed an apparatus by help of 

 which hydrogen gas was condensed to liquid ; and the 

 boiling-point of liquid hydrogen is much lower than that 

 of liquid air; it is 252 - 5 C. On cooling the mixture 

 of gases which had been separated from the argon, a 

 portion only condensed, while about one- third still remained 

 as a gas ; the gaseous portion was helium, and the liquid (or 

 solid) portion evaporated into a gas which was named 

 ' neon,' the Greek word for ' new.' 



It was also found that two other gases could be sepa- 

 rated from air by allowing a large quantity of liquid air 

 to boil away. These gases have a much higher boiling- 

 point than oxygen, nitrogen, or argon, and therefore they 

 remain mixed with the last drops of liquid after most of 

 the air has evaporated. They were separated from each 

 other by ' fractionation ' ; one was named 'krypton,' the 

 Greek for ' hidden ' : and the other ' xenon/ or ' strange.' 



Five new gases were thus obtained ; they are given with 

 their atomic weight in the following line : 



Helium, 4 ; Neon, 20 ; Argon, 40 ; Krypton, 81 '6 ; Xenon, 128. 



Their position among other elements is well seen from the 

 following extract from the whole table of the elements : 



Hydrogen, 1 Helium, 4 Lithium, 7 Berylium, 9*1, etc. 



Fluorine, 10 Neon, 20 Sodium, 23 Magnesium, 24'3, etc. 



Chlorine, 35 '5 Argon, 40 Potassium, 39 '1 Calcium, 40, etc. 



Bromine, 80 Krypton, 81 Rubidium, 85*4 Strontium, 87'6, etc. 



Iodine, 127 Xenon, 128 Caesium, 133 Barium, 137'4, etc. 



