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"An Introduction to Chemical Science"
R.P. Williams
For example, hydrogen would be number 1, helium number 2, lithium of which you perhaps never heard, would be number 3, and so on.
"Letters of a Radio-Engineer to His Son"
John Mills
Nor had he tried to steal any of the fusion materials; the heavy isotopes of hydrogen or any of the lithium isotopes.
"Anything You Can Do"
Gordon Randall Garrett