Noble gas in the United States alone. For large-scale use, helium is extracted by fractional distillation from natural gas, which can contain up to 7% helium. Neon, argon, krypton, and xenon are obtained from air using the methods of liquefaction of gases, to convert elements to a liquid state, and fractional distillation, to separate mixtures into component parts. Helium is typically produced by separating it from natural gas, and radon is isolated from the radioactive decay of radium compounds. The prices of the noble gases are influenced by their natural abundance, with argon being the cheapest and xenon the most expensive. As
Copia: Foundations of the Abundant Style on Quintillian's rhetorical guide, "Institutio Oratoria". The first chapter of book 10 in Quintillian's "Oratoria" is titled ""De copia verborum"". This is quite possibly where Erasmus received his most direct inspiration for the book. In that 10th chapter, Quintillian declined to give examples for employing the abundant style, on the grounds that each individual case requires a unique solution. This left the door open for Erasmus to detail the abundant style in "Copia". Erasmus acknowledges Quintillian in the preface, and borrows from him (and other classical authors) throughout "Copia", sometimes citing, sometimes not. As further revisions of "Copia" are printed,