Asphyxiant gas can smell the odorants, and assigning a different smell to each gas may be impractical. Another difficulty is that most odorants (e.g., the thiols) are chemically reactive. This is not a problem with natural gas intended to be burned as fuel, which is routinely odorized, but a major use of asphyxiants such as nitrogen, helium, argon and krypton is to protect reactive materials from the atmosphere. The dangers of excess concentrations of nontoxic gases has been recognized for centuries within the mining industry. The concept of black damp (or "stythe") reflects an understanding that certain gaseous mixtures could lead to
Most common words in Spanish (CREA), a text corpus compiled by the Real Academia Española (RAE). The RAE is Spain's official institution for documenting, planning, and standardising the Spanish language. A "word form" is any of the grammatical variations of a word. The second table is a list of 100 most common lemmas found in a text corpus compiled by Mark Davies and other language researchers at Brigham Young University in the United States. A "lemma" is the primary form of a word—the one that would appear in a dictionary. The Spanish infinitive "tener" ("to have") is a lemma, while "tiene" ("has")—which is a conjugation