Chem: inflammable and flammable

The following is the explanation:

Linguistics: Flammable vs. inflammable
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Look up flammable, inflammable in Wiktionary, the free dictionary. The word "inflammable" came from Latin inflammāre = "to set fire to", where the prefix in- means "in" as in "inside" (compare English "in flames"). But there have been instances of people thinking that this "in-" prefix means "not" as in "invisible" and "incombustible" etc, and thus wrongly thinking that "inflammable" means "cannot burn". To avoid this safety hazard, the shortened word "flammable" has come into use in recent years.
(The French for "non-inflammable" is ininflammable, with a negative in- plus an in- meaning "inside".)
The Elements of Style ("Strunk and White"), on the other hand, says:
Flammable. An oddity, chiefly useful in saving lives. The common word meaning "combustible" is inflammable. But some people are thrown off by the in- and think inflammable means "not combustible." For this reason, trucks carrying gasoline or explosives are now marked FLAMMABLE.