caffeine

noun

1. (uncountable, usually)An alkaloid, C₈H₁₀N₄O₂, found naturally in tea and coffee plants, which acts as a mild stimulant on the central nervous system.

   “For example, 0.100 grams of caffeine yield by combustion, by weight, 0.180 grammes of carbonic acid.”

   “Hitherto, in consequence of its slight solubility, caffeine has been administered hypodermically only in very small doses ; in fact, at the ordinary temperature, it requires 93 parts of water to dissolve, so that a cubic centimeter would contain scarcely more than a centigram.”

   “The US Food and Drug Administration defines this limit as anything more than 400 milligrams of caffeine daily for healthy adults. This is equivalent to four or five cups of coffee.”