The existence of reactions which are reversible on slight alteration of conditions at once invalidates the principle, for if the action proceeding in one direction evolves heat, it must absorb heat when proceeding in the reverse direction.
Thus by transposition we may write the last equation as follows 2HI =H2+12+12200 cal., and thus express that hydriodic acid when decomposed into its elements evolves 12200 cal.
Reason in its own strength and with its own instruments evolves a system of the universe which coincides, according to Erigena, with the teaching of Scripture.
At a red heat it evolves oxygen with the formation of potassium nitrite, which, in turn, decomposes at a higher temperature.
Magnesium oxychloride when heated to redness in a current of air evolves a mixture of hydrochloric acid and chlorine and leaves a residue of magnesia, a reaction which is employed in the Weldon-Pechiney and Mond processes for the manufacture of chlorine.