144 The Evolution of Chemistry. 



reduction of temperature be brought into the conditions of 

 liquid or solid. About thirteen years ago the most stub- 

 born gave way and the belief was verified. The air we 

 breathe has been made into a water-like liquid that boils at 

 337 F. below zero. At a somewhat lower temperature two 

 liquids with different specific gravities are plainly seen. 

 The one floats upon the surface of the other. Xitrogen, 

 one of these two, has been frozen into crystals like snow 

 The lowest temperature that has yet been reached in ex- 

 periments of this kind is 373 F. below zero, and the highest 

 pressure used was upward of 3,000 pounds to the square 

 inch. Between this very low temperature and the high 

 ones used in volatilizing metals a wide range exists within 

 which some rather startling chemical facts have appeared. 

 Bodies having very powerful affinities for each other at one 

 temperature may have none at another higher one, while at 

 a still higher the original affinity is restored. Here, as else- 

 where in nature, the rhythm of motion exerts its sway. 

 This is particularly apparent in chlorine and its behavior 

 toward platinum. Every one knows how sulphuric acid 

 and ammonia boil and splutter the instant they touch each 

 other, yet pure liquefied ammonia at a low temperature will 

 rest on the surface of the same acid as peacefully as a sleep- 

 ing babe. Chlorine and oxygen in the liquid state can not 

 be made to unite with bodies that at normal temperatures 

 they seize upon with avidity. Every chemist is familiar 

 with reactions that are only possible within not only certain 

 temperature limits, but also certain degrees of dilution. At 

 one time it was supposed that most chemical changes were 

 immediate and direct. Now we know that the majority, 

 and possibly all, are mediate and indirect. It is coming to 

 be the belief of chemists that no two bodies can unite with 

 each other without the aid of a third. So common a re- 

 action as the burning of wood, that was long supposed to 

 be merely a direct union of oxygen and carbon, is now 

 found to involve a number of hitherto unsuspected inter- 

 mediate changes in which water and peroxide of hydrogen 

 take a part. Pure water can not be decomposed by elec- 

 trolysis. An acid is needed in the matter. The action of 

 this acid and that of all such go-between chemical bodies 

 used to be called catalysis. We now speak of it as contact 

 action. As electricity was once considered a rare and re- 

 markable phenomenon when exhibited after the rubbing of 

 a piece of amber, so contact action was long believed to be 



