THE ROLE OF WATER 425 



With the discovery of an isotope of hydrogen, there came the 

 prediction of G. N. Lewis that "heavy water" would not support 

 Hfe. The two hydrogen isotopes of atomic weights 1 and 2 and 

 the three oxygen isotopes of atomic weights 16, 17, and 18 could 

 theoretically combine so as to form nine kinds of water, all 

 differing in weight. Among the known forms of water are 

 H2O, H^RiQ, and H^H^O (H^O). The freezing point of the 

 last is 3.8° higher and its boiling point 1.42° higher than that of 

 ordinary water. Lewis predicted that this heavy water would 

 not support life and proved it by showing that tobacco seeds do 

 not sprout in it. Others have since demonstrated that lowly 

 forms of animal life do not long survive in heavy water. Tre- 

 lease, however, finds little effect of dilute heavy water on fungi. 

 Ewart finds an effect, but it is a retarding one on the movement 

 and growth of bacteria and an accelerating one on spore 

 production. 



It appears also that plants react differently to water formed 

 by the condensation of steam than they do to water formed by 

 the melting of ice. 



