126 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 19 34 



guch as nitroethane, CH3CH2NO2, the two hydrogen atoms next to the 

 NO2 groiq^ are replaceable by deuterium in basic solutions of heavy 

 water. In this case the rate of reaction can be measured and it has 

 been shown that H atoms leave this molecule more easily in the heavy 

 water solutions than they do in light water solutions. Similarly, cane 

 sugar is broken up by reaction with heavy water faster than by light 

 water. In other reactions the velocity is slower in heavy water. The 

 accelerating or retarding effect obtained is used by the chemist to de- 

 cide the detailed picture of what is occurring in such solutions. With 

 deuterium atoms as labeled hydrogen atoms, much can be learned 

 about these detailed occcurrences ; and what is found for deuterium 

 must also occur with hydrogen under the same conditions, even 

 though, without the label, this cannot be demonstrated. Eeactions 

 of deuterium and deuterium compounds which are slower than those 

 of hydrogen are due to the fact that the lowest energy states (the 

 zero-point energies) of the former are less than those of the latter. 

 To become equally activated, by heat or light, deuterium must receive 

 greater increments of energy; vice versa^ under equal energy condi- 

 tions the deuterium compounds will in general be less reactive. In 

 cases where this does not hold it is to be concluded that reaction does 

 not involve molecules of the deuterium compound, but rather an atom 

 or an ion. Comparative velocity measurements are, therefore, of 

 great importance theoretically. 



In the physics laboratory deuterium is being put to spectacular use 

 as a projectile in atomic transmutation. Immediately after the isola- 

 tion of deuterium the nuclei or deutons were so employed to bombard 

 lithium, the results showing them to be much more effective missiles 

 than protons. Two processes are possible with the isotopes of 

 lithium of masses 6 and 7. 



8Li« + iD2 = 2oHe* 



sLi^ + iD- = 2oHe* + ou^ 



The subscript to the left represents the nuclear charge; the super- 

 script is the mass. Here also oU^ represents a neutron of zero charge 

 and unit mass. Helium of mass 4 and charge 2 is the other product. 



Experiments in Cambridge under Lord Kutherford suggested that 

 deutons could be used to bombard deutons and produce new forms of 

 matter. Here, also, there are two possibilities. 



iD= + iD2=iT^ + iHi 



iD' + iD-=2He^ + oni 



In the first, transmutation gives two hydrogen atoms, one of mass 1, 

 the other of mass 3, in other words, tritium. In the second, the 

 change is to a helium isotope of mass 3 and charge 2 and a neutron 



