30 SECTIONAL ADDRESSES 
Washburn showed that its heavier atoms could be concentrated by the 
electrolysis of water. ‘This method was developed so rapidly and bril- 
liantly by Lewis that, soon after its discovery, pure heavy water had been 
obtained in appreciable quantity. ‘The isotope of hydrogen of mass 2 
cannot be treated as a normal isotope. Its exceptional difference in mass 
enables it to be separated with comparative ease in a pure state. It has 
been given the name deuterium, symbol D, and heavy water D,O is 
now obtainable in quantity at reasonable prices, one of the most surprising 
reagents in the history of science and certainly one which would have 
dismayed the founders of the C.G.S. system of units. 
Now comes the interesting sequel. Deuterium and its triatomic 
molecule supply two links, missing before, of the three forming a closed 
chain of masses by which H can be directly connected with O, given a 
mass-spectrograph of sufficient resolving power. These links are the 
doublets D—H,, at mass 2, C++—D, at mass 6, and O—CH, at 
mass 16. By means of an improved collimator I have recently increased 
the resolving power of my mass-spectrograph to that necessary to achieve 
at least a partial separation of the extremely close doublet D—H,;, and 
to make a much more accurate estimate of the doublet O—CH,. The 
latter has disclosed the disturbing fact that-this is really wider than I had 
taken it to be and so no longer confirms the early value of C and H. 
Provisional work on the wide doublet C ++—-Dg makes it reasonably 
certain that my original value for H is 2 or 3 parts in 10,000 too low, as is 
also suggested by nuclear transformation experiments. Here we have 
the pretty paradox of the element discovered providing the means to 
remove that very discrepancy which seemed to point the way so clearly 
to its discovery. In view of its valuable results I am not likely to regret 
my mistake, however serious it turns out to be. The only moral to be 
drawn from this seems to be that you should make more, more and yet 
more measurements. Even a bad one may be of service, but, fortunately, 
it will be essential for you to make a considerable number of good ones 
first, or no notice will be taken of it. 
In the field of isotopes, as in so many fields of physical and chemical 
research to-day, the objective we now aim at is the next decimal place, 
an elusive object which always appears to be running away from the 
observer, like a distant spiral nebula. The need for isotopic weights of 
the highest accuracy is urgent. In artificial radio-activity and trans- 
mutation we see the real beginnings of a great new subject, the nuclear 
chemistry of the future. Its equations can only be founded securely 
upon direct determinations of masses by the mass-spectrograph, and the 
nuclear chemist already demands these to an accuracy of 1 in 100,000. 
I have little doubt we shall be able to provide him with these in the course 
of a year or two. Armed with reliable equations, and thereby with more 
and more definite knowledge of nuclear construction, he will transmute 
and synthesise atoms as his elder brother has done molecules, with results 
to be wondered at and possibly even misused by his fellow creatures. 
I foresee a time, not immeasurably far distant, when it will be possible for 
us to synthesise any element whatever, wherever and whenever we please; 
alchemy indeed in the service of man. 
