July 22, 1942
Dr. Worth H. Rodebush
Department of Chemistry
University of Illinois
I enclose herewith a copy of an informal report showing recent progress in
the development of an instrument for particle-size determination. You will note that
the results look promising. The size determination for particles collected at three
different distances along the collecting plate, as determined by the electron microscope
in the Physics Department here, agree reasonably well with the theoretical curve.
During the last week Dr. Rubin has taken many more electron microscope photographs
with the RCA electron microscope in Berkeley, but these photographs have as yet not
been interpreted. The half width of the size distribution curves obtained from our
electron microscope photographs are rather large, showing that the resolution of the
present instrument is not great. I think that the new instrument, the design of which
is now under consideration, will be much more satisfactory in this respect. my general
opinion, in which Professor Sturdivant concurs, is that it should be possible to develop
the instrument into a satisfactory one to cover the range of sizes 0.1 to 4.
During the last year most of the work under the contract has been under the
direct supervision of Professor J.H. Sturdivant, Assistant Professor of Chemistry
at this Institute. I discussed the original sketched design with him, and he made
a detailed design of the present instrument, supervised its construction, and since
then has supervised the refinements which have been made and the tests. In view of
this, I recommend that Professor Sturdivant be appointed Official Investigator under
the new contract.
We are preparing a final report for the old contract, and it will be submitted
to you before long. Since the present instrument is not very satisfactory, we do not
propose to include detailed drawings for it, but rather to describe the various difficulties
which arose, the methods devised to overcome them, and the results which have been
obtained so far.
This document contains information affecting the National Defense of the United States
within the meaning of the Espionage Act, U.S.C. 50; 31 and 32. Its transmission
or the revelation of its contents in any manner to an unauthorized person is pro