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