CONFIDENTIAL

July 22, 1942

Dr. Worth H. Rodebush

Department of Chemistry

University of Illinois

Urbana, Illinois

Dear Worth:

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.

Sincerely yours,

Linus Pauling

LP:jr

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