Oct. 22, 1928
Dear Professor Bragg:
I was very pleased to learn that West had found the structure
of topaz, and that it approximates the one I suggested. Your letter came just about
the time my paper appeared, so that I could make no reference to West's work. I have
not yet tried applying the rules governing deformation to see whether the atomic positions
agree with West's or not.
The last of August I sent two papers to the Editor of the Journal
of the American Chemical Society. In one of them are rules governing the structures
of complex crystals. I realize that nothing I have done is highly original - in particular
was I gratified to read in your letter a statement of the rule governing the sharing
of polyhedron elements. I have written the Editor asking whether or not these papers
will appear in December. When I hear from him I'll drop you a note. The same rules
are included in a paper in Sommerfeld's Festschrift, which will appear in December.
I am pleased with the clarity that the study of crystals has introduced
into the very complex tungsten and molybdenum compounds. Mr Craxton has begun the
study of these crystals with X-rays.
I have suggested a structure for the rare-earth sesquioxides in
place of Zachariasen's improbable one. A copy of the manuscript is included. It is
interesting that on starting out with octohedra deformation led to 7-cornered polyhedra.
It is impossible to predict the slope of the coordinated polyhedrom
about large cations; and even their coordination number is uncertain. Your mention
of diopside has served to excite my curiosity immensely - I'd like very much to know
what the structure is like. I have no doubt that there are strings of si tehahedra
(possibly in the direction) or perhaps rings as in beryl. I'd like to know too whether
Taylor's structure for rillimanite and mullite agrees with my predictions in regard
to the amount of sharing, and whether he has found another structure for cyassite.
My vacation and my book on line spectra have prevented me from doing as much work
as I'd like recently.