September 16, 1929
Professor W.L. Bragg,
University of Manchester,
Dear Professor Bragg:
We have not very much to report as the result of the summer's work, but several problems are coming along nicely. I am
writing up my work on pseudobrookite. It has a =9.70, b = 9.78, c=3.69 Å, space group Vh17, 4Fe2TiO3 in the unit. I verified
the structure with great care, analysing five Laue photographs completely as well as a number of oscillation photographs.
A few obstinate spots on each photograph gave great trouble until it was finally shown that they were due to small crystals
of rutile in parallel growth with the large pseudobrookite crystal. Since the X-ray data ruled out the formula Fe4Ti3O12,
this explained the excess TiO2 over Fe2TiO5 reported for the catural crystals used in our investigation. There are strings
of titanium octahedra along the c-axis, each attached by a corner, to the one above and the one below. Each iron ion is 1.9
Å from four oxygens and 2.2 Å from two more, so its coordination number is either four or six. The structure is not related
to those of sillimanite and andalusite, in which there are rutile strings of aluminum octrahedra, nor to that of brookite.
I am glad to see that you also are turning your attention to the micas, feldspars, and zeolites. I have begun work on the
zeolites too, for no particular reason except that I had some good crystals at hand.
There are five of us doing crystal work here now. We have a pretty extensive collection of apparatus, lacking only an
ionization spectrometer, the one which Dickinson used having been dismantled some years ago. I hope to have one next year
since your work has made quantitative data so important for structure determinations. we have a weekly conference during the
winter, with interesting discussions. they would be much more interesting if one of your men were here to participate in them.
If you send one of your men to America on a fellowship I hope you will keep us in mind in advising him. He would find research
(as well as living) conditions here second to none. No matter how physical his training he would not need to be frightened
at coming to a chemical laboratory.
My wife and I will bring our boy, five years old, with us to England. He is very anxious to come - he half believes that
he didn't go to Europe at one year because he hadn't behaved! We are already as excited as he about the trip.