X-ray guide tube for diffraction experiments

For diffraction experiments with an extremely small crystal or with very long distance from X-ray source to detecting instrument, the use of an `X-ray guide tube' (XGT) is proposed on the basis of a simple consideration and experiment with a Pyrex-glass tube. X-ray intensities through an XGT of glass and also through a pin hole were measured as a function of photon energy and compared to derive the gain by use of XGT. At wavelengths between Cu Kα and Mo Kα radiations, the observed gain in brightness is about thirty to twenty for the present setup, corresponding to about 50 to 80% of the maximum possible gain calculated on the assumption that the reflectivity of X-ray total external reflection is 1.0.

The determination of ferrous iron in resistant silicates

The determination of ferrous iron in minerals, such as staurolite and kornerupine, which cannot be effectively dissolved by dilute sulphuric and hydrofluoric acids has been made possible on the macro-scale by the work of H. P. Rowledge; the mineral is fused with sodium fluoride and boric oxide at 900°C. in a sealed pyrex glass tube, the fusion cake dissolved in hot dilute sulphuric acid in a current of carbondioxide, and the solution titrated with potassium permanganate. We have met with no difficulty in applying the method on the macro-scale, but when only small amounts of a mineral are available several difficulties arise, and modifications become necessary.The air present in the sealed tube of a Rowledge fusion, using the quantities and dimensions he specifies, is already sufficient to oxidize about 3 to 5 mg. of ferrous oxide. But when the weight of the sample is reduced to 10 mg., it is not possible to reduce the dead-space in the tube in proportion ; it can hardly be reduced below about ¼c .c. which is sufficient to oxidize 0·3 mg. or 3% FeO and is likely to be more effective in this direction than on the larger scale, since the surface of the fusion is proportionally greater.