Quantitative Analysis by X-Rays

Abstract

IN their interesting letter to NATURE of April 5, p. 524, Prof. T. H. Laby and Mr. C. E. Eddy agree with many of the statements in my address to the British Association, but dissent in some respects from my conclusions. According to their view, I was not sufficiently generous in stating the sensitiveness of the method. The sensitiveness depends on numerous factors such as the energy applied, the time of exposure, the wave-lengths to be photographed, and so on, and in a very high degree on the constitution of the sample; traces of copper present in aluminium will give an X-ray line incomparably stronger than when present in the same atomic concentration in lead. The state of aggregation of the sample is also of great importance; an alloy available in comparatively large amounts, which can be soldered massively on to the anticathode, and, on account of its high heat and electrical conductivity, can be bombarded very intensively by cathode rays, is much better than a sample of mineral possibly available in minute quantity only, which must be rubbed as a powder into the anticathode.