Measurements of the absorption coefficients are made with a double crystal spectrometer in the parallel position, placing the sample between the two crystals, and between the second crystal and the chamber. In the first position the beam is cut down by the ordinary absorption and also by the power going into small‐angle scattering; in the second position it is cut down only by the ordinary absorption. The difference in the two measured absorption coefficients gives directly the total power in small‐angle scattering. From the latter, an average spherical particle size can be computed.