According to Guinier the low angle x‐ray scattering of particles should disappear when they are immersed in a fluid of equal electron density. This furnishes a way of measuring the electron density of powders, providing a suitable impregnating fluid can be found. Experiments of this type have been carried out with carbon black. A method of calculating the low angle scattering coefficient defined by Warren is given for impregnated samples. Measurements of the total low angle scattering intensity were made using a double crystal spectrometer and Geiger counter. No liquid was found that would give complete matching but approximate matching was obtained with phosphoric acid solution. The data extrapolate to show an electron density of 1.1N±0.1NwhereN=Avogadro's number. This compares with a value of 0.99Nas calculated from the helium immersion mass density measurement on the same sample.