Powder‐size measurement by a combination of the methods of nephelometry and photo‐extinction

In the present paper it is shown that a combination of the methods of nephelometry and photo‐extinction offers a means for the determination of the size‐frequency of a fine powder, dependent upon two curves—one of scatter index against particle size as well as the curve of extinction coefficient versus particle size, as required by the conventional photo‐extinction method. Should these two curves, as appears possible, be more easily defined in terms of the physical characteristics of the powder and suspension fluid than is the curve of extinction coefficient, then the combined technique might prove a more convenient and accurate method of powder size analysis than the photo‐extinction method. Certain relationships have been derived and, on the basis of a limited number of tests, are shown to be in agreement with experiment. From the results of scattered‐light tests the extinction‐coefficient/particle‐size relationship has been computed and reproduces in detail a significant feature of the curve as determined by direct measurement. Although it is not claimed that the present tests, which are largely preliminary to a more detailed investigation, are conclusive, it is felt that they lead to conclusions of such interest as to justify publication in the present form.