Grain Size Measurement by the Mean Transmittance Method

There are various methods for grain size measurement. A new method is proposed in which the grain size can be obtained rapidly, simply and precisely by its direct measurement in the electron micrograph negatives. The grains are transparent on the photographic negative; therefore the larger the grains are the higher will be the rate of their mean transmittance, provided the grain number is kept constant. The mean grain size (a) expressed in the mean projection area is related to the mean transmittance T according to the formula where S represents the total area measured in the negative, n the number of the grains, Ta the transmittance of the grain part, Tb the transmittance of the back ground and m the magnification of the negative. A convenient apparatus has been made which will carry this principle into practice. Good agree-ments were obtained between the results hereby obtained and those by the conventional rule-method for both silver halide dispersions and model patterns