A dust-sampling method in which samples of dust are collected on filter paper and then placed in a photometer. The instrument shows the intensity of a beam of light after it has passed through the paper, and the fall in intensity is a direct measure of the dust concentration. With dark dust, such as in coal mines, a rough indication of the dustiness may be obtained by comparison of the depth of tone with a graded series of samples that have been calibrated against some other instrument. There are two methods of collecting 2316 samples for photometric estimation: (1) by passing the air through a filter paper, as for gravimetric estimation; or (2) by impingement, as in the konimeter.