The effect of adhesive film thickness on the sampling efficiency of the konimeter.

The method at present used in Britain for the preparation of konimeter slides, namely, the application of a film of glycerine jelly with the finger, was felt to be insufficiently controlled to give reproducible results by different operators, and it was therefore decided to test the improved technique recently introduced by the Transvaal Chamber of Mines (1947) which consists of coating the slides with a film of petroleum jelly applied as a solution in xylene. During the investigation of the different methods of slide preparation a number of unforeseen problems arose. It was found that the appearance of the dust samples varied considerably according to the thickness of adhesive film. Initially it was thought that this might be attributed to inferior optiCal properties of the thicker films. Further work revealed that, on the contrary, thicker films were giving the truer results, and that thin films of the type hitherto used lead to spurious dust concentration values through the larger particles shattering and rebounding on impact with the slide.