Experimental Determination of Void Content of Close-Packed Mineral Powders

Abstract

This method has been found very accurate when the unknown contains between 3 and 10 mg. of potassium, but less than 1 mg. and more than 50 mg. have been satisfactorily determined. For small amounts a 0.05 N potassium permanganate solution was used. In the case of large amounts only 0.1 A permanganate was used, but it was standardized against a similar amount of known potassium. Ammonium salts have been the only salts which have interfered, because ammonia also forms an insoluble precipitate with sodium cobaltinitrite. Organic matter must not be present in the unknown solution in such a form that it will be occluded in the precipitate or retained on the filter pad. The method is rapid, as one worker can easily make from 20 to 40 determinations a day. By proper precautions the asbestos can be used over and over, and since the sodium cobaltinitrite and alcohol are not exceedingly costly substances the method is not very expensive. This method has been used on many kinds of ash, soil extracts, and total potassium determinations in soils, with very satisfactory results.

Particle-size Studies. Properties of Finely Divided Materials.

“…The per cent voids, V, may be calculated from the bulk density by means of the following equation: V = 100(1 -B/D.) (15) Traxler and coworkers (44) give a discussion of the packing of mineral powders, as do also Work (55), Roller (37), and Burmister (11). These methods are suggested for use only as approximations in evaluating relative sizes, since size distribution and particle shape have a considerable effect on the results.…”