When a silicon wafer containing oxide precipitates was etched preferentially with Yang etch, the precipitate etch pit density was found to increase linearly with respect to etch depth. This indicates that the precipitate etch pits, once formed, replicate themselves and that those shown on the etched sample surface represent not just the precipitates on the surface plane, but all the precipitates in the volume of material removed by etching. Thus, the usual method of obtaining the density of volume defects, such as oxide precipitates in silicon, by raising the etch pit density to the power of 3/2 is incorrect. Instead, a true volume density, which is independent of etch depth or time, should be obtained by dividing the etch pit count by the volume of the etched-away material or by dividing the etch pit density by etch depth. For 3, 6, 9, and 12 min of etching in Yang etch, the volume densities of oxide precipitates in silicon calculated in this manner converged to within about +/- 20%, while the volume densities obtained by raising the etch pit densities to the power of 3/2 diverged by more than an order of magnitude.