Bulk density

Bulk density, also called apparent density or volumetric density, is a property of powders, granules, and other 'divided' solids, especially used in reference to mineral components (soil, gravel), chemical substances, (pharmaceutical) ingredients, foodstuff, or any other masses of corpuscular or particulate matter. It is defined as the mass of many particles of the material divided by the total volume they occupy. The total volume includes particle volume, inter-particle void volume, and internal pore volume. Bulk density, also called apparent density or volumetric density, is a property of powders, granules, and other 'divided' solids, especially used in reference to mineral components (soil, gravel), chemical substances, (pharmaceutical) ingredients, foodstuff, or any other masses of corpuscular or particulate matter. It is defined as the mass of many particles of the material divided by the total volume they occupy. The total volume includes particle volume, inter-particle void volume, and internal pore volume. Bulk density is not an intrinsic property of a material; it can change depending on how the material is handled. For example, a powder poured into a cylinder will have a particular bulk density; if the cylinder is disturbed, the powder particles will move and usually settle closer together, resulting in a higher bulk density. For this reason, the bulk density of powders is usually reported both as 'freely settled' (or 'poured' density) and 'tapped' density (where the tapped density refers to the bulk density of the powder after a specified compaction process, usually involving vibration of the container.) The bulk density of soil depends greatly on the mineral make up of soil and the degree of compaction. The density of quartz is around 2.65 g/cm³ but the (dry) bulk density of a mineral soil is normally about half that density, between 1.0 and 1.6 g/cm³. Soils high in organics and some friable clay may have a bulk density well below 1 g/cm³. The reason why soils rich in soil organic carbon do have lower bulk density is due to the low density of organic materials. For instance peat soils have bulk densities from 0.02 g/cm³ to 0.98  g/cm³. Bulk density of soil is usually determined from a core sample which is taken by driving a metal corer into the soil at the desired depth and horizon. This gives a soil sample of known total volume, V t {displaystyle V_{t}} . From this sample the wet bulk density and the dry bulk density can be determined. For the wet bulk density (total bulk density) this sample is weighed, giving the mass M t {displaystyle M_{t}} . For the dry bulk density, the sample is oven dried and weighed, giving the mass of soil solids, M s {displaystyle M_{s}} . The relationship between these two masses is M t = M s + M l {displaystyle M_{t}=M_{s}+M_{l}} , where M l {displaystyle M_{l}} is the mass of substances lost on oven drying (often, mostly water). The dry and wet bulk densities are calculated as