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Name: Krista
Status: other
grade        other
location     PA
Age: N/A
Location: N/A
Country: N/A
Date: 2/21/2005
Question:
How do you find the volume and density of a powder?

Replies:
There are two ways to define the volume and/or density of a powder. One is the packing volume, or density. This refers to the volume/density of the powder including the voids. Obviously this is going to depend upon how hard you pack the powder, but sometimes this definition is important if, for example, you are interested in the packing of soil. The more common definition if volume/density of a powder is the volume/density of the solid material comprising the powder. This determination is as follows: Use a liquid that will not dissolve or react with the solid powder. It will also be necessary to make sure that no air remains adsorbed on the powder when the powder and liquid are mixed. Often this is not a problem, but for very fluffy powders like baking flour some steps would have to be taken to assure that the air is removed. For the present, assume that is not a problem. Weigh out a known amount of powder, call it Wp. Weigh out a known volume of liquid, Vl, call that weight Wl. The ratio: Wl / Vl = Dl, the density of the liquid. Now mix the weighed powder, Wp and a sufficient amount of the liquid so that the volume of the powder, Vp, (which you do not know yet) + the volume of the liquid = the original volume of the liquid, Vl. This tell you how much liquid was replaced by the powder particles. So we have three weights: Wl the weight of the known volume of liquid, Wp the weight of the dry powder, and Wmixture = Wp + (Wl - Wd) where Wd is the weight of liquid that has been replaced by the powder. Since you know the density of the liquid, Dl = Wl / Vl, from above, you can calculate the volume of liquid that has been replaced by the powder, so this is equal to the volume of powder, Vp, because the powder and liquid have not reacted, dissolved or otherwise interacted. And since you know the weight of the powder Wp you know its density, Dp = Wp / Vp.

Vince Calder


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