Pycnometry is a method for measuring the density of materials. Density is a simple characteristic of a material defined as the mass of the sample divided by its volume. While mass is readily measured with a balance, volume is not so easily determined for all samples. Pycnometry is typically used only in cases when the sample’s volume is somewhat difficult to calculate. The most common example would be a powder, since some quantity of air is trapped between the individual particles of the powder, making the powder appear to have a volume greater than the sum of the volumes of the individual particles.

The basic method behind pycnometry owes its origin to Archimedes’s famous “Eureka” moment in his bath. When an object—regardless of its shape—is submerged in water, it displaces a volume of liquid equal to its own volume. If a container is completely filled, the volume of the object can be calculated by subtracting the volume of the remaining liquid from the volume of the container.

Immersion in water would be unsuitable for many samples, so different materials are used as the displaced substance in modern pycnometers. While some pycnometers make use of mercury, it is more common to use a nonreactive gas, such as helium or nitrogen. The measurement principle remains essentially the same, with the displaced gas forming the basis of the measurement. Operationally, the direct measurement is made of the gas pressure before and after its introduction into the sample chamber. In any event, the combination of the sample’s volume and mass yield the measurement of density.

Many different types of samples can be analyzed via pycnometry. Powders are a common sample format. Specific examples include pigments, carbon blacks, cements, polymeric materials, starches, silica and other chemicals. Other possible samples include fibers, foams, ceramics and building materials. While most laboratory instruments measure relatively modest samples, some larger pycnometers exist for measuring larger samples, such as concretes and aggregate particles used in construction. These, however, are typically not automated systems.

There are relatively few participants in the pycnometry market. Most of the vendors are generally also suppliers of related instrumentation for porosity, surface area and particle characterization. Micromeritics is the market leader, followed closely by Quantachrome. Porous Materials is the next most significant vendor. Among the major instrument manufacturers, Thermo Fisher Scientific is the only one to offer a pycnometer. Another competitor is HMK Test, a Chinese company with a significant involvement in particle characterization. A few vendors also supply non-automated pycnometry equipment for manual measurements. Among the vendors offering such products are Cole-Parmer (Thermo) and Sartorius. The total 2011 market demand for automated pycnometry amounted to only a few million dollars.

Pycnometry at a Glance:

Leading Suppliers

• Micromeritics

• Quantachrome

• Porous Materials Inc.

Largest Markets

• Chemicals

• Catalysts

• Pigments

Instrument Cost

• $20,000–$50,000