Law of Diffusion of Gases

Thomas Graham studied the behavior of the diffusion of gases of unequal densities when placed in contact with each other, using air as his control. He wanted to numerically prove how the diffusion of the gas volumes was inversely proportional to the value of the density of the gas, under constant temperature and pressure.

The significance of this experiment was that in led to a reevaluation of the concept of the movement of matter, realizing that diffusion dealt with small immeasurable elements of matter, as opposed to large volumes of air, as perceived in the corpuscular theory, shedding light into the study of the behavior and structure of matter. Graham’s initial objective was to establish a numerical value regarding the gas density and its diffusiveness for ten different gases, establishing that the greater the gas’s density the smaller the value and rate of diffusiveness compared to air.

He predicted that gases moved by diffusion when placed together in the form of minute volumes, were the heavier gas would tend to accumulate on one side while the lighter gas displaced towards the denser gas until a uniform mixture was achieved. In light of this, he predicted that if controlling temperature and pressure he would achieve the gases to diffuse and establish a numerical value. However no hypothesis was established based on the limited information at their disposal of matter.

However seeing how gases diffused proportionately despite the aperture size, Graham perceived that diffusion dealt with minute particles as opposed to large volumes. The gas’s diffusion volume was achieved once the gas inside the stucco container was entirely replaced by external air, being this new volume the equivalent volume of diffusion. Once established the volume, he used his law of diffusion to provide a numerical value and verify the exactness of his formula.

This was achieved by observing the change in height of the level of mercury. The use of a stucco plug channel containers was suitable to lessen the effect of gas absorption by the material and avoid the gas’s expansion or contraction when atmospheric conditions varied; in addition to this the fact that temperature and pressure were kept constant meant the movement of the gases was because of simple diffusion and not by an external force.

Using air as a unit measure, meant variations in duplicability of results due to the air’s heterogeneous nature making the experiment inconclusive. They used air as their measure unit since they did not have the technology to test the direct interaction of single separate samples of gases, being unable to study properly their behavior. This experiment was accurate when comparing the results with the theoretical values, and consistent to previous experimental observations.

The results showed to be always below the theory value explained by means of their materials absorption nature and slight variations in conditions and instrument’s precision. Despite this Graham was able to establish a clear numerical relationship using equivalent diffusion volumes, however with slight exceptions to certain gases that had to be further tested. Graham’s prediction of being density a factor, which determined the diffusiveness of gas, was corroborated at the sight that lighter gases than air such as hydrogen diffused more easily.

In addition the accuracy of the results helped to determine the value of the gas’s gravity, which would further provide evidence for the study of matter. In addition the fact that intermixture of gases was achieved under controlled conditions, despite the size of contact surface, provided evidence of minute particle diffusion and led Graham to speculated further on the constituents of matter, not explained through the corpuscular theory, would lead to development of the colloid theory in the future.

In conclusion this research paper showed that Graham verified a numerical value for the diffusion of gases with varying densities. However Graham’s observations led him to further speculate on the idea that diffusion was related to immeasurable elements, as opposed to sensible volumes. This paper provides valuable evidence on how the study and discovery of minute particles evolved as the corpuscular theory failed to explain the nature of matter.