chemi~tryon ~ t m p ~ edited by.
JAMES 0. SCHRECK Unlvemty of Norihern Colorado Greeley, CO 80639
C.MARVINLANG Unwrsily of Wisconsin Stevens Point. WI 54481
Some Stamps Related to the Kinetic Molecular Theory of Gases Foil A. Miller University of Pittsburgh, Pittsburgh, PA 15260 Of all the great theories and concepts of chemistry, the kinetic molecular theory of gases has probably been second only to the atomic theory of matter in its importance and generation of new ideas. Since it depends on the idea of atoms and molecules, its roots go back to the speculations of the ancient Greeks. Democritus (born in the late fifth century B.c.) was the first to propose' that matter consists of an infinite number of tiny atoms moving randomly and ceaselessly in a void, a view remarkably like our modern one. The Greek stamp (no. 1) was issued to commemorate the dedication of the Nuclear Research Center named in honor of Democritus. The next significant event was the experimental discovery of the gas laws.2 Robert Boyle (1627-91) found in 1660 that, for a fixed amount of gas a t constant temperature, the volume of a eas is inverselv..orooortional toits Dressnre. V = 11P . (now known as Hoyle's Law). Stamp no. 2showsa portrait of Bosle and his air . oumo. . Because of the orohlem of definingan adequate temperature scale, over a century elapsed before the second gas law was discovered. Jacques A. C. Charles (1746-1823) in 1787, and Joseph Gay-Lussac (1778-
1850) independently in 1802, found that for a fixed amount of gas a t constant pressure, the volume of a gas was directly proportional to its absolute temperature, V T (variously called Charles' Law or Gay-Lussac's Law). Combining these proportionalities gives V = TIP, or P V = T. In 1804 Gav-Lussac (no. 3) made two remarkable ascents ~, inu hot air balloon in order tostudy both theearth's magnetic field and the comnosition of air as a function of a l t i t ~ d e . ~ He was alone on the second ascent, and reached the incredible height of 7016 meters (23.020 ft). a record that stood for . . more &an a century. This ascent was in an opengondola and without an oxvaen s u ~ p l v In ! an effort to attain more alti& various items, among which was tude G ~ ~ - L U S jettiionid a white kitchen chair. The balloon was out of sight above some clouds, and when the chair landed near a peasant girl tending a flock of sheep, she grew frightened and began to scream. The sheep then started to bleat and the dog to hark, and soon a group of villagers gathered. They called the village priest. He was unable to explain the event hut, like his ~~~
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'Biographical works, e.g., Gillesple, C. C., Ed. "Dlctlonary of ScientificBiography"; Scribner's: New York, 1971; Dalntith. J. et al. "A Biographical Encyclopedia of Scientists"; Facts on File: New York, 1981; Asimov, I. "Asimov's Biographical Encyclopedia of Science and Technology". 2nd ed.; Doubleday: New York. 1982. Textbooks of physical chemistry, e.g., Atkins, P. W. "Physical Chemistry". 2nd ed.; Freeman: San Francisco. 1982; Moore, W. J. "Physical Chemistry", 4th ed.; Prentice-Hall: Englewood Cliffs, New .larssv. 1972. -. ..,, Oesper, R. E. "The Human Sldeof Scientists"; University Publlcations. Univ. Cincinnati. Cincinnati, OH, 1975: p 78-80.
ldentlflcallonand Descrlptlon of Stamps Stamp No.
lssulng
year of
Country
Issue
scon Catalog No.
Greece
Ireland France
Italy Sweden Mexico
Austria Sweden Sweden USA Some stamps related to the kinetic theory of gases. See table fw identlfication.
France
Belgium Volume 63 Number 8 August 1986
685
parishioners, was inclined to believe that the chair bad either fallen from the heavenly regions or had been thrown out by its inhabitants, The only problem was why those ahiding in the heavens, where poverty was presumed to be nonexistent, should have such shabby furniture! The mystery was not cleared up until several days later when news of the balloon ascension reached the village about 20 miles from Paris. Gay-Lussac's experiments involving gases required the use of glass tubes that were not then available i n France and had t o i e imported from Germany. In his opinion the import duty was excessive. His efforts to obtain a lower rate were unsuccessful, so he instructed his German supplier to seal the tuhes before shipment and label them "German air". When the tuhes arrived a t the Customs Office, the officials searched their manuals to find the rate to he assessed. Since "German air" was not listed, the tubes came into France duty-free. At this time the difference between atoms and molecules was not understood. In 1811 Amadeo Avogadro (1776-1866) stated his famous nrinciole. . . "Eaual volumes of eases at the same conditions of temperature and pressure contain the same numher of molecules" (no. 4). (Incidentallv. this st am^ may he the only one that states a physical law in'its entire& in words., From this ~ r i n c ithe ~ l distinction ~ between atoms and mol&des could be made, hut Avogadro's work was ienored for nearlv 50 vears. In 1860. four vears after his ieath, the first ikernkional chemieal congress was convened in Karlsruhe, Germany to attempt to settle the confused prohlem of atomic weights. At that meeting Stanislao Cannirnaro (18261910) showed how Avogadro's h.wothesis made i t possible to distinguish between-atoms a"d molecules. The idea was quickly accepted and the difference between atomic and molecular weights clearly recognized. The ideal gas law could now be written P V = nRT. I t was recognized that real eases deviate from ideal hehavior, and vari&s efforts were k a d e to express this quantitativelv. Johannes D. van der Wads (1837-1923) (no. 5) enunciateh his famous equation of state in 1873.~1tho"~hthe equation is not as accurate as several others, i t has the virtue of using very clear physical reasons to explain deviations from idealitv. Stamp no; 5 is exceptionally interesting. It has a portrait of twn 1910 Nobel Prize winners: Otto Wallach (1847-1931) (left), who received the chemistry award for his work on aliphatic substances, and van der Waals, who received the physics award. Beneath their pictures is an open laboratory notebook. Notebook entries are shown in such fine print that maenification is needed toread them. On the left-hand naee. .-. unier Wallach's picture, is the structural formula for camphor. The right-hand page, under van der Waals' picture, shows P - V isotherms for a real gas, including the liquid region, and below them is his famous equation. In the latter half of the 19th century the KineticMolecular Theory as we know i t was being formulated, primarily by James Clerk Maxwell (1831-79) (no. 6). Ludwig Boltzmann (1844-1906) (no. 7), and Rudolf Clausius (1822-88). Again the model was simple and straightforward: a gas consists of a large numher of particles whose dimensions are small compared to the distances between them and the size of the container. These particles are in continuous, random motion, and the collisions are perfectly elastic and follow the
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686
Journal of Chemical Education
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laws of ordinary mechanics. A further postulate is that the average kinetic energy is proportional to the absolute temperature. From these simple postulates a truly remarkahle set of results was obtained. I t was possihle to calculate the pressure, the mean free path, . . the numher of collisions per second, the viscosity, the rate of diffusion, the thermal eondurtivity, and still other quantities. The very important question of the distribution of molecular speeds and velocities was given by the Maxwell-Boltzmann equation (18591. One of the consequences of the Kinetic Molecular Theory is that the rate of effusion of a gas through a small hole can he calculated. Theory shows that, for a fixed temperature and pressure, the rate is inversely proportional to thesquare root of the molecular weieht. Thomas Graham (1805-69) had shown this experimentally as early as 1829, so i t is termed Graham's Law. It provides a means to separate molecules on the basis of their mass and has been of great importance. William Ramsay (1852-1916) (no. 8) and Morris Travers (1872-1961) used i t to isolate helium from other gases. John Strutt (that is, Lord Rayleigh as he is universally known in scientific circles. 1842-1910). (no. 9) and Ramsav . used it to separate argon partially from nitrogen. They w& the 1904 Nohel Prizes in Physics and Chemistry, respectively, fnr isolating the raregasesand showing where they belong in the Periodic T a h l ~The . formula of ozone. 0 2 . was first established from effusion experiments, and &e atomic weieht of radon was found that wav. In more recent times effGsion was used to separate the &anium isotopes, uranidiffusion plant a t um-235 and uranium-238, in the gaseous Oak Ridge. In 1879 Ramsay gave the first kinetic interpretation of Brownian motion. This led to kinetic theories of the effect hy Albert Einstein (1879-1955) in 1905 and Marian Smoluchowski (1872-1917) in 1906. Einstein (no. 10) showed that small particles suspended in a liquid should follow the gas law5 dean Perrin (1870-1942) (no. 11) made experimental measurements on such systems that confirmed Einstein's re dictions and that in 1909 eave the first reliable exnerimental value for Avogadro's number. He obtained 6.8 x iOz3; the present value is 6.022 X lon. The Kinetic Molecular Theory of gases4 had had many other ramifications. It gives the coefficients of viscosity, diffusion, and thermal ionductivity in terms of molecular diameters. Measurements of these properties gave early exnerimental values for molecular radii. T h e v a r e crude hv today's standards, but they were important at the time be"cause they showed the approximate size of a molecule. The Kinetic Molecular Theory has also been applied to the calculation of ahsolute rates of easeous chemical reactions. based in part on the frequency of collisions. In summary, the Kinetic Molecular Theory has provided a straightforward, easily visualized physical model that bas been immenselv prolific and useful. This model can he presented as a teach& tool by using a modest numher of postage stamps.
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The word "gas" was coined by Jan Baptista van Helrnont (15771644) (no. 12). He thought that vapors are in complete chaos and
around 1620 named them that. However, he gave "chaos" its phonetic spelling in Flemlsh, and the result was "gas". The word was ignored for 150 years, but was reintroduced by Lavoisier.
