PHENOMENA OF MOTION 51 



concerning the laws of gases and the movement of colloidal particles 

 have essentially agreed in showing that the laws of gases proved 

 applicable to very dilute solutions of hydrophobe colloids and con- 

 versely, that the laws of gases could be developed from the move- 

 ments of colloid particles. BOYLE'S law asserts that the volume (v) 

 of a gas is inversely proportional to the pressure (p) exerted upon it : 

 v : v' = p f : p. According to GAY-LUSSAC'S law the volume change 

 of a gas having the temperature (t) is v = v (1 -f- at) in which v is 

 the volume at and a. is the coefficient of expansion. From the 

 standpoint of molecular kinetics under doubled pressure twice as 

 many moving particles are present in the same space. With increase 

 of temperature (assuming the same pressure) at times fewer parti- 

 cles are present than in the same gas volume at 0. This assumes 

 average values, though in fact, the number of particles in a definite 

 volume varies from moment to moment. If this assumption is correct 

 the average of the "instant values" must give values which sat- 

 isfy BOYLE-GAY-LUSSAC'S law. M. VON SMOLUCHOWSKI developed 

 mathematically the relation between this law and the " instant 

 values." He obtained experimental verification when TH. SVEDBERG 

 counted the number of particles for an " instant value" directly in 

 the ultramicroscope and R. LORENZ counted the particles in cine- 

 metagraphs of the ultra-microscopic field. The assumption also 

 bridges the gap between Thermodynamics, which studies phenomena 

 on the basis of the involved energy and its transformations, and the 

 Kinetic Molecular Theory, which views matter as the smallest possible 

 particles in motion. 



The impact that our ultramicroscopically visible particles exert 

 against the walls of a vessel is the pressure they exert, and it is 

 measurable for a molecularly dispersed system as the osmotic 

 pressure. 



The osmotic pressure, a function of the mass and motion of a sus- 

 pension whose particles are visible and measurable, was shown by 

 J. PERRIN to coincide with the requirements of the Kinetic Theory 

 of Gases and of Thermodynamics; that is, with its energy content in 

 the form of heat. 



The following considerations make this clear. Under the influence of gravity 

 the lower layers of the atmosphere have a greater density than the upper; i.e., 

 the number of gas particles (molecules) in 1 cc. is greater in the immediate 

 vicinity of the earth than at higher altitudes. This applies not only for gases 

 but also for solutions or suspensions. 



J. PERRIN prepared a very fine suspension of gamboge which he placed in a 

 tall cylinder. Gradually under the influence of gravity an equilibrium developed 

 in which there was dense suspension at the bottom of the cylinder with gradually 

 diminishing concentration of particles in the upper layers an atmosphere in 



