MOLECULAR WEIGHT AND POLYMERISM 



under the same temperature and pressure, contain equal 

 numbers of molecules, and therefore the molecular weights 

 of the gases are in proportion to the weights of those 

 volumes. 



The law in question, which, when first stated, was a happy 

 combination of known facts, received confirmation in that 

 it allowed of predicting new ones, such as the dissociation 

 of ammonium chloride on volatilization. But it may also 

 be deduced from the kinetic theory. As we shall bring 

 forward the confirmations of the law later, under the head 

 of 'results/ we will here begin with its theoretical 

 deduction. 



The kinetic theory of gases, treating gases as consisting 

 of small, perfectly elastic spheres, involves Avogadro's law 

 as the limiting case of extreme dilution. When the 

 dilution is sufficiently great, the attractions between the 

 molecules cease to be of account, and the volume of 

 the molecules may be neglected in comparison with the 

 total volume occupied by the gas. The deduction of 

 Avogadro's law from the kinetic theory in the general 

 case is complicated, and for the purpose of this work it 

 is sufficient to follow it out under special simplifying 

 circumstances. 



In the first place, for simplicity it may be assumed that 

 the velocity of all the molecules is the same, viz. metres 

 per second. Secondly, that the 

 movement inside the cubical 

 vessel of V cub. metres ca- 

 pacity (Fig. i) that we shall 

 consider, is so distributed that 

 the molecules move only at 

 right angles to the bounding 

 planes, and equally so, there 

 being always one-sixth of the rio . 



N molecules moving forwards, 



backwards, right, left, up, or down. Hence there strike 

 unit surface (one sq. metre) in unit time (one second), one- 



B 



