Mr. J. A. Wanklyn on Vapour -densities. Ill 



The change from solid to liquid and liquid to gas, is admi- 

 rably represented by a top in its three states of simple rotation, 

 of eddying round in an orbit as well, and of flying off still spin- 

 ning at a tangent, the taps which cause these changes in a top 

 being, in the case of molecules, represented by application of heat. 



It has been assumed throughout that a molecule is spherical 

 or spheroidal, and that a force only when acting has effect on a 

 molecule. The former assumption perhaps scarcely admits of 

 proof, but is in keeping with the fact that the heavenly bodies 

 as well as the smallest natural divisions of organized matter are 

 globular. The latter is a natural view to take ; for though the 

 effect of a force is exhibited by a mass after it has ceased to act, 

 e. g. of pressure on a plastic hody, yet this is owing to the inertia 

 and cohesion of the mass, properties due to molecular motion, as 

 has been shown, and which there is no reason for thinking belong 

 to molecules. Liquids and gases have not inertia, their mole- 

 cules having lateral movement, and a force has no permanent 

 effect on them, which confirms this view. In addition to these 

 proofs, the mind cannot but be influenced towards the acceptance 

 of such a theory as the above by its simplicity, by its yielding a 

 rational explanation of such phenomena as inertia and cohesion, 

 instead of calling them properties of matter, and by the harmony 

 to which it points between the motion of the minutest portions 

 of matter, and of those grand globes which perform their majestic 

 movements in space. 



XVIII. Note on Vapour- densities. — A Reply to M. H. Ste. -Claire 

 Deville. By J. Alfred Wanklyn*. 



IN the Uomptes Rendus, vol. lix. No. 26 (December 26th, 1864), 

 M. Deville renews the discussion of the vapour- density of 

 chloride of ammonium. Having repeated his experiment of 

 bringing together hydrochloric acid and ammonia at the tempe- 

 rature of boiling mercury, he concludes that these gases enter 

 into combination at that temperature with evolution of heat, but 

 not of so much heat as would result if the entire quantity of 

 ammonia and hydrochloric acid had entered into combination. 

 Before examining the account which M. Deville gives of his last 

 experiment, I will make the remark that this conclusion is in 

 itself nowise opposed to the theoretical views respecting vapour- 

 densities entertained by so many eminent chemists. 



The doctrine of the correspondence between molecular weight 

 and vapour-density does not require that the vapours given off, 

 on exposing chloride of ammonium to the heat of boiling mer- 



* Communicated by the Author. 



