278 Mr. J. J. Waterston on the Application of the Vapour-density 



potash, which stands red heat without change or giving off one 

 particle of steam ; but it is not likely that this argument has 

 now much weight with chemists who agree with him otherwise 

 because the intense heat given out during the union of the water 

 with the oxide shows that a high degree of chemical action has 

 taken place between them, and it cannot be expected under such 

 circumstances that the physical characteristics of the water- 

 molecule should be retained. The only way I can imagine the 



idea H 2 O 2 K 2 to have taken root is from incompleteness in the 

 conception of a compound molecule as an absolute entity. There 

 is at least one distinct case where a compound molecule splits up 



like a simple molecule, N 2 C 2 appearing in compounds, but un- 

 known in a separate form. There is also the organic proteus 



CH 2 , which not only divides into two, C 2 " H, which does not exist 

 in a separate form, but also appears in an indefinite number of 

 multiple forms. There may be others, too ; but no one upholds 



the possibility of HO 2 being divisible into two atoms, H 2 ¥ , or 

 KO* into two, K* OK; for although IF, K* undoubtedly exist, 

 ¥ is not admitted even by the new school. The idea of sub- 

 stitution-equivalent which suggested and now upholds H 2 O 2 K 2 , 

 implies 2 as the ultimate atom of oxygen, and K 2 as the substitute 



for H 2 in HO 2 . The vapour-density of caustic potash cannot 

 be measured; but in coming to a decision as to whether the 



molecule of caustic potash is H 2 O 2 K 1 or HO K, it is well to 



keep in view that the K in KO 2 and the H in HO 2 must be 

 decomposed in the former case, and not in the latter. There is 

 also to be considered the intensity of the force that unites the 

 molecules of the oxide together : their cohesion-integral must be 

 very great, since the heat of a wind-furnace liquefies it, but does 

 not volatilize it. "We have an idea of the dynamic value of the force 



that unites the K with O 2 , from the heat of combustion evolved 

 in burning K. In the production of water from the union of 

 H with O 2 to form HO 2 steam, and the union of HO* with 

 HO 2 , HO 2 ", HO*, &c. to form water HO*. HO*. HO*. &c, the 

 dynamic value of each of these two forces has been measured, 

 and the ratio of the chemical to the cohesive integral found to 

 be about 7 to 1. There are cohesive affinities of vast potency as 

 well as chemical ; and we have to consider whether it is more 

 probable that, when water and the oxide are brought into con- 

 tact, the heat evolved (which indicates molecular force expended) 

 is due to cohesive affinity between KO* and HO*, or to chemical 



