364, Mr. Davy’s Electrochemical Researches on 
thesis, still the alkalies, the earths, and the metallic oxides will 
belong to the same class of bodies. From platina to potas- 
sium there is a regular order of gradation as to their physical 
and chemical properties, and this would probably extend to 
ammonium, could it be obtained in the fixed form. Platina 
and gold in specific gravity, degree of oxidability, and other 
qualities, differ more from arsenic, iron, and tin, than these 
last do from barium and strontium. The phaenomena of 
combustion of all the oxidable metals are precisely analogous. 
In the same manner as arsenic forms an acid by burning in 
air, potassium forms an alkali and calcium an earth ; in a man- 
ner similar to that in which osmium forms a volatile and acrid 
substance by the absorption of oxygene, does the amalgam of 
ammonium produce the volatile alkali ; and if we suppose 
that ammonia is metallized, by being combined with hydro- 
gene, and freed from water, the same reasoning will likewise 
apply to the other metals, with this difference, that the ad- 
herence of their phlogiston or hydrogene, would be exactly 
in the inverse ratio of their attraction for oxygene. In 
platina * it would be combined with the greatest energy ; in 
ammonium with the least ; and if it be separable from any 
* The common metallic oxides are lighter than their bases, but potash and soda 
are heavier ; this fact may be explained on either theory ; the density of a compound 
will be proportional to the attraction of its parts. Platina, having a weak affinity for 
oxygene, cannot be supposed to condense it in the same degree as potassium does ; 
or if platina and potassium be both compounds of hydrogene, the hydrogene must be 
attracted in platinaj with an energy infinitely greater than in potassium. Sulphuric 
acid is lighter than sulphur ; but phosphoric acid (where there is a stronger affinity) 
is heavier than phosphorus. The oxide of tin (wood tin) is very little inferior to tin 
in specific gravity- In this instance the metallic base is comparatively light, and the 
attraction for oxygene strong ; and in a case when the metal is much lighter and the 
attraction for oxygene stronger, it might be expected a priori that the oxide would be 
heavier than the base. 
