378; 



Mev. Mr, Emmett on the 



[Nov.: 



in which »^ is tfeie weight of the metal ; n, that of oxygen ; a the 

 specific gravity of the metal, and c the specific gravity of the 

 compound, trom this the reason is evident, why the oxygen 

 in some oxides, as that of mercury, ffold, silver, the peroxide of 

 lead, is highly energetic, whilst in others, as protoxides of iron, 

 manganese, potassium, &c. its power as a supporter of com- 

 bustion is scarcely sensible. The coilclusions here drawn 

 depend not upon any hypothetical views ; they are merely de- 

 ductions from observed phenomena : I have no desire to insti- 

 tute any researches into the nature of electricity or gravity ; 

 because in all probability we shall never know mote of them than 

 we do at present ; and if known, perhaps science would receive 

 but little benefit from the discovery ; I have endeavoured 

 simply to ascertain, from phenomena, their relative effects as 

 chemical agents. Another law of chemical action merits at- 

 tention : in general, a simple substance will not combine with 

 a compound. No simple substance is soluble in water ; the 

 small quantity of oxygen, hydrogen, or azote that is frequently 

 found, cannot be regarded as cnemically united. Chlorine is 

 soluble : but its elementary nature is very doubtful ; it certainly 

 has never been proved ; its high atomic number is against the 

 idea ; for, the metals excepted, together with iodine, which is 

 in the same predicament as chlorine, elementary, or rather un- 

 decompounded substances, have very low numbers. The solu- 

 tions of sulphur and phosphorus in oils or ether, or the sulphu- 

 rets of alkahs are not exceptions, because decomposition ac- 

 companies^ the solution. There are certainly triple compounds, 

 particularly in animal and vegetable substances, which seem to 

 be exceptions ; but this is a class of phenomena of a different 

 nature ; three atoms of different substances may be combined, 

 as in the prussic acid ; but we find that generally a simple or 

 undecompounded substance cannot be united directly to one 

 that is compound. It is of importance to determine experi- 

 mentally, the law of repulsion in gases ; two gaseous particles 

 repel each other with a force which is very nearly as the dis- 

 tance inversely (Newton's Principia, lib. 2, pi^op. ^3u) ^^^^^jg 

 the aggregate efiect of the force . liLot ydj rr^d ^ 



between the particles, but it is yfn, 



not the variation in the elastic -^^^ ^« bd&Baion 



force of the calorific atmosphere. 

 Let P and p be two particles of a 

 gjEM^_,bisect P/? in A ; and through 

 A pass' a plane D A H, perpendi- 

 cular to P7?, which divides the 

 calorific atmospheres, and there- 

 fdt^'m which th« repulsive force 

 id' exei'ted. Take E indefinitely 

 near to D; join PD, PE ; and with the centre 



A and fadii 



