432 Rev, Mr» Emmett on Combustion, [Dec. 



ive order in the galvanic series, or in the order of the force of 

 gravity. 



The order of inflammability with regard to oxygen is nearly 

 inversely as the atomic capacity : the capacity of gold is lO'O, 

 silver 8*8, copper 7*04, lead 4-1 6, tin 4*06, iron 3*64, zinc 3-4, 

 charcoal \'5b, and oxygen being the supporter, those bodies 

 which have the least atomic capacity have the most powerful 

 attraction for it, and evolve most heat during combustion; 

 whilst oxygen seems to have the greatest atomic capacity of 

 all known bodies. 



Since heat is evolved whenever condensation takes place, and 

 since when the combination of two or more bodies is attended 

 with condensation, heat is evolved, if we consider every such 

 case as an example of combustion, provided heat and light are 

 both evolved, we recognise only one general law applicable to 

 every case of chemical union, one extreme of which is termed 

 combustion ; i. e. that where their electric states or forces of 

 attraction are most remote from each other ; or rather when they 

 differ most from some one substance, on either side, positive or 

 negative, whose force with each is to be compared according to 

 the electro-chemical law of Sir H. Davy. 



Some cases of combustion are accompanied with flame, as in 

 the example of sulphur, phosphorus, potassium in oxygen ; 

 others are not, as that of iron wire in oxygen gas ; bismuth or 

 antimony powder in chlqrine. Here again we may trace the 

 operation of a general law. When any part of the combustible 

 is volatilized, the combustion of its vapour produces flame ; if 

 not, flame is wanting. If a large flame be made by burning 

 pitch or resin, a large reddish- white flame is produced; if a 

 large flame of defiant gas be examined, the flame is whiter, yet 

 red at the top ; if the common carburetted hydrogen gas be used, 

 the flame is less brilliant ; if pure hydrogen, yet paler, and paler 

 in proportion to the purity of the gases ; so that if the oxyhy- 

 drogen blowpipe be used, the flame is faint and small. Newton 

 (who, as was said of him, could see more clearly through a mist 

 than others through a microscope) said, " Flame is vapour 

 heated red-hot." Now if we examine the matter fairly, we shall 

 find that he was not far from the truth. If much of the inflam- 

 mable body, if solid at a high temperature, as carbon, be volati- 

 lized, as in the case of resin or pitch, the flame is brilliant, owing 

 to the combustion of the volatilized particles ; but owing to their 

 excess (for much soot is deposited) the flame is red. In a large 

 flame of defiant gas, less soot is produced, and the flame is 

 whiter. In the case of common carburetted hydrogen gas, httle 

 or no carbon is deposited, and the flame is whiter : below this 

 limit, the flame becomes paler; so that when very pure oxygen 

 and very pure hydrogen gas are used, the flame is very pale ; 

 and the purer the gases, the paler the flame. Hence then it 



