]4 REMARKS ON COMBUSTION. 



either, 1 . water, or 2. an acid, or 3. a metallic oxide. It is 

 true indeed, that other bodies fometimes make their appear- 

 ance during combuftion, but thefe will be found upon exa- 

 mination not to be products, nor to have undergone com- 

 buftion. 



Thus one of the two characteriftic marks which diftinguifli 

 combuftion, namely, the apparent wafte and alteration of the 

 combuftible body, has been fully explained. For the expla- 

 nation of it we are indebted to Lavoifter. It conftitutes 

 what is ufually, but abfurdly, termed the neiv theory of die- 

 miftry, and is the moft important ftep which has been made 

 towards a complete theory of combuftion, 

 Facility of com- But though the combination of the combuftible with oxigen 

 ro ortioned to ^ e a con ^ ant P art or combuftion, yet the facility with which 

 the attraction combuftibles burn is not proportional to their apparent affinity 

 for oxjgen. £ or ox jg en# Phofphorus, for inftance, burns more readily 



than charcoal ; yet charcoal is capable of abstracting oxigen 

 from phofphorus, and of courfe has a greater affinity for it. 

 The combuftible oxides take fire more readily than fome of 

 the fimple combuftibles; thus charcoal burns more eafily than 

 carbon or diamond : alcohol, ether, and oils, are exceed- 

 ingly combuftible, whereas all the metals require a very high 

 temperature when the fupporter is air. This greater com- 

 buftibility of combuftible oxides is probably owing to the 

 But chiefly de- weaker affinity by which their particles are united. For the 

 ^rt^of^eftroy- cone ^ on °f heterogeneous particles, when oxigen conftitutes 

 ing the cohe- a part of them, is ufually weaker than the cohefion of homo- 

 fion * geneous particles. Hence they are more eafily feparated 



than homogeneous particles, and of courfe combine more rea- 

 dily with oxigen ; thofe fimple combuftibles which melt ea- 

 fily, or which are in the ftate of elaftic fluids, are alfo very 

 combuftible, becaufe the cohefion between their particles is 

 eafily overcome. 

 Hence compound It is owing to the fame inferiority in the cohefion of hete- 

 fupperters are rogeneous particles, that fome of the compound fupporters 

 burned. occafion combuftion in circumftances when the combuftibles 



would not be acted on by fimple fupporters. Thus phofpho- 

 rus burns in air at the common temperature ; but it does not 

 burn in oxigen gas, unlefs the temperature exceed 90°. In 

 oximuriatic acid gas phofphorus burns rapidly at the common 

 temperature of the air, and fo do feveral of the metals; 

 4 though 



