430 Ignition from compressed Air. 



oxygen with a proper force for producing inflammationj 

 the s])unk, which commonly takes fire only at the anterior 

 part, was almost burned: yft for this experiment I used a 

 copper instrument, the piston of which lost air so much, 

 that it would no longer kindle spunk with common air. 



Perhaps it will be said that ilie vapour came from the 

 greasy matter on the pislon, which adheres to the sides of 

 the tube ; and that it is expanded by the heat produced by 

 the friction. To this I answer, in this case, 1st, The va- 

 pour should not s-how itself before the greasy matter is de- 

 posited on the sides of the tube; yet it appears at the first 

 stroke of the piston, before the tube becomes greasy. 

 2dly, It should show itself below the piston, in the part 

 which the piston has left j but, on the contrary, it always 

 shows itself above, 3dly, There is no vapour, when the 

 piston loses much air, if the friction be ever so rapid, 

 4thly, 71ie vapour should be more apparent, when the 

 piston exerts its friction throughout the whole length of 

 the tube, thjin when it is confined to a small part of its 

 upper extremity; yet the reverse frequently happens. 5thly, 

 When the air is entirely decomposed no more vapour ap- 

 pears, but it shows itself again, if ever so little fresh air bs 

 introduced. 



As it was essential to ascertain whether the vapour did 

 not contain an acid principle, T fastened to the surface of 

 the piston, with a little green wax, a piece of muslin 

 clipped in infusion of litnius, and afterwards dried. After 

 twenty strokes of the piston the colour was not changed. 

 I put on a second piece of muslin larger than the first, and 

 the edjies of which were loose. This burned all round, 

 without the colour of the rest being altered. Lastly, a third 

 piece, which was wet, experienced no chapge of colour. 



From these experiments it folhnvs, that no acid princi- 

 ple is developed ; that all aeriform substances, as well as 

 common air, produce a light vapour: that no other gas, 

 except oxygen and connuon air, kindles the spunk : that 

 oxvRen produces a nvuch more powerful coiTibustion than 

 coiinnon air, consequently oxygen acts an important part 

 in the inflammation: that as it can exert its action only 

 when set fiee by the decomposition of the common air, of 

 which it constitutes a fourth part, it follows, that the air 

 contained in the tube is decomposed by the simple force of 

 compression : that the vapour produced is not owing to 

 the oxygen, since it shows itself etjually in gases that con- 

 tain no oxygen: that this vapour is the effect of some 

 ?.geat common to all gases : and that \v^ may presume it 



