226 ^ IGNITION FROM COMPRESSED AIR. 



as a thing proved^ acquires more probability from the following 

 experiments*. 

 Trials, with I substituted hidrogen for common air, and the vapour 

 other gasse8. si^owed itself as before ; but the spunk did not take Ere. With 

 carbonic acid gas, and with nitrogen the effects were the same. 

 The latter, which contained a little nitrous gas, gave a some- 

 what denser vapour, Oxigen, lightly compressed, yielded a 

 vapour more rare and transient than that from common air. It 

 had scarcely fallen on the piston, when it rebounded and dis- 

 appeared. When I compressed oxigen with a proper force for 

 producing inflammation, the spunk, which commonly takes fire 

 only at the anterior part, was almost entirely burned : yet 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]. 

 The vapour Perhaps it will be said, that the vapour came from the greasy 



cannot arise matter on the piston, which adheres to the sides of the tube j 



Kre?.seenu)loy- ^"'^ *^^^^ '*• ^^ ^^P'*"'^^^ ^y ^^^^ ^^^^'^ produced by the friction. 



fd. To this I answer, in this case, 1st. The vapour should not show 



itself before the greasy matter is deposited 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 ; but, on the con- 

 trary, it always shows itself above. 3dly, There is no vapour, 

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

 4ibly, The vapour should be more apparent, when the piston 

 exerts its friction throughout the whole length of the tube, 

 than when it is confined to a small part of its upper extremity ; 

 yet the reverse frequejitly happens. 5thly, When the air is 

 entirely decomposed no mere vapour appears, but it shows 

 itself again, if ever so little fresh air be introduced. 



It contains no ■^■'' ^^ ^^^ <3sseniial to ascertain whether the vapour did not 



i»cid. contain an acid principle, I fastened to the surface of the pistod, 



with a little green wax, a piece of muslin dipped in infusion of 

 litmus, and afterward dried. After twenty strokes of the pis- 

 ton the colour was not changed. I put on a second piece of 

 muslin larger than the first, and the edges of which were loose. 



* Ml'. De Luc ascribes the ignition to the condensation of the matter 

 of heat. See Joarnal, vol. XXI, p. L'34.-.C. 



This 



