COLLISION OF STEEL WITH HARD BODIES. 1Q3 



VII. 



Oqfervqtioiv! on the Appearances produced by the Collifion of Steel 

 with Hard Bodies. By Mr. Davy, Lecturer on Chemijlry 

 at the Royal lujlitution *. 



I. IVlR. HAWKSBEE long ago (hewed, that no fparks Hawkft > ee 'sexp. 

 could be produced by the collifion of flint and ft eel + in the in vacuo . 

 exhaufted receiver of an air pump, and that in this cafe a faint 

 light only was perceived. And, iince his time, the fame ob- 

 servation has been very often made. 



The developement of the theory of combuftion has clearly Sparks thus pro- 

 fhown that the vivid fparks obtained from fteel in the atmof- JJJ n "^ com" 6 

 phere, are owing to the combination of the fmall abraded and buftion of the 

 heated metallic particles with oxigen. But it has been a mat- ee • 

 ter of doubt whether, in the experiment made in vacuo, the 

 faint, luminous appearance is owing wholly to the light pro- 

 duced by the fracture and abrafion of the parts of the flint, or 

 only partly to this caufe, and partly to the ignition of the mi- 

 nute filaments feparated from the fteel. 



II. I have often found, that when a fine and thin flint, Light in vacuo 

 which may be eafily broken, is ufed for the collifion in vacuo, with°athin Aaro 

 the light is much more vivid than when a thick and ftrong one flint. 



is employed : and with a ftrong flint, but juft fliarp enough to 



give fparks with fteel in the atmofphere, it is feldom that any 



light at all is produced in the exhaufted receiver. Thefe facts The collifion 



feem to (hew that the abraded particles of fteel are not ren- t h e fteel red hot. 



dered at all luminous by collifion, except in confequence of 



combuftion ; and the opinion is almoil fully proved by the 



following experiment, which was made in the courfe of a 



lecture on the properties of light, in the theatre of the Royal 



Inftitution, and which has been flnce often repeated. 



III. A thin piece of iron pyrites J (fulphuret of iron) was Pyrites in ftead 

 inferted in a gunlock in the place of the flint. It gave bynj^*™ ™ 



* Journal of the R. I. 264. ■• * 



f Philofophical Tranfaaions, Vol. XXIV. p. 2165. 



% The etymology of the name of this fubftance {hews that its 

 property of giving fire by collifion was very anciently known. It 

 was ufed in the old gunlocks, with the revolving wheels for in- 

 flaming the priming. 



collifion 



