424 Ignition from compressed Air. 



It has been often suspected, that the contraction o^ 

 vohim'e produced in the pure earths bv heat is owing to 

 the expulsion of water combined uith them. The following 

 fact seems to confirm this suspicion, and offers a curioui 

 phs'nomenon. 



Zircona, precipitated from its solution in muriatic acid 

 by an allcali, and dried at a temperature below 300% appear* 

 as a white powder, so soft as not to scratch glass. When 

 heated to 700° or 800% water is suddenlv expelled from it, 

 and notwiihstaiidiug the quantity of vapour formed, it be- 

 comes at the moment red hot. After the process, it is 

 found h.irsh to the i'eel, has gained a tint of <;ray, its parts 

 cohere together, and it is become so. hard as to scratch 

 (Quartz. 



LXXV. On ike Construe lion and Effects of the Pneumatic' 

 Tinder-Box. By Le Bouvier Desmortiers*. 



JL HE inflammation of spunk f in the Pneutriatic Tinder- 

 box, by the compression of air alone, is a phaenomenoit 

 with which chance, the father of discovery, has lately en- 

 riched naiural philosophy. Many have reasoned on its 

 cause ; which some consider to be caloric, others electri- 

 city; but no one, that I know of, has attempted to sup- 

 port his opinion by experiments. Without bias for au\' 

 hypothesis, I have made seme researches on the construc- 

 tion and eflects of the pneumatic tinder-box, the results of 

 which shall be the subject of the present paper. In the 

 first part, I shall consider what relates to the structure of 

 the inslruHJcnt ; in the second, 1 shall give an account of 

 the experiments that tend to the discovery of the cause of 

 its effects. 



I. The first construction of these tinder-boxes was a 

 little faulty, in the j^iston being commoniy 18 or 20 lines 

 long. This was said to be necessary, that the air might 

 not escape when the piston was in action ; for, if there 

 were any point not accurately fitted to the inside of the( 

 tube, the air escapes, and the spunk does not kindle. 



The goodness of the instrument does not depend on thtf 

 length of the piston, but on the accuracy with which it fills 

 the bore of the tube ; with a tube well bored and a piston 



♦ Journal de Phys. torn. Ixvii. 



f Spunk is prepared troni agaric, which is first bf)iled in water i beptcn 

 ■Well wlien dry; steeped iu a strong solution of saltpetre; and lastly dried 

 in an oven. If the solution of nitri be too strong, iLe agaric is loadtd willi 

 tikit talt, wliich retardc its innunuu^iioa. 



•f 



