62 M. P. H. Boutigny on some facts relative to 



to six centimetres, which escaped by the tap, then I immedi- 

 ately plunged the other hand in a pot filled with incandes- 

 cent metal, which was truly frightful to look at. I invo- 

 luntarily shuddered. But both hands came out of the ordeal 

 victorious. And now, if any thing astonishes me, it is that 

 such experiments are not quite common. 



I shall of course be asked, what precautions are necessary 

 to preserve oneself from the disorganizing action of the incan- 

 descent matter? I answer. None; — only to have no fear, to 

 make the experiment with confidence, to pass the hand ra- 

 pidly, but not too rapidly, in the metal in full fusion. 



Otherwise, if the experiment were performed with fear, or 

 with too great rapidity, the repulsive force might be overcome 

 which exists in incandescent bodies, and thus the contact with 

 the skin be effected, which would undoubtedly remain in a 

 state easy to understand. 



To form a conception of the danger there would be in 

 passing the hand too rapidly in the metal in fusion, it will 

 suffice to recollect that the resistance is proportionate to the 

 square of the velocity, and, in so compact a fluid as liquid iron, 

 this resistance increases certainly in a higher ratio. 



The experiment succeeds especially when the skin is 

 humid ; and the involuntary dread which one feels at facing 

 these masses of fire, almost always puts the body into that 

 state of moisture so necessary to success; but by taking some 

 precautions, one becomes veritably invulnerable. The fol- 

 lowing is what has succeeded best with me : I rub my hands 

 with soap, so as to give them a polished surface ; then, at the 

 moment of making the experiment, I dip my hand into a cold 

 solution of sal-ammoniac saturated with sulphurous acid, or 

 simply into water containing some sal-ammoniac, and, in de- 

 fault of that, into fresh water. 



Regnault, who has occupied himself with this subject, says, 

 " Those who make a trade of fire handling and holding it in 

 the mouth, sometimes employ an equal mixture of spirit of 

 sulphur, of sal-ammoniac, of essence of rosemary, and onion- 

 juice." All volatile substances, we see, which, in evaporating, 

 render a certain portion of heat latent. 



Let us now seek the rational explanation of these facts. 



We have the formula m, c t^ which gives the quantity of 

 heat contained in any body. 



Let m be the mass expressed in kilogrammes, 

 c the specific heat of the body, 

 t its temperature. 



But here the factor m must be abstracted, because there is 

 no contact between the hand and the metal in fusion, and the 



