CHEMICAL SCIENCE. 243 



Of this class of facts, to none has more interest attached than to the 

 recent experiments of Boutigny with molten metals. To him are 

 \ve indebted for the first scientific consideration of this subject, al- 

 though it appears that jugglers performed the feat of washing the 

 hands in molten lead many years ago, and the act of plunging the 

 bare hand into molten iron is an experiment which has been performed 

 by furnace men in this country for at least twenty years. In one in- 

 stance, the feat of plunging the hand into a pot of melted iron, and of 

 placing a red-hot iron upon the tongue had become so common, as to 

 cease to excite curiosity. In the experiment of passing the fingers 

 into molten iron, which I have repeatedly performed without the 

 slightest discomfort, it is necessary only, as noticed by Boutigny, that 

 the surface of the skin should be wet, or covered with some body like 

 powdered resin, which upon the application of heat will readily 

 vaporize. That the experiment may be safely performed, any one 

 may satisfy himself, by passing through the molten mass any highly 

 combustible substance previously moistened. It will not be affected 

 by the heat. The experiment with melted lead is less satisfactory 

 than with molten iron, because the temperature is lower; it will, 

 however, satisfactorily show the character of the phenomenon. 



When the hand is passed into the liquid metal, the vapor is vapor- 

 ized, interposing between the metal and the skin a sheath of vapor. 

 In its conversion into vapor the water absorbs heat, and thus still fur- 

 ther protects the skin. The explanation of Berzelius, offered some 

 years since, and confirmed by all the experiments, so far as I know, 

 that have ever been performed, is the following. In the Leidenfrost 

 experiment a layer of vapor continually evolved from the inferior 

 surface of the liquid provides an aeriform medium which does not 

 conduct, but merely transmits, radiant heat, which, passing through 

 the liquid, as through most transparent substances, heats it but slight- 

 ly. Thus evaporation is slow. The temperature of the liquid, it is 

 well known, remains constantly below that of the boiling point. This 

 accounts for the much greater length of time required for water tc 

 evaporate when resting upon an oiled surface, than when in contac 1 

 with wood or metal ; and for the length of time that dew-drops on 

 spiders' webs will sustain exposure to the air, when compared with 

 that which would be required to evaporate an equal quantity of water 

 from a leaf surface, where there is actual contact, and where conduc- 

 tion makes it take place. 



The explosions sometimes following the first contact of a piece of 

 potassium with water are due to the admixture of evolved hydrogen 

 and atmospheric air. The explosion at the conclusion of the experi- 

 ment is of another character. It is due to the sudden contact of the 

 hydrate of potassa with the water, when the temperature has become 

 sufficiently low to permit it, and is analogous to the phenomena wit- 

 nessed when the surface supporting a mass of water in a spheroidal 

 state is permitted to cool down until contact takes place. The explo- 

 sions occasionally witnessed when large quantities of fused saltpetre 

 have come in contact with water, are of this description. The explo- 

 sions of steam-boilers have recently, in several instances, been ascribec 



