CHAPTER SEVEN.
THE SPHEROIDAL CONDITION OF LIQUIDS .-- WHY THE HAND MAY BE DIPPED IN MOLTEN METALS .-- PRINCIPLES OF HEAT-RESISTANCE PUT TO PRACTICAL USES: ALDINI, 1829 .-- IN EARLY FIRE-FIGHTING.

TEMPERATURES THE BODY CAN ENDURE.
The spheroidal condition of liquids was discovered by Leidenfrost, but M.Boutigny was the first to give this singular subject careful investigation.

From time out of mind the test of letting a drop of water fall on the face of a hot flat-iron has been employed to discover whether it may safely be used.

Everybody knows that if it is not too hot the water will spread over the surface and evaporate; but if it is too hot, the water will glance off without wetting the iron, and if this drop be allowed to fall on the hand it will be found that it is still cool.

The fact is that the water never touches the hot iron at all, provided the heat is sufficiently intense, but assumes a slightly elliptical shape and is supported by a cushion of vapor.