on the Steam Engine. ; 3 329 
such steam would be 0°; but its elasticity would be prodigious. The 
instant that the pressure upon it was removed, it would expand, and 
its latent heat would increase at the expense of its sensible heat: It 
isobvious from this that the existence of latent heat in steam is owing 
to its expansion, and that the moment we reduce it to the bulk of 
the water from which it was generated, all the iia heat becomes 
sensible.”* 
5. Steam has certain remarkable and anomalous’ properties when 
brought into contact with a highly heated surface. 
Ifa polished spoon of iron be taken and heated to a white heat, and 
adrop of water be let fall upon it, the drop divides at first into several 
smaller ones, which, however, speedily unites This if it be closely 
observed, willbe seen to have acquired a rotary motion ; it continual- 
ly decreases in bulk and finally explodes. A second anda third drop 
exhibit the same phenomena, but the continuance of the drop upon the 
metal becomes less and less as the latter cools. While the first drop 
Temained forty seconds, the third remained only six seconds, and the 
sixth evaporated instantly. 
- Perkins has recently observed similar phenomena in the generator 
of his engine. This vessel being heated red hot while empty, water 
Was admitted. The elastic force “of the vapor, was at first but small, 
and increased eres as the temperature ars the generator was dimin- 
ished, —pp.- 
- Having now adel the toast properties of steam, we are pre- 
pared to consider the methods of insuring safety i in the use of this 
powerful agent. 
ose tremendous explosions which occasionally afford such mel- 
ancholy proofs of the dangers with which the steam engine is en- 
Compassed, arise from the energy inherent in the moving force it- 
seli—from a deficiency in the supply of water to the boiler—from 
the weakness of the material of which the boiler is‘constructed— 
from its becoming incrusted with saline and earthy mpeg pif from. 
what is called a collapsing of the boiler. 
More or less danger is always involved in the shel of pow- 
ers of great energy. The horse will sometimes grow furious and 
throw his rider ; winds become hurricanes and wreck the mariner ; 
Water wheels seize upon the manufacturer and tear him in pieces ; 
Powder-mills explode in spite of all the vigilance of man. _Wherev- 
iy ne ee eee EN ed 
* Outlines of the dic and Electricity, p. 231. 
® 
