on the Steam Engine. 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 

 is obvious 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 latent heat becomes 

 sensible."* 



5. Steam has certain remarkable and anomalous properties when 

 brought into coptact with a highly heated surface. 



If a polished spoon of iron be taken and heated to a white heat, and 

 a drop of water be let fall upon it, the drop divides at first into several 

 smaller ones, which, however, speedily unite. This if it be closely 

 observed, will be seen to have acquired a rotary motion ; it continual- 

 ly decreases in bulk and finally explodes. A second and a third drop 

 exhibit the same phenomena, butthe continuance of the drop upon the 

 metal becomes less and less as the latter cools. While the first drop 

 remained 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 rapidly as the temperature of the generator was dimin- 

 ished.— pp. 73, 74. 



Having now reviewed the leading properties of steam, we are pre- 

 pared to consider the methods of insuring safety in the use of this 

 powerful agent. 



Those 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- 

 self — 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 matter — and from 

 what is called a collapsing of the boiler. 



Mo7X or less danger is alivciys involved in the employment of pow- 

 ^"^^ of gi'^at 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, Whcrev- 



* OuUines of the Sciences of Heat and Electricity, p. 231. 



