672 TRANSACTIONS OF THE 



instantaneously decomposed, generating an explosive gas which 

 rends the boiler. Not such is my opinion. Explosion takes 

 place in this v/ay : solid bodies absorb heat and increase in tem- 

 perature. Water, under ordinary ch-cumstances, does not. Un- 

 der pressure it does so slowly, and to a limited degree, and so 

 far refuses to convert itself into vapor, liolding itself in readiness 

 to do at once, in any sudden change of circumstances, then it 

 becomes an auxiliary in explosions. 



Steam, however, does readily absorb heat; and while the steam 

 escapes freely, either by use or sufleraiice, danger is avoided. If 

 this uniform issue is checked, the fire being still in force, addi- 

 tional temperature must ensue somewhere, and this goes, in the 

 main, to the steam. So soon as the issue of steam ceases, the 

 water assumes a state of comparative quietude, and the more as 

 the pressure above it increases. In this state I can conceive the 

 particles of steam to be held in suspension throughout the water 

 itself I said that the water is in a state of rest, and for the rea- 

 son that it has attained a temperature throughout of at least 

 202*^, and the specific gravity become uniform. Philosophy tells 

 us that as the temperature of steam increases, its previous latent 

 heat becomes sensible heat. Here the natural equilibrium has 

 been again destroyed, and is preparing an infinity of force for 

 reaction whenever the inflexible law belonging to lesser tempera- 

 ture comes into action. The commotion that takes place on the 

 opening of the supply pipe brings the superheated steam in con- 

 tact with the water, for which it has an extraordinary affinity, 

 and instantaneously an immense quantity of steam is generated, 

 which no shell or covering can resist. 



Much reliance is placed on the safety-valve, as it is supposed 

 that this will give issue to the steam at a fixed pressure within 

 the limit of safety. But temperature and pressure do not increase 

 in like ratio, in other words the former temperature will have 

 very materially increased, without indication of much increase 

 of the latter; then there is the difference between static and dy- 

 namic forces; a quiet pressure is a very different thing from one 

 to which velocity has been imparted. 



Explosions then result ordinarily, not denying that the heat- 

 ing to redness may be an auxiliary, from the instantaneous ab- 

 sorption of the excess of heat pervading the water and steam 

 chambers. There does not appear to be a totally safe relief ex- 

 cept through radiation and drawing of the fire, for commotion or 

 excitement of the water should be most cautiously avoided. To 

 open the supply pipe is most dangerous. 



