Perkins'' Steam Engine. 55 



artificial pressure would be taken off, and the water would 

 rise with the steam in proportion to the suddenness and ra- 

 pidity of its escape. The water and steam in this mix- 

 ed state, thus filling every part of the boiler, the excess of 

 caloric in the surcharged steam, as well as the extra heat 

 from the boiler, will be instantly taken up by the water which 

 rises with the steam, by which means the steam becomes 

 sufficiently dense (or powerful) to produce the fatal effects 

 too often experienced, not only from high, but from low 

 pressure boilers. If for instance, the water (as has before 

 been noticed,) should be suffered to get below any part of 

 the boiler, which is exposed to the fire, the steam will soon 

 become surcharged with heat. If a boiler, thus circumstan- 

 ced, should have the weight taken from the safety valve,* or 

 a small rent be effected in the boiler from its giving way by 

 the pressure of the steam, an explosion will be sure to fol- 

 low. A remedy for this kind of explosion, which appears 

 to be the only serious one, is that of not allowing the water 



* It was stated in evidence at the coroner's inquest taken at the 

 Humber, in the case of an explosion on board of the Graham steam 

 boat, that just before the explosion took place, twenty pounds were 

 taken off the safety valve. Now, if the steam in this boiler had been 

 properly generated, the relief given to the safety valve, could not have 

 produced explosion ; but if the water had got low in the boiler, (as 

 was probably the case,) and the steam surcharged with heat, the ready 

 way to produce explosion, was to allow the steam to escape faster than 

 it was generating, when kept in the lower part of the boiler by the pres- 

 sure of the confined steam. 



Several instances have occurred when there has been sufficient war- 

 ning, by the rushing of the steam from a rent or fracture, for the by- 

 standers to escape from injury before the explosion took place. There 

 has been, at least, one case, where tho boiler was raised from its bed, 

 into the air, by the force of the steam issuing from the rent, (upon the 

 principle of the rocket,) before the water had sufficiently expanded by 

 the removal of the steam, caused by the rent or fracture, to take up 

 the heat of the boiler, and the surcharged steam ; when an explosion 

 took place after the boiler had been raised many feet in the atmos- 

 phere, and it separated with a very great report, one part rising still 

 higher, while the other was dashed with great force on the ground. It 

 is, I believe, a fact, that more persons have been killed by low, than by 

 high pressure boilers. 



It is but about twelve months, since sixteen persons were killed by 

 the bursting of a low pressure boiler, in Flintshire. High pressure 

 boilers have since been substituted. Some of the most dreadful accidents 

 from explosions which have taken place in America, have occurred 

 from low pressure boilers. 



