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Processes in the Useful Arts. 161 



ti ]yjj Taylor," says he, " proposes several questions which I shall en- 

 deavour to answer, 



*' The Pen-y-frau engine," says Mr Taylor, " had been stopped a few 

 minutes, and the workmen had opened tlie fire-doors of three of the boilers, 

 and closed the dampers of two of them. The engineman observed a gust 

 of flame from the fire-place, which was almost immediately succeeded by 

 an explosion." — " In this case," asks Mr Taylor, ** had the rush of the 

 flame from the fire-place any thing to do with the subsequent explosion ?" 

 I think there can be little doubt that the rush of the flame was in conse- 

 quence of sorne fracture having already taken place in the boiler ; probably 

 the fissure was not at first of very considerable size, as we know that 

 wrought iron does not break at once, as cast iron, but rends. The rent 

 being at first small it would have occasioned the rush ; but as the fissure, 

 once made, weakened the boiler, and the aperture not being sufficiently 

 large to permit the escape of a very considerable quantity of water or steam, 

 a moment between the gust of flame and the explosion would in all proba- 

 bility have elapsed. " And admitting that the steam was so far within 

 the pressure that could, by mere expansive force regularly excited, injure 

 Buch a boiler, might not the rupture be occasioned by the void that a vacuum 

 suddenly created might produce ?" That the expansive force of the steam, 

 30 lbs. on the inch, was not sufficient to injure the boiler, remains yet to be 

 proved, as we do not know the strength of the boilers. Admitting the pos- 

 sibility of a vacuum, it might perhaps help us towards a real knowledge of 

 the cause ; but I am not aware of any circumstances to which the power 

 of forming a vacuum can be ascribed. 



" Does not the bursting of one boiler after another as at Polgooth seem 

 to indicate that exterior causes operated ? Is it possible to conceive,— sup- 

 posing the pressure equal in two boilers as at Polgooth, both being con- 

 nected to the same steam pipe, — that the relative strength of the two should 

 be so exactly the same as that which would by mere expansive force burst 

 the one should haVft the same effect upon the other?" 



Mr Taylor informs us that the plates of which the interior tubes are 

 made are \ an inch thick, and those of the outer f ths. Now, if we sup- 

 pose each boiler to be made of 200 plates, would it not be truly surprising 

 if in 400 plates there were not two of the same strength, the thickness be- 

 ing the same, and (as we suppose both boilers were made at the same 

 manufactory) the quantity similar in each ? Here then we have an ex- 

 pression of two known quantities only ; whilst, if we refer the accident to 

 the agency of an explosion of coal gas with atmospheric air, we must take 

 into consideration the activity of the distillatory action, the facilities of 

 escape afforded to the gas in either boiler, the intensity of combustion in 

 the fire-place, the influx of air, &c. which leads us into a much more com- 

 plicated calculation. The evidence then appears to preponderate in favour 

 of the idea of its explosion originating in the expansive force of the steam, 

 which it would seem w^as permitted to obtain too strong an elasticity. 



** At the Pen-y-fras engine we see that the fire-door is thrown open, 

 and then the current of air up the flue is stopped by closing the damper ; 

 VOL. VIII. NO. I. JAN. 1828. L 



