320 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Septkmber, 



safety valve could relieve the pressure. The Doctor deduced from Mr. 

 Parkes's theory of " the percussive action of steam," and his own experi- 

 ments, that if, from any cause, such as the hreaking up of a i)ortion of crust 

 adhering to the bottom of the Ijoiler, a volume of steam of high elastic force 

 was suddenly evolved, a rupture of the bottom would be the consequence, or, 

 the boiler might be separated into two parts. Mr. Parkes coincided in this 

 opinion, and cited several examples in support of it. 



It appeared to liim that a force different from, and greater than, the simple 

 pressure of the steam, was the principal agent. The Committee of the 

 Franklin Institute, and others, who in their experiments Iiad endeavoured to 

 produce explosions of boilers, liad very rarely succeeded, and the effects ob- 

 tained fell far short of those which continually occurred by accident. It 

 might be safely inferred from this fact, that the experimenters had not ar- 

 rived at the tnie cause of the ruptures and projections of boilers, otherwise 

 the production of similar effects would not have been difficult. 



Sail Pans. — Describing the sudden development of a volume of steam, 

 from highly heated plates, which no practicable number of safety valves could 

 discharge tpnckly enough to save a boiler from destruction, he instanced the 

 effects |iroduced by the lircaking up of the scale in salt pans. Carbonate 

 and sulphate of lime were separated from brine by eva]ioration, and adhered 

 very firmly to heated surfaces. A crust of salt frequently formed upon this 

 deposit ; the cessation of ebullition (if the deposit occmTed over the furnace) 

 was the consequence, and the bottom of the pan became red hot. The man- 

 ner in which the pan scale was disengaged, was to strike it with the edge of 

 a heavy iron pricker, which allowed the brine to reach the plate; it was also 

 frequently broken through by the expansion and bagging down of the plates, 

 leaving tlie crust above like an arch. In such cases the plate was seen for 

 an instant to le red hot, and immediately afterwards an immense column of 

 brine was projected from the pan, the steam evidently being of high momen- 

 tary elasticity. Mr. Parkes had seen a yard square of scale thus burst, the 

 whole siuface of the plate being at a glowing red heat. Had the pan been 

 closed, like a steam boiler, he conceived that the blow of the steam on the 

 roof, bottom, or sides, would liave destroyed the vessel. 



A thin copper salt pan at Mr. Parkes's works, bad a hole burst through 

 its bottom by the sudden action of steam thus generated. The spot had no 

 doubt been previously injured by heat. lie conceived that similar pheno- 

 mena might, and frequently did, occur in steam boilers. 



Healed Plates. — A theory has been adopted by many writers on the ex- 

 plosion of steam boilers, that red-hot iron plates would generate less steam 

 than plates at a less heat. This was founded on the experiments of Leiden- 

 frost, Klaproth, and others, on the length of time requisite to evaporate a 

 small globule of water in a red-hot spoon. But there was no analogy be- 

 tween the condition of a hot spoon containing a drop of water, and that of 

 a body of water and heated plates in boilers. 



Steam of great force would instantly be produced from a thin sheet or 

 wave of water, passing over hot plates, the molecular attraction of a drop 

 falling a short distance upon a plate would be destroyed, and the whole be 

 instantly converted into steam of a high momentary elasticity. The theory 

 of the hot spoon experiment, as applied to boilers, had been demonstrated to 

 be fallacious by Dr. Schafhaeutl in a paper pubUshed in the Mech. Mag. 

 vol. XXX. No. 799. 



" Vnion ' Steamer at Hull. — The explosion of several boilers had been at- 

 tributed, and Mr. Parkes thought justly, to a wave of water washing over 

 highly heated plates. He believed that the fatal accident to the " Union " 

 steamer at Hull was so produced. The boilers of steam vessels were not at 

 that period so well arranged as at present, for preventing the water from 

 flowing to one side, and leaving a portion of the top of the flues dry with 

 the fire beneath. Under such circumstances, the disaster which occurred 

 would be inevitalde, on the vessel's coming on an even keel. Mr. Parkes 

 was not of opinion that it required the exposure of a large area of heated 

 metal to effect the separation of a boiler and the projection of the upper half 

 of it ; as, in this case, it was the suddenness of the action, no number of 

 safety valves could have deprived the steam of its instantaneous force, so as 

 to have saved the boiler. The entire circumference of large boilers had been 

 frequently divided as clean as a pair of shears would ha\e accomplished the 

 work. These phenomena were evidences of a force very suddenly exerted. 



Sudden actions on the surfaces of boilers arose aUo from other causes than 

 the heating of plates. During the inquiry into the causes of steam vessel 

 accidents, he ascertained that of twenty-three explosions, ninetecu occurred 

 on the instant of starting the engines, or whilst the vessels were stationary; 

 three only whilst the engines were at work : the greatest number took place 

 at the moment of admitting the steam upon the piston. He attributed this 

 effect to the steam's jiercussive force, which would be as much felt by the 

 boiler as by the piston ; if the boiler was weak, and, distended by steam to 

 nearly the bursting point, the shock would be suflicieut to cause its rupture. 

 Mr. Parkes then gave several instances of such occurrences. 



Steam Ves.fel e.iphsion at jYoru'icA. — In 1817, the boiler of a steam vessel 

 at Noi-nich burst, and killed many persons. Previous to the accident, the 

 boiler Irakcd in several places ; the steam issued coi>iously from the safety 

 valve, which was evidently very heavily loaded. The engine had scarcely 

 made a revolution before the explosion occurred. By applying the present 

 state of our knowledge to these facts, he felt assured that the steam's impact 

 on the piston bad been the immediate cause of that accident. 



Erplosian at Passy. — In 1826 or 1827, Mr. I'arkes witnessed the effects of 

 an explosion, a few minutes after its occurrence, in the neighbourhood of his 



works, near Paris. The boiler was of wrought iron, G feet long by about 2 

 feet C inches or 3 feet <liameter. By his advice the owner had previously 

 put in a new end, formed of one piece of hammered iron, and he was strongly 

 dissuaded frou) overloading his engine, or using habitually such enormous 

 pressures. The cylinder of the engine was horizontal, and was connected 

 with the boiler by a short pipe and cock. The proprietor informed him, that 

 finding his machinery working too slowly, he went into the engine-house and 

 stopped the engine. He held down the lever of the safety valve, and on 

 turning the cock to start the engine, the explosion instantly occurred. The 

 new end of the boiler, which was opposite lo the engine, was found separated 

 from the body, and lying in the flue. The line of rivets and a complete ring 

 of the new end remained upon the body, apparently little forced, and the 

 faces of the fractured ends were as sharp and clean as if cut by a chisel or 

 shears. The boiler, engine, and masonry, were driven into the yard in the 

 opposite direction to the escape of the w.iter and steam ; thus, though the 

 entire end of the boiler was removed, and the whole contents evacuated, it 

 acted too late as a safety valve. 



Explosion at Camden Town. — He observed similar effects last year in an 

 cx)ilosion at Camden Town, being fortunately on the ground to investigate it 

 before much change had been made. Two boilers were set .end to end with 

 a chimney between them. The end of one was blown out, and was lying 

 close to its original seat. It was forced backwards into the chimney, which 

 it iiartly supported on a pipe flange, and pushed the other boiler and entire 

 masonry in a horizontal direction fully two feet. He considered that the 

 percussion of the steam from its re-action against the opposite ends of the 

 boiler in the act of tearing it off (which was the effect in tliis case) produced 

 the recoil. In this case there were upon the boilers (which were connected 

 together) two safety valves in good order, and not heavily loaded. The acci- 

 dent occurred during the breakfast hour, whilst the engines were not at 

 work. One of the two stays which originally held the fractured end of the 

 boiler, was found to have been previously broken, as its separated ends were 

 covered with old lime scale — the other had evidently been long cracked, and 

 was only held by a fragment. The fractured end of the boiler was not exposed 

 to the fire, nor did the shell or the flue within it exhibit any marks of injury 

 from fire or from dislodgnient of scale. The steam, in its effort to escape, 

 acting first against one end, not only raised the boiler from its horizontal 

 position to an angle of about 45°, but gave it a twist obliquely from the line 

 of its bed. 



High and low preisure. — Mr. Parkes could not agree in the often expressed 

 opinion, that what are called high-pressure steam boilers were more dangerous 

 or more liable to explode than others. Much depended on care and manage- 

 ment. He believed that he was in possession of accounts of nearly all the 

 explosions which had occurred iu Cornwall since the expiration of .Mr. Watt's 

 patent, when higher pressures began to be used, and they amounted only to 

 five or six instances, exclusive of some cases of collapsed flues. More explo- 

 sions had occurred in a small district round M'cdnesbury during the present 

 year with low pressure boilers, than in Cornwall in forty years, where the 

 lughest pressures were employed. He believed also that the coal districts of 

 Northumberland, Durham, and Staffordshire, would furnish more cases of 

 these disasters from boilers both of high aud low pressure, than all the rest 

 of England put together. 



The coal districts.— When the practice in the coal districts was contrasted 

 w ith that of Cornwall, the explanation was simple. AVhere coal was so cheap, 

 the quantify used was unlimited, the negligence was great, and the allowance 

 of boiler was small for any given sized engine, as enough steam could he 

 raised by fires of greater intensity — the rule there being, to save in the first 

 cost of the boiler ; in Cornwall, on the contrary, the object was to insure 

 economy in the consumption of fuel ; consequently, all that class of accidents 

 arising from injury to plates by fire and deposit, would be in about the ratio 

 of the intensity of the combustion. 



Notwithstanding the bad practice generally prevading in the coal districts, 

 there were some exceptions. .\t an iron work near Dudley, there were boilers 

 now in good order after nearly thirty years' use, having required but trifling 

 repairs during that period. In those boilers the plates of the bottoms w hich 

 were exposed to the fire were all made of hammered, not of rolled iron — the 

 boilers were large for their work, and were cleaned thoroughly every week. 



Hammered plates. — Tilled plates were alone used for salt pans in those 

 parts where the heat was most intense. Though continually heated to red- 

 ness, and distorted by the action of the fire, the quality of the iron in plates 

 thus formed did not appear to be deteriorated, for when taken out the smiths 

 used them for making rivets, nails, &e. Rolled iron plates would do for 

 making coarse salt, which required a heat below ebullition, but they were 

 quickly injured when used for fine salt, and were useless when taken out. 



Eiplosion at Esuonne. — Mr. Parkes then adverted to several other remark- 

 able cases of explosion. It was a well authenticated fact, that a boiler be- 

 longing to Messrs. Ferey, at Essonne in France, exploded on the uistant of 

 opening the safety valve. 



Explosion at Lyons. — Three successive reports were heard when Steele's 

 steam boat boilers exploded at Lyons, indicating that they did not burst at 

 the same instant. Now, though Mr. Steele had fastened down the safety 

 valve to increase the pressure of the steam, v«t the explosion of the first boiler 

 should, according to the received opinions, have acted as a safety valve to the 

 second and third, aud have saved them — for, by the destruction of the first 

 boiler, the pipes would be broken, and a free exit be afforded for the steam 

 in the others ; nevertheless, they all three burst in succession. Several similar 



