44 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Fkb, 



gas, but not to such a degree as to become explosive, because a con- 

 siderable quantity of oxygen, or atmospheric air, which does not al- 

 ready exist in the boiler, is required to render it so. It is, however, 

 this very air, which, I consider, does really enter the boiler in con- 

 siderable quantity, and is evidently supplied by the feed-pump itself, 

 which, from some cause or other, although it continues at work, thus 

 permits the water to lower in the boiler. In such case every stroke 

 of the pump injects a certain portion of air into the boiler. There 

 might also exist a slight crack, or i defect in the working barrel, or in 

 the packing of the stuffing-box. These defects would cause the feed- 

 pump to become a real air-pump, if any accident happened to the 

 valves of the induction pipe, or if the water in the reservoir got below 

 its proper level. There can be no doubt that these accidents do 

 occur. 



"Let us now examine what takes place when atmospheric air is thus 

 forced into the boiler. This air passes through the remainder of the 

 water in the boiler, and occupies the space above the injection pipe, 

 without being immediately mixed with the gas, which continues to be 

 produced from the heated sides of the boiler, but so soon as the engine 

 is set to work, a considerable ebullition is produced in the water, and 

 a detonating mixture of air and gas is formed. So soon, therefore, as 

 this explosive mixture comes in contact with the heated surface of 

 the boiler, it inflames in the same manner as carburetted hydrogen 

 gas does against the wire of a Davy's lamp when heated to a cherry 

 red. 



" There is also another means of accounting for the tiring of the ex- 

 plosive mixture, namely, by the electric spark which is formed every 

 time that the steam is struck or forcibly pressed by the edges of the 

 valve, as was shown in the experiments made by the Commission at 

 the Museum, and as you yourself witnessed in those with the engineer 

 Tassin. The experiments of Lavoisier show that if a valve be opened 

 at the moment the explosive mixture is in contact with it, the slight- 

 est electric spark is sufficient to cause an explosion. It might also 

 happen that the disc of the valve produced the eftect of the plate of 

 the electrical apparatus, and caused the spark on being lifted from its 

 seat. 



"This will account for the greater part of the explosions happening 

 at the moment the engine is set to work, or the valve opened, as oc- 

 curred on the I3th of November, 1841, at the manufactory of Messrs. 

 John Elce and Cottam, at Manchester. 



" There can be no longer any doubt as to the production of hydrogen 

 gas in boilers where the water is deficient, since the dangerous expe- 

 riment made by Mr. Goldsworthy Gurney, when he proved that the 

 steam emitted from a boiler heated red hot (the feed pumps being 

 stopped and the water suffered to get low), burnt like hydrogen gas : 

 the onlv reason that this boiler did not explode must have been, that 

 in this particular instance there was no atmospheric air mingled with 

 the gas. 



" In support of this theory, several cases of explosion have come to 

 my knowledge, among others, one that took place at Ghent in the 

 year 182G, which puzzled all the believers in the efficacy of safety 

 valves, as the man-hole was open, and there was no water in the 

 boiler, or fire under it ; yet it exploded, and caused great damage. 

 This accident may be thus explained : — 



" The boiler had been emptied on the Saturday, in order to clean it 

 on Sunday, leaving only a little water in it to wash it out. This boiler 

 having been emptied before the fire was completely extinguished, 

 must have been heated in parts to a red heat, and thus the steam 

 decomposed. The next morning, the workman, having taken off the 

 man-hole lid, held his lamp, according to custom, within tlie boiler. 

 The hydrogen gas, rendered explosive by the admission of atmos- 

 pheric air, immediately exploded, and destroyed the boiler and work- 

 shop, and killed the man. 



" As the water cannot be thus decomposed in copper boilers, they 

 are consequently not liable to explosion from the cause thus shown. 



"In discovering this cause of accident, its remedy is evident; if the 

 reservoir for the feed is placed above the pump, as is invariably done 

 in Prussia, the introduction of air into the boiler becoming impossible. 



This arrangement, enforced by law in Prussia, has caused explosions 

 to be of rare occurrence. 



" If my opinion on the cause of explosions be correct, and which it is 

 desirable should be verified by official experiment, the regulations at 

 present in use are worse than useless, safety valves become dangerous, 

 and the fusible plates are of no avail. The chief attention ought to 

 be bestowed on the supply of water in the boilers, and then the ex- 

 plosion of boilers rivetted by machinery need not be feared, because 

 the rivet holes become oval before giving way, and permit the steam 

 and water to escape by the seams of the boiler. It is hoped this suc- 

 cinct explanation will enable the proprietors of steam engines to take 

 the necessary measures to avoid explosions. 



JOBARD." 



ENGINES OF H. M. STEAM SHIP "VIRAGO," OF 

 THREE HUNDRED HORSE POWER. 



By BouLTON, Watt, and Co. Designed June 1841. 

 ( With an Engraving, Plate II.) 



These engines are of the kind termed " direct," and were designed 

 to meet the views of the late Board of Admiralty, with reference to 

 the saving of weight, space, and placing all the moving parts below 

 the line of flotation, out of the reach of shot. 



They are of the collective power of 300 horses, cylinders 04^ dia- 

 meter and 5 feet stroke, the velocity of piston being fixed at 215 feet 

 per minute, agreeably to the general rules of the late Mr. Watt. 



Tlie Boilers are made to the full power of the engines, as it regards 

 evaporating surface, and occupy 19ft. x 20ft. superficial, and in height 

 they are 12 feet. 



The length of the engine room is 53ft. Gin., and the coal boxes are 

 constructed so as to entirely protect the boiler and engines, and con- 

 tain from 350 to 360 tons of coals, (at 48 cubic feet per ton). The 

 space required by the engines is 18ft. Gin. athwart, and 11 feet fore 

 and aft, that is, over the air pumps, which being placed in the centre 

 of the vessel, occupy comparatively useless space, — for so large a 

 power as 300 horses we believe this to be unprecedented. It will be 

 observed that there are two condensers, air pumps, &c., so that either 

 engine can be worked separately; in consequence of the compactness 

 of the engines, the weight must be very much reduced in comparison 

 with the beam engine. 



REFERENCE TO THE ENGRAVINGS. 

 Similar letters refer to similar parts in each figure. 



Fig. 1 is a Front View of the Engines. Fig. 2, Plan. Fig. .3, Side View. 

 Fig. 1, Horizontal Section of Air Pumps and Condensers. 



Fig. .5.— Transverse Section tbvough Condensers, 

 Hot Water Cisterns, and Eduction Pipes. 



A, cylinder; B. piston tod ; 

 C. connecting rod ; D, guides 

 for pistun rod cross bead ( 

 E, brass sliding valves ; /, 

 induction sleam pipe ; g, 

 eduction pipe trom lower 

 thoroughfare ; A. ditto from 

 upper thoroughfare ; /.-, open- 

 ings into condensers from 

 eduction pipes ,f and h ; L, 

 condensers divided in the 

 centre ; M, hot water cis- 

 tern ; N, air pumps ; c, foot 

 valves two to each air- 

 pump ; P, beam to work air 

 rumps, feed and bilgepumps; 

 H, teed pumps ; .S, bilge 

 pumps ; 1, waste pipes; D, 

 tiilge water pipes ; c, holding 

 down bolls; jc, doors to 

 condensers ; X, keelson run- 

 ning through condensers ; 

 J/, engne sleepers. 



