1847.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



333 



in the same plane, and the inner part being considerably bulged. From 

 the best examinatirn I can give the subject, I have come to the conclusion 

 that the strength of this front plate, aided by the two very imperfect stays 

 which were put in the boiler, was not sufficient to bear, for a length of 

 time— that is, during the usual time a boiler may be supposed to last — a 

 pressure of steam of 60 lb. on the square inch. At present it would bear 

 It, no doubt; there is no question of that, if any person wished to tie 

 down the weighted valves he would, most likely, prevent the spring- 

 balance valves from working, which he might easily do by putting in a 

 pieee of wood. 



I have calculated, in a rough way, what would be the effect of keeping 

 all the valves tied for five minutes. Supposing no steam were permitted to 

 escape, and the pressure was 60 lb., at the end of five minutes it would in- 

 crease to more than 90 lb. ; and, at the end of ten minutes, be between 

 ISO lb. and 140 lb. ; in a quarter of an hour, at least 180 lb. That is, sup- 

 posing no steam escaped, that the fires were burning briskly, and the boiler 

 in full operation. I cannot conceive four valves getting out of order, or 

 sticking, at the same time. One valve, supposing ihe other three to be 

 fast, would not relieve the boiler of steam as fast as the steam was gene- 

 rated, looking at the size of the steam-pipe. If two were in operation, one 

 of Salter's, and one of the others, they ought to relieve the boiler ; but the 

 area of the steam valve is larger than that of Ihe waste steam-pipe, which 

 is not a good arrangement. 'I'he area of the former is nearly five inches, of 

 Ihe latter, only 2-7 inches. If the two weight-valves were tied, and the 

 epring-balanccs free, 1 think a dangerous pressure would be brought upon 

 the boiler. 



TV** of the Tenacity of the Plates of the Boilers. — After making 

 an examination of the boiler, I thought it proper to test the goodness of 

 the materials ; for which purpose 1 took pieces of the plates of the 

 boiler which had been rent by the explosion. These plates, as I said 

 before, are | inch in thickness. I cut strips of two inches in width from 

 them, both with and against the grain, and tore them asunder by a machine 

 for that purpose at Woolwich. Four of the pieces produced are four of 

 the strips of the boiler; two torn with, and two against the grain ; the 

 other four pieces are good metal from Woolwich, with which I compared 

 the former. The former, are, in fact, part of the plates which were rent in 

 the explosion. M'ithout troubling you with the details of the experiments, 

 I may mention that the average tensile force per square inch of these plates 

 was 17 tons, that of plates of the same thickness, of the best kind, which 

 1 tried at the same time, was 21| tons. Specimens of those are also pro- 

 duced. They are Low Moor plates, of the same thickness, but of a very 

 superior quality. The plates of Ihe Cricket are very much laminated or 

 shelly, not only in one part but all that I saw. This is owing to the bad 

 quality of the metal. It will happen sometimes in plates of Ihe best 

 quality, but it is very much to be avoided. This piece exhibits the frac- 

 ture actually made by the explosion, the appearance of which proves it to 

 have been bad iron — that is, for the purpose to which it was applied, to a 

 high-pressure boiler, and considering that it was employed in Ihe part 

 which was most likely to break. I tried also some common Staffordshire 

 plates at Woolwich, and found their strength nearly the same as that of 

 the Cricket's plates. They bore 16§ tons on the average, which is very 

 low. 



I do not consider the workmanship of the boiler to have been such as it 

 ought to have been in a boiler of this kind. The rivets generally did not 

 fill the holes, and they were generally not sufficiently long to make a good 

 rivet. The boiler does not appear to be seriously deteriorated by wear, 

 except at the lower part of the front, and possibly the bottom too may be 

 to ; but I do not attribute the explosion to that. The part which exploded 

 was the whole of the front, which was turn out bodily. Of course the 

 part was weaker than when quite new, but not materially so. The experi- 

 ments I have mentioned are not tests of the pressure of steam on the plates. 

 All we can is, that a pressure of 60 lb- ought not to be permanently put 

 upon them, say for three years. From these experiments, and another of 

 bending the iron, I should say that the metal was not such as ought to 

 have been employed. It was good common metal, such as is usually em- 

 ployed in the boilers of the navy fur parts where there is no great strain ; 

 but not such as ought to have been put in the front of the boiler. The plate 

 was torn where it was weakest, and in the stronger part it was torn from 

 its fastenings 



By consent of Mr. Smith, Mr. Joyce, and other parties interested, who 

 have afforded me every facility, I have made experiments on the unex- 

 ploded boiler. I brought on it a pressure of 1361b. to the square inch, 

 allowing that ihe other must have been subjected to a very severe pressure. 

 In the unexploded boiler both the slays were separated, and a part of the 

 «ngIe-iron, which unites the front to the shell of the boiler, was cracked. 

 Upon this boiler I brought a pressure of water of 136 lb. on Ihe square 

 inch, and then the boiler leaked to so great an extent that a greater pres- 

 sure could not be obtained. My opinion is, that the pressure of steam 

 which caused the explosion could not have been leis than 136 lb. to the 

 equare inch. That is, of course, a matter of opinion ; but it is the conclu- 

 sion to which I have come. I should not have expected it to burst with a 

 less pressure ; but, as I said before, it is utterly impossible to calculate it. 

 You can calculate perfectly well what the shell of the boiler ought to bear. 

 I should say it was not less than 136 lb. ; how much more I cannot say. 

 I do not believe there is any reason to suppose that there was any dtH- 

 tieucy of water in the boiler. It is called a tubular boiler, from the cir- 



cumstance of a number of small tubes being introduced, for the purpose of 

 absorbing the heat. We consider them rather a safe boiler. The business 

 of one or two of these tubes is a matter of no importance. The tubes 

 seemed to be all perfectly good. Two or three of them were bent, but the 

 cause of that was very evident from striking against the inside. My great 

 objection to the boiler is its form, the front being flat, without proper stay- 

 ing ; and, in a far less degree, the quality of the materials and the work- 

 manship. 



Cause of the Ea-jjlosion. — There can be no doubt as to the cause of the 

 explosion — namely, the improper increase of the pressure of the steam 

 shortly before and at the lime of the explosion. If the pressure was 

 gradually increased, say from 60 lb. to 130 lb. or 140 lb. in the course of 

 ten minutes, that would be enough to account fur it — certainly, if the 

 pressure rose to 150 lb. ; but that is a mere matter of opinion. That the 

 boiler had never before been subject to such an extreme pressure is evi- 

 dent from the fact that the other builer leaked considerably at almost no 

 pressure at all : and I consider that it had been rendered thus leaky by 

 the extreme pressure on the day of the explosion. The boilers are con- 

 nected in the water spaces and in the upper part of tie steam, so that 

 the pressure on both would be the same at the same time. If only one 

 valve was in operation on one boiler, the pressure on both would be the 

 same ; and even if both valves of one boiler were secured so as not to 

 work. To show the great pressure brought on the unexploded boiler, I 

 may mentiun that the flat plate in front was bulged to the extent of IJ 

 inches before I commenced my experiments. After it had been subjected 

 to the water-pressure of 136 1b. on the square inch, the bulging of that 

 plate increased to 216 inches; and the lower front plate of the boiler 

 liegan to break exactly like the one that was broken in the exploded 

 boiler. Had all the four valves been at liberty, it appears to me impossible 

 that the pressure of steam could have so increased as to cause the explo- 

 sion. Had both the balance-valves been open, I think they would hardly 

 have saved it ; they migiit have deferred the time, and prolonged it from ten 

 to perhaps twenty minutes. I think the valves must have been closed, or 

 open only to a small extent, when the explosion occurred. [Here Mr. 

 Lloyd exhibited a plan of the vessel and boiler, and explained to the jury 

 how he conceived the explosion to have occurred.] When the front began 

 to bulge the stays would be the first to go ; the plate would then bulge 

 more and more, and the moment the separation took place the inside of Ihe 

 boiler would be projected in one direction, and the shell in another. The 

 former was driven against Ihe engine, which resisted it, and to this the 

 people in the fore part of the vessel owed their safety. The shell of the 

 boiler was carried in the other direction, and tore away everything in the 

 stern part of the vessel. Assuming the actual gross pressure at 180 tons, 

 and adding a ton and a half for the weight of the shell, it would give a 

 force a hundred times greater than that of gravity, which will account for 

 the enormous power exerted in a comparatively short space of time. 



You can always raise a valve in a well constructed boiler, but not pull 

 it down. The engineers in the Koyal Navy have not access to the valves ; 

 in locomotives the engineers have access to the safety-valves. I found the 

 spring of the unexploded boiler correct ; as nearly as can be calculated, it 

 was about 40 lb. per square inch when the valve was shut, but as the valve 

 opened the pressure increased. For anything I can tell, the safety-valve 

 was nut permitted to rise in the unexploded boiler. If both the Salter's 

 balance valves had been in a fit stale, a longer time would have been 

 necessary to get up the steam to the bursting pressure. I cannot tell 

 whether they would have opened sufliciently to let out the steam of them- 

 selves; I doubt very much whether they would. The waste pipe of the 

 Cricket is small, and is a bent pipe, and all that impedes the passage of 

 the steam into the chimney, but to what extent it is impossible to say. The 

 noise would have been very great if any of the valves had been acting, 

 and the steam had been 5 lb. above 40°. There were two stays to the un- 

 exploded boiler ; both had been separated. Either sudden or gradual 

 pressure would have accounted for that separation. The stays themselves 

 were strong enough ; it was the fastenings that had given way. If the 

 valves were closed at 60°, the pressure would in five minutes have got up 

 to 1)0°. I know very few engineers who understand these matters tho- 

 roughly. I wish we could get people who did understand them ; but no 

 man is allowed to drive an engine iu the Royal Navy who has not under- 

 gone such an examination as may from time to time be considered neces- 

 sary. I think that you ought to get the best men that can be got as en- 

 gineers, and the only course to pursue is to increase the wages, if any 

 difficulty arises in obtaining qualified men. 



In the dockyards some high-pressure engines are used for particular 

 purposes. I should prefer low-pressure engines, if they were suitable for 

 those purposes. I should say the boiler that exploded must have been 

 weaker than Ihe one that remains, because the pressure would be alike 

 upon both. The boiler that I tested did not stand a very severe test for a 

 high-pressure boiler. Me tried it without the ordinary stays ; and it was 

 then bulged in consequence of a previous strain. The maker of a boiler 

 ought to allow for any weakness that may be caused by corrosion. I hare 

 been told the boilers were proved before they were put iu Ihe Cricket. 

 Mr. Joyce, and everybody connected with Ihe vessel, aflbrded me every 

 facility. Low Moor iron is S'nie of the best iron that can be got. It is 

 not used much for the boilers of commercial steamers ; but it ought to be 

 used fur high-pressure boilers. 1 think the pressure a steam boiler 

 ought to he worked at should not exceed oue-'enth of its calculated 

 strength, supposing it to be made of the very bett materials and wurkmau- 



