240 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[July, 



This class is divided into eight sections. 



Fiisl Section. — Tlie fiist section embraces those designs by wliich the 

 competitors proiiose to diseli;irge a quantity of water into the furnace, or 

 into tlie flues leading from them, whenever the force of the steam is sntiieieut 

 to raise the water from the lioiler to a certain height in a pijie, so that 

 thereby the intensity of the tire may he diminislied. 



• Second Sec/ion. — The iirinciple on which the designs in this section are 

 construeted, is, lliat when the pressure of the steam is sutticicnt to raise 

 water from the lioilcr to a certain height, it rises round a hollow vessel or 

 float, susjieuded at that height from one end of a lever, the other end being 

 connected with a safety-valve of tlie common furni. In some of tlie jilaus, 

 the hollow vessel or tloat is designed to act as tlie load on the safety-valve, 

 so that, to whatever extent it may be immersed in the water, so raised by 

 the strengtli of the steam, to that extent is the safety-valve lightened of its 

 load. In others, the weight of water dis]daced by the float, is a force, in 

 addition to the steam, to raise a valve loailcil in the ordinary way. 



T/iird Sedion. — This section embraces the greatest number of plans, 

 wliich contain, in general, the common safety-valve enclosed in a ease, so as 

 to jireveut all access to it. The design of some of the plans is, however, 

 worthy of .ittention, from their ingenious complexity. 



Fourth Section. — These designs have the common safety-valve cased in, 

 to prevent it from Iieing overloaded, but have attachments to the valve, by 

 which it can he openeti by the engine-man whenever he fluds it necessary to 

 jicrmit the steam to eseajie. 



Fiftti .Section. — The distinguishing feature of the plans in this section, is 

 the introduction of a piston in cunncxion with the safety-valve, with the 

 design that the gradual increase in the force of the steam shall, by acting 

 on the under side of the piston, become a proportionally increasing power to 

 open the safety-valve. 



SLith Section. — The arrangement of the apparatus in this division is de- 

 signed with the view of loading the safety-valve when the engine is at work, 

 and of taking oft' the load when it is at rest. 



Seimitlt Section, — In this section the exhibitors propose to substitute mer- 

 cury for the loaded valve, which is usually employed to confine the steam 

 uiitd it has acquired a certain amount of force. 



Eiffhth .Section. — The competitors included in this section jiropose a con- 

 nexion to tie made between the throttle and safety-valves, by which, when 

 the speed of the engine is required to he reduced, the safety-valve is opened, 

 and the steam allowed to escape. 



Sp;C0ND CLASS. 



The second class of competitors arc those who are of opinion that the 

 explosion of boilers is the cfl"ect of the instantaneous production of steam, 

 on the evolution and ignition of inth'imnialile gases in the boiler, in conse- 

 quence of a deliciency of water ; by which the flues (or passages through the 

 boilers for the flame from the furnaces) being uncovered, they become red 

 hot, and on water being brought in contact with them, explosion is jiroduced. 



This class is divided into two sections. 



First Section. — The first section jiroposes self-acting apparatus for feeding 

 the boilers while the engine is in operation, so as to prevent the water from 

 falling below a certain level. 



.Sccoml Section. — The seeoiid section ])roposes means of giving information 

 when the water shall have fallen below a certain point in the boiler, h\' 

 means of a pipe open at both ends and approaching to within a short 

 distance from the flues, so that, when the water shall have been sunk below 

 this pipe, the steam will he allowed to escape. 



THIRD CLASS. 



The third class are those competitors who consider explosions to be the 

 result of weakness in the boiler, and propose that they shall be frequently 

 proved. 



This class might be divided into two sections, viz., those who recommend 

 that periodical attempts he made to explode the boilers with a great pressure 

 of steam, and those who suggest that they shall be frequently proved by a 

 forcing pump ; but it is unnecessary to make this distinction. 



We shall close this summary by stating that there are several ingenious 

 designs which cannot he classed with any of those mentioned, nor with each 

 other; and, consequently, for an explanation of the principles of their con- 

 struction and intended mode of operating, it would he necessary to transcribe 

 the several essays in which they are contained ; but this we consider unnc- 

 eessary, from their being nothing of sufficient merit in them to recommend 

 them to the notice of the Trustees. It will be remarked that, almost all the 

 competitors jiropose their several designs to be adopted only as additions to 

 the existing means of preventing explosion ; that they almost unanimously 

 reeouimeniied the continued use of the existing safety-valve ; that several 

 recommend the frequent proof of boilers: while a few only propose the 

 ap|)ointiuent of inspectors. 



In recommending to your favourable consideration some of the designs, 

 we beg to lay before you the circumstances which guided our selection. 



The theory advanced in the Essay No. 1 , of explosions jirocceding from 

 the formation of gas in the boiler, by the flues becoming led-hot, thereby 

 decomposing t e water, and then inflaming these gases, has been, in our 

 opinion, most conclusively set aside by the eminent philosopher, Mons. 

 Arago, in a memoir on the sidiject of the present re|)ort. " Some persons," 

 he writes, " struck with the prodigious and instantaneous efteets which often 

 result from the explosion of boilers, are persnaUecI that steam alone is in- ^ 



capable of producing them, and they call to their aid some gases susceptible 

 of explosion." On this he remarks, " Hydrogen alone, or mixed with vapour, 

 cannot explode — a mixture in the suitable projiurlions of oxygen and livdro- 

 gen is snscejitihle of explosion ; but how are these gases to be collected in 

 the boiler ? Hydrogen is the product of the oxidation of metal — from whence, 

 therefore, proceeds the oxygen ? (an it be from the air contained in the 

 feed water .^ It is warm, wliich prevents it from containing much air. I 

 shall add, in fine, that the oxygen of the air would combine it^elf much more 

 readily with the incandescent sides of the boiler, than with hydrogen ; and 

 that the |irodiict of the drcompo»ition of water would he — not hydrogen and 

 oxygen, lint h_\ drogeii and azote," — a non-explosion mixture. And further, 

 in a llcpnit by the Comniittee of the Franklin Institute, on the explosions of 

 steam boilers, made at the request of the Treasury department of the I'liited 

 States, (hey state, as the result of direct experiment, that the gas obtained 

 by injecting water into a red-hot boiler, was a " non-supporter ot combustion, 

 and non-combiistihle." 



The other theory advanced by the Essajists Nos. 1, 4, 7, 8, 9, aiid20, is, 

 that if the flues become red hot, and water be poured into the boiler, a vo- 

 lume of steam, of dangerous elasticity, is instantaneously formed, to which 

 the safety-valves cannot give vent witli suflicient ra|iidity, and, iu consequence, 

 the boiler explodes. In regard to this supposed cause of ex]>losion, — the 

 American Commissioners succeeded in exploding an experimental boiler, by 

 injecting water into it while not only the flues, but the top, bottom, and 

 sides, were assiduously kept red hot. This was done to ascertain the greatest 

 effect that could be produced by steam generated under such circumstances. 

 Their other experiments prove that w.ater does not evajiorate so ra|iidly when 

 brought in contact with red-hot iron, as when the iron has been cooled down 

 to a niucli lower temperature, and at this redncerl tem)ierature iron does not 

 contain any considerable quantity of heat. In all experiments made by them 

 and others, //?«? has been a necessary constituent in the eircumstances which 

 liermit a certain volume of water to he evaporated, and confinement to give 

 it force ; and the opening of a safety-valve has ah\ ays been found to diminish 

 the pressure, and lower the temperature of the steam. AVe are inclined, 

 under a peculiar and merely possible combination of circumstances, to view 

 this as a cause of danger ; Init we have not been able to discover any authen- 

 tic instances in which explosion has been clearly traced to it. The general 

 jiraetical result of the flues being allowed to get red hot, is, that the plates 

 composing them crack on admission of water, and from the copious dis- 

 charge of boiling water and steam which ensues, many serious accidents have 

 happened to the engine-men and fire-men, through whose negligence they 

 have been occasioned. 



Notwithstanding of the above theories advanced by the competitors, and 

 also of several others promulgated by persons of high standing in the scien- 

 tific world, we cannot, after a careful comparison between their reasoning 

 and our own experience, arrive at any other conclusion than — that the ex- 

 plosions of steam boilers proceed from a gradual accumulation of steam, 

 which, being deprived of sufhcient means of escajie, is, by the continued 

 action of the fire in the furnaces, raised to a dangerous, and often destructive 

 degree of density ; and we conceive that all danger can be avoided by the 

 regular action of the common safety-valve, if properly constructed and made 

 of snfficient capacity. It sometimes happens that these valves, from neglect, 

 become fixed; and we are of opinion, that the apparatus designed by the 

 Essayists Nos. 2 and 4 1 , which are draw n as figures 1 and 2,* are well cal- 

 culated to apply a force, in addition to the strength of the steam, to over- 

 come this adherence ; and they have the advantage of being so designed, 

 that after the overjilus of steam shall have escaped, the safety-valve is 

 allowed to resume its useful position. 



We have remarked, that the greater number of explosions of steam boilers 

 have occurred at the instant of starting the engine. Without taking on our- 

 selves to assign any reason for this, or our being able to trace the immediate 

 circumstance which precedes, and may have caused the explosion, we are of 

 opinion, that the risk of accident may be lessened by the weight on the safe- 

 ty-valve being diminished until the engine is in motion, and the steam flowing 

 away by a regular current. We are not satisfied with the efficiency of the 

 various plans which are designed to attain this object; but we recommend 

 to your notice, for its novelty, the design in Essay No. 18. 



We conceive it to be of importance, that the safety-valve should be se- 

 cm-ed from improper interference ; but, at the same time, that it should be 

 so connected with the ordinary occupation of the engine-man, as to be put 

 into almost hourly use. This must lessen, if not entirely prevent, the chance 

 of it becoming fixed to its seat. Of the designs submitted to us, we consider 

 that the plans iu the Essays 4, .'^8, .')5. and 50, are best adapted for this ob- 

 ject, though they have been found liable to the inconvenience of becoming 

 fixed at the joints which are inside of the boiler. Figiu-es 33, 36, 38, and 

 40, are, we believe, in use iu several steam vessels on the Thames, the Clyde, 

 and the Mersey, and No. 3ti has been seen on board the French Government 

 steamer, " I.e Meteore." 



A number of the competitors recommend that the safety-valve should he 

 locked up, to prevent all access to it by the engine-man ; but in this recom- 

 mendation we do not concur, — for, if those in charge of the engine be pre- 

 vented from ascertaining the condition of the safety-valve, no reliance can be 

 placed on it as a mean of preventing accident. 



' Tiie figures 1 and 2 will he found in auotherrpart of the Journal.— En. 

 C. and K, Journal. 



