into a tube leadinz to ttie ehimnev, at:~dfiehinstant;(tl~:~V~ t~m ~,alve E 77 ClOseS, ~nd~siiUtS Oil seven-e~'~i~ths bf;t~e s t e a ~ h ~ i ~ S up the dfimne% and the 6ttmi; ei~hth,~iun~lei" tile Piston; i s ~asil:) i0~: densed by a soray of water, wlnch ~s afterward used for genel m z th e steam. S t t[~e next put~; the condensed st~eam, wa~er, a~ :~tir~( are thrown ouf~ and the heated water runs into the Cistern c t h e u m , from whence it is forced into the ,enerator, dis ensln~ ~ifl~ P P . g

the complicated and expensive air-pump, as well as wit~ eonde fi,,ing water. :

Th6 second difficulty is removed bY renderin~ the empl0ymea~:of an eduction valve unnecessary; fbr ~he inductiSn valve-re~uires~ t9 be only one thousandth part of the area of tlie cylinder; the power required tberetbre to lift it, (even if the valve waffnoti so constructed as to neutralize the pressure,'} would be very little.

The third difficulty, wificffwas a very serious onei when the tem- iPerature of flie steam employed was five hundred pounds upon the rmh, is removed by using'a metallic piston, made of'a peculiar.alloy,: requiring no lubrication whatever, since it glazes by its working. And as for valves, there is only one little, simple, lifting, induc- tion valve, and that, being destitute of friction, requires, of course, no oil.

Fourth, preventing the steam fl~Qm becoming surcharged w!th ca- lorie. This important part of Mr. P.'s invention, we, for certain rea- sons, are restrahled from explaining, at present~ it is, however, accom- plished, and will be made known when the specification of the last patent is enrolled.

W'e understand that Mr P has taken some orders for bisHi~h-, pressure, safety-englnes, an'd guarantees the saving of half the t~et commonly used, for' a 'given power, the weight not to exceed: one,

third of ordina~:y condensifig enginesi and not to occupy more thari One,third fl~e spaed:- wifia absolute security fi'om the dangerous effects :i of explofion. : ' i ~ ~ : . : ~: . . . . ' '

On the ~Tlosion Of Steam Boilers. By 3Aeo~ Pr~aKx~s, Esq:: Ix has been generally considered a we!! establi.shed faet~ flint the

caloric of steam, at a givert elasticity, is:invariably the same, when in contact with water~ but this is far from being the case. I t may be~ and often is, so generated as to indicate very high degrees of tempe- rature without a corresponding increase of power; so as evidently ~o prove, that temperature, alone, cannot be relied on as a measure o f tim elastic power of steam. Many experimentalists have thus u n . doubtedly been led into error, especially in reference to high tem- peratures. If any part of the boiler which contains the steam be

' become of a hi~her tern ~erature than the water contained sutlered to ~. I . . . . 1 " in it, from want of a suffiment supply, the steam wilt read~ y receive an excess of caloric, and become surcharged with it, without ac- qulring proportional elasticity. In some recent experiments, I have heated steam to a temperature that would have given all the power

VoLo I l l , ~N o , 6.~J~;x~. 18~27, 53

413 l'Ftb. FII.ANI(LIL'~ Jt)Un.NAL AND

that the highest .ateam is capable of exerting, which wouhl have beeu 56,000 pounds to the square inch, if it had had its full quantum of water; yet the indicator showed a pressure of less than live atmo- spheres. IIaving satisli'ed myself, by repeated experiments, as to the cm'tainty of ti~is curious fact, the thought struck me, that if heated water were suddenly injected into the superl!eated steam, the ett~et wouhl instantly be, the fi)rmatiun of highly elastic steam; the strength of which would depend upon the temperature, and quantity, of the surcharged steam, anti of the water injected. To ascertain the truth of this theory, I made the tblh)wing experiments.

A generator was tilled with water~ and heated to about 500-de- grees, and, consequently, exerted a fm'ee of about 50 atmospheres; but the pressure valve being loaded to about 60 atmospheres, it pre, vented the water frmn expanding into steam. The receiver, wrich was destitute of botl~ water and' steam, was heated to about 1~200 degrees: a small quantity of water was injected into the generator, by the forcing pump, which tbreed out, from under the pressure valve, into the receiver~ a corresponding quantity of heated waIer, and this instantly tlashed into steam; which from its having ignited the hemp cord, that covered the steam-pipe~ ten feet from the generator, must have been at a temperature of, at'least, 800 degrees, which would be equal to about 800 atmospheresl but, fi*om want of water, to give it its necessary density, the indicator showed a pressure of ai;out five atmosphere;. Whether tlie pressure of the steam, which was rusl~- ing through the steam-pipe, was at 5 or 100, or more atmospheresi the steam-Ifipe kept till at the high temperature befbre mentioned; which I attributed to the steam being surcharged with calm'ic. The pump was now made to inject ~t much larger quantity of heated water, and the indicator showed a pressure of fi'om 50 to 80 atmosl)heres l the throttle valve being partly ol)ene(t , it soon expandcd~ to ll~e tbrmer pressure of about 5 atmospheres. The water was then injected again and again, and the indicator was observed to oscillate at each stroke of the puml) ~ ft'(m: 5, to between 40~ and 100~ atmospheres, aceordin,,'. ~, to the qu~,ntitv-. . of w:.ter in'eeted ; j clearly~showin,_'~ that at this reduced pressure, there was a great redundancy of heat, with little elastic force. It soon occurred to me, that to this might be traced the t:'ue cause of the tremendous explosions~ that suddenly take t~lace, in low, as well as in high, pressure boilers.

There are many instances, where, immediately before one of these terrific explesions had taken place, the engine labouredj showin~ evidently- a decrease of i2ower in the engine. To illustrate the tl~eor~ of su,ldcn e'q~losiorls, let us suppose the feed pipe, or pump, to be choked ~ in this case, the water would soon sink below some parts of the boiler, which should be constantly covered by it. thus causin,,

• J • o

them to become heated to a much h@~er temperature tlian the water. The steam now being in contact with the heated metal, readily takes up the heat, and becomes surchaNed with it.* Since caloric wilt

Practical eng'ineers have fi'equently witnessed the destructicm of the pack- ing of pistons, by their becoming" charred, although tile steam issuing" w'ts in contact w th t ~e water, the leinperature of which (tld not exceed 230 dc.~rees.

not descend in water, it ¢allliot be taken "up by the.w~te~'?~:~!ek ~s below It. The steam thus surclarged~ wall:heat" the'upper=Slnf~ee: of the b o i l e r , in some cases, red-hot,* a n d w i l l igni: te: 'co~ls, :))~; '~i~y other combustible m a t t d r which m a y be in contact with it. I f ~ e water which is kent below tie surchar,-~ed steam~bvthe~nresSUre of it, should, by an~y circumstance, be m'~(le to take up the e'xcess 5f caloric in. the steam\ as well as that fi'om the upper part of the boilel'~ which has become heated above the temperatur~ of tim Watei'~:in con- seq~uence of the water having been allowed to get too low: it will instantly become highly elastic steam, and an explosion cannot be p r e v e n t e d by any sa fe ty va lve h i t he r to used. To show how the water m a y be s u d d e n l y b r o u g h t in c o n t a c t w i t h the over-heated parts of t he bo i le r , as we l l as w i th the s u r c h a r g e d s t e a m , i t wi l l be neces- sary to s t a t e the f i ) l lowing litcts.

As l o n g as w a t e r is n o t h e a t e d above o~1~ deg rees , i t wi l l s i m p l y boil,, and-f iveg off atmos, l~heric ,steam, , w i t h o u t the w a t e r h a v i n g a n y t e n d e n c y t:) r ise wi th i t ; I)ut. as i t b eem nes more and more elevated m t e m p e r a t u r e , i t s dis l )osid(m to rise w i th the s t e a m becomes n m r e and m o r e apl )arenr . A s t im s team presses on the su r face of the water, in the s a m e rati¢~ as the w a t e r i nc reases in t empera tu rc~ i t only bo i l s wi thou t r isina ' , as w h e n a t a tmos ~heric p r e s s u r e ; bu~: i f t he s t e a m should be d r a w n off t i t s ter t ime ~t is ~;enerated, th~s a r h h c m l p r e s s u r e would be t a k e n (~tl: and the w a t e r would r ise wi th the s t e a m in pro- porgi(m to the s u d d e n n e s ~ and r a p i d i t y of i!s escape . T h e w a t e r and s t e a m in th is mixed s ia ie . ~hu::, f i l l ing e v e r y part. of the boiler~ the exces s ~)f ca lo r ic in the surcb.arged s i eam, a~s well as the e x t r a hea t f r o m the boiler~ wil l be i n s t a n t l y t a k e n tip by the w a t e r M i l c h r ises w i t h the s t e a m , by which m e a n s t h e s t eam b e c o m e s suf f ic ien t l~ dense (or power f id ) t o /n ' ( , duce t h e fittal eiti~cts too ot'to~n c x p e r i c n c e % m)t o n | y fi'-bm hi~li , bfi t fl:om low p r e s s u r e bmle r s . . I f , fi)r h~stance~ t h e w a t e r (as ha~ 'be . tbre been no t i ced) shou ld b e suf fe red to ge l b e ,

It is very evident, that this steam was "surchar?..:ed With heat . and was m u c h above tl~e temperature of t he water upon which it was reposing', :ind in a snit- able state to produce explosion, had the water been allowed f~o rise With the steam, by (h'awin~ it off titster than it was ffenerated.

:~r. Moyle, e. practical engi~:eer from Cornwall, gave me the following" in- t e r c s t i ~ fi~e~:

On going into his boiler room. he observcd a ladder, the foot of which rested on the top of his boiler, to be in fl;m'es: he instantly ascertained that the top of the boiler, fi'om some cxusc which tte was thee unable to determine, had be- come rcd-ho~; with all possi!de pr~mptitude he ordered the fire to he quenched, which, probably, saved his premises, and, perhaps, his life. Nr. Moyle found, upon examining the boiler, when co/d, that very tittle watcr remained in it.

A stronger case still, was float of an explosion at the iron foundry at Pitts- burffh, North America. As is the practice in North America, a high pressure eng'ine, of sixty or eig'hty hm':~e power, was SUpldied with steam fi'on: three sepa- rate cylimh'ical boilers, each being" thirty inches diameter, and eighteen feet lon~. One of these boilei-s had fin' smnc time bern observed to be getting r~d - hot; hut, as the other tw¢) supplied a suP, ici<-ncy of ste:'.m f(~l' the work then doin;::, it wns disrcl~:~rd.:d, tm~.il it expi(~dcd. Tb.c i'll:ill| bOk~y Of 1.he boiler sepal'sled i"r~)m one ~)f it:; cml:~, at an :m~'i~: ~t" ~.:~; dc!~l'ecs, mid 1):tsscd el]' like ~ rocket lhr(>m;i~ lt~( ~ :'~)~i" ~)!" ~.!~<- I,~fiid;.!,-, .;~d l,mded ab,ut (;(,0 l~'et J)om it,

420 ThE vr~A.~t~LI~ JOURNAL A~D

low any part of the boiler, which is exposed to the fire~ the steam wiii soon become surcha,'~ied with heat . I f a boiler~ thus c i rcumstanced, should have the weight taken from the safety" va iv%~or a small rent be effected in the boiler ti'om i ts ~ivin~ way b~ the pressure of the steam, an explosion will be sure to ~'olioxV. X r e m e d y ' f o r this kind of explosion, which appears to be the 0nly serious one, is that of not allowing the water to subside below a n y part of the boiler which is exposed to the fire. In ca se the water shoubl sett le, i t may be known by" having a tube, with i ts upper end t ru!npe t -mouthed , and its lower end fixed m the boder , en te r ing a few inches beh)w the smface of the water ; then, as soon as i t subsides suif iciently to allow the s team to blow ott; the b las t will give warn ing flint no t ime should be l o s t i n Supplying water , or checking the fire.¢ W l i e n highly surcharged s team is rusll inz from the safety valve~ or any other aper ture , i t may be known by it,~ perfect invisibi l i ty, even i n ' t h e coldest day, no r ca~ i t be seen at any d i s tance from the valve or cock; i t is, however, condensible; as may be seen by hold ing any cold substance in its range.

* It was stated in evidence at the coroner's inquest taken ~t the IIumber, hi the case of an explosion on board of ~he Graham steam boat, that just before the explosion took place, twenty pounds were taken off the safety valve. ~Now, if the steam in this boilcr bad been properly generated, the relief'.~iven to the safety valve, could not have produced explosion;' but if the water lind got low in the boiler, (as was probably the case,) and the steam surcharged with heat, the ready way to produ'ce explosion, was to allow the steam to escape hs ter than it was generating', when kept in the lower part of the boiler by the pressure of the contined steam.

Sever:d instances ]lave occurred when there has been sufficient warning, by the rttshing- of the steam from a rent or fi'acture, for the bystanders to escape from in illry before tile explosion took place. There has ])een, at least, one case, where the boiler was raised fl'om its bed, into tbe air, by the force of the steam issuing" from the rent, (upon the principle of the rocket,) hcfbre the water ha,.i stdtlciently expanded by the removal of" the steam, caused by the rent or fracture, to take up the heat of the boile15 and tile surcbar~ed stearrl; wt!ea an explosion took place "tfter the boiler had been raised many ik.et in the atmo. sphere, aud it separated with a very ffreat report, one part rislngstill higher, while the other was dashed with g'reat force o~ the around. It is, I believe, a tb.ct, tl,at more persons have been killed by low, than by high, pressure boilers.

It. is but about twelve months, since sixteen persons were killed by the burst- lag of a low pressure boiler, in Ftintsbire. Hig'b pressure boilers have since been s~tbstit~tted. Some of the most dreadful accidents from explosion,s which have taken place in America, h.'~ve occurred from low pres~ure boilers.

This will apply only to low pressure boilers, on account of the heiffht of the column which would be required to balance the pressure of the steam. The hig'h pres:~ure eng'itles, as used in Cornwall, would require a cobrmn, oa- r) iiI g" fl'nm 60to 120 tk'et; and the new high pressure safety el,g-the, now coming' heft)re the public, wo,lhl require a cohmm nmre than fottr times as hig'h as St. P:III]~:-. " (',l'OS¢,~ t o b ' , t I a t l c e ~,lle s t e a n l ,