By P . H. Wilson, M.I.Mech.E. (Stanton Ironworks Company, Limited).
Efficiency a n d econom y a re th e two essentials in th e successful o p e ra tio n of an y process. As th e c u p o la is o fte n re f e rre d t o as th e h e a r t of th e fo u n d ry , i t is e ss e n tia l t h a t i t sh o u ld n o t be con
s id e re d m erely as a s h a f t in to w hich so m uch iron a n d coke is d u m p ed , a n d a ir blown th ro u g h to p ro d u ce iro n in a m o lten s ta te . T his used to be th e case y e a rs ago, b u t to -d ay m o st foundrym en re a lise th e im p o rtan ce of m ore scientific control in th e process o f m e ltin g iro n .
Tin th e p ro d u c tio n of any class o f c a stin g i t is, in th e firs t place, im p o r ta n t t h a t th e m o lten iron is o f th e c o rre c t com position an d a t a su itab le te m p e r a tu r e fo r castin g . I t is false economy to a tt e m p t to red u ce coke co n su m p tio n a t th e ex
pen se of a h ig h p e rc e n ta g e of w aster castings.
To p ro d u ce s u ita b le m o lten iro n economically m a n y fa c to rs m u s t be d e a lt w ith. These will be tr e a te d in th e i r p ro p e r sequence.
T h e r e a l efficiency of a cupola m ay be m easured by th e r a tio of th e h e a t in th e m o lten m etal to th e h e a t g e n e ra te d in th e cupola. T herm al balance-sheets h av e been published in P a p e rs by m a n y w rite rs on th is s u b je c t d u rin g th e la s t few y e a rs. T he conclusions a rriv e d a t fro m these balan ce-sh eets show t h a t i t is chiefly th e value of th e p e rc e p tib le a n d la t e n t h e a t lo st in th e gases w hich decid es th e th e r m a l efficiency of a cupola fu rn a c e . I n o th e r w ords, th e cooler th e escaping gases, th e h ig h e r th e p e rc e n ta g e of carbon d io x id e, o r conversely, th e low er th e carbon m onoxide in th e gases, th e g re a te r th e h e a t effi
ciency of th e cupola. M any id eas h a v e b een tr ie d to u tilis e th e w aste h e a t p assin g u p th e cupola s ta c k , b u t very litt le success h as been a tta in e d in th is d ire c tio n . *
M an y cupolas o p e ra tin g successfully to-day vary v ery li tt le in d esig n fro m th o se in use fifty y ears ago. W h ilst th e re s u lts o b ta in e d d ep en d on ce r
ta in p rin c ip le s in th e d e sig n of a cupola, i t is n o t th e w r ite r ’s in te n tio n to d e a l in th is P a p e r w ith
th ese d e ta ils , a p a r t fro m th e c o n stru c tio n w hich d ire c tly affects th e a ir su p p ly a n d d is trib u tio n of th e p ro d u c ts o f com bustion.
T he com position of th e m o lten m e ta l is m ore o r less d e te rm in e d by th e an aly sis o f th e m a te ria ls ch arg ed in to th e cupola, b u t inefficient w o rk in g lias a serio u s effect o n c e rta in e le m e n ts in th e iron d u rin g th e m e ltin g o p e ra tio n . S ilicon a n d m a n gan ese m ay (be co n sid erab ly re d u c e d d u e to exces
sive o x id a tio n . F u r t h e r , th e a b so rp tio n o f d e t r i m e n ta l gases affects th e te m p e ra tu re a n d flu id ity of th e m o lten m e t a l ; also its p hysical and m ech a n ical p ro p e rtie s.
T he efficient w o rk in g o f an y cu p o la dep en d s p rim a rily o n th e q u a n tity of a ir s u p p lie d a t a s u ita b le p re s su re a cco rd in g to its c a p a c ity . T he m e ltin g c a p a c ity of a cu p o la is d e te rm in e d by its effective d ia m e te r a t th e m e ltin g zone.. I t h as been p ro v e d t h a t good re s u lts a re o b ta in e d in p ra c tic e by b u rn in g 1 lb. o f good coke p e r h o u r p e r sq. in. of cross-sectional a re a a t th is p o in t.
T his is e q u iv a le n t to fro m 10 to 12.5 lbs. o f iron m elted p e r sq. in . of a r e a p e r h o u r. T h erefo re, a c u p o la w ith a d ia m e te r o f, say , 4 f t . 6 in . is cap ab le of m e ltin g econom ically a p p ro x im a te ly 10 to 12.5 to n s p e r h o u r.
B y th is i t will be seen t h a t th e figures given fo r th e m e ltin g c a p a c ity of a cu p o la re la tiv e to its cross-sectional a re a .at th e m e ltin g zone v arv to th e e x te n t of 25 p e r c e n t. T his is d e p e n d e n t on th e p e rc e n ta g e of coke co n su m p tio n to iro n m elted , an d .also th e p e rc e n ta g e of c arb o n in th e coke.
T h e m e ltin g r a t e p e r h o u r can be c a lc u la te d fo r an y sized cu p o la g iv en th e coke consum ption p e r to n of iro n a n d th e d ia m e te r, as fo llo w s: —
M = Melting rate in tons per hour.
D = Diameter of cupola in inches.
P = Percentage of coke to iron (by weight).
M _ ttD- x 1 X 100 _ D2 X 100 _ 0.0351 x D2 4 x P X 2240 “ 2851 P P
F o r exam ple, in a 4 f t. 6 in . d ia . cu p o la w ith a coke c o n su m p tio n of 8 p e r c e n t, th e m e ltin g ca p a c ity w ould b e : —■
0.0351 x 542
M = --- = 12.78 tons per hour.
I f th e coke r a tio is 1 to 10, o r 10 p e r cen t., th e m e ltin g r a t e -would be 10 .2 to n s p e r h o u r.
F ro m th e albove i t w ill be seen t h a t th e h ig h er th e coke to iro n ra tio th e g r e a te r th e m eltin g c a p a c ity of t h e cupola p e r h o u r.
H a v in g d e te rm in e d th e o u tp u t of th e cupola, th e a m o u n t of a ir re q u ire d can be a rriv e d a t fro m th e e q u a tio n :
C + 02 = CO, 12 + 32 = 44 '
T h a t is to say , to com bust 12 lbs. of carbon com pletely to 0 0 2, 32 lbs. of oxygen are req u ired . T his is e q u iv a le n t to 1 1 . 6 lbs. of a ir o r 152.4 cub. f t. p e r lb. of carbon.
As th e q u a lity of coke v aries, th e carbon con
t e n t m u s t be ta k e n in to c o n sid eratio n in calcu
la tin g th e volum e of a ir req u ire d p e r lb. of coke.
F u r th e r , th e volum e of a ir p er to n of iro n m elted w ill v a ry w ith th e q u a n tity of coke used p er to n of iro n .
T his can be e s tim a te d fo r d iffe re n t d iam eters of cupolas fo r an y given coke r a tio of a known c arb o n c o n te n t, as follows : —
V = Vol. of air per hr. in cub. ft.
v = Vol. of air per ton of iron melted.
D = Dia. of cupola in inches.
P = Percentage of coke to iron charge (by weight).
C = Percentage of carbon in the coke.
ttD2 X 1 X 152.4 x C
V - 4 100
r = ~ = 34.54 C.P.
M
T h is gives th e th e o re tic a l volum e of a ir neces
sary , b u t in a c tu a l p ra c tic e allowance m u st be m a d e fo r loss th r o u g h v ario u s causes. This a m o u n t of loss w ill d ep e n d on th e position of th e b la s t-in d ic a tin g in s tru m e n t re la tiv e to th e tu y è re s. U su ally i t is placed on th e a ir m ain le a d in g to th e w ind b elt, an d in >a position con
v e n ie n t to th e o p e ra to r. T he a c tu a l loss between th e b la s t g au g e a n d th e tu y e re s can be e stim ated fo r a n y cu p o la a cco rd in g to th e g en eral a rra n g e m e n t of th e p ip in g , e tc .
H a v in g o b ta in e d th is , th e a c tu a l volum e re
q u ire d .at th e p o in t a t w hich th e b la s t in d ic a to r is fixed can be c a lc u la te d as fo llo w
s:—-L = The percentage loss.
Vm = Actual volume of air per min.
w _ ^ X i X 1 5 2 . 4 x C \ / , L \ V 4 x 60 x 100 / X V J00/
Vm = 0.01994 D2 C X ( l +
T he m eth o d of in tro d u c in g th e a ir in to th e f u r naces is th e n e x t c o n sid e ra tio n . V a rio u s ty p e s of tu y è re s a re in use, being c ir c u la r , s q u a re , r e c t
a n g u la r an d oval sh a p e d , b o th p a ra lle l an d flared.
I n som e cases a sin g le row a n d in o th e rs tw o or m ore row s a re used.
T h e n u m b e r an d s h a p e o f tu y è re s h a s lo n g been a d e b a ta b le p o in t. The m a in p o in t, how ever, is t h a t th e y should be sufficeintly la r g e to a d m it the c o rre c t q u a n tity o f a ir , a t a p re s su re n o t h ig h e r th a n necessary fo r th e a ir to p e n e tr a te th e coke bed a n d d is tr ib u te i t u n ifo rm ly a t th e m e ltin g zone.
H a v in g fo u n d th e p re s su re necessary , an d know in g th e volum e of a ir to be p assed , allow ing for loss in fric tio n , e tc ., th e c o rre c t tu y è r e a re a can be c a lc u la te d t o g iv e th e n e c e ss a ry r e s u lt fo r any size of cupola. T h e re fo re , th e r a tio o f th e a re a of th e tu y è re s to t h a t of th e cu p o la w ill v a ry a cco rd in g to th e a re a of th e cupola.
T h e 4 f t . 6 in .-c u p o la u n d e r c o n sid e ra tio n , in w hich m o st of th e te s ts re p o rte d in th is P a p e r w ere c a rr ie d o u t, h a s a s ta g g e re d row o f tu y è re s oval in sh a p e , th e a re a b e in g 18 p e r c en t, of th e cupola a r e a , a n d i t h as been fo u n d t h a t a p re s s u re of 18 in . w .g. is a d e q u a te to give a p ro p e r d is tr i
b u tio n o f th e a ir.
A n o th e r im p o i'ta n t d e ta il in tu y è r e d e sig n is t h a t e a c h tu y è r e sh o u ld be fitte d w ith a u x ilia ry valves, so t h a t w hen w o rk in g d ir ty th e y can be s h u t off a n d b u rn e d c le a r. P o k in g o f tu y e re s should n o t be necessary, b u t i t is ad v isab le to p ro v id e h in g e d s ite holes, th r o u g h w hich a b a r m ay be in s e rte d to rem ove an y o b s tru c tio n . S u ch an a rr a n g e m e n t is show n in F ig . 1.
T he effective h e ig h t of th e cupolas ( t h a t is, th e d is ta n c e fro m th e to p of th e tu y è re s to th e c h a rg in g door) is im p o rta n t. T h e d e p th of th e well is n o t so im p o rta n t, th is d e p e n d in g on th e re q u ire m en ts of th e fo u n d ry . As th e effective h e ig h t
d e te rm in e s th e tim e c o n ta c t betw een th e h o t gases a n d th e b u rd e n , th e h ig h e r th is is th e m ore h eat is ta k e n fro m th e gases iby th e descending charge.
T h ere is, o f course, a lim it to th e c a rry in g ca p a c ity of th e coke. A h e ig h t e q u iv a le n t to from fo u r
Fi g. 1 . — Hi n g e d Si t e Ho l e f o r Re m o v i n g Ob s t r u c t i o n s.
o r five tim e s th e d ia m e te r a t th e tu y e re level has been fo u n d to give good results.
I n m echan ically -ch arg ed cupolas these may be g re a te r to allow a level d ep o sitio n of th e charges below th e c h a rg in g doors. To prove how the 11 effective h e ig h t ” of a cupola affects th e
tern-p e r a t u r e of th e ris in g gases, te m tern-p e ra tu re s of th e gases w ere ta k e n sim u lta n e o u sly a t d iffe re n t h e ig h ts up th e sta c k on tw o cupolas. The figures o b ta in e d w ere as fo llo w s: —
Cupola A Cupola B
Effective height . . . . 21 ft. 12 ft. 6 in.
Diameter a t tuyeres .. 4 ft. 4 ft. 6 in.
Ratio (height diameter) 5.25 2.77
T he te m p e ra tu re s o b ta in e d in deg. C. w e re : —
Cupola A. Cupola B.
At charging door .. 280 At charging door .. 450 9 ft. below 440 2 ft. 6 in. below . . 600
13 ft. „ 900 6 ft. below 900
16 ft. „ 1,160 8 ft. 6 in. below .. 1,220
At tuyères 1,600 At tuyeres.. 1,650
Blast volume per min. (cupola A ).. .. 5,000 cub. ft ,, „ ,, (cupola B ).. . . 5,400 cub. ft.
Blast pressure w.g. in inches (cupola A) . . 19
,, ,, ,, ,, (cupola B) . . .. 18
I t is obvious fro m th e above figures t h a t th e effective h e ig h t o f cu p o la B as to o low com pared w ith A, th e loss in p e rc e p tib le h e a t b e in g high, e sc a p in g gases b ein g imuch cooler in th e h ig h e r cupola. These re s u lts a r e show n in g ra p h ic a l form in F ig . 2. T h e te m p e r a tu r e s w ere ta k e n w ith th erm o -co u p les of v a rio u s ty p e s. F o r th e h ig h e r te m p e ra tu re s th e s e w ere enclosed in n ichrom e steel s h e a th s, w hich m e lte d im m e d ia te ly a f t e r th e re a d in g s h a d been ta k e n . T he te m p e r a tu r e a t th e tu y e re s was ta k e n w ith a “ D is a p p e a rin g F il a m e n t P y ro m e te r.”
I t is in te r e s tin g t o n o te t h a t th e cu p o la A m elted d u rin g th e one h e a t 250 to n s of m e ta l, an d v ery l i t t l e v a r ia tio n in te m p e r a tu r e w.as n o te d d u rin g t h a t p erio d . T hom pson a n d B e c k e r p o in t o u t in th e i r P a p e r* o n “ T h e C h e m istry of th e C u p o la ” t h a t w hen in e q u ilib riu m a m ix tu r e of CO a n d C 02 te n d s as th e te m p e r a tu r e fa lls to ch an g e its co m p o sitio n so t h a t ,a d e fin ite a m o u n t of each gas is p re s e n t a t a d efin ite te m p e r a tu r e . T his w ould te n d to c au se in th e s ta c k a g ra d u a l d is a p p e a ra n c e o f CO an d its conversion in to CO„.
T h is is a s lig h t ¡argum ent in fa v o u r of cooling of th e gases. O f course, th i s re a c tio n w ill be g re a tly m in im ised o w in g t o th e h ig h v elo city of
* P roceed in gs, I n s t. B rit, F ou n d ryn ien, V o l. x ix ., p . 1 5 6 .
X 33J Nl S3H3M U 3A0Stf 1H0I3H
Tlmpzrrtuzz/V °c Fig, 2.—TemperaturesoftheGasestakenSimultaneouslyatDifferentHeightson
th e ascen d in g s tre a m o f gases, b u t m ay 'be f u r th e r aid ed by re d u c in g th e sp eed of th e gas s tre a m — t h a t ,is, th e b la s t p re s su re . Also', t o a ss ist in th is re a c tio n , th e a r e a o f th e s ta c k m a y 'be e n la rg e d above th e m e ltin g zone. T h is h a s been fo u n d to be effective a n d to in crease th e m e ltin g r a t e ow ing to> p re h e a tin g of th e d e sc e n d in g ch arg e.
The m o re slowly th e gases rise, th e m o re com plete th e h e a t tr a n s fe r e n c e , a n d th e lo w er th e CO in th e e sc a p in g gases, th e cooler th e to p o f th e cupola a n d th e b e tt e r th e c o n d itio n s f o r c h a rg in g .
A n o th e r im p o r ta n t f a c to r in c u p o la p ra c tic e is th e c h a rg in g of t h e m a te ria ls . P ig -iro n , scrap , coke a n d flu x in g m a te ria l sh o u ld b e p ro p erly w eighed, an d to o b ta in th e n ecessary r e s u lt ,in th e r e s u lta n t m e ta l th e iro n sh o u ld be c h a rg e d a c c o rd in g to an aly sis. T h e w e ig h t a n d d is tr ib u tio n o f th e charges w ill v a ry a c c o rd in g t o th e size of th e cupola. I t is of v ita l im p o rta n c e t h a t th e lay ers of m a te ria ls should be d ep o sited in a level plan e.
T he w eig h t of ir o n c h a rg e s u ita b le fo r an y size of c u p o la can be e s tim a te d fro m th e w e ig h t o f th e coke la y e r. T he d e p th of th e coke la y e r should be sufficient to fill com pletely th e cross se c tio n of th e fu rn a c e w ith a m inim um i th ic k n e ss. No accu
r a t e figures can be g iv en fo r th is r e la tiv e t o th e a r e a o f th e cupola, as th e p h y sical c o n d itio n of d iffe re n t b ra n d s v a ry , also th e c a rb o n c o n te n t.
T o o b ta in th e w e ig h t of th is volum e o f coke, th e comm on p ra c tic e is t o c o n s tru c t >a r in g of b rick s co rresp o n d in g w ith th e d ia m e te r of th e cu p o la lin in g , in to w hich th e coke is placed.
L im esto n e, o r o th e r flu x in g m a te r ia l, should be of u n ifo rm size, an d ch a rg e d in p ro p e r q u a n titie s acco rd in g t o t h e a m o u n t o f s a n d an d fo re ig n m a te r ia l a d h e rin g to th e p ig -iro n a n d sc ra p ; 35 lbs. to 50 lbs. o f lim e s to n e p e r to n of iro n should be sufficient. A n excess o f lim esto n e in creases th e coke co n su m p tio n land causes a g r e a t e r w ear on th e lin in g . A f u r t h e r p o in t is th e h e ig h t of th e coke bed above th e tu y è re s . The effect o f th is on th e q u a lity an d te m p e r a tu r e of m o lte n m e ta l, also th e coke c o n su m p tio n , is
im p o r ta n t in cu p o la p ra c tic e .
I n m a n y cu p o la p la n ts know n t o th e w rite r insu fficien t (a tte n tio n is p a id to th e p e rio d s of sla g g in g . I t is b a d p ra c tic e t o hold th e sla g in
th e cupola to o long, as i t ten d s to b la n k e t th e m e ta l fro m th e h e a t. C upolas n o t ta p p in g con
tin u o u sly should Ibe slagged a t in te rv a ls of n o t lo n g e r th a n tw o hours. F u r t h e r , p erio d ical
¡analyses ¡of th e sla g should be ¡made to check th e iro n losses. W ith iro n charges fa irly free from r u s t, t h e FeO c o n te n t of th e slag should ¡not exceed 3.0 ¡per cen t.
H a v in g d e a lt briefly ¡with some ¡of th e condi
tio n s w hich ¡affect th e w orking of a cupola, th e p o in ts w hich, in th e w r ite r ’s ¡opinion, are of v ital im p o rta n c e will be d e ta ile d .
To' m e lt iro n , th e tw o p rin c ip a l m a te ria ls re q u ire d ¡are fu e l (coke) ,and ‘b last (¡air). I t is in th e icorreot d is trib u tio n ¡of these tw o facto rs th a t t h e efficient w o rk in g o f th e cupola depends, ¡par
tic u la r ly th e a ir supply. T h e oxygen in th e a ir is cap ab le of com bining w ith th e carbon of tb e coke to form tw o oxides of carbon, c arb o n dioxide 0 02 an d carb o n m onoxide CO. C arbon dioxide is fo rm ed w here th e r e is excess of oxygen, ¡and c a r
bon m onoxide w hen th e r e is an excess of carbon.
T he th e r m a l v alu e of th ese reactio n s varies g re a tly . C arbon b u rn in g to CC2 g en erates 14,500 B.Th.TJ. p e r lb. of carbon. C arbon b u rn in g toi CO ¡generates only 4,500 B.Th.TJ. p er lb.
of c arb o n .
I t is obvious, th e r e fo re , t h a t th e m axim um th e r m a l efficiency is o b ta in e d w hen th e carb o n is b u rn e d to- 0 02 in one sta g e . I f th e carbon is b u rn e d t o CO, an d is f u r th e r oxidised to C 0 2, th e th e r m a l efficiency is red u ced by ap p ro x im ately 38 p e r cen t. T o o b ta in m ax im u m efficiency th e p e rc e n ta g e of CO fo rm e d m u s t be k e p t a t a m in i
m um . W h en th e ¡air is forced in to th e la y e r of in c a n d e sc e n t ooke above th e tu y e re s, com bustion ta k e s place. I f th e -coke la y e r is u n ifo rm in size, sh a p e ¡and d isp o sitio n , ¡and th e a ir is supplied a t th e c o rre c t velocity a n d volum e, th e n com bustion w ould be u n ifo rm ¡across th e coke la y e r. I f these co n d itio n s in th e ¡cupola a re n o t sufficiently u n i
fo rm , an d th e a ir a d m itte d ¡at too low a pressure, i t 'will n o t p e n e tr a te sufficiently to th e c e n tre ¡of th e fu el, conseq u en tly t h e com bustion does n o t ta k e p lace evenly across th e section. I t te n d s to be g r e a te s t n e a r th e lin in g of th e cupola, and
th e (com bustion ta k e s t h e fo rm of an in v e rte d cone.
O n th e o th e r h a n d , if th e b la s t p re ssu re is high, th e n th e r e is a te n d e n c y fo r th e com bustion to be g r e a te r ;at th e c e n tre a n d th e .cone to be reversed.
I n o rd e r t o d e te rm in e th e a m o u n t of a ir
pene-Fi g. 3 . — De t e r m i n i n g t h e Am o u n t o p Ai r Pe n e t r a t i n g t o Di f f e r e n t
Po i n t s i n t h e Ar e a a t t h e
Me l t i n g Zo n e.
t r a t i n g t o d if fe re n t p o in ts in th e a re a a t th e m o ltin g zone, a n e x p e rim e n t was ¡made on a 4 f t . 6 in . d ia . cu p o la. P rim a rily , a se rie s of tu'bes eq u ally sp aced w ere placed acro ss th e cu p o la, th e low er ends of w hich w ere p e rfo ra te d a n d re s te d o n t h e to p of th e coke b ed , th e u p p e r
3i>™o ¿ n±ar\ S3H3M n i l a n s s i x d
n 2
DinOFCupolbIN PIET Fia. 4.—DiagramshowingPressureObtainedatEachTubeinExperimentDeterminingAmount cfAirPenetratingtoDifferentPointsattheMeltingZone.
en d s ¡being c o n n e c te d t o w a te r-p re ssu re g auges.
A photograph, ta k e n a t t h e tim e o f th e e x p e ri
m e n t is show n in F ig . 3.
T he cu p o la w as c a re fu lly ch a rg e d a n d blow n in in th e u su a l w ay, p ro v isio n b e in g m a d e to m a in ta in t h e c o rre c t sp a c in g o f th e tu b e s d u r in g th e te s t. T he p re s su re s o b ta in e d a t e<ach tu b e in d i
c a te d th e volum e o f a ir p a s s in g a t t h a t p o in t.
A rra n g e m e n ts w ere m a d e to m a in ta in a n ap p ro x i
m a te ly c o n s ta n t volum e o f a ir w ith v a ry in g p res
su res. I n th e firs t p lace, th e a ir w as a d m itte d a t a p re s s u re o f 12 in . w .g. T his w as in creased to ~24 in . w .g. T h e p re s su re s o b ta in e d fro m each tu b e w ere p lo tte d a n d a r e show n on d ia g ra m , F ig . 4, fro m w hich i t w ill b e n o te d t h a t in th e fo rm er case th e c u rv e fo rm s a d is tin c t in v e rte d cone, w h e re a s t h e cu rv e o b ta in e d fro m th e h ig h e r p re ssu re is d ir e c tly o p p o site .
T h e d e p th of th e cone fo rm e d by t h e h ig h e r p re s su re as n o t iso in te n s iv e as t h a t o f th e low er p re ssu re s. T h is m a y a c c o u n t fo r th e tr o u b le ex p e rien ced w ith d ir ty tu y e r e s (r e fe rre d t o p re viously) w hen th e tu y e r e a r e a is la r g e com pared w ith th e d ia m e te r of t h e cu p o la, o r th e velocity of th e a ir is insufficient t o p e n e tr a te t h e charges fu lly , t h e te n d e n c y b ein g fo r t h e slag a n d ir o n to flow th r o u g h a n o u te r r i n g o f th e m e ltin g zone, th e p re s s u re o f a i r a t th e tu y e r e s b e in g insuffi
c ie n t t o p re v e n t scaffolding a t t h e tu y e re s , cau sed by lo cal ch illin g . T his em p h asises t h e f a c t t h a t a c o rre c t c o m b in atio n o f p re s s u re a n d volum e is necessary t o o b ta in a n id e a l m e ltin g c o n d itio n .
T h is e x p e rim e n t was re p e a te d , m a in ta in in g th e siame volum e a t a p re s su re o f 18 in . w .g ., w hich h a d been fo u n d to be t h e c o rre c t w o rk in g p re ssu re
T h is e x p e rim e n t was re p e a te d , m a in ta in in g th e siame volum e a t a p re s su re o f 18 in . w .g ., w hich h a d been fo u n d to be t h e c o rre c t w o rk in g p re ssu re