LABORATORY AND PLANT - The Journal of Industrial and Engineering Chemistry, Vol. 6, No. 5

T H E P Y R O M E T E R I N T H E A S S A Y M U F F L E 1 B y Frederic P . Dew ey*

Standing alone, b y itse lf, t a p y ro m e te r rea d in g has absolutely no v a lu e as a co n tro l of a ssa y o p eratio n s in a muffle or as a gu id e to th e a ssa ye r in c a rry in g on such operations. T h e reasons fo r th is are v a rie d an d co m plex. (1) T h e te m p e ra tu re t h a t co n tro ls th e success of the operation is th a t of th e le a d b u tto n u n dergoing oxidation. A t p rese n t we h a v e no m eans of learn in g this tem perature u n der p ra ctica l w o rkin g co n d itio n s, so that some su ita b le p lace m u st be selected w ith in the muffle for th e lo c a tio n of a p y ro m e te r. (2) U n fo r

tunately, h o w e ver, th e re is a b so lu te ly no ap p ro ach even to a fixed relatio n b e tw e e n th e p y ro m e te r readin g at any given p o in t a v a ila b le and th e te m p e ra tu re of the oxidizing b u tto n . T h e o x id atio n of th e lead su p plies much h ea t to th e b u tto n , b u t its effect upon th e pyrometer is n eglig ib le. One fa c to r g o ve rn in g th e amount of h ea t u tilize d b y th e b u tto n is th e ra te of oxidation of th e lead , and th is in tu rn is, w ith in w ide limits, largely influ enced b y th e p assage of th e air o v er the button, so t h a t to fu lly u tilize and a p p ly th e p y rometer reading w e m u st also k n o w th e h e ig h t of th e barometer and th e e ffe ct of v a ria tio n s in th e b aro m eter readings upon th e d ra ft of th e p a rticu la r m uffle u nder consideration. F u rth e r an d m ost im p o rta n t, fro m a practical sta n d p o in t, is th e freed o m of e n tran ce fo r th e air to the m uffle. In o th e r w ords, b y m a n ip u la tin g the door or th e sto p p e r of th e m uffle, w id e ly v a r y in g differences b etw e en th e b u tto n te m p e ra tu re and th e pyrometer readin g m a y be prod u ced . T h e effe ct of the door conditions is tw o fo ld . I t a ffects th e su p p ly of air to the b u tto n and also th e a ctu a l te m p e ra tu re of the bottom s of th e m uffle on a cco u n t of th e v a r y in g amounts of air th a t h a v e to b e h e a te d th e re in passing through th e fu rn ace . F in a lly th e relatio n of th e p o si

tion of the b u tto n w ith in th e m uffle to t h a t of th e p y rometer is v ita l. T h erefo re , to in te llig e n tly u tilize any stated p y ro m e te r re a d in g it is essen tial to h a v e exact inform ation u po n a v a r ie ty of o th er con d itio n s surrounding th e op eratio n.

Bradford3 p o in te d o u t th e in co n sisten cies of v a rio u s statements regard in g p y ro m e te r read in gs in a ssa yin g and well estab lish ed fa cts, such fo r in s ta n ce as ad vising a tem p eratu re of 700° to 750° for cu p ellatio n when it requires a t lea st 906° to fu se lith a rg e . In a series of tests he d em o n strated th e larg e a m o u n t of heat supplied b y th e o xid atio n of th e lea d and th e higher te m p eratu re ' th e re b y a tta in e d b y th e b u tto n . His arrangem ent of a p p a ra tu s w as in gen iou s, b u t nsky to th e p y ro m e te r cou p le an d n o t a p p licab le to routine work. H e g iv e s an e x ce lle n t d escrip tio n of the conditions im m e d ia te ly su rro u n d in g a cu p ellatio n .

Pulton, A n d erson , G oo dn er an d O ssa4 d eterm in ed

1 l resen tc d a t th e 4 9 th M e e tin g o f t h e A . C . S ., C in c in n a t i, A p ril 7 -1 0 , and p u b lish e d b y p e rm is s io n o f th e D ir e c to r o f th e M in t. P u b lis h e d niu ta n co u siy b y th e A m e r ic a n I n s t i t u t e o f M in in g E n g in e e rs .

A ssayer, B u r e a u o f th e M in t.

1 T h is Journai,, 1, 181.

* West. C hem . M e t., i , 3 1 .

th e d ifference in te m p e ra tu re b etw e en an e m p ty cupel and th e cu p ellin g lead in an a d jo in in g cupel as 1 4 5 0, an d also g iv e va rio u s oth er te m p e ra tu re d ete rm in atio n s, u n der th e con d itio n s em p lo ye d b y th em .

F o r a lo n g tim e I h a v e been e n gage d u po n an in v e s tig a tio n in to th e co n d itio n s su rro u n d in g th e a ssa y of gold b u llion as a ffectin g th e a cc u ra c y of th e resu lts ob tain ed . N a tu ra lly th e q u estion of th e te m p e ratu re of c u p ella tio n e a rly a ttr a c te d a tte n tio n , b u t th e re w ere so m a n y o th er co n d itio n s to be in v e s tig a te d w here our in fo rm a tio n w as m eagre, w hile th e te m p e ra tu re q u es

tio n seem ed to be u n d e r f a ir ly good co n tro l b y th e ey e of exp erien ced cu p ellers, th a t th e use of th e p y ro m e te r w as n o t a c t iv e ly ta k e n up u n til re ce n tly .

In th e e a rly d a y s of th e in v e s tig a tio n v a rio u s p o in ts rega rd in g te m p e ra tu re w ere c a re fu lly considered and som e of th e p rob lem s w ere w o rke d ou t. Som e of th e problem s p rese n ted th e m se lve s w ith em p h asis. In th is co n n ectio n a carefu l d istin ctio n sh ould be d raw n b etw e en th e p ro b lem of a sce rtain in g th e effe ct of th e va rio u s c o n d itio n s . of th e cu p e lla tio n upon th e te m p e ratu re of th e cu p ellin g b ead and th e p ro b lem of th e re g u la tio n an d a d ju stm e n t of th e se co n d itio n s so as to p rod u ce th e b e st p o ssible co n d itio n s for cu p ellin g, an d th e final p rob lem of estab lish in g a su ita b le in d i

cato r or gu id e to show th a t th e p ro p er co n d itio n s are being m a in ta in e d , and e sp e c ia lly an in d ica to r w hich m a y be ap p lied in d ifferen t m uffles and under v a r y in g conditions.

In a b ro a d and gen eral w a y th e tim e req u ired to w o rk off a g iv en w eig h t of lea d is a crude in d icatio n of th e te m p e ra tu re of th e c u p ella tio n . W h en c a rry in g on u niform w o rk in q u a n tity th e d ecreasin g size of th e b u tto n is a general gu id e fo r th e te m p e ra tu re and a rou gh n o ta tio n of th e tim e w ill o fte n be u sefu l in e x p la in in g irreg u larities o f th e resu lts. If th e general co n d itio n s rem ain u n ifo rm , a p ro lo n ged cu p ella tio n in d icate s la c k of h e a t, and a rap id one an excess of h eat.

In m a k in g tim e o b se rva tio n s it is essen tial to a d o p t som e fixed p o in t in th e o p eratio n s to b egin ta k in g th e tim e and a n o th er to sto p . If all th e o th er cond itio ns co u ld be rig id ly co n tro lled and th e tim e be v e r y c a re fu lly o b served , it w o u ld fu rn ish a good gu ide to th e te m p e ratu re , b u t it w o u ld b e a v a ila b le o n ly a t th e finish of th e ru n and co u ld n ot be used to chan ge con d itio n s d u rin g th e ru n. A lso , it cou ld n o t b e a p p lied a t o th er tim e s or p laces or u n der d ifferen t co n d i

tion s. A g a in it fu rn ish e s no p re lim in a ry e v id en ce th a t th e fu rn a ce is in go od co n d itio n before s ta rtin g th e w ork.

I t is, h o w e ver, h a rd ly e v er possible to co n tro l th e oth er con d itio n s and som etim es a cc id e n ta l v a ria tio n s creep in. On one occasion , w hen th e con d itio n s, in clu d in g th e te m p e ra tu re , a p p e ared to b e n orm al, it b ecam e e v id e n t - th a t th e lead w as n ot o xid izin g fa s t en ough.

A n ex a m in a tio n sh o w ed th a t in se ttin g a n ew m uffle th e w o rkm a n h a d n o t p u t th e slit in th e b a c k of th e m uffle e x a c tly o p p o site th e ch im n ey o u tle t. T h is ch o k ed off th e d ra ft and re ta rd e d th e o x id atio n . T h e re ta rd a tio n of th e w o rk w as, o f course, ex cessive, b u t

T H E J O U R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 6, No. 5 th is exp erience em p h asizes th e n a tu ra l effect of chan ges

in th e b aro m eter u po n cu p ella tio n . A re se ttin g of th e m uffle co rrecte d th e d ifficu lty.

A n o th e r post facto te m p e ra tu re in d ic a to r is th e a m o u n t of go ld abso rb ed b y th e cu p el in go ld bu llion a ssa yin g , h igh a b so rp tio n u n der sim ilar con d itio n s, in d ic a tin g high te m p e ra tu re . H ere again co n tro llin g th e o th er co n d itio n s is d ifficu lt and I h a ve fo u n d th is in d ic a to r to be of v a lu e la rg e ly in em p h asizin g th e fa c t th a t v a ria tio n s in th e o th er con d itio n s m a y fa ls ify th e p y ro m e te r readin g. I t m akes a d ifference w h eth er th e p y ro m e te r is risin g or fa llin g. I f we cou ld hold th e p y ro m e te r a t th e sam e p o in t for a lo n g tim e before m a k in g th e cu p e lla tio n th is cause of difference w ou ld be m inim ized, b u t th is is im p ra ctica b le in e v e r y -d a y w ork.

I t m akes a difference if th e m uffle be new and in good co n d itio n or old and n e a rly w orn out, and it m u st n ot be fo rg o tte n th a t a new m uffle m a y be poor and leak m ore th a n an old one, w h ich w as of good q u a lity w hen new .

T h e o n ly feasib le p lace to p u t a p y ro m e te r in an a ssa y m uffle is close to th e to p of th e arch of th e m uffle and fo r co n ven ien ce it m u st be in serted from th e b ack . W e all kn o w , of course, th a t clo sing th e m uffle increases th e te m p e ra tu re and th a t on m o v in g to w a rd th e b a ck of th e m uffle th e te m p e ra tu re rises, as p ra ctic a l e v e r y d a y w o rkin g fa cts. In order to g e t a m ore e x a ct id ea as to th e differen ce in th e te m p e ratu re in differen t p a rts of th e m uffle and th e relatio n s b etw e en th e se te m p e ra tu re s and th e fixed p y ro m e te r readin gs, a second p o r

ta b le p y ro m e te r w as p laced on th e b o tto m of th e m uffle in v a r y in g relatio ns to th e fixed p y ro m e te r as fo llo w s: d ire c tly under th e fixed p y ro m e te r, a t th e rig h t side an d a t th e le ft side in th e sam e cross-section as th e fixed p y ro m e te r, close to th e fro n t in th e m iddle and on each side of th e m uffle. In som e of th e arran ge m en ts e m p ty cupels w ere p lace d beside th e b o tto m p yro m eter.

T h ere are th ree p rin cip al causes fo r d ifferences in th e tw o p y ro m e te r read in gs: p o sition w ith in th e m uffle, freed om of en tran ce of air to th e m uffle, and con d itio n of th e bu rn ers on eith er side o f th e m uffle. In general, th e door con d itio n s, go ve rn in g th e en tran ce of air to th e fu rn a ce , e x e rt a p o w erfu l influ ence u po n th e te m p e ratu re w ith in th e m uffle, and o ften cause w ide d if

feren ces in te m p e ra tu re in d ifferen t p a rts o f th e m uffle.

U nder th e cond itio ns of th ese te sts, on op en in g th e closed m uffle, eith er p y ro m e te r m a y fa ll 10 0 0 or m ore in ten m in u tes, and a fu rth e r i o ° or 200 before becom ing s te a d y . In th e closed m uffle th e tw o p yro m ete rs registered a lik e in o n ly one in stan ce, and differed 40 0 in one. In e v e r y in stan ce th e m o v ab le p yro m ete r, on th e b o tto m o f th e m uffle, fell m ore th a n th e fixed p y ro m e te r, a t th e top of th e arch , on op en in g th e closed m uffle, and in one in stan ce 4 0 0 m ore.

A p o in t of g ra v e con cern is th e s ta b ility of th e p y ro m ete r. In th e a b o v e te sts b o th of th e p yro m ete rs w ere p r a c tic a lly new an d m a y be dep en ded upon, b u t th e effe ct of lo n g use, for co n tin u o u s periods, in th e lith a rg e-lad en atm o sp h ere of th e m uffle upon th e in stru m e n t is u n kn o w n . I t is k n o w n th a t th e h ot lith a rg e fu m e is d e stru c tiv e to th e tu b e , and it is o n ly a q u estio n of tim e w hen it w ill a ffe ct th e enclosed couple.

A t presen t th ere are no re a d y m eans for te stin g th e a c c u ra c y of th e p y ro m e te r from tim e to tim e, and

it is d ifficu lt for an a ssa ye r to ju d g e w hen it is beginning to fail.

In conclu sion , I w ou ld s a y th a t, n o tw ith stan d in g the o b jectio n s I h a v e described, th e p y ro m e te r occupies a useful field as a general gu id e to th e h ea t conditions in th e a ssa y m uffle. In th e old an d estab lish ed prac

tic e of a ssa yin g in th e M in t service, in th e large labora

tories, one or tw o m en do p r a c tic a lly all of th e cupelling and th e y grow to be v e r y e x p e rt in ju d g in g th e heat of th e m uffle and th e co n d itio n of th e cu p ellin g bead by th e ey e, b u t th e carefu l and prop er use of a pyrometer w ou ld o ften help th e m , w h ile th e m an who cupels o n ly in te r m itte n tly w ill find it a good general aid.

B u t to o m uch d ep en dence m u st n o t be p lace d upon the p y ro m e te r, and th e m an w ho dep en ds upon it entirely w ill n e v e r be a good cupeller.

Bureau op the Mint Treasury Department, Washington

A P P R O V E D B U R E A U O F M IN E S E X P E R I M E N T STATION A T P I T T S B U R G H

P lan s for th e pro p o sed $500,000 E x p e rim e n t Station of th e U n ite d S ta te s B u re au of M in es to be located in P itts b u rg h , h a v e been a p p ro v e d b y th e commission a p p o in te d b y C o n gress fo r th a t purpose.

C on gress, a y e a r ago, in th e P u b lic B uildings Bill, au th o rized a new hom e for th e B u re a u of Mines to cost $500,000. I t is n ow e x p e cte d th a t Congress, in its presen t session, w ill m ake a sp ecific appropriation so th a t c o n stru ctio n w o rk m a y begin . It is hoped that c o n tra c ts m a y be le t b y J u ly 1st and th e buildings com

p le te d in th e fa ll of 1915.

T h e S ta te of P e n n s y lv a n ia h as ap p ro p ria ted $25,000 for co o p eratio n in estab lish in g th is E x p e rim e n t Station.

T h e grou p con sists of th ree m ain bu ild in gs facing F o rb e s S tre e t. T h e cen tra l b u ild in g o f th e group, the M in in g B u ild in g, w ill be th ree sto ries in h eigh t, flanked b y tw o m ain b u ild in gs, one th e M e ch a n ica l and the o th er th e C h em ical B u ild in g. In th e rear of these and en clo sin g a c o u rt w ill be th e S ervice B u ild in g. Beyond th e S e rvice B u ild in g and sp an n in g w h a t is known as P a n th e r H o llo w and th u s co n n ectin g th e Bureau of M in es B u ild in gs w ith th e C arn e gie Schools, will be tw o b u ild in gs o v e r th e roofs o f w h ich w ill pass the ro a d w a y fro m F o rb e s S tre e t to th e C arnegie School B u ild in gs and S ch e n le y P a rk .

B etw e en th e m ain gro u p an d th e p o w er and fuel grou p w ill be th e en tran ce to a series of m ine shafts.

One of th ese w ill be used as an e le v a to r to carry heavy m a terial and passengers from th e low er level to the u p p er; a n o th er w ill be fo r te sts of h o istin g ropes and sim ilar m inin g ap p lian ces; a n o th er w ill be an entrance to tu n n e ls e x te n d in g under th e b u ild in gs and in which m ining exp erim en ts, such as fig h tin g m ine fires, will be co n d u cte d .

T h e p o rtio n of P a n th e r H o llo w a b o v e th e Power B u ild in gs w ill be a rran ge d as a M in e rs’ F ield , the slopes of th e rav in e b ein g u tilize d as an am p h ith e atre which w ill a cco m m o d a te 20,000 sp e ctato rs w ho m a y assemble here to w itn ess d em o n stratio n s and te sts in mine rescue and first-aid .

T h e M in in g B u ild in g w ill c o n tain th e administrative offices, and th o se of th e m ining force. In it will be

May, 1914 T H E J O U R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 407

1 1 1 HE " “ ■ "

Approved Bureau of Mines Experiment Station at Pittsburgh

an assem bly and le ctu re hall, a lib r a r y and sm oke and other room s for d em o n stratio n s and tra in in g in m ine rescue and first-aid . T h e M e ch a n ica l B u ild in g w ill be for exp erim ents an d te sts of m ining m a ch in ery and appliances and th e C h e m ica l b u ild in g for in v e stig a tio n and analyses of fu els, ex p lo sives and v a rio u s m ineral substances.

T H E C H E M I S T ’ S D U P L E X S L I D E R U L E B y H . H . Hanson

R e c e iv e d F e b r u a r y 12, 1914

In these d a y s of efficien cy an d sp ecia lizatio n , a n y contrivance or d e v ice w h ich te n d s to s a v e tim e w ith o u t sacrifice of a cc u ra c y is e a g e rly seized upon. T h e slide rule has long b een used b y engineers. I t is o n ly w ith in

— u & î M m p f i i - ù ^{I ;} m M l 5 i f f i H s f f v i | $ £5 5

w , i î m H

..... .... F. • f-f - t,. K Ml j î $ f i i f f is_ i n %

3 »■ 1 ^ ‘ t ‘ i. Li; j- | j I !•

“ 1

t » r orrnrn ai »i vf4 • “t è - ‘ i- > '

* recent years, h o w e ver, th a t its use has been ap p lied

to chem ical problem s. T h e re h a v e been p la ce d upon the m arket several so-called “ C h e m is t’s Slide R u le s ,”

but the “ D u p le x ,” in v e n te d b y D r. R . H arm on A s h ley, of th e U n iv e rs ity o f M a in e , and m a n u fa ctu re d b y the K euffel & E sser C o ., of N e w Y o r k , seem s to be a material a d v a n c e o v e r p rev io u s rules of th is kin d . This rule has b o th th e reg u la r and th e

inverted scales, w ith th e gra d u atio n incident to in stru m e n ts of th is kin d , so th at in itse lf it is co m p lete, and upon it m a y be carried o u t all of

the arith m etical co m p u ta tio n s w hich are u su ally required of a ch em ist or ch em ical engineer. In addition to th is it carries one h u n d red and th ir ty - five chem ical sy m b o ls, th e acid s, bases an d salts being on th e regu la r side, and oxides and elem ents

b eing on th e in v e rte d side. T h e le ft in d ex of th e rule is m arked “ S o u g h t,” th e le ft ind ex of th e slide is m a rk ed “ G iv e n ,” so th a t no m istak e can be m ade in th e s e ttin g it be u sed. W ith th e large n u m b e r of ch em ical sym b o ls g iv e n a lm o st a n y sto ich io m e tric p ro b lem m a y be so lv ed , as h u n d red s of co m b in atio n s arc po ssible w ith th e in stru m e n t. C o n versio n fa cto rs are v e ry e a sily an d q u ic k ly o b ta in e d w ith one se ttin g of th e rule. T h e p e rcen ta ge com po sitio n of vario u s com p o u nd s m a y be fo u n d , and prob lem s in b o th g r a v im e tric and v o lu m e tric a n a lysis m a y be e a sily so lv ed as describ ed in th e m a n u a l w h ich acco m p an ies th e rule. T h e m o lecu lar w eig h ts of su b stan ces n ot in scrib e d on th e rule are e a sily o b ta in ed , ev en th o u gh

W dokumencie The Journal of Industrial and Engineering Chemistry, Vol. 6, No. 5 (Stron 43-66)