The Journal of Industrial and Engineering Chemistry, Vol. 6, No. 7

The Journal of Industrial and Engineering Ghemistry

Pub l i s hed b y T H E A M E R I C A N C H E M I C A L S O C I E T Y

AT B A S T O N , P A .

Volume VI J U L Y , 1914 N o 7

BOARD OF EDITORS Editor: M . C . W h i t a k e r

Assistant Editor: Le o l a E . M a r r s

Associate Editors: G . P. A d am so n , E . G . B a ile y , H. E . B arn a rd , G . E . B a rto n , A . V . B lein in ger, f f m . B lu m , ffm . B ra d y, C . A . B row n e, F . K . C am e ro n , f f m . C am p b e ll, F . B . C arp e n te r, C . E . C a sp a ri, V . C o b le n tz , W. C . G eer, W . F . H illeb ran d , W . D . H orne, T . K a m o i, A . D . L ittle , C . E . L u ck e, P . C . M c llh in e y , J. M. M a tth e w s, T . J. P a rk e r, J. D . P en n o ck , C liffo rd R ich ard so n , W . D . R ich a rd so n , G . C . S to n e, E. T w itch ell, R . W ah l, W . H . W a lk e r, W . R . W h itn e y , A . M . W righ t.

P u b lish e d m o n th ly . S u b sc r ip tio n p rice t o n o n -m e m b ers of th e A m eric a n C h e m ica l S o c ie ty , $ 6 .0 0 y ea r ly . F o r eig n p o sta g e , se v e n ty -fiv e c e n ts, C a n a d a , C u b a a n d M e x ic o e x c e p te d .

E n te r e d as S e c o n d -c la s s M a tte r D e c e m b e r 19, 1908, a t th e P o st-O ffice a t E a s to n , P a ., u n d er th e A c t of M a r ch 3 , 1879.

C ontributions sh ou ld be addressed to M. C. W hitaker, Columbia U n iv ersity , N ew York City

Communications c o n cern in g a d v ertisem en ts should be se n t to T he A m erican C hem ical S o c ie ty , 42 W est 39th S t., N ew York City S u b scrip tion s and c la im s for lo st c o p ie s sh ou ld be referred to Charles L. P arsons, B ox 505, W ashington, D. C.

Es c i i e n b a c h Pr i n t i n o Co m p a n y, Ea s t o n. Pa.

T A B L E O F Ed i t o r i a l s :

N itrates in C olorado S o ils ... 532 Or i g i n a l Pa p e r s:

E lectric F urnaces for H eatin g S teel. B y A lc a n H irsch. 533 Stud y of A u th e n tic Sam ples of G um T urp en tin e. B y

A. W . S ch o rg er... : ... 541 The H yp och lorite of Lim e T re a tm e n t of a M u n icip al

W ater S u p p ly and a S tu d y of C e rta in R esista n t B acteria. B y S ta n le y Judson T h o m a s ... 548 The R a d io a c tiv ity of th e W aters of S ara to g a Springs,

N ew Y o rk . B y R ich a rd B . M oo re and C . F . W h it- tem ore ; ... 552- The E ffect of F erric S a lts and N itrite s 011 th e O rtho-

T olid ine and Starch -Iod id e T e sts for F re e Chlorine.

B y J. W . E llm s and S. J. H a u ser... 553 A N ew M eth o d for th e D eterm in ation of H yd rocyan ic

A cid and th e A lk a li C yan id es. B y G . E . F . Lundell

•and J. A . B rid g m a n ... 554 A M ethod for th e R a p id Q u a n tita tiv e A n alysis of

Bronze and B rass. (P b, C u, Sn, Sb, F e and Zn.) B y R ichard E d w in Lee, John P . T ric k e y and W a lter _ H. F e g e ly ... 556

• The C hem ical E v a lu a tio n o f W ood for Pu lp . B y M . L. G riffin ... 560 D eterm ination of C arb o n in Soils and Soil E x tracts.

_ B y J. W . A m es and E . W . G a ith e r... 561 The M eltin g and S olid ifyin g P o in ts of M ix tu res of

F a t ty A cid s and th e U se of T h e se P o in ts to D e ­ term ine the C om position of Such M ix tu res. B y E. T w itc h e ll... 564 The Specific H e at of M ilk and M ilk D erivatives.' B y

Arden R . Johnson and B . W . H a m m e r... 569 Note on th e P recip itatio n of L a ctalb u m in in C o w s’

M ilk . B y W . O. W alk er and A . F . G ra n t C ad enh ead The A bsorp tion of C e rta in R a d icals b y L e a ve s in V aryin g S tag es of D e ca y , and th e E ffe c t of Leaves on th e A bsorp tion of T h ese R a d icals b y a Soil. B y H. A . N o y e s ... 574 D istribution of C e rta in C on stitu en ts in th e Separates

of Loam Soils. B y L. A . S te in k o en ig ...

The P rep aration of “ N e u tra l” A m m on ium C itrate.

B y E rm on D . E a stm a n and Joel H . H ild eb ra n d . . . A Procedure for Sep aratin g O rgan ic A m m on iates from

the M in eral P ortion of C om m ercial F ertilizers. B y

^ C. H. Jones and G . F . A n d erson ...

The A v a ila b ility of N itro gen in K e lp . B y J o h n A . C ullen La b o r a t o r y a n d Pl a n t:

P itot T u b es for the M easurem en t of G as V elocities.

^ B y A n drew M . F a ir lie ...

The N o n -U n ifo rm ity of D ry in g O ven T em peratures.

B y Lorin H . B a ile y ... 585 573

576 577

580 581

583

C O N T E N T S

A M a n o sta t for U se in G as A n alysis. B y H a rv e y N . G ilb e rt... 5 8 5 Ad d r e s s e s:

T h e E xcessive Q u an tities of N itra tes in C erta in C o lo ­ rado Soils. B y W m . P . H e a d d e n ... 5 8 6 T h e W orkin gs of the C aliforn ia Insecticide Law'. B y

G eo. P . G r a y ... 5 9 0 C u r r e n t I n d u s t r i a l N e w s : C orrection ; M easurin g

R a p id ly C han gin g T em p eratu res; T h e A u stralian C oal T ra d e ; A N ew R ecord ing D e vice; T h e K o n g sb erg S ilve r W orks, N o rw a y ; P rod uction of Z in c in Europe,

1913; M in in g in C h in a; T h e Oil R esources of th e B r it­

ish E m p ire; C oal S torag e and G as M an u fa ctu re ; T h e C orrosion of Iron b y D issolved O xygen ; T h e L igh tin g of R io de Janeiro; T h e U tiliza tio n of Sulfite-C ellulose W aste; C an ad ian C o k e O vens; G erm an and English E x p o rts of A m m onium S u lfate in 1 9 1 2 and 1 9 1 3 ; D e ­ stru ction of an A rtificial L e a th er F a c to r y ... 5 9 4 Am e r i c a n In s t i t u t e o f Ch e m i c a l En g i n e e r s:

A cco u n t of M eetin g ; Papers; E x cu rsio n s... 5 9 8 Som e Professional O bligations. B y M . C . W h ita k e r. 5 9 9

\ N o t e s a n d Co r r e s p o n d e n c e : T h e In ven tion of C e llu lo id ; Sym posium on the R ecovery' of W ool G rease; G u a ran ­ teed C hem icals; T o x ic ity of V arious W ood P reserva­

tives— A N o te ; N o te on M ean in g of "Im p u ritie s” and H ow T h e y Shou ld be D eterm ined in G rease, T allo w , E tc .; T e s t of G ila R iv e r N a tu ra l A lu m in um S u lfate in W ate r Pu rification; T h e E ffects of th e E n silage Process on th e S o lu b ility and M etab olism of F lo a ts r M in e In ­ spectors In stitu te of the U . S .; N in th International C o n ­ gress of A p p lied C h em istry; V a n ’t H off F u n d for the En dow m en t of R esearch in Pure and A p p lied C h em ­ istry; A m erican C hem ical S o ciety — A n n u al' M eetin g ; A . C . S. D irectory, 1 9 1 4 ; Ind ustrial C hem ists and Chem ical E ngineers— A . C . S .— C om m ittee on A lum Specifications— C orrection and N o tice; T h e D ifferen ­ tiation of N a tu ra l and O il A sp h alts— C o rre ctio n 60 1 P e r s o n a l N o t e s ... 6 0 7 G o v e r n m e n t P u b l i c a t i o n s ... 6 0 8

B o o k R e v i e w s : E ngineering T herm od yn am ics; D as

L eb en sm ittelgew erb e; Exercises in G as A n alysis;

T reatise on th e C eram ic Ind ustries; U n tersu chu ng der K ohlenw asserstoffole und F e tte ; C oal T a r D istillatio n ;.

T asch en buch fiir die anorganischchem ische G ro ssin -' dustrie; D etails of C y an id e P ractice; T asch en b uch fiir G erb erei-C h em ik er... 6 1 1 N e w P u b l i c a t i o n s ... 6 1 4 R e c e n t I n v e n t i o n s ... 6 1 5 M a r k e t R e p o r t ... 6 1 6

532 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 V o l . 6, No. 7

EDITORIALS

V

In a n u m ber of p u b lica tio n s, H eadden , of th e C olorad o E xp e rim e n t S ta tio n , has show n th a t th e soils of C o lo ­ rad o co n tain in v a rio u s places excessive q u a n titie s of n itra tes. O rd in a rily go od , c u ltiv a te d soil he fo u n d to co n tain from 5 to S p a rts of n itra tes per m illion of th e d r y soil. In th e n itra te areas, h o w e ver, m an y th o u san d p a rts per m illion of n itra te n itrogen w ere foun d. In one sam ple of su rface soil th e re w ere fo u n d 6.54 per cen t of sodium n itra te or n e a rly 11 to n s in an acre of gro u n d ta k e n to th e d ep th of 1 inch. T h e high n itra te co n ten t is ge n e ra lly fo u n d in sp ots b u t these sp ots often g ro w to co ve r larg e areas. T h u s w h a t w as five or six y e a rs ago a sp o t has gro w n to in v o lv e as m uch as . six, eigh t, an d m ore acres. T h e n itra te s are present in large q u a n titie s in n um erous areas scatte re d o v er 300 to 400 sq u are m iles. T h e orch ards in a single d istrict in clu d in g 50 sq u are m iles h a v e been p ra c tic a lly ruined.

T h ese o b serva tio n s an d stu d ies are of so g rea t in terest an d im p o rta n ce to a g ricu ltu ra l in v e stig a to rs th a t it is a m a tte r fo r co n g ra tu la tio n th a t P rofessor H ead d en has been p re v a ile d upon to fu rnish his ow n sta te m e n t of his w o rk in o th er colum ns of T h i s J o u r n a l .

A b rief rep e titio n of the, p rin cip al resu lts, how ever, can be g iv e n here.

A s a resu lt of th e n itra te accu m u latio n , in a n um ber of p lace s large areas h a ve been m ade sterile. W h e th er large or sm all th e affected areas are ch ara cte rize d b y a b row n co lo ratio n , m ealiness of th e soil, a high n itra te c o n te n t, and, unless th e n itra te co n ten t is e x cessiv ely h igh , b y th e presence of n itrog en -fixin g organism s such as a zo to b a cte r. W ith .the increase in th e colored p atch es a n d th e a m o u n t of n itra te , th e crop s co ve rin g th e in ­ v o lv e d areas ra p id ly d ete rio rate and e v e n die ou t. T h e g re a te st in ju r y has been to th e apple orch ard s th o u gh o th er crop s such as a lfa lfa , su gar beets, etc., h a v e been serio u sly in ju red . T h e tro u b le is com m on to several sectio n s of th e S ta te . Som etim es it has occu rred in lig h t sa n d y loam s, som etim es in c la y soil, som etim es in c o m p a ra tiv e ly lo w -lyin g lands, again on hillsides.

Sodium ch lorid e is also presen t in large am ou n ts in th e C o lo rad o soils. A cco rd in g to H eadden , h o w ever, th is s a lt th o u gh in ju rio u s in larg e a m ou n ts does n o t produce a n y of th e ch a ra cte ristic ph enom ena ob served in th e d y in g o rch ard s, w hile a p p licatio n of large q u an tities (5 po u nd s to a fo u r-ye ar-o ld tree) of sodium n itra te to an exp erim e n tal o rch ard and irrig a tin g to brin g the n itra te in c o n ta c t w ith th e fee d in g ro o ts reproduced th e id e n tica l p h eno m ena n o ticed in th e o th e r'o rch a rd s w here th e trees h ad died. I t w ou ld seem th en th a t w h a te v e r co n trib u tin g cause th ere m a y be, th e sodium n itra te presen t in th e soil is sufficien t to brin g a b o u t th e d ete rio ratio n and d ea th of trees and crops in the affected areas.

T h o u g h th e presence of th e h ig h ly excessive q u an tities of n itra te w hich b rin g a b o u t loss of general p ro d u c tiv e ­ ness in v o lv e s o n ly a sm all p e rcen tage of th e arable C olorad o soil, th e fo rm atio n of these high n itra te areas

in th e v a rio u s sectio ns of th e S ta te is a problem of g re a t im p o rtan ce and concern to agriculturalists of C o lo rad o and a p h enom enon of th e greatest interest to ch em ists and b acterio lo gists.

In soils in general th e fo rm atio n of n itrates is brought a b o u t b y sev eral soil m icroo rgan ism s w hich fix nitrogen from th e air, fo rm am m onia fro m more complex n itrogen ou s com po unds, and fo rm n itrite s and nitrates fro m am m oniu m com pounds. A s a rule th e nitrates in soil are sm all in am o u n t. A c c o rd in g ly , th e Colorado situ a tio n is e x ceed in gly rem ark ab le.

A s to th e origin of th e n itra te s th e re is some dispute.

H ead d en holds th a t th e ab n o rm al accum ulation of n itra te s can n o t be due to e v a p o ra tio n of surface waters co n tain in g n itra te s com in g from a d istance from soil or shale since: (1) n eith er soil nor shale contain a sup­

p ly of n itrogen a d e q u a te to a cco u n t for the forma­

tio n of n itra te s fo u n d ; (2) th e n a tu ra l w ater and the irrigatio n w a ter co n tain o n ly sm all quantities of n itra te s ; (3) th e b ro w n n itra te -co n ta in in g areas often occu r a t a high ele v a tio n . In ad d itio n th e accumulation of n itra te s m a y occu r on w ell d rained lands, where the w a te r le v e l is som e d istan ce fro m th e su rface. Headden’s p o sitive conclusion is th a t th e source of th e nitrates is th e atm osp h ere, th e n itrogen of w hich is fixed by a zo to b a cte r. In su p p o rt of H e ad d en ’s conclusions, S a c k e tt fo u n d th a t th e C o lo rad o soils were rich in a zo to b a cte r w h ich h a d th e p o w er to fix nitrogen in solu tio n and in soil and fixed it a t a ra te sufficient to a cco u n t fo r th e n itra tes fo u n d in th e soil, provided the n itro g en is n itrified b y oth er organism s.

S a c k e tt likew ise fo u n d th a t th e C o lo rad o soils have a h igh er a m m o n ifyin g po w er th a n h a v e ordinary soils and a h igh er n itrify in g po w er and com es to the con­

clusion th a t th e excessive n itra te presen t in certain C o lo rad o soils has resu lted fro m th e com bined action of n itrogen -fixin g, a m m o n ify in g , and n itrify in g organ­

ism s. Since th e C o lo rad o soils are poor in organic m a tte r and a zo to b a cte r requires a su p p ly of carbohy­

d ra te fo r its d evelo p m e n t and th e fixatio n of nitrogen, it seem ed difficult to a cco u n t for th e source of energy n ecessary to su p p o rt su ch a rich nitrogen-fixing flora as possessed b y th e soils in question . R o b b in s, however, fo u n d th e alg ae flora esp ecially th e blue-green algae ( Cyanophyceae) to be v e r y ab u n d an t. I t is well known th a t certain b a c te ria and algae en ter into symbiotic relatio n sh ip in w hich th e algae fu rnish th e bacteria w ith a su itab le form of c a rb o h y d ra te s. T h e algae in th e C o lo rad o soil m a y fu rnish th e necessary food m aterial fo r a zo to b a cte r.

A n opposin g vie w is th a t of S te w a rt and G r e a v e s

(A gric. E x p t. S ta ., U ta h , B u ll. 1 1 4) th a t th e nitrates of th e C o lo rad o soil h a v e th e ir origin in th e co u n try rocks.

T h e fa c t th a t in w id e ly d istrib u te d areas in the arid w est dep osits of n itra tes are fo u n d w hich do owe their origin to lea ch in g fro m th e c o u n try rock, supports, in th e ir opinion, th e th e o r y th a t th e excessive q u a n t i t i e s

of n itra te s fou n d in th e soil of C o lo rad o owe their origin

July, 1 914 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 533 to the sam e source as do th e o th er w ater-solu ble salts.

Further, S te w a rt and G re a ve s claim th a t in H ead d en ’s work w herever th ere w as a v a ria tio n in n itric n itrogen there was a v a ria tio n in chlorine in th e sam e direction which w ould seem to' in d icate a com m on origin of th e nitrates and chlorides. T o ta k e a p a rticu la r case, th e y point out th a t w here th e re w as an increaese in th e su r­

face soil of 561 pounds of n itra te s per acre tw o inches of soil during th e years from 190 9-1911 th ere w as an increase of 10,430 po u nd s or over five to n s of chlorine.

In another case, referred to b y H ead d en in B u lle tin 1 5 5» the n itra te n itro gen increased from 1907 to 1911 from a trace to 621 pounds. In th e sam e in te rv a l th e chlorine co n ten t in creased 236,883 p ounds. T h e y come to the in e v ita b le conclusion th a t th e re m u st be an upward m o vem en t of th e w ater-so lu ble salts, th a t the chlorides m ust com e from th e gro u n d w ater. A c ­ cordingly, th e y ask th e p e rtin e n t q u estion , “ W h y may not th e n itric n itro g en be acco u n ted for in the same w a y ? ” E v a p o r a tio n ' of th e soil w ater w ould explain th e d ep osit of n itra te s since acco rd in g to th e ir calculations, assum ing th e op tim u m a m o u n t of w ater, 18 per cent, to be p resent, o n ly on e-half y e a r of m axi­

mum evap o ratio n w ou ld d ep osit th e q u a n tity of n itro ­ gen a ctu a lly d ep osited in tw o yea rs. If th e ground water contain s o n ly 74.48 p a rts per m illion of chlorine as com puted b y H ead d en , th e ev a p o ra tio n w ould account for o n ly 203 po u nd s of ch lorin e, w hereas the actual am o u n t fo u n d in th e sam p les m en tion ed was

E L E C T R IC F U R N A C E S F O R H E A T IN G S T E E L 1 B y A l c a n H i r s c h

R e c e iv e d M a y 25, 1914

The field of usefulness of th e electric fu rn ace for m etallurgical purpo ses is so e x te n siv e th a t it is deem ed advisable to lim it th e scope of th is p a p e r to a discus­

sion of electric fu rn aces used fo r h ea tin g steel for th e various k ind s of h e a t tre a tm e n t, fo rgin g and en am eling.

A broad vie w of th e d ev elo p m e n t of electric fu rnaces by the w riter and his a sso ciates d u rin g th e p a st y ea r, together w ith d etails of design, co n stru ctio n and op era­

tion, as d eterm in ed b y th e m are presen ted herein.

The essential d a ta o n ly are g iv en as it is b elieve d th a t extensive d etails are lik e ly tp lead to confu sion. I t is thought such a p resen tatio n o f b asic principles will make the p aper of m ore v a lu e to users of electric furnaces th a n an exte n d ed rep o rt of all th e d a ta co l­

lected.

Prior to 1 913 a tte m p ts w ere m ade to p u t fo rth fu r­

naces for m etallu rg ica l purposes, b u t excep t for th e very sm all fu rn aces, th e se can n o t be considered as having had com m ercial success. T h e fa cts w hich form the basis of th is p aper occurred under th e w riter’s observation and are p r a c tic a lly e x c lu siv e ly gath ered from his exp erience of th e p a st y ea r.

By reason o f in d u stria l p ra ctice and certain oth er

1 A uthor’s a b stra ct o f report on research carried o u t under a C arnegie Fellowship gran ted b y th e Iro n an d S te e l I n s titu te o f G r ea t B ritain . T h e complete report of th is w ork w a s p resen ted a t th e A n n u a l M e e tin g o f th e institute, M a y 7 , 1914.(

m an y tim es greater. So th e y conclude th a t thp grou n d w a ter has a greate r co n cen tratio n in chlorine an d n itro ­ gen th a n assum ed and th a t b o th a ccu m u late in th e su rface soil b y e v ap o ratio n o f th e w ater.

S te w a rt and G rea ves do n ot d en y th a t n itrogen fixatio n m a y ta k e place to a certain e x te n t in th e C o lo ­ rado soil and in som e places to an ap p reciab le degree, b u t do hold th a t w h a te v e r th e o ry acco u n ts fo r th e accu m u latio n of chlorides in th e C o lo rad o soils m u st acco u n t also for th e greate r p o rtio n o f th e .n itra te s p resent. T o th ese argu m en ts of S te w a rt a n d 'G re a v e s , H eadden has opposed n um erous o b jectio n s w hich can ­ n o t be considered here. Suffice it to sa y , th a t w hile th ere can be no possible q u estion of th e occasion al o ccu rren ce of a bn orm al q u an tities of n itra te s in th e

“ a lk a li” soils of C o lo rad o , th e origin of th ese excessive n itra te accu m u latio n s is not settled .

In th e ir en d eavo r to exp lain th e origin of th e n itra te and to rem ed y th e con d itio n s as th e y arise, th e vario u s in v e stig a to rs sh ould m eet w ith general en cou ragem en t.

I t is g r e a tly to be desired t h a t th e n itra te fo rm atio n should be considered from all vie w p o in ts to th e end th a t a ccu m u latin g d a ta and suggestion s m a y th e m ore q u ic k ly develop an h arm on ious conclusion , to th e a d ­ van tag e. of p ra ctica l a gricu ltu re and to th e increase of th e sum to ta l of h u m an know ledge.

B u r e a u o p S o i l s M . X . S U L L I V A N

De p a r t m e n t o f Ag r i c u l t u r e Wa s h i n g t o n

lim itatio n s, both fu el and electric fu rn aces can be d ivid ed in to tw o classes:

I— F u rn aces o p eratin g a b o v e i8 o o ° F . F o rge fu r­

naces are th e m ain and m ost im p o rta n t d ivisio n of th is class.

I I — F u rn aces o p eratin g below 1800° F . T h is class com prises fu rn aces for p ra ctic a lly all h ea t tre a tin g as w ell as en am elin g. A lth o u g h fu rn a ce s o p eratin g a t th e low er te m p eratu re s w ill be considered first it m ust be borne in m ind th a t th e g rea te r p a rt of the principle and th e o ry u n d e rly in g th e co n stru ctio n and op eratio n of m od erate and low te m p e ratu re fu rn a ce s also applies to th e h igh er te m p eratu re furnaces.

T R A N S F E R E N C E O F H E A T F R O M H E A T I N G M E D I U M TO M E T A L

T h e m etal restin g on th e h earth of th e fu rn a ce re­

ceives its h eat in several differen t w a y s: ( i) F ro m th e b rick w o rk in th e fu rn ace in c o n ta c t w ith th e m etal;

(2) b y co n d u ctio n fro m th e p ro d u cts of com bu stion ; (3) b y rad iatio n from th e h o t w alls, roof and in can d es­

cen t p a rticles in th e b u rn ing gases. G e n e rally sp e a k ­ ing, in th e fu el-fired fu rnaces, each of th ese p a th s de­

livers h eat of th e sam e order of m agn itu d e, b u t u su a lly th e a m o u n t of h ea t passing b y m eans of b rick and m etal in c o n ta c t is less th a n th a t b y a n y oth er p a th . If o n ly a sm all p o rtio n of th e h e a t passes in to th e m etal b y d irect c o n ta c t w ith th e b rick , th e rate of h e a tin g in 'a ll ex cep t th in pieces is q u ite slow . M o re fre q u e n tly

th a n is g e n e ra lly sup posed th is p a th of h ea t tr a n s ­

ORIGINAL PAPERS

fer is th e d eterm in in g fa c to r in th e rate of h ea tin g.

A n excellen t exam p le of th is k in d w as b ro u g h t to th e w rite r’s a tte n tio n w here die b lo ck s w ere b ein g heated . In this in stan ce th e fu rn a ce w as h eate d to a su fficien tly h igh te m p e ra tu re so th a t th e h e a t co n ten t of th e b rick w o rk w as su fficien t to su p p ly th e n ecessary h e a t to raise th e b lo ck s to th e desired te m p e ratu re . Som e­

tim es th e h ie l w as allow ed to ru n sp a rin g ly th ro u g h ­ o u t th e op eratio n , w hile a t oth er tim es it w as sh u t off e n tire ly a fte r th e b lo ck w as p lace d in th e fu rn ace.

A T M O S P H E R E I N F U R N A C E S

T h e atm o sp h ere of fuel-fired fu rn a ce s is exceed in gly u n ce rtain . S lig h t va ria tio n s in con d itio n s h a ve been fo u n d to m ake m ark ed va ria tio n s in resu lts, an d as th e atm o sp h ere is cap ab le of a g re a t m a n y va riatio n s, i t is, th erefo re, q u ite d ifficu lt to m a in ta in it a t a definite com p o sition. W ith o xid izin g con d itio n s th e form ation of scale occurs, w hile in a' red u cin g atm osp h ere local ca rb u riza tio n resu lts fro m th e so o ty flam es. In th e p ro d u ctio n of h igh -grad e steel th e con d itio n of h earth atm o sp h ere is, of course, e x ceed in gly im p o rta n t.

T h e e le ctric fu rn ace p rovides in m an y respects ju s t w h a t th e fu el fu rn a ce la ck s; i. c., a m eans for th e tran sferen ce of h e a t in a v e r y effe ctive m anner, and a fu rn a ce atm osp h ere w hich is n ot o n ly of a v e r y de­

sirab le com po sition, b u t w hich is a b so lu te ly d ep en dable.

T h is atm o sp h ere is u su a lly of a slig h tly red u cin g n atu re, cau sed b y th e presence of carbon m onoxide, due to th e com bu stion of th e g ra p h ite or carbon resistor w hich lib e ra te s th e e lectrica l en ergy in th e fo rm of h eat.

In som e fu rn aces h a v in g m ore th a n one door, or op erated w ith doors open all th e tim e, th e atm osp h ere m ay be n eu tral. I t is due to th ese n eu tral or red u cin g con d itio n s th a t th e fo rm atio n of scale is g r e a tly m in i­

m ized. T h e w riter has in m ind an electric fu rn ace w h ich w as o p erate d w ith a loss of scale am o u n tin g to e ig h ty or even n in e ty per cen t less th a n w as occasioned b y th e e m p lo ym e n t of an oil-fired fu rn a ce fo r th e sam e w o rk. F o r special w o rk w here an oxid izin g atm osp h ere is requ ired , as fo r in stan ce in en am elin g, th is is easily accom p lish ed in th e electric fu rn a ce b y em p lo yin g a m uffle, th e resistors b eing p laced in a n y desired p o si­

tio n on th e o u tside of th e m uffle.

E L E C T R I C F U R N A C E S F O R T E M P E R A T U R E S B E L O W l 8 0 0 ° F . f u r n a c e s w i t h m e t a l l i c r e s i s t o r s— -The in d u strial e lectric fu rn a ce s of th is ty p e w h ich h a ve o b ta in ed com m ercial success h a ve e m p lo ye d a resistan ce w ire or rib b on as th e h e a tin g elem ent. T h e lim ita tio n s of th ese wire or rib b o n -w o u n d fu rn aces are q u ite m arked , g e n e ra lly sp ea k in g, as regards b o th te m p e ratu re and c a p a c ity . A s w ill be show n su b seq u en tly, te m p e ra ­ tu re and c a p a c ity o f a fu rn ace are clo sely in terrela ted . T h is in terrela tio n of te m p e ratu re and c a p a c ity , h ow ­ ever, is n o t o f so m uch consequence in th e sm all fu r­

n aces w here th e com bin ed w a ll and door losses are co n sid e ra b ly in excess of th e h e a t a c tu a lly u tilize d in raisin g th e m etal to th e desired te m p e ratu re . T h e c a p a c ity of th e m etallic resistor fu rn ace is a t m ost b u t a v e r y fe w k ilo w a tts. F u rn aces w ith a large r c a p a c ity w ou ld be q u ite ou t of th e qu estion b ecause of th e cost of th e resistance elem en t due to th e large am o u n t of

534 T H E J O U R N A L O F I N D U S T R I A L

w ire req u ired an d th e exp ense of w inding. The fur­

naces are, th e re fo re , lim ited to prod u ction s of small size and also to rath er m o d erate te m p eratu re s as danger of b u rn in g o u t due to o v e rh e a tin g is qu ite imminent.

F o r sm all fu rn aces, h o w e ver, th is ty p e has proven q u ite s a tis fa c to ry in a large q u a n tity of w ork of an ex p e rim e n ta l'n a tu re .

f u r n a c e s e m p l o y i n g n o n-m e t a l l i c r e s i s t o r s com­

prise tw o ty p e s : (1) T h o se w here th e m etal to be h eate d is in c o n ta c t w ith th e resisto r; (2) those where th e m etal to be h eate d is o u t of c o n ta c t w ith the re­

sistor.

F u rn a ce s of th e first class h a v e had b u t one com­

m ercial exam ple, and th a t h as h ad v a ry in g success.

T h is is th e b a th fu rn a c e 1 w h ich em p lo ys a conducting b a th of salt, u su a lly b ariu m chloride and potassium ch lorid e, w h ich is fu sed b y th e passage of the current th ro u g h it. T h e steel to be h eate d is im mersed in th is b a th of fused salts. T h is ty p e of fu rn ace appears to th e w riter to be to o lim ite d fo r exte n sive industrial a p p licatio n , an d , th erefo re, w ill be given only this b rief m ention.

F u rn a ce s of th e second class, th o se em p lo yin g non- m etallic resistors, w here th e m etal is h eated out of c o n ta c t w ith th e resisto r, hold fo rth m uch promise for fu tu re d evelo p m e n t, in th e op inion of th e writer.

R e ce n t exp erience w ith th e ir op eratio n has demon­

s tra te d th e ir s u ita b ility to m a n y k ind s of work. In general, fu rn aces of th is class ap p e ar to th e casual ob­

server, v e r y sim ilar to th e fuel-fired furnaces, save fo r th e fa c t th a t in stead of eq u ip m en t for burning fu el, electrical eq u ip m en t w ill be n oted . T h e electric cu rren t is b ro u g h t to th e fu rn a ce b y su itab le cables w hich are co n n ected to electrod es p ro jectin g from the fu rn ace . T h ese electro d es run th ro u g h th e furnace w all and c a rry th e cu rren t to th e resistor w hich liber­

ates, in th e form of h e a t, th e electrica l en ergy put into th e fu rn ace . T h e resisto r is of a re fra c to ry conducting m aterial, such as g ra p h ite , u su a lly in granu lar form, and has a cross-section of 30 to 100 square inches acco rd in g to th e cu rren t desired. T h e resistors are u su a lly p lace d b en e ath th e h earth , th e h ea t from them b eing co m m u n icated th ro u g h th e h earth to the metal.

F o r th e design of a h e a t-tre a tin g fu rn ace to operate a t a h earth te m p eratu re of 1800 0 F ., or less, th e follow­

in g d a ta h ave been fou n d n ecessary fo r th e prelim inary calcu latio n of th e m ajo r p o in ts of design:

1— T h e h earth dim ensions.

2— T h e p ro d u ctio n o f m etal per u n it of tim e.

3— T h e m axim u m a m o u n t of m etal on the hearth at a n y tim e.

4— T h e desired te m p eratu re .

5— T im e fo r ch arg in g and disch argin g.

l o c a t i o n o f r e s i s t o r— T h e first step in th e design is th e ap p ro xim atio n of th e lo catio n of th e resistor, b u t th is depends so m e w h at on th e ph ysical charac­

te ristics of th e m aterial em p lo ye d for the resistor.

R e sisto rs p laced in th e fu rn ace in g ran u lar or similar form h a v e been m uch m ore e x te n siv e ly e m p l o y e d

in th e larger fu rn ace th a n a n y o th er kind . Rods of

1 A n a rticle on th is fu rn ace b y L. M . C ohn w ill be found in the Electrotech. Z e it., A ug. 2, 1906.

A N D E N G I N E E R I N G C H E M I S T R Y V o l. 6, No. 7

July, 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 535 graphite and also of oth er m aterials, m etalloids as

well as the ch a ra cte ristic n o n -m etallic m aterials, have been tried fo r use as resistors. A lth o u g h som e of these will u n d o u b te d ly find com m ercial fields, as y e t nothing has p ro ven s a tis fa c to ry in th is d irection.

Attention, th erefore, w ill be confined to gran u lar or similar m aterials, of w hich gra n u la r g ra p h ite has served m ost s a tisfa cto rily .

For the usual ty p e o f electric fu rn a ce w ork of th is class the lo catio n of th e resisto r is lo g ic a lly in th e base of the hearth. F o r a sm all p ro p o rtio n of th e furnaces, however, resistors can be p laced elsew here ad vised ly.

These positions are a lo n g th e side of th e h earth and possibly even alo ng th e to p . F u rn a ce s requ irin g re­

sistors in th ese la tte r lo catio n s are th o se ta k in g piles of sheet m etal or p o ts of m aterials, and th e like. H ow- ever, with one la y e r of pieces, w hich rests d ire ctly on the hearth, th e lo catio n of th e resisto r h ad b est be exclusively in th e base. T h e reasons for th is are:

(1) heat has a te n d e n c y to ascend rath er th a n to de­

scend; (2) c o n ta c t b etw e en h o t b rick and th e m etal to be heated fa c ilita te s h e a tin g; (3) th e design is fa cili­

tated as w ill be su b se q u e n tly d evelop ed . W hen the resistors are p lace d in th e base of th e fu rn ace th e y are put in tro u g h s of su ita b le re fra c to ry m aterial and usually, b u t n ot a lw a y s, co vered p a r tly or com ­ pletely w ith b rick or-tile, w h ich form s th e h earth .

s h a p e o f r e s i s t o r s— T h e shape of th e resistors can be ex ceed in gly va ried . T h e y m a y be stra ig h t, U-, S-, T -, or Y -sh a p e d . T h e y m a y be e le ctrica lly connected in series or p arallel, or som e in series and others in parallel. T h e y m a y be p e rm a n e n tly elec­

trically conn ected, or th e y m a y be cap ab le of variou s electrical arran gem en ts b y sw itch in g.

p e r m a n e n t l y e l e c t r i c a l l y c o n n e c t e d r e s i s t o r s

Furnaces w ith these resisto rs are co n stru cte d so that they m ust be o p erate d in one m anner, a t all tim es from the p o in t of v ie w of electrica l arran gem en t.

F i o . I — Se r p e n t i n e Re s i s t o r f o r Mo d e r a t e l y La r g e Fu r n a c e s

In practically all fu rn a ce s of th is class eith er a serpentine 0r U-shaped resisto r m a y be em p lo yed , b u t tw o or more straigh t resistors co n n ected eith er in series or

■n parallel m a y be used in stea d . F ig . I shows th e serpentine resistor w hich h as been e m p lo ye d in m oder­

ately large fu rn aces on ly, it b eing im p ossible to a d ap t this typ e to th é sm aller fu rn ace s. T h e U -shaped

resistor show n in F ig . I I has been em p lo ye d in fu rnaces o f a n y size b u t h as som e lim ita tio n s w hich w ill be con ­ sidered later.

e l e c t r i c a l l o a d— T h ere are sev eral w a ys to d eterm in e th e electrical lo a d fo r a given fu rn ace, b u t th e y all resolve th e m selve s in to one m eth od, w hich is th e o n ly one deem ed su fficien tly p ra ctica l to be g iv en con sid era­

tio n in th is paper. O n ly fu rn a ce s of 200 k ilo w a tts c a p a c ity or less w ill be considered and it m a y be said th a t fu rnaces for h e a t tre a tin g larger th an th is are ex ceed in gly rare. T h e e lectrica l load is th e sum of th ree fa cto rs: (1) th e electrica l e q u iv a le n t o f th e am o u n t of h e a t n ecessary to raise th e m etal to th e requ ired te m p eratu re ; (2) th e electrica l e q u iv a le n t of th e loss of h ea t th ro u gh th e w alls; (3) th e e lectrica l e q u iv a le n t of th e loss of h ea t th ro u gh th e door, in consid eration of th e fa c t th a t th is is a lte rn a te ly opened and closed. Since th e pow er fa cto rs of fu rn a ce s of th is size are from 97 to 99 per cent, th e y can be neg-

Fi g. I I — U - Sh a p e d Re s i s t o r

lected' in th e calcu latio n of th e n ecessary w a tta g e . F ro m th e d a ta in T a b le I th e w a tts n ecessary to op erate a n y p a rticu la r fu rn ace m ay be a p p ro x im ated q u ite clo sely. T h e door loss shows th e w a tts passin g th ro u g h th e door opening if th e door is open all th e tim e. If th e door is open o n ly h alf th e tim e, o n ly h a lf th e a m o u n t giv en in th e ta b le sh ould be ta k e n , and so on in p ro ­ portion. T h e w all upon w hich th e w all loss figures are based is 12 inches th ick , con sistin g of 9 inches of silica b rick and 3 inches of kieselg u h r. B y a ctu a l p ra ctice th is has been fo u n d to be a co n v e n ie n t sta n ­ dard . A s an exam p le of th e m eth od o f calcu latio n , the electrical lo ad for a p a rticu la r fu rn a ce w ill be de­

term ined . A ssum e th e fo llo w in g d a ta for th is illu s­

tr a tiv e case:

1— O utside dim ensions— 4 ft. X 4 ft. X 6 ft. long.

2— P rod u ction — 500 pounds of steel per hour.

3— T em p eratu re— 1700° F.

4— D oor— 2 sq. ft., open 40 per cen t of th e tim e.

T h is fu rn ace h a d a to ta l o u tside area of 128 sq. ft.

T h e ta b le show’s a w all loss of 0.060 w a tt per sq. ft., m akin g a to ta l loss o f 7.68 k .w . fo r th e w alls, top and base. T h e door loss w^ould be 10.0 k. w. if th e door w ere open all th e tim e, b u t it b ein g open b u t 40 per cen t of th e tim e, th e loss is 4.0 k. w. A s 0.0881 k. w. is requ ired to raise 1 lb. of steel to 1700° F . from 60° F . in 1 hr., 500 lbs. per hr. w ou ld requ ire 44-05 k. w.

536 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 V o l . 6, No. 7

Ta b l e I

W all lo ss (a)

T em p era tu re K ilo w a tts in k . w . D o o r

o f op era tio n to raise per sq . ft. lo s s (6)

1 lb. per hr. o u tsid e in k . w.

0 F. 0 C. from 6 0 ° F . surface per sq . ft.

1000 5 3 8 ' 0 .0 3 6 6 0 .0 3 5 0 .6

1100 594 0 .0 4 6 0 0 .0 3 9 0 . 9

1200 649 0 .0 5 2 7 0 .0 4 2 1 .3

1300 704 0 .0 5 9 7 0 .0 4 6 1 .7

1400 760 0 .0 6 6 8 0 .0 4 9 2 .3

1500 815 0 .0 7 3 3 0 .0 5 3 3 . 0

1550 843 0 .0 7 6 5 0 .0 5 5 3 . 5

1600 8 70 0 .0 7 9 6 0 .0 5 6 3 . 9

1650 898 0 .0 8 4 0 0 .0 5 8 4 .5

1700 9 26 0 .0 8 8 1 0 .0 6 0 5 . 0

1750 9 54 0 .0 9 2 6 0 .0 6 2 5 . 6

1800 9 82 0 .0 9 7 0 0 .0 6 4 6 . 3

1850 1010 0 .0 9 9 4 0 .0 6 5 7 .1

24 0 0 1316 0 .12 2 0 .0 8 5 20.0

(а) B a sed on w all 12 in c h e s th ick (9 in c h e s of silica + 3 in ch es o f k ieselg u h r).

(б) D o o r open all th e tim e .

T h u s it w ill be seen th a t th is fu rn a ce w ill require 55.7 k. w. for op eratio n. N o fa cto r of s a fe ty need be a p p lied to th is figure if th e con d itio n s selected are a t th e m axim u m . On th e c o n tra ry , if th ese are norm al o p eratin g con d itio n s a fa cto r of s a fe ty sh ould be ap p lied acco rd in g to th e p o ssibilities of greate r de­

m ands b ein g m ade on th e fu rn ace.

A fte r ca lcu la tin g th e n u m ber of k ilo w a tts n ecessary fo r op eratio n , th e le n gth of th e resistor is a p p ro x i­

m ated in order to determ in e th e v o lta g e . W ith g ra n u la r g ra p h ite 1 exp erience h as show n th a t th e m ost s a tis fa c to ry v o lta g e is e q u iv a le n t to 1V2 v o lts per inch le n gth of th e resistor. F ro m th is v o lta g e and th e w a tta g e as co m p u ted a b o ve, th e n um ber of am peres m a y be easily determ in ed.

e. m. f. r e q u i r e m e n t s— T h e e lectrica l resistance of a resisto r in a fu rn a ce can n o t be su fficien tly clo sely p red icted to w a rra n t ca lc u la tin g th e size of th e resis­

to r w ith a v e r y g re a t degree of c e rta in ty . O f n ecessity, th erefore, th e e x a ct v o lta g e w h ich w ill b e requ ired fo r a fu rn ace to ta k e a certain n u m ber of k ilo w a tts can be d eterm in ed o n ly a p p ro x im a te ly . A p rovision fo r o b ta in in g v a rio u s v o lta g e s is, th erefo re, n ecessary, an d a tran sfo rm er w ith several ta p s is o rd in a rily em ­ p lo y e d for th is purpose. H o w ever, it is p e rfe ctly possible to p ro v id e a v a ria b le v o lta g e gen e ra to r for th e sam e purpose. Since th e precise p ro d u ctio n of steel for a g iv en fu rn a ce can n o t be v e r y clo sely as­

certain ed . and since, in m ost cases, d ifferen t prod u ction s are desired a t d ifferen t tim es, it is a b so lu te ly n eces­

sa ry th a t p ro vision be m ade fo r alterin g th e k ilo w a tt in p u t a t w ill of th e o p erato r.

T h e usual an d sa tis fa c to ry m eth od of m eeting these req u irem e n ts ap p ears to be th e em p lo ym e n t of a tra n s ­ form er w ith 10 to 15 tap s. U s u a lly 13 is a sa tis fa cto ry n u m ber, h a v in g a ran ge of v o lta g e s on th e seco n d ary from a m inim um e q u iv a le n t to one v o lt per inch len gth of th e resisto r to a m axim u m e q u iv a le n t to tw o vo lts per inch len gth of th e resisto r. T h e v a rio u s ta p s on th e tran sfo rm ers used in m ost in stan ces h a v e g iv en vo lta g e s w h ich are in a rith m e tica l progression, b u t it is th e opinion of th e w riter th a t a progression of v o lt ­ ages in u n equ al ste p s is b est su ited fo r th e w ork. F o r th e purpose o f m a k in g p ro vision for th e u n ce rta in ty o f th e resistan ce of th e resistor, th e v o lta g e s w ould lo g ic a lly be chosen in a rith m e tica l progression. F o r purposes of regu latio n , h o w e ver, since th e k illo w a tt in-

1 A rtificial gra p h ite av era g in g V i-in c h m esh, b u t co n ta in in g n o fine pow der.

p u t increases as th e sq u are of th e vo ltag e , it would ap p ear, fro m th is po in t of v ie w , th a t th e vo ltage steps sh o u ld be gra d u ate d to b est m eet th is condition.

T h e tw o con d itio n s m u st be m et, an d th e most satis­

fa c to ry arran gem en t is to m ake th e steps in such pro­

gression th a t th e difference of th e k ilo w a tt inp ut on ad­

ja c e n t ta p s in th e high er v o lta g e s w ill n o t be .so very m uch larger th a n on th e a d ja c e n t ta p s on the lower v o ltag e s. A cco rd in g ly , a s a tis fa c to ry range of po­

te n tia ls on a tran sfo rm er w ith 13 ta p s would have vo lta g e s e q u iv a le n t to th e fo llo w in g, per inch length of th e resisto r: 1.00, 1.10 , 1.20, 1.29, 1.38, 1.47, 1.56, 1.64, 1.72, 1.80, 1.87, 1.94, 2.00.

e l e c t r i c a l r e g u l a t i o n w i t h o u t t r a n s f o r m e r

A m e th o d 1 for o b ta in in g th is regu latio n and ad­

ju s tm e n t w ith o u t th e use of a tran sfo rm er has been d evised in th e w rite r’s la b o r a to ry v e r y la rg e ly through th e .work of M r. R ic h a rd S. B ick n e ll. In th is type of fu rn ace several resisto rs are em p lo ye d , w hich are not p e rm a n e n tly e le c trica lly con n ected, and w hich b y means of su ita b le sw itch es m a y be co n n ected in various w a y s w hile th e fu rn a ce is in op eratio n . T h e y may be arran ged in series, in p arallel or in a n y combinations n ecessary to effect th e desired regu latio n . In other w ords, th is is regu la tio n b y a lterin g th e resistance of th e resistor as co n tra ste d w ith th e aforementioned m eth od w here regu la tio n w as effected b y altering the v o lta g e im pressed upon th e resistor. A s will be show n su b seq u en tly th is ty p e of regu la tio n is particularly a d a p te d to fu rn aces h a v in g 10 sq. ft. of hearth area or o ver. A n exam p le of a fu rn a ce cap ab le of such regu la tio n is sho w n in F ig . I I I . W ith these four re­

sistors in th is p a rticu la r fu rn a ce it is possible to ob­

ta in n o inches in le n g th of resistor, or equivalent of sam e, in th e circu it a t one tim e, and 220 inches in le n gth of resistor a t anoth er. A large n um ber of inter­

m ed iate len gth s of resisto r b etw e en th is maximum an d m inim um figure m a y also b e p lace d in operation.

T h is p a rticu la r fu rn a ce is designed to operate on 220 v o lts an d it w ill be re a d ily seen th a t th e maximum v o lta g e o b ta in a b le per inch of resistor is tw o volts and th e m inim um is one v o lt. A q u ite surprisingly large n u m ber of in term e d iate len gth s of resistor are o b ta in e d b y e m p lo yin g th e fo u r T -sh ap ed resistors, as show n. T h e len gth of th e resistor is, of course, m erely an o th er w a y of s ta tin g th e resistance of the fu rn ace . T h ese T -sh a p e d resistors h a v e each three u n eq u a l legs. R e sisto rs A and D are sim ilar and B and C are sim ilar, b u t A an d B h a ve corresponding legs of differen t len gth s. T h e resistance of the fur­

nace resistors fo r a n u m ber of in term ed iate steps is m ade b y co n n ectin g tw o legs in p arallel in instances w hen a lo w resistan ce is desired. W hen a high re­

sistan ce is w a n te d th e resisto rs are run in series the cu rren t passin g th ro u g h th e lo n gest legs only. By p ro p e rly p ro p o rtio n in g th e legs, it w ill be seen that th e n u m ber of in te rm e d iate step s fo r purpose of regula­

tio n m a y be m ade as large as desired.

I t is, of course, possible to com bin e these tw o methods o f reg u la tio n , n am ely b y v o lta g e and resistance, having a fe w step s on th e tran sfo rm er and h avin g one or a

1 P a te n te d .

July, 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 537

¡ ¡ ■ ■ I B

few resistors cap ab le of b eing arran ged eith er in series or parallel. A fu rn ace so re g u la te d is sho w n in plan in Fig. I V and th e m eth od is q u ite su ita b le for sm all furnaces of fro m 4 to xo sq. ft. h ea r h area. T h e construction of th e resisto r as sho w n in v e rtic a l section would be qu ite sim ilar to th a t in F ig . I I I .

W ID T H A N D D E P T H O F R E S I S T O R T h is discussion

applies to b o th ty p e s of fu rn a ce s w here th e tw o m ethods of regulation are e m p lo ye d , i. e., eith er a lte rin g the voltage or th e resistan ce. I t has b een fo u n d th a t a resistor p lace d b en eath th e h earth can be com posed of two la y e rs of m aterials to a d v a n ta g e , th e upp er of granular g ra p h ite and th e low er of som e m aterial

of lower electrica l c o n d u c tiv ity th a n g ra p h ite , such as charcoal. T h e low er la y e r ta k e s a sm aller p a rt of the curren t th a n does th e u p p er la y e r of grap h ite, thus placing th e m ajo r p a rt of th e h e a t lib e rated quite near to th e to p of th e resistor. T h is m ethod seems to p ro te ct th e p a rt of th e lin in g upon w hich the resistor rests. I t p ro te cts it su fficien tly w ell n o t on ly to warrant its use, b u t to m ake its use a b so lu te ly necessary in th e case o f fu rn a ce s o p eratin g close to or above 1800° F . A resisto r con sistin g of h a lf ch ar­

coal m oderately ta m p e d b y h an d and h a lf gra p h ite gently tam p ed in is v e r y sa tis fa c to ry . T h e resistance of an inch cube co n sistin g in th e u p p er h a lf of g ran u lar graphite (pieces 3/zn to l/s in.) and th e lo w er h a lf of hard

^ood charcoal p u t in acco rd in g to th e m eth od de­

scribed above is a p p ro x im a te ly 0.125 ohm a t 1700° F . Thus the area of th e cross-section o f th e resistor m a y be easily d eterm in ed a fte r th e cu rren t n ecessary h as

been co m p u ted for th e n orm al ru n n in g con d itio n of 1V2 v o lts per inch len gth of resistor.

s h a p e o f r e s i s t o r— T h e w id th and d ep th of th e resistor sh ould be such th a t as m uch h e a t as possible is lib e ra ted in th e desired d irectio n . F o r resistors in th e h earth th is directio n is, of course, u p w a rd . A c ­ cordin g to th e th e o ry , th erefore, th e lo g ical shape of resistors of th is sort w ou ld be as w ide as possible and q u ite shallow . T h is section, h o w ever, is n ot a t all feasib le for sev eral reasons. T h e resisto r burns a w a y m ore ra p id ly w hen it is w ide and it is m ore difficult to spread th e g ra p h ite on a w ide resisto r w hen it is replenished. W id e resistors require m ore lin in g and th e expense of th e linin g is a re la tiv e ly im p o rta n t item in th e cost. W hen w ide resistors are m ade to run a t rig h t angles th e cu rren t has a te n d e n cy to flow across th e in terio r corner in m uch h igh er in te n sity th a n a t th e exterior corner. Som etim es carbo n or g ra p h ite b lo ck s h a ve been p laced in th e resisto r at th e corners for th e purpose of red u cin g th is lo cal effect.

T h is, how ever, is n o t a v e r y go od rem ed y, as th e h e a t

Fi g. I V — Fu r n a c e Re g u l a t e d b y Vo l t a g e a n d Re s i s t a n c e— Su i t­ a b l e f o r 4 t o 1 0 Sq. Ft. He a r t h Ar e a

lib e ra te d in a n y e v e n t is n ot so g rea t p e r u n it area of th e resistor in th e corner as in oth er p a rts of th e fu rn ace . T h e cross-section of th e resisto rs h ad, th erefore, b e tte r be m ade a b o u t square, or w ider th a n th e d ep th b y a sm all am o u n t. If p ossible th e resisto rs should n ot be narro w er th an th e ir d ep th , b u t it is im p ossible to o b serve th is req u irem e n t in all cases.

R e sistors less th a n 2V2 in. w ide sh ould n ot be used.

T h e y should be n o t less th a n 6 in. deep and p re fe ra b ly a b o u t 7 in., ex ce p t for resistors o v er 10 inches w ide w hich can be m ade 8 in. deep, th o u gh m ore th a n th is is lik e ly to cause excessive h ea tin g in th e base of th e fu rnace.

M A X IM U M L I M I T A T I O N I N S IZ E O F R E S I S T O R S T h e designer fre q u e n tly has th e o p p o rtu n ity of e m p lo yin g one large resistor or tw o sm aller ones to do th e sam e w ork. S m all resistors less th a n 3 in. w id e should be avo id ed becau se sligh t va ria tio n s in sh ape h a v e a m ore m arked effe ct on th e ir resistance th a n in th e case of th e large resistors. I t is m uch b e tte r as a rule to em ­ p lo y a sh o rt resistor 4 or 5 in. w ide th a n a corresp on d ­ in g ly lon ger one 2l / i or 3 in. w ide. On th e oth er h an d , larg e resistors are also to be a vo id ed . Since th e

f o r m e r— Ad a p t e d f o r 1 0 Sq. Ar e a

th e rm a l c o n d u c tiv ity of g ra p h ite is rath e r low it is e v id e n t t h a t large resistors are m uch m ore lik e ly to becom e e x cessiv ely h eate d in th e ir cen ters th a n sm all ones. R e sisto rs 6 to 9 in. w ide are to be used w h erever possible, and for resisto rs of th is ty p e 12 inch es w ide and 8 inches deep are a b o u t th e m axim u m dim ensions for fu rn a ce s used for h e a tin g steel. T h is is q u ite too large, h o w e ver, for a n y h e a t-tre a tin g w o rk, b u t it is m en tion ed m erely to g iv e an a p p ro xim atio n o f th e m axim u m lim ita tio n of th is ty p e of fu rn ace. A 12 b y 8 in. resistor w ou ld c a rry 1000 am peres and a n u m ­ b er of th em cou ld be arran ged in a fu rn a ce so as to lib e ra te 16 k . w. per sq., ft. of h earth . T h is is e q u iv a ­ le n t to a p ro d u ctio n of a b o u t n o lbs. of steel h eate d to 1700 ° F . per hr. per sq. ft. of h earth u nder th e usual cond itio ns. T h is p ro d u ctio n is n o t o n ly m ore th a n is u su a lly desired, b u t is fa r too m uch for go od w ork.

E xp erie n ce h as sho w n th a t a m axim u m p ro d u ctio n of a b o u t 50 lbs. per hr. per sq. ft. of h earth a t 1700° F.

is all th a t can be exp ected in electric h e a t-tre a tin g fu r­

naces.

p r o d u c t i o n o p s t e e l— T h e te m p e ratu re and th e p ro d u ctio n of steel from an electric fu rn ace are m u tu a lly d ep en den t. T h e h e a t lib e ra ted in th e resisto r, if n o t ta k e n up b y th e m etal, w ill occasion a rise in te m ­ p e ratu re o f th e fu rn ace . T h e larger th e electrical c a p a c ity per u n it area of h earth , th e g rea te r th e effect on th e te m p e ra tu re b y a lteratio n in .the pro d u ctio n . I t is fo r th is reason th a t p ro d u ctio n s o ver 50 lbs.

per hr. per sq. ft. o f h earth sh ould be a vo id ed . W ith m o d erate cap acities of 4 or 5 k. w. per sq. ft. of h earth area (e q u iva le n t to a p ro d u ctio n o f 30 to 35 lbs. of steel per hr. to 1700° F .) va riatio n s in p ro d u ctio n h a v e b u t v e r y little effe ct on th e te m p eratu re . T h e h e a t c a p a c ity of th e resistor linin g and b ric k w o rk in fu rnaces of th is size is am p ly able to com p ensate for ch an ges in p ro d u ctio n , so th a t th e te m p e ratu re re­

m ains p r a c tic a lly th e sam e. A fu rn ace designed for a norm al ru n n in g lo a d of 4 k. w. per sq. ft. of h earth (w ith 1 V s v o lts per inch len gth of th e resisto r) will p ro v e v e r y sa tisfa cto ry . T h e u n ifo rm ity of te m p e ra ­ tu re on th e h earth in fu rn a ce s em p lo yin g th e T -sh a p ed resistors show n in F ig . I l l is q u ite rem ark ab le, b u t ev en w ith th e U -sh ap ed or serpentin e resisto r a te m ­ p e ra tu re v a ria tio n of less th a n i o ° F ., in a n y p o in t of th e h earth from th e desired te m p eratu re , is to be ex p ected .

e n a m e l i n g f u r n a c e s fa ll q u ite in th e sam e c a te g o ry w ith th e h e a t-tre a tin g fu rn aces. A lth o u g h th e y are larger in size th e y are n o t co rresp o n d in gly large in electrica l c a p a c ity . F o r en am elin g fu rn aces resistors sh o u ld b e p laced on th e sides, b u t a b o u t th ree -q u arte rs o f th e k ilo w a tt in p u t sh o u ld be lib e ra te d in th e base. R e sisto rs w hen p lace d alo ng th e sides of a m uffle of an en am elin g fu rn a ce sh ould be sm all, 10 to 20 sq. in. in sectio n and sh o u ld consist e n tire ly of g rap h ite.

T h e lin in g o f su ch a resisto r is u su a lly designed so as to fo rm a p a rt o f th e in terio r w all of th e muffle.

E L E C T R I C F U R N A C E S F O R T E M P E R A T U R E S A B O V E l8 o o ° F .

W ith resp e ct to th e class of fu rn aces op eratin g o v er 1S000 F ., th e w riter k n o w s o f no exam p le in in d u stria l w o rk, ex ce p t on a sm all scale, w h ich has S38 T H E J O U R N A L O F I N D U S T R I A L

p ro ven s a tisfa cto ry . A n u m ber h a v e b een constructed and trie d for v a rio u s len gth s of tim e , b u t a durable fu rn ace , certain of op eratio n , is y e t to be produced.

M o st of th e exp erim en ts w hich h a v e b een conducted h a v e e m p lo ye d fu rn a ce s w ith a single resistor about h alf g ra p h ite and h a lf ch arco al, as m en tion ed above.

T h ese resistors h a v e been m ade a b o u t a fo o t and a h a lf w ide and p lace d in a tro u g h of a m ixtu re of re­

fracto ries, th e b asis of w hich is firesand. T h e metal to be h e a te d w as p la ce d d ire ctly a b o v e th e resistor, b u t n o t to u ch in g it. T h e m etal w as steel bars for fo rgin g and h eate d to a b o u t 24000 F . In order to effe ct a p ro d u ctio n sim ilar to th a t of an oil-fired forge fu rn a ce of th e sam e size, th e te m p eratu re of the resisto r h ad to be a b o v e 2900 0 F . F o r th is tempera­

tu re it seem s im possible to co n s tru ct a fu rn ace which w ill h a v e a v e r y lo n g life. In th e course o f a few weeks th e lin in g or th e b rick s w ill h a v e fluxed to some de­

gree and reb u ild in g w ill be fo u n d n ecessary. A lining of su b s ta n tia lly pure silicon carbid e b rick m igh t stand up u nder th e se con d itio n s, b u t it is questionable if a re fra c to ry a n y poorer th a n th is w ould be satisfactory.

T h e electrod es, to o , are d ifficu lt to h old in p lace without c o s tly su p p o rts w h ich m igh t h a v e to be water-cooled.

T h ese fu rn aces h a v e b een used for h eatin g metals for fo rgin g and h a v e show n in som e instan ces good econ om y. A cu rren t con su m p tion of 370 k. w. hrs.

per 2240 lbs. of m etal on a 100 k . w . fu rn a ce was noted.

In general, th e ty p e of c o n stru ctio n on th e se furnaces w as sim ilar to th a t sho w n in F ig . II , ex ce p t th a t the U -sh aped resistor w as s u b s titu te d b y a single straight one ru n n in g from one end of th e h ea rth to the other.

F o r w ork a t fo rgin g te m p eratu re s a fu rn ace employ­

in g a g ra p h ite resisto r does n o t seem cap ab le of be­

com in g a co m m ercial r e a lity unless a v e ry unique lin in g can be d eveloped .

E L E C T R I C F O R G E F U R N A C E O F T H E A R C T Y P E

T h e w riter h as g iv e n con sid erable th o u g h t to this im p o rta n t field of electric fu rn aces for fo rgin g and has d ev elo p e d a fu rn a ce w hich app ears to elim inate most of th e d ifficu lties en cou ntered . T h is fu rn ace is as y e t o n ly in th e exp erim e n tal sta ge , a lth o u gh it appears to offer a ttr a c tiv e com m ercial possibilities. It is of th e arc ty p e and th u s im m e d ia te ly m any of the d ifficu lties in h eren t to th e resisto r fu rn ace disappear.

A s th e re is no resistor th e re is, of course, no resistor linin g. T h e m etal is p lace d on th e h earth and is h ea te d d ire ctly b y th e arcs, th e bases of w hich play a fe w inches a b o v e th e m etal to be heated , thus ob­

ta in in g a h ig h th e rm a l efficien cy. T h e arcs are de­

flected b y m eans of an a u x ilia ry electro d e w hich spreads th e flam e of th e arcs so as to d istrib u te th e heat com­

p a r a tiv e ly e v e n ly and also serves to p ro te ct the roof of th e fu rn ace . T h e roof, if b u ilt of silicon carbide b rick , w ill h a v e a lon g life. A s th e electrical equip­

m en t is p lace d a b o v e th e h earth it is easily accessible and m a y be rem o ved b y a crane so th a t a new top can be p lace d on th e fu rn a ce in a v e ry few minutes.

A s arcs of a fe w k ilo w a tts are difficult to operate, it w o u ld p ro b a b ly be n ecessary to b u ild a fu rnace capable o f a v e r y su b sta n tia l p ro d u ctio n . T h e w riter hopes A N D E N G I N E E R I N G C H E M I S T R Y V o l . 6, No. 7