Coal Age : devoted to the operating, technical and business problems of the coal-mining industry, Vol. 29, No. 10

M c G r a w - H i l l

P u b l i s h i n g C o m p a n y , I n c . Ja m e sH . McGr a w, P residen t E. J . Me h r e n, V ice-P resident

Devoted to the Operating, Technical and Business

Problems of the Coal-Mining Industry

Engineering BM tot

V olum e 29 N E W Y O R K , M A R C H 11, 1926 N u m b e r 10

T he Coal Myth

W HA T everybody believes is likely to be in the m ain untrue, for, when all a re agreed, th en exaggera­

tions are inevitable, statem en ts a re not questioned or examined and no one fe a rs to give rein to his im agina­

tion. So it has been w ith th e coal in d u stry . I t has been declared the w o rst of all th e w orld’s in stitu tion s.

I t has been the prey of m asters of superlatives. Is it sick? There is none m ore sick. Is it overdeveloped?

None is more so. Is it irre g u la r in operation? None works more irregularly. Is it deficient in mechanicaliza- tion? None is m ore deficient.

Some tim e when coal has p a rtly re-established itself by a superhum an effort we shall begin to see it in its rig h t light. Day laborers a t m ines, fo r instance, who get $7.50 fo r an eight-hour day will be seen to be b e tte r paid th a n snow shovelers who w ork fo r ten hours and obtain a wage one-third lower, paying also m ore fo r shel­

ter, tran sp o rtatio n , food and com fort th a n th e laborers a t coal mines. Some day th e irre g u la r tra d e s will be examined, and coal will be seen to be nowhere in the running. Some day th e prim itive in d u stries will hold a congress and refu se to recognize such a well-developed and highly m echanicalized in d u stry as coal m ining.

Some tim e th e m iner will be seen not as a feudal se rf b u t as one of th e m ore independent of a rtisa n s. There will come à day also when we shall see the in d u stry as one in which the operators a re grossly undercom pensated.

The world is happy in having a m yth, a scapegoat fo r simple m inds to discuss. We have so m any difficult problem s to solve. H ere is som ething we all agree on

— a sto ry which we can believe w ith ou t doubt or ques­

tion. W hy th en trouble about th e fac ts!

Talleyrand de P érig o rd said h isto ry was “a fable agreed on.” T h at expression will serve to describe the coal ind u stry un til someone comes to s h a tte r our fa ith and to convince us once m ore th a t the m ore superlatives th e re are in an assertio n th e m ore unsafe it has become.

If all th a t has been said of th e coal in d u stry is tru e th ere is no certain ty in hum an n atu re.

Snap Judgm ent

A T A M E E T IN G of the C ham ber of Commerce of l \ th e S ta te of New York on Feb. 4, its com m ittee on public service w as asked to in v estigate coal prices in New Y ork City. On M arch 4, th e com m ittee reported th a t it was “quite ap p aren t th a t profiteering is and has been going on” and th a t th is price-gouging “ is not confined to th e cellar dealer or peddler.” M ark-ups of 54 to 106 p e r cent by those d istrib u to rs of fuel in bag lots did not im press the com m ittee as exorbitan t.

L arge reta ile rs, sta te d an appendix to th e rep o rt, “m u st b ear some sh are of responsib ility fo r oppressive p rices.”

The m an date to th e com m ittee w as “to a scertain the fac ts concerning th e relatio n betw een th e cost of coal

delivered in New York and the price demanded by re ­ tail dealers of all classes.” Yet, nowhere in the rep o rt is th ere any evidence th a t th e comm ittee had any ac­

curate knowledge eith er of m ine prices, prices a t tid e ­ w ater or th e cost of handling coal th ro u g h th e retail pockets. The te x t of th is document reveals a clouded conception of th e different agencies of coal distrib u tio n and th e ir respective functions. The only statem en t p u r­

porting to represent wholesale prices m ade on the com­

m ittee’s a u th o rity is a hopeless jum ble of m ine prices on domestic an thracite, tid ew ater quotations on b itu ­ minous m ine-run and reta il delivered prices on coke.

The committee excuses its failu re to develop all th e facts called fo r in its in stru ction s by pleading th a t th e task was difficult and th a t it lacked a u th o rity to compel the subm ission of p e rtin en t data. T he evidence g a th ­ ered, it says, was conflicting—b u t the im perfect record did not deter it from pronouncing judgm ent and from m aking recom m endations fo r legislative action. J u s t how difficult it would have been to g a th e r th e necessary inform ation is lost in m ystery. T here is, however, nothing in the rep o rt to indicate th a t the com m ittee or its paid investigators unduly exerted them selves to c a rry th e ir studies beyond th e peddler to apportion responsibility and, if need be, condemnation.

F o r seventy-five y ears it has been th e proud boast of th e Chamber th a t it has taken no action upon questions

“we confessedly do not feel ourselves qualified to judge.”

In the present case, however, th e C ham ber has seen fit to accept and indorse a rep o rt th e im perfections of which are p aten t and in th e face of a req u est from the chairm an of th e s ta te relations com m ittee of th e New York S tate Coal M erchants’ A ssociation th a t th e re ta il tra d e be heard before th e C ham ber com m itted itself.

T his d ep artu re from well-seasoned tra d itio n h ard ly adds to the glory of the Cham ber of Commerce of th e S ta te of New York.

Liquid-Oxygen E xp losives

D URIN G the p a st few y ears m uch in te re s t has been shown in th is country concerning th e use of com­

bustible m a tte r soaked in liquid oxygen as an explosive fo r use in in d u stria l b lastin g. P e rh ap s it would be m ore proper to say “cu rio sity ” th a n “in te re s t,” because up until quite recently everybody w as m ildly anxious to know m ore about th is explosive, its possibilities and lim itatio n s; yet nobody seemed to be doing a n y th in g in p a rticu la r about it.

As is well known, explosives, from th e chemical sta n d ­ point, a re of two general types— compounds and m ix­

tu re s. H igh explosives a re usually compounds while th e m ix tu res are, as a rule, slow er in th e ir action be­

cause th ey evolve th e ir gases fro m actual com bustion which progresses from p article to particle. Common black gunpow der is an excellent example of a m ix tu re explosive.

353

354

C O A L A G E

Liquid-oxygen explosives partake of the n a tu re of

m ixtures although in many respects they behave much like dynam ite which is a good example of a chemical compound. We p rin t elsewhere in this issue an a b stra ct of the extremely valuable paper on th is subject recently presented before the Am erican In stitu te of M ining and M etallurgical Engineers. This will be of keen in terest to m any m ining men.

Several characteristics of the new explosive recom­

mend it for strip pit m ining and tunnel work in rock although its heat of explosion and quickness of action unfit it for shooting coal. The rig id ity of th e cartridges and yie fact th a t the smaller sizes, in order to even approxim ate th eir possibilities m ust be fired w ithin 10 to 15 min. a fte r th e ir placement in the shot hole are detrim ental qualities.

It is in the strip p it and rock quarry, therefore, th a t the new explosive can be used to best advantage. Here the 4-, 6-, or 8-in. drill holes used perm it th e employment of cloth-bound cartridges of large diam eter which may rem ain in place as much as 2£ hr. before firing and yet evolve a large proportion of th e ir m aximum possible energy. A nother interesting featu re of th e liquid oxy­

gen cartrid g e is the fact th a t it is entirely successful in wet holes or may be used w ith w ater stem m ing.

Such stem ming soon freezes a fte r insertion of the c a rt­

ridge.

Other excellent characteristics of th e new explosive are its freedom from detonation by im pact and the fac t th a t it m ust be used practically as soon as it is m anufactured. The cartridges may be made up a t any tim e and t a n be safely stored in any q u an tity as they do not become explosive until soaked in th e liquid oxy­

gen. Atmospheric conditions have small effect upon them when either soaked or unsoaked. F u rth erm o re th e ir total cost as used is somewhat less th a n th a t of dynamite.

An operation using th is explosive needs neither magazine nor thaw house. In its stead a suitable place m ust be provided fo r the storage of detonators, fuse and cordeau. Sim ilarly a small oxygen plan t m ust be installed as well as a place fo r soaking cartridg es.

However, in addition to a decreased expense all or p rac­

tically all of the danger incident to storing, tra n sp o rtin g and handling high explosives is elim inated while the useful effects realized are approxim ately the same.

I t is reported th a t liquid-oxygen cartridg es are being used a t a large coal strip p in g operation in Indiana for blasting th e overburden ahead of the strip p in g shovels.

The progress of th is work will be watched w ith more than usual in terest by the rest of the coal industry.

“ B ootlegging” Coal

S OME have wondered how the m iners m et the long strik e w ithout any large w ithdraw al of savings funds and w ithout any extensive m easure of relief from the public, th e tra d e s unions in general or th eir own union M any of them wandered to the big centers of industry such as New York and P ittsb u rg h and obtained work there. P erhaps in all 20 per cent of the workers left th e a n th ra cite region.

Some were reported in th e bitum inous mines and in one case a t least, they were willing to perform ’ more dead work w ithout com pensation th an were the m iners of the locality they invaded. A room had caved in and

th e a n th ra c ite m en consented to clean it up w ith o u t charge in order to g et th e opp o rtun ity to m ine th e coal a fte r th e face w as reached. B eing aw ay fro m th e ir own homes they did not h e sita te to create conditions th a t they w ere unw illing to introduce or a fra id to practice in th e ir home m ines. T h eir action w as equivalent in c h a ra c te r to th e “d um ping” policy of m a n u fa c tu re rs who relentlessly dem oralize d ista n t m ark e ts b u t are careful of th e ir own.

M any m iners, however, did not move aw ay b u t lived on the earn ing s of wives and d a u g h te rs employed in the silk mills. Silk m an u fa ctu rin g is a g re a t in d u stry in the an th ra cite region, because th e a ir is n o t sullied w ith soot and because th ere is an abundance of fem ale labor.

B ut th e re w as an o ther in d u stry available and th a t, stran g e to say, was coal m in ing — “bootlegging” coal.

The m iners would not w ork fo r th e com panies, b ut they were w illing to e x tra c t coal fro m th e culm banks. G reat activ ity was shown in th is in d u stry . The m iners, each fo r him self, paid a h igh ro y alty on th is coal to the owner of the culm bank. T eam sters hauled i t sho rt distances, and even into New Jersey . These “snow­

b ird ” operators m ade $7 or $8 a day, an d th e coal, im properly prepared and containing larg e q u a n titie s of slate and bone, w as sold a t prem ium prices. These men, so long as the w in ter lasted, did n o t find their strik e unprofitable. The d ista n t cities h ad to do w ith­

out an th ra cite b u t th e home tow ns and those around the region had h ard coal-—of a sort.

The operators m ade no com plaint. I t is usually found th a t when these disagreem ents occur th e owners of m ines have a sym pathetic eye to th e su fferin g s th a t the men have brou gh t and a re b rin g in g on them selves. They find it difficult to d istin g u ish those who a re th e mere victim s of circum stances th a t th ey cannot control from those who have invited m isfo rtu n e by advocacy of a dogged resistance.

M any y ears ago a bitum inous s trik e occurred during which one company, having a larg e sto re and being obliged to refuse credit to th e idle m in ers, was im­

portuned to lend the services of its m ules and teamster to the m iners. This was conceded and th e men were soon scouring the surro u n d in g cou n try fo r farm ers ready to supply them w ith food. In m ost instances the aid was afforded, and much provender w as b ro u g h t in as the farm ers were a t th a t tim e m ore frien d ly to the m iners th an today, p a rtly because w ages w ere lower but more because th e fa rm in g population had fu rn ished m any rec ru its to the coal in d u stry . Even th e company stores have not in frequently extended c re d it to the friendly m iners and those whose financial difficulties appealed to the store m an agem en t; an d th en w hen the bars were let down it was difficult to se p a ra te deserving from undeserving.

A Gambler’s Chance

N OT a few m ines covered w ith u n tre a te d , com bustible dust are in operation. I t m u st be tru e t h a t m ine officials and th e h ig h e r executives a re now th o roug h ly aw are of the degree of inflam m ability of coal dust.

W ith little doubt th e re fo re those who allow com bustible dust to accum ulate in larg e q u a n titie s w ith o u t a tte n u a t­

ing it w ith rock dust, or even so m uch as soaking it

w ith w ater, a re deliberately ta k in g a g am b ler’s chance

in hoping fo r freedom fro m d isa ster.

Ma r c h

11, 1926 C O A L A G E 355

Shoveling Machines Reduce Costs and Speed Rock Removal

P a r ticu la rly U s e fu l W ith U n certain R oof and R o ll­

in g B o tto m — Can C lean U p R ock F a ste r T h a n A ll th e M en T h a t Can B e G otten A round a F a ll

By Frank H . K neeland

A s s o c i a t e E d i t o r , N e w Y o r k , N . Y.

M ANY m ines a re afflicted w ith a rock problem more or less severe. Som etimes th e thickness of the coal is such th a t th e roof m ust be brushed in order to secure th e necessary headroom on haulage- ways and entries. As a rule all such rippings m ust be removed from th e m ine and disposed of outside.

Again, in m any cases the bottom m u st be lifted eith er to give the necessary headroom or to afford a reasonable grade for the haulage. P a rtic u la rly w here th e coal is th in and its contour uneven e ith e r or both of these methods m ust be followed if a n y th in g resem bling f a ­ vorable haulage conditions a re to be^approxim ated.

Such are th e conditions encountered in a c e rtain group of m ines in Kentucky. The thickness of th e coal in these operations ranges from approxim ately 3 ft. 6 in.

to about 5 ft. Local dips and rolls a re num erous, and th e re is scarcely a haulage road to be found in these m ines anyw here th a t does not req u ire grad ing. In m any places, also, th e roof caves, som etim es to a height of 20 ft. or more, necessitatin g th e rem oval of large q u an tities of rock.

Shoveling m achines have been adopted fo r th is p u r­

pose, not only because they cheapen th e process involved but also because th ey do the w ork m ore rap id ly th an all th e m en th a t could possibly be used to advantage.

In a typical instance as will be described late r the bottom w as lifte d to a m axim um depth of 3 ft. th ro u g h ­ out a distance of 245 ft. along one of th e m ain haulage headings and all th e m ate ria l fro m th is cut, am ounting to 166 cu.yd. in th e solid w as loaded out over a week end.

Rock w ork on h aulage roads is alw ays expensive,

not alone because the m aterial handled is w orthless but also because only a lim ited num ber of m en can be employed. F u rth erm o re a fall on a m ain haulage blocks traffic on th is roadw ay and m ay th u s cause an in direct loss th a t m ay f a r exceed th e direct loss represented by the expense of rock handling. I t is in such places th a t mechanical m eans of loading, inasm uch as th ey are f a r more rapid th a n hand m ethods, are especially advan­

tageous, and such m eans are accordingly employed in the m ines to which reference has been made.

I t has now been practically eighteen m onths since th e first M yers-W haley type of shoveling m achine was sta rte d to work. The savings m ade by th is loader, how ­ ever, w ere such th a t a second m achine of th e same kind, size and model, w as installed in J a n u a ry of 1925.

Typical examples of th e w ork done by these m achines are shown in th e accom panying illu stratio n s, F ig s. 1 to 7. In F ig. 1 practically all th e w ork was liftin g bot­

tom. The grade was m ade unifo rm from A to E w ith two cuts and two fills betw een these points. The first cut extended from A to B , a distance of 280 ft., the m aximum depth of th is cut being 3 ft., th e to ta l y ard ag e being 202^ cu.yd. in th e solid. The y ard ag e of loose m aterial or spoil handled would be roughly tw ice th is am ount or approxim ately 400 cu.yd. F rom B to D a sho rt fill had to be made, m ate ria l fo r w hich w as ob­

tained by shooting th e roof a t C. Only enough roof was

shot down to m ake th e req u ired fill and th e m ate ria l

th u s obtained w as allowed to rem ain w here it fell, no

work being done upon it o th er th a n leveling th e su rface

sufficiently to enable th e tra c k to be laid sa tisfa c to rily .

356

C O A L A G E

From D to E the cut m easured 295 ft., its m aximum

depth being 3 ft. The volume (in the solid) was 252.2 cu.yd., m aking nearly 500 cu.yd. of loose rock. I t was not necessary to shoot top to secure m aterial fo r the little fill from E to F. The maximum depth of th is fill was about 1 ft. and m aterial fo r it was readily obtained from the end of the cut from D to E.

Fig. 2 shows how an ab ru p t dip was straig htened out and excessive grades avoided. I t represents another case of both brushing top and liftin g bottom. H ere the maximum fill was 15 ft. and the maximum cut was only 2% ft. The total length of th e fill was 630 ft.

and of the cut 220 ft. The m aterial blown down from the roof was 2,100 cu.yd., of which the shovel loaded out 942$ cu.yd., both figures representing m aterial in th e solid. The volume of rock removed from the cut was 150 cu.yd. m easured in th e solid.

Fig. 3 represents a case sim ilar to F ig. 2 in th a t both a cut and fill are involved. The m aximum depth of fill here was 10 ft. and its length to 470 ft. The volume of m aterial shot down was 1,332 cu.yd. in the solid, of which it was necessary to move w ith th e shovel 642$ cu.yd. also in the solid or roughly 1,280 cu.yd. of loose rock. The cut was about 130 ft. in length and its maximum depth approxim ately 2 ft.

Fig. 4 shows a long cut, so long, in fac t th a t its extrem ities are om itted from th is draw ing, only 850 ft.

of its length being shown. The maximum depth of this cut was 5 ft. 6 in. The spoil amounted to 1,108 cu.yd.

in the solid, or approxim ately 2,200 cu.yd. of loose rock.

As may be seen, however, the track grade obtained was excellent, the many humps and hollows originally exist­

ing being replaced by a level stretch of track and a uniform slight grade over which heavy trip s can be hauled w ith comparative ease.

Fig. 5 shows a long heavy roof fall. F or a distance of 950 ft. the top of th is en try fell to a maximum height of 14 ft. 6 in. The above statem ent is m isleading in th a t the fall did not take place entirely unaided. When th e tim bers along this heading began to show signs of

distress and failure, th e roof w as drilled and shot, b rin g in g rock and tim b ers down to g eth er. The rock was th en loaded out, m any of th e tim b ers being re ­ claimed in th is process fo r use elsewhere. In th is p a r­

tic u la r fall 4,941 cu.yd. of m ate ria l in th e solid w ere loaded by th e shovel, slig h t inequalities in th e floor being filled in the process. The actual y ardage of loose m ate ­ rial loaded and hauled away th u s am ounted to alm ost 10,000 cu.yd.

F ig . 6 is an o th er case of both a cut and a fill, but in th is instance th e fill was unusually thick and heavy.

I t was made in a sh arp local dip w here th e pitch of the coal a t one end w as so steep th a t a locomotive could not ascend w ith m ore th a n one or tw o cars an d not even then unless it had a ru n n in g s ta r t. To overcome th is difficulty th e roof w as shot down to a m axim um depth of 17 ft. and over a distance of 207 ft. A total of 907 cu.yd. of solid rock w as th u s b ro u g h t down, of which 411 cu.yd. were loaded out.

B ordering th is dip on th e left w as a roll. H ere the bottom was shot up over a length of 257 ft. and to a m aximum depth of 5 ft. All of th is m ate ria l am ounting to 333 cu.yd. of solid rock was loaded out by th e shovel.

The resu lting grade now has an inclination of 2.8 per cent a g ain st the loads, w hereas originally th e maximum grade had been one of 22 per cent a g a in s t them .

F ig. 7 shows how a hum p or roll w as cut down.

This was on one of the m ain h aulage roads and was causing much trouble. The im provem ent w as accom­

plished in two operations, th e first from A to B and the second from C to D. The total length of th e en tire job was 380 ft. and the y ard age moved 322 cu.yd.

Probably th e chief in te re st in th is c u ttin g down of a bothersome hum p centers in th e first cu t m ade because of the rap id ity w ith which th e w ork w as accomplished.

The first cu t was approxim ately 245 f t. long, its maxi­

mum depth about 3 ft. and its cubical contents 166.6 cu.yd. in th e solid. W ork of te a rin g out tra c k was begun a fte r th e day’s run on F riday. The tra c k was removed, the place drilled and shot and all loose m aterial loaded

M a x im u m c u t = ^ 6 "L en& o f c u t - 2 2 0 ’ M a x i m u m f i l l = 15'l e n g t h o f f i l l - 6 3 0 ' Y a r d a g e = f S 9 . 3 Y a r d a n e s h o t d o w n = 2 1 0 0 .4 4Y a r o ia g e s h o t d o w n = 2 1 0 0 .4 4

Y a r d a g e m o v e d b y s h o v e l ~ 9 4 2 .4 8

L e n g t h o f c u t -Ö S 0 ' M a x i m u m c u t S ’- 6 " Y a r d a g e ‘ 1,1 0 6 .3 M axim um a /f- 3 ' Length

Yardage = 2S2.2

M a x im u m * 1 1 * 1 0 'L en g th o f f i l l = 4 7 0 Y a rd a g e s h o t dow n =1332 2 Y a rd a g e m o v e d b y s h o v e !-6 4 2 .6

L e v e l

shove.1*4, 94I S M a x i m u m c u t = L e n g t h o f c u t = 2 S 7 '

Y a r d a g e = 3 3 3 .4

. f i l l = 1 7 '

L e n g t h o f f i l l = 2 0 7 ' Y a r d a g e s h o t d o w n =907■ 3 Y a r d a g e m o v e d b y s h o v e l =*4H.3

Mine-Grade A d ju stm en ts in a K en tu ck y C oal M ine M e c h a n ic a l lo a d i n g o f r o c k , w i t h a n i n e x p e n s i v e m e a n s o f r e m o v -

f r o m t h e m i n e c a r s a n d d i s p o s i n g o f i t o n t h e s u r f a c e , m a d e tn e w o r k , t h o u g h e x p e n s i v e , a n o t a b l e e c o n o m y in o p e r a t i o n . T h e r e m o v a l o f t h e f i s s u r e d r o c k s h o w n in F ig . 5 e l i m i n a t e d h e a v y

t i m b e r i n g a n d s o m e d a n g e r f r o m f a l l i n g r o c k . M a x i m u m

A to B '

Ma r c h

11, 1926 C O A L A G E 357 out by Sunday afternoon. The tra c k was th en relaid

and was ready fo r traffic by Monday m orning. In th is case, however, th e cut was accessible from both ends.

Accordingly, one shovel s ta rte d a t A and th e other a t B, the shovels w orking tow ard each other. Thus, sta rtin g to shovel on S atu rd ay m orning, they m et on Sunday afternoon, a fte r loading as stated, 166 cu.yd. of solid, or approxim ately 325 cu.yd. of loose, bottom rock.

Rock shoveling in these m ines is done m ostly at night. W here no tra c k is laid in th e place ten 7-ft.

sections of 40-lb. rail laid on steel ties have been pro­

vided. These can be laid section a fte r section in fro n t of the m achine as it advances. Each of these sections is provided w ith fish plates which m ay be slipped over or a-straddle th e webs of th e rails of th e tra c k already in place and quickly bolted fa st. A t th e first oppor­

tu nity , usually the next day, th is tem porary tra c k is replaced w ith one of a m ore perm anent n atu re. Of course if perm anent tra c k is already in place and only the roof is to be brushed, th e top is shot down directly onto th e rails and th e fall cleaned up w ithout recourse to tem porary track of any kind.

Speed of loading depends largely upon th e conditions of th e m aterial to be handled and th e distance over which both th e loads and em pties m ust be hauled. A car containing about 5 tons of rock can be loaded in about 5 min. This m ig ht be tak en to indicate th a t 140 to 145 cars of th is m aterial could be loaded in the course of a 12-hr. n ig h t sh ift. As a m a tte r of fac t sh iftin g cars and the breaking down of big lumps either w ith sledges, by hand or by m ud capping consumes so much tim e th a t especially when cleaning up falls only about seventy cars a re norm ally loaded out per sh ift.

Chunks much larg e r th a n 1-ft. cubes cannot be readily handled in th e car dump employed a t th e tipple. As a resu lt pieces of much la rg e r size m u st be broken down. T his is done eith er by hand sledges or by explosives.

In shooting roof th e same explosive is employed as fo r brin g in g down th e coal. F o r liftin g floor 40 per cent dynam ite is sometim es used, although here also a perm issible will do the work. Sticks 1x6 in. are em­

ployed, all firing being done electrically using a low- voltage b a tte ry instead of a b lastin g m achine.

F o r drilling th e holes jackham m ers are used. These are operated from a portable com pressor th a t is elec­

trically driven from th e trolley w ire. Steel 8 ft. in length is about th e longest th a t is used w ith these

T h e s e c o n v e y o r s a r e i n t h e m i n e s o f t h e P h e l p s D o d g e C o rp . a t D a w s o n , N . M . T h e y a r e u s e d e x c l u s i v e l y i n r e t r e a t i n g r o o m s t u m p s a n d c h a i n p i l l a r s . T h is p r o c e s s s a v e s c o n s i d e r a b l e b r u s h ­ i n g a n d r e l a y i n g o f t r a c k s a c c o r d i n g t o W . C. H o l m a n , c h i e f e n -

machines, so th a t if a fill is of g rea ter depth th a n th is th e rock m ust be taken down in lifts. However, it is seldom necessary to do this.

Inasm uch as a cut in th e bottom can be shot h a rd e r and can th u s be broken up m uch m ore thoroughly th an a cut in th e roof it represents a much b e tte r condition fo r the machine. The w o rst condition encountered in machine operation is w hat m ight be term ed a n a tu ra l fall or a roof th a t breaks and comes down of itself.

Most such falls can be anticipated and th e roof shot before the tim b ers a re crushed. Even th is la tte r pro­

cedure, however, resu lts in b rin g in g down th e roof in such large pieces th a t it is sometimes necessary to mud cap and shoot a fte r each two or th re e cars are loaded.

This m eans much delay.

Ro c k Is Wa s t e d Ou t s id e

In these m ines practically all th e rock th a t is loaded by power shovel underground is hauled to th e outside.

H ere it is discharged in th e same dump as th e coal being segregated from it by m eans of fly valves in the chutes. The rock takes a course th ro u g h the tipple th a t is separate from th a t taken by th e coal and a fte r being joined by th e slate and refu se picked from the m ine product is conveyed by belt to the slate bin.

Thence it is taken by slate larries, hauled around a small spu r on th e hillside and dumped.

D irect savings made by th e use of power-operated equipment, even though they m ay be large, a re f re ­ quently f a r outshadowed by and become a secondary consideration when compared w ith the in d irect savings obtained. In th e specific case of th e power shovel as used a t the m ines m entioned, although it m akes a large saving in the cost of handling rock, yet its chief advan­

tage probably lies in th e speed w ith which its w ork is accomplished.

A t best only two hand shovelers can w ork to advan­

tag e in a 12-ft. heading— any m ore would be in each oth er’s way. On th e average two such men would load out about five cars of rock each, or ten in all durin g a sh ift. The shoveling m achine on th e other hand, operated by a crew of from two to five men, depending upon the condition of th e m aterial to be handled, as has been stated, can load an average of about seventy cars p er sh ift. Thus a m achine removes roughly seven tim es th e qu an tity of rock th a t could be handled by th e gang th a t it supplants. I t is th is speed of operation th a t p a r­

ticularly commends its use.

g i n e e r a t t h e S t a g C a n y o n B r a n c h o p e r a t i o n s o f t h e c o m p a n y . T h e i l l u s t r a t i o n s h o w s tw o 2 0 - f t c o n v e y o r s i n t a n d e m r e t r e a t i n g o n a c h a i n p i l l a r . T h e l e f t - h a n d p i c t u r e s h o w s t h e d e l i v e r y e n d w i t h c o a l b e i n g d e p o s i te d i n a c a r .

358

C O A L A G E

Liquid Oxygen Desirable For Strip-Pit Work

oxygen can be produced a t an estim ated cost of 2.29c.

per pound.

Theoretically the oxidation of pure carbon to carbon dioxide (C 0 2) requires 2.67 u n its of oxygen by weight fo r each u n it of carbon. Sim ilarly, its oxidation to carbon monoxide (CO) req u ires 1.33 u n its of oxygen.

As commercial carbons are not chemically pure, and as the c artrid g e w rapper is cellulose and not carbon, it has been assum ed th a t 2.5 tim es the w eigh t of th e cartridge is required fo r its oxidation to C 0 2 and 1.25 tim es the w eight of the cartrid g e fo r its oxidation to CO.

Ideal requisites fo r a c a rtrid g e of th is kind are as follows : (a) Maximum density in o rder to provide a maximum of explosive in a given volume. (6) Ability to absorb liquid oxygen in excess of all requirem ents fo r complete combustion so as to provide fo r oxygen evaporation p rio r to detonation, (c) The physical prop­

erties of both the filling m ate ria l and th e w rapper should be such as to ren d er th e soaked c a rtrid g e me­

chanically strong in order th a t it m ay be handled w ith­

out breakage. This applies p articu la rly to th e w rapper which m ust not be too b rittle a t the low tem p eratu re of the liquid. (d ) The price of th e filling m aterial m ust be low enough fo r com m ercial use. ( e) The soaked c artrid g e m u st be firm and dry. W ith some filling m aterials, especially when lig h tly packed, liquid oxygen readily squeezes out of th e c a rtrid g e s m aking them difficult to handle.

It should be noted th a t a m ate ria l g iv in g m aximum requirem ents of density tends to give m inim um capacity for absorption. The com m ercial c a rtrid g e , therefo re, will be a compromise betw een th ese tw o requirem ents.

A pproxim ately 400 v a rie tie s of carbon blacks, lam p­

blacks, hydrocarbons and v ario u s m ix tu re s w ere in­

vestigated. M any of th ese m a te ria ls w ere rejected in the labo rato ry because of th e ir h ig h cost, low densities or low absorptive qualities. Several v a rie tie s of c ar­

bon blacks and lam pblacks of s a tis fa c to ry cost (from 6 to 9c. per lb.) and of s a tis fa c to ry d en sity and ab so rp ­ tion qualities w ere selected. F ro m th is list of possibles B ein g C om bustible B ut N o t Subject to

D eto n a tio n F lam e or L i g h t C oncus­

sio n s th e C artridges Are S a fely H an d led

T HAT liquid-oxygen cartridges are not suitable explosives fo r use in coal mines, because of the long flame th a t results from th eir detonation and because they are quite readily combustible, is conceded now by everyone. They have, however, been proved advantageous for use in open-pit work including in th a t designation coal and other strip pits.

D uring th e past few years much has been heard in th is country concerning the possibilities of using as an explosive for m ining some form of combustible s a tu ­ rated w ith liquid oxygen. Such an explosive commonly known as L.O.X., has fo r some years been used in b last­

ing down ore in the iron mines of L orraine, France.

An investigation of th is substance, its possibilities and lim itations has been conducted by Frederick W. O’Neil, chief engineer of the Ingersoll-Rand Co. and H erm an Van Fleet, vice-president of the A ir Reduction Co.

The following is an ab stract of th e ir paper as presented before the w inter m eeting of the A m erican In stitu te of M ining and M etallurgical Engineers, Feb. 17, 1926, by Mr. O’Neil.

Reliable app aratus fo r the production of liquid oxy­

gen has been fully developed and perfected. O perating on the so-called Claude system, which requires compres­

sion of the a ir to only about 900-lb. pressure, liquefac­

tion of the a ir and fractional distillation w ith recon­

densation of its oxygen content, commercially pure

Pouring Liquid Oxygen on Cartridges

j S S s » * t s , t u x

c a r r i e r a t t h e s a m e s t a t n n s r a 1 0 a a i T

Ma rc h

11, 1926 C O A L A G E 359 a lampblack and carbon black were finally chosen as the

best absorbents, and fu rth e r laboratory te sts and p rac­

tical experim ents were confined to these m aterials. Both of these absorbents are procurable in larg e q u antities and at reasonable prices.

C artridge w rappers m ust possess th e following quali­

ties: (a) The m aterial should be com bustible; ( b) it should allow liquid oxygen to perm eate it readily and

(c) it m ust not be b rittle or frag ile during soaking, in order th a t the soaked cartrid g e m ay be handled w ith ­ out breakage. I t is desirable also th a t it should reta in liquid oxygen while a t the same tim e allowing sufficient evaporation to prev en t ru p tu re of the cartrid g es by expansion of the gas. A fte r experim entation and te s t­

ing, the m aterial finally selected w as a pure rag-stock paper v arying in thickness from 0.007 to 0.010 in.

P ap ers which are filled or sized are unsuitable because of th eir brittleness a t the low tem p eratu re of soaking.

Considerable difficulty w as experienced in m aking a suitable cartridge. Gum m ing or gluing th e w rapping paper renders it im pervious and brittle, and a spirally wrapped ungummed c a rtrid g e is liable to s if t filling m aterial. A satisfacto ry c a rtrid g e was finally devel­

oped, rolled from a piece of paper of rhomboid shape.

A machine gums th is paper along one edge, so th a t when rolled into shape th is edge circles th e c a rtrid g e spirally.

One end of the cartrid g e is crim ped by th is machine and the other is crim ped by hand a fte r filling. Both ends are then imm ersed in paraffin to a depth of about i in., thus preventing siftin g .

It was soon discovered th a t hand filling of cartrid g es was unsuccessful, and a simple m achine was developed fo r th is purpose. In th is m achine a spiral screw acting w ithin the storage hopper causes the filling to exude from a nozzle a t its lower extrem ity. The c a rtrid g e is placed on a weighted platform below this nozzle, and the carbon is forced into i t a g a in st th e p ressu re exerted by the weight. Any desired density of filling m ay thus be attained. The term density as here used indicates th e mean app aren t density obtained by dividing the gross w eight of th e c a rtrid g e by its gross volume.

The cost of unsoaked c a rtrid g e s is about as follows:

7 x 20 in. 8 lb. cartridge, cost p er lb. 15 c. — cost p er cartridge $1.19 4£ x 18 in. 3 lb. cartridge, cost per lb. 14 c. — cost per cartridge .4 2 H x 1,2 in. } lb. cartridge, cost per lb. 24 c. — cost per cartridge .04

In th e accom panying illu stratio n s F ig . 1 shows th e relation between th e w eight of larg e c a rtrid g e s th a t have been soaked and th e tim e th a t th ey have been exposed a fte r absorbing oxygen, and F ig . 2 shows the same relation fo r small cartrid g e s. F ig. 3 shows the tim e in m inutes taken by c a rtrid g e s of different den­

sities bu t of th e same composition fo r th e evaporation of excess oxygen down to th e q u a n tity necessary fo r complete com bustion to carbon dioxide. This g rap h would a t first indicate th a t th e low -density ca rtrid g e s a re preferable as they give a longer life. As a m a tte r of fact, however, the q u a n tity of carbon p resen t is sm aller and th e ir stre n g th per u n it of volume is th u s decreased. The selection of th e prop er density, th e re ­ fore, becomes a comprom ise betw een long life (low density) and explosive s tre n g th (sh o rt life and high d e n sity ). C artrid g es of extrem ely low d ensity are unable to hold th e liquid oxygen and some of it ru ns out when th e c a rtrid g e is rem oved from th e soaking bath.

F ro m E urope has come m any rep o rts of th e excellent resu lts secured from th e use of a substance known as

carbene. This is made from acetylene gas and not much difficulty is found in its m anufacture. L ittle hope is seen fo r th e use of th is m aterial as an oxygen ab­

sorbent because its cost is prohibitive, and the te sts already m ade show it to be in fe rio r to lampblack.

Liquid oxygen m ay be stored and tran sp o rted in D ew ar flasks or vacuum bottles. These consist essen­

tially of an inner and an outer shell w ith a vacuum space between them containing a com partm ent in which is placed a small q u an tity of activated charcoal. The outer vessel is provided w ith a lead tube which is con­

nected to an a ir pump and by th is th e vacuum space is exhausted. W hen th e required degree of vacuum has been obtained th is pipe is pinched off and the end soldered over. A t th e low tem p eratu re existing in th e flask when filled w ith oxygen th e activated charcoal absorbs the residual a ir in the vacuum space. The whole flask is then surrounded by a sheet-steel case, the space between it and th e outer container being filled w ith excelsior or sim ilar m aterial. Such flasks have shown them selves to be highly efficient in the shipm ent of liquid oxygen by combined railro ad and m otor-truck tran sp o rtatio n , th e en tire journey takin g th re e or fo u r days. The average loss in tra n s it from eighty 15-liter containers am ounted to 10 per cent per 24-hr. day.

A t re st these same flasks had a loss from evaporation of 7.6 per cent per 24-hr. day.

I t is believed entirely feasible in liquid-oxygen plants to store the oxygen in double receivers larg e enough to hold a 24- to 28-hr. supply. A lthough no d ata a re available concerning the evaporation th a t would take place from vessels of th is capacity, it is believed th a t owing to th e large ratio between th e volume and ra d ia t­

ing su rface as compared w ith small flasks, vacuum in ­ sulation would probably be unnecessary and h a ir felt or m ineral wool could be used instead. Such receivers should, however, be made of copper or of a copper allo y ; steel is unsuited to th is purpose because it is liable to develop fine cracks a t th e low tem p eratu res encoun­

tered.

Experience concerning th e m aintenance of vacuum equipm ent has not extended over a period sufficiently long to give sa tisfa c to ry data. Out of 55 such con­

tain e rs fifteen had to be re-evacuated a t th e end of one year. Loss of efficiency in containers of th is kind arises less from a loss of vacuum th a n from th e fa c t th a t the inner and outer shells come into contact from rough handling. The re-evacuation of vessels of th is kind is not difficult and can be readily perform ed a t th e mine.

F ig . 1— T yp ical T im e-E v a p o ra tio n C urves fo r 12-in.

C artridge o f L a rg e D iam eter

T h e c a r t r i d g e s o f 6 - in . d i a m e t e r a f t e r tw o h o u r s h a v e l e s s t h a n h a l f a n d a f t e r f o u r h o u r s a b o u t o n e - t h i r d o f t h e i r o r i g i n a l c h a r g e s t i l l l e f t . T h e c a r b o n is in a c o t t o n b a g . T h e e x p o s u r e i s m a d a

to t h e o p e n a i r .

360 C O A L A G E

A suitable vacuum gage and a small 2-stage oil-im­

m ersed vacuum pum p a re all th e equipm ent required.

C a rtrid g es a re soaked in straig h t-sid ed D ew ar flasks.

These a re b u ilt on th e same constructional principles as th e tra n sp o rta tio n containers. In order to fac ilita te handling, th e ca rtrid g e s a re placed in copper-wire bas­

kets which fit easily w ithin th e container. B efore s ta r t ­ ing to use a flask of th is kind a small q u a n tity of oxygen should be placed in it so th a t it m ay become chilled before th e soaking of ca rtrid g e s begins. In containers of th is kind h a ir-fe lt insulation gives alm ost as good resu lts as a vacuum.

In soaking, th e cartrid g es a re placed in a copper-wire basket which is lowered into th e soaking container a f te r which the oxygen is poured in. F ig. 4 shows th e resu lts of tests, se ttin g fo rth th e tim e req u ired to soak cartrid g es of various diam eters. I t will be noted th a t when a c a rtrid g e sinks it is practically sa tu ra te d and th a t the tim e required fo r complete sa tu ra tio n is from 15 to 18 m in. A 5-in. c a rtrid g e req u ires about 30 m in. fo r complete satu ratio n .

Because vacuum soaking containers a re r a th e r aw k­

w ard to handle and liable to damage, and inasm uch as h a ir-fe lt insulation has practically th e sam e efficiency, w hat is term ed a dry c a rrie r has been developed. This consists of a double-wall vessel w ith about 1J in. of h a ir-fe lt insulation between the walls, th e in n er vessel being m ade of copper and the outer one of steel. A fte r th e soaked ca rtrid g e s have been removed in th e ir basket fro m th e soaking container, they a re placed in a dry c a rrie r into th e bottom of which a little liquid oxygen has been poured. The c a rtrid g e s th en tend to rem ain s a tu ra te d th ro u g h cap illarity from th e oxygen in the bottom of th is c a rry in g vessel. T ests to determ ine th e a b ility of th e c a rtrid g e to take up liquid oxygen by c a p illa rity a re set fo rth in F ig . 5, w hich gives the effect of stan d in g a dry unsoaked c a rtrid g e on end in one of these dry c a rrie rs in w hich a little liquid oxygen has been placed, th is liquid being m ain tain ed a t a con­

s ta n t level. T his te s t shows th a t th e d ry c a rtrid g e is able by cap illarity alone to absorb enough oxygen to reach a point betw een its carbon-monoxide and carbon- dioxide requirem ents.

F ig . 6 shows th e evaporation th a t tak es place when soaked c a rtrid g e s a re placed in a d ry c a rrie r w ith a little liquid in th e bottom . T his sets fo rth conclusively th a t it is en tirely practicable to keep c a rtrid g e s in th is w ay 14 h r. a f te r soaking before use. The resu lts shown w ere obtained w ith c a rtrid g e s of ra th e r low d ensity and w ith th e c a rrie r only tw o -thirds full. W ith ca rtrid g e s

F ig . 2— T yp ica l T im e-E vap oration Curves for 10-in. C artridges

C u r v e s s h o w t h a t t h e w e i g h t o f t h e l i q u i d o x y g e n d e c r e a s e s r a p i d l y i n t h e c a r t r i d g e s a s t i m e p a s s e s . T h e c a r b o n is h e l d i n a p a p e r w r a p p e r , a n d t h e c a r t r i d g e s a r e e x p o s e d i n t h e o p e n a i r a f t e r s o a k i n g . N o t e t h i s g r a p h h a s a d i f f e r e n t t i m e s c a l e f r o m

t h a t o f F i g . 1.

of h ig h er density, such as a re usually employed and w ith th e c a rrie r well filled, th e loss of oxygen would be reduced about one-half. The vacuum soaking con tainer th u s need not be carried into the w orking places, b u t th e c a rtrid g e s m ay be prep ared a t a convenient central point. T his p erm its a larg e saving in labor and tra n s -

v-<D

LO 0 2 4 6 8 10 12 14 16 18 20 22

§ L i f e in M i n u t e s

Q

F ig . 3— H ow C artridge L ife V aries w ith D en sity D e n s e c a r t r i d g e s h o l d b u t l i t t l e l i q u i d o x y g e n a n d h a v e a s h o r t life . L o o s e c a r t r i d g e s t a k e u p a l o t o f o x y g e n b u t l e a k b a d l y w h e n t h e y a r e n o l o n g e r i m m e r s e d a n d s o t h e y a r e u n d e s i r a b l e .

A h a p p y m e a n is t o b e p r e f e r r e d .

po rtatio n as well as a reduction in w ear and te a r on th e vacuum equipm ent. I t also allows th e use of la rg e r containers and m akes possible th e saving of a larg e q u a n tity of oxygen w hich would otherw ise be lost.

The s tre n g th of any explosive is a function of th e to tal energy it develops and th e ra te a t w hich th is energy is liberated. The m ethods m ost commonly used fo r d eterm in in g the to ta l energy a re th e b allistic pen­

dulum and th e Bichel gage. M any te s ts c a rrie d out in th e explosives lab o rato ry of th e B ureau of M ines a t P itts b u rg h indicate th a t carbon is th e best ab sorb en t fo r liquid oxygen of all th e m ate ria ls tested and when properly soaked is practically equivalent to 40 per cent dynam ite.

In the Bichel gage, o r closed bomb, various c a rtrid g e s w ere tested. As th e in sertio n of th e ca rtrid g e , closing of the bomb and g e ttin g ready fo r firing req uires about 10 m in., th e soaked c a rtrid g e s cannot be fired in th is device a t the theoretically correct tim e. The conclusion could be draw n from these experim ents, howevert th a t carbon L.O.X. c a rtrid g e s are su p erio r to those m ade from o th er substances volume fo r volume.

Com parisons w ith ra te of detonation of trin itro to lu o l cordeau by th e D autriche m ethod showed th a t th e ra te of detonation of L.O.X. c a rtrid g e s when fired a t th e CO, point, rang ed from 5,520 m eters (18,100 f t.) to 5,950 m eters (19,400 f t.) per second. T his ra te varies som ew hat w ith the length of tim e th a t th e c a rtrid g e s have been removed from contact w ith th e liquid oxygen before firing. The longer th e c a rtrid g e s a re exposed to th e a ir th e slower th e ir r a te of detonation. W ith 14x8-in. carbon c a rtrid g e s th is ra te of detonation changed from approxim ately 4,850 m eters (15,900 ft.) per second a t 5-min. exposure to th e a ir to 4,150 m eters

(13,600 ft.) per second a fte r an exposure of 30 m inutes.

T ests w ere also m ade on th e co n tin u ity of detonation.

F o r th is purpose a s trin g of l ix l 2 - i n . c a rtrid g e s 40 ft.

long, w as laid w ith th e c a rtrid g e s end to end and in contact. T his was detonated by a cap in th e end c a r­

trid g e . All c a rtrid g e s in th is s trin g detonated u n i­

form ly. C a rtrid g es of th e sam e size w ere th e n laid on

th e ground end to end w ith an a ir gap betw een a d jacen t

c a rtrid g e s. I t was found th a t s tr a ig h t carbon c a r­

Ma r c h 11, 1926

C O A L A G E

# trid g e s would detonate in th is way across an a ir gap of

from 5 to 7 in. By the addition of suitable hydro­

carbons, or m etallic powders, th e gap across which they could be made to detonate could be increased to 20 in.

or more. Tests conducted on l |x l2 - in . cartrid g es in a drillhole, placing one c artrid g e in the bottom and detonating another a t th e collar, dem onstrated th a t the bottom c a rtrid g e can be detonated across a gap of 34 ft.

or more. Evidently no difficulty will be experienced in m ining because of failu re of the cartrid g es to touch each other in the hole.

It was found impossible to detonate any of th e c ar­

bon L.O.X. cartrid g es in th e open a ir by flame alone, th a t is, by a fuse in serted in th e cartrid g e. Caps in th is case were necessary in order to assure detonation.

W hen confined in a drill hole, however, th e ca rtrid g e s can be detonated by a fuse w ithout cap, th is being the stan d ard practice in the iron m ines of L orraine.

The te sts on different stre n g th s of detonators showed th a t they all had a like effect upon th is explosive and th a t one s tre n g th of cap was as effective as another.

Tests were also conducted to determ ine how small the q u an tity of oxygen in the c a rtrid g e could be and still secure detonation. C artrid ges w ere exploded th a t contained only 3.3 p er cent of th e oxygen necessary fo r th e ir combustion to carbon dioxide. As the oxygen evaporates from one of these cartrid g es th e re is a ten d ­ ency to leave a sa tu ra te d core in its center, and detonation can be obtained as long as th is core is p res­

ent provided th e cap is in contact w ith it. A 4-in.

c a rtrid g e was detonated a fte r th e lapse of fo u r hours in th e open air.

Sensitiveness of the new explosive to im pact w as also tested. In the large im pact te stin g m achine a t the B ureau of M ines lab o rato ry th e explosive was placed between steel disks and a w eight of approxim ately 440 lb. dropped on it from varyin g heights. The ex­

plosive can be fired in th is m an ner w ith o ut difficulty.

M any attem p ts have been m ade to detonate it by th ro w ­ ing cartrid g es a g a in st rock faces in stopes a t distances of from 60 to 80 ft. In every case th e c a rtrid g e failed to detonate. D ropping a m in er’s acetylene lamp th a t had previously been lighted into a container full of p repared ca rtrid g e s was also trie d . The c a rtrid g e s did not detonate bu t w ere set on fire, producing a larg e flame of intense heat. A high-pow er rifle bullet fired th roug h the container detonated its contents.

T ests made in th e fric tio n -te stin g m achine in the B ureau of Mines lab o rato ry showed th a t L.O.X. would not detonate under e ith e r the fiber or steel shoe. These and num erous o th er experim ents have dem onstrated

F ig . 4— T im e R equired to Soak Carbon C artrid ges B e g in n in g w ith P ourin g

N o t e t h a t t h e l a r g e c a r t r i d g e is s o a k e d a l m o s t a s r a p i d l y a s t h e s m a l l e r c a r t r i d g e s . A f t e r s i n k i n g t h e l a t t e r g a i n l i t t l e , i f a n y .

w e i g h t , b u t t h e l a r g e c a r t r i d g e m a k e s a s l i g h t a b s o r p t i o n .

th a t w ith the sm aller cartrid g es having densities of approxim ately 0.3, fired w ithin 10 to 12 m in. a fte r soaking, L.O.X. is equivalent to 40-per cent dynam ite, volume for volume. F o r the larg e r cartrid g es, the same holds tru e fo r firing a t 30 to 45 min. These firing

F ig . 5— C apillarity T est, H x l2 - in . C artridge

d r y c a r t r i d g e is s e t o n e n d in 1 -in . o f liq u id , t h e li q u i d b e i n g m a i n t a i n e d a t c o n s t a n t d e p t h . T h e d r y w e i g h t o f t h e c a r b o n

c a r t r i d g e is 69 g.

periods are based upon th e loss of oxygen tak in g place in the open a ir and are extended considerably when the cartrid g es are confined in a drill hole. This extension in the sm aller diam eter of c a rtrid g e s ran ges from 15 to 20 per cent.

One of the chief disadvantages in th e use of L.O.X.

in highly abrasive rock lies in th e fa c t th a t th e gage of the drill is appreciably decreased d u rin g the drilling process w ith th e resu lt th a t the holes a re tam p erin g . Inasm uch as th e ca rtrid g e s a re practically solid th ey will not deform and fill th e hole perfectly in loading. T h eir effectiveness in b reaking rock is th u s som ew hat de­

creased.

In practical operation electric firing was found to be effective b u t under the conditions w here th e explosive was trie d b e tte r resu lts were obtained by shooting w ith fuse. T his was crim ped into an o rd in a ry cap which w as placed w ith in a b rass tube, into the o th er end of which a piece of o rd in ary cordeau w as inserted. The brass sleeve protected the detonator d u rin g loading, and the cordeau acted som ew hat as a booster.

All practical te s ts w ith these explosives te n d to v erify the w ork done in the lab o ra to ry and th e con­

clusions draw n th erefro m . In th e lig h t of th e w ork done a t Mineville, th e following conclusions m ay be draw n so f a r as und erground m in ing is concerned__

f l ) W here th e ground is heavy and abrasive, causing the drillholes to be considerably tap ered, L.O.X costs m ore th a n dynam ite. (2) W here th e m ethod of m ining involves drilling of com paratively shallow holes w ith o ut a large loss of gage, th is explosive m ay be com m ercially profitable, especially w here th e price of dynam ite is high. (3) The use of L.O.X. does aw ay w ith th e neces­

sity of m ain ta in in g a stock of explosives a t th e m ine and ren d ers the powder supply independent of in te r ­ ru p tion s in tra n sp o rta tio n . (4) I t h as been shown th a t th e re is no d ang er from th e p re m a tu re d etonation of th is new explosive. T here is, however, a d an g er of p rem atu re ignition re su ltin g in violent long-flame con­

flagration, w hich would be d angerous in confined spaces

underground. In loading holes, th e re is some d an g er

ot th e lib erated g as blowing out th e stem m ing and

perhaps, of ig n itio n of carbon-laden gas by m in e rs ’

lamps. The d an g er of d rillin g into m issed holes is

362 « C O A L A G E

elim inated, and upon th is score th e new explosive is sa fe r th a n dynam ite. (5) The use of th e new explosive fo r shooting down coal is not recommended because of its long hot flame. (6) W hen firing m u st be done sim ultaneously in a larg e num ber of ad jacent places, it is much m ore difficult to synchronize th is w ork if L.O.X. is used th an if dynam ite is employed. (7) More holes are lost w ith L.O.X. th a n w ith dynam ite because the fuse is not held as firmly. Also, inasm uch as the c a rtrid g e s fit the hole loosely, they a re sometim es ja rre d out by the detonation of adjacent holes. If a c a rtrid g e jam s in loading, because of the hole being crooked, th ere is no tim e to rem edy it, and th e re is usually no tim e to reload a hole th a t blows out its stem m ing by evolved gas.

W hile operations w ere going on a t Mineville, oxygen was shipped to various q u a rries and such highly s a tis ­ facto ry results obtained th a t th e liquid-oxygen plan t was moved to Lebanon, Pa. From th is point m any q u arries and open-pit operations could be reached. T ests were then m ade in a wide v a rie ty of rocks. These tria ls w ere m ostly conducted in 6-in. holes, th e re being a few 2-, 4- and one 8-in. hole. The depths to w hich these holes w ere drilled varied from 6 to 106 ft., and the num ber of holes fired sim ultaneously ranged from 1 to 40. From th e plant a t Lebanon oxygen w as shipped over long distances sometim es being held in th e tr a n s ­ p o rtation container as long as 96 hr. F o r th is purpose containers of 50-liter capacity, w ith a loss of about 3 per cent in w eight per 24-hr. a t rest, were employed.

The loss w as about tw ice th is q u a n tity when th e con­

ta in e rs w ere a g ita te d d u rin g travel.

M ost of th e c a rtrid g e s used in th is w ork m easured 44x18 in. and a few w ere 7x24 in. These w ere made of th e s tra ig h t carbon black b u t w ere incased in cyl­

indrical cotton bags, instead of in paper, as th e large paper containers w ere found to be too fra g ile to w ith ­ stan d handling. Because of th e large size of th e car- rid ges and th e necessity fo r soaking a g re a t num ber a t a tim e, larg e soaking tan k s w ere developed. These w ere m erely copper-lined boxes insulated w ith h a ir felt.

A continuous length of cordeau from th e bottom to th e top of th e hole was used in th ese larg e blasts. This was first placed in th e hole and all th e cordeau from th e various holes w ere spliced to a common tru n k line w hich w as detonated electrically by a single cap.

In introd u cin g th e c a rtrid g e s into th e hole a flared copper funnel, about 6 ft. long was used. T his both guided th e c a rtrid g e s and kept surface m aterial from fallin g into th e hole. The stem m ing used was generally loose e a rth m erely shoveled into the hole w ith o ut tam p ­

ing. As a rule each hole w as filled to th e collar. In no instance was th e stem m ing blown out. N e ith e r w as difficulty experienced in loading w et holes, and some w ere fired th a t w ere filled w ith w a te r to the collar.

In forty -n in e b lasts of th is kind only fo u r encountered difficulty, and investig ation of these disclosed th e fa c t th a t th ey w ere not charged or fired properly due e ith e r to m iscalculation or to inadequate facilities a t th e tim e of c h arg in g th e hole. W ith these exceptions all the shots w ere successful in every respect.

From th e to tal q u a n tity of dynam ite replaced, as well as from the q u a n tity of oxygen and d ry c a rtrid g e s used in all of these blasts, it would ap p ear th a t 1 lb. of dynam ite could be replaced by 0.935 lb. of oxygen, m easured as produced a t th e liquid-oxygen plant. This, therefo re, includes all losses of every sort. I t also appears th a t 0.201 lb. of dry c a rtrid g e are required to replace 1 lb. of dynam ite.

As to cost, to replace 1 lb. of dynam ite fo r th is class of service, 0.935 lb. of oxygen is req u ired a t 2.29c. per lb., m aking a cost of 2.14c., also 0.201 lb of. c a rtrid g e a t 14c. p er pound, or 2.83c. T his m akes a to tal cost of 4.94c. to replace 1 lb. of dynam ite.

R o ck -D u stin g G ains S lo w ly In A labam a Coal M ines

E le v e n C o m p a n ie s N o w D u s t F i f t e e n M in e s — P o w d e re d D o lo m ite is U se d E x c lu s iv e ly — M o st

M a c h in e s F o r A p p ly in g I t A re H o m e -M a d e

D URIN G th e past calendar y ear rock-dusting did little b e tte r th a n hold its own in th e coal m ines of Alabama. I t was in au g u ra te d a t a nu m b er of m ines in 1924 aw akening wide in te re st th ro u g h o u t th e sta te but g a th e red only two converts in 1925. The W oodward

T h is One Is E lectric

R o c k - d u s t i n g m a c h i n e u s e d a t S a y r e m i n e o f t h e G u l f S t a t e s S te e l C o . T h e m o t o r a t t h e r i g h t d o e s t h e p r o p e l l in g . P u s h - B u t t o n c o n t r o l m a k e s t h e m a c h i n e s i m p l e a n d s a f e t o o p e r a t e . W h e n n o t e n g a g e d i n e m p t y i n g b a g s o f d u s t i n t o t h e h o p p e r t h e o p e r a t o r s i t s

o n t h e p l a t f o r m b e s id e t h e h o p p e r a n d d i r e c t s t h e f le x ib le l e a t h e r n o z z le .

Iron Co., w hich has been recognized as a leader in safety m easures has not yet seen fit to slacken its in ­ tensive w a te r sp rink ling p ro gram in fav o r of rock dust.

The p resen t s ta tu s of d u stin g in th e s ta te is as follows: A pproxim ately 1,700 tons of rock d u st has been applied by eleven com panies in fifteen m ines.

P ra ctica lly all of th e dust used was powdered dolomite.

A t least six of th e eleven com panies a re usin g d u stin g m achines of th e ir own design and m an u factu re. Some a re sc a tte rin g th e d u st by hand. Few d u st b a rrie rs have been installed.

The Gulf S ta te s Steel Co. and th e Galloway Coal Co.

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Time in C arrier, In Hours a n d Minutes

F ig . 6— O x y g en L oss in D ry C arrier

H e r e t h e f a l l i n t h e o x y g e n c o n t e n t is m u c h s l o w e r , o f c o u r s e , t h a n in o p e n a i r . C o m p a r e t h i s w i t h F i g s . 1 a n d 2 w h e r e t h e e v a p o r a t i o n i s u n h i n d e r e d . N o t e a l s o t h e d i f f e r e n c e i n t h e t i m e s c a l e s . T h e c a r t r i d g e s a r e s t a b l e e n o u g h t h a t t h e y c a n b e m a d e

in a c e n t r a l l o a d i n g s t a t i o n .