THE NANUFACTCRE OF S L A C K I,EAD CRlrCTBLES.

13Y tTAMIIS c:. I3OOTl1, 1'11. 1).

[Concluded from Page ?8R, Volriinc VI.]

Pulverizing the Gwrp/iite.-'l'he iii:iiiner of grinding graphite being of considerable influence on the quality o f the crucible, some details upon the subject will be p r 0 1 ~ e ~ wid riwfril. Tlic larger masses of graphite beiiig rouptily 111~)keri b y tiairliner into smaller pieces, the whole mixtiirc of piews aiid filie stuff is fed into ail

ordinary bark mill, consisting of two cast iron inverted cones, thv smaller with iron teeth on its outer surface, revolving inside the larger one, similarly armed 011 its inner surface. The liimps arc caught and crushed between these cones, a i d tlie resulting coarse and tine powder, being immediately passed lxtween ordinary mill ~ t o l i e s , is %round to a more uniform and finer powder, which is then assorted by sieves into finer and coarser portions, tlie latter being again ground and sifted until the requisite fineness is attained. I have iiothing to suggest to improve thc machinery 01' mode of

grinding, but i l k I differ from crucible makers in regard to the degree of tirieiic+s, I lierepresent rny views ant1 tlie i'easons for them. T o economize time the ground glfapliite, passiiig tliiwiigli the sieves and consisting of fine flour on one cxtrenic> :i11(1 oii the other of flakes that can be split 1))- a knife or gronnd to thiniier scales, is usually mixed dircctly with the wet clay.

I regard the coarser flakes of insufficiently grouricl graphite as positively objectionable, liecause they lessen the strength of the crucible, mhich'is the supreme consideration. I liave often observed the surfaces of S l J d l S split off' from a crucible while iii use, ant1 noticed on them graphite scales of & inoh or mow i n iliameter, wi th a part of the same scales remaining 011 the crucible ant1 in the samc spot. The knife easily separated more scales from the corre- sponding locality on spa11 and cruciblca. The facility of splitting offered by these graphite scales increases the facility with which pieces of the crucible itself split off through the feebly adhering laminations of the graphite. I have often seen a half dozen suclt scaling plates of graphite on a spalled surface of 2 to -i square inches, and instantlyread the cause of spalling and of seiious injury to the criicible. If those coarser and thicker plates of graphite had been

THE: >IANUFAC1’17RE: OF HI..\CK L E A l ) CRUCII%LES. 5

ground, spnlling would not have occurred. Graphite is a very feeble substance in the plane of its lamination but strorigly resists a force at right nnglei to this plane, and, wh:ii is niore extraor- dinary, i t will do so at a whitc heat.

Hence black lead should be *ground c~xceedirigl y fine, not leaving n plate of it more than da to +,, inch in diameter. I have tried crucibles made of black Icnd powdev that would not quite pass through a 126 wire sieve, and found them excellent. The dust that passed through such a sievc c+onsisted of aboiit i 5 pr. ct. of good aiid tough flakes, and 35 pr. ct. of a fine black powder, with- out apparent sti’uctiire, consisting of siliceons sand and iron Iiprites. “ If fine grinding were adopted,” the economic manufac- turer asks, ‘‘ \Vhat should be done with the tine powder passing the 115 wire sieve?” About 4 ;€ it, being siliccous, is not hurtful, but the 4 iron pyrites is injurious, and althorigli it is so exceeding small in quantity, yet it would be preferable ta utilize it in one of three ways: 1. To separate it by a still finer sieve iiito good flaky graphite, to be used with the rest, and dirt, to he thrown away j or, 2. To use it in mixture with good material for covers, etc.; or :3 . To sell the whole mass passing the 125 sieve, with other inferior residues, for store blacking, &c. In such case it may sell for half the value of good black lead.

CZay.-Admirable 8s are the qualities of black lead to resist the action of a white heat, burning off as it does only partially and with some difficulty, it must, in order to hold melted metal, be held firmly i n the crucible shape given to i t and this is effected by clay, that when wet mixes easily with the powdered black lend, and when dried and burned holds i t rigidly and a t the same time resists the highest white heat of the furnace. A clay from Klingenburg in the Palatinate seems to be pre-eminently adapted for such crucibles, and I strongly advise employing exclusively the best quality, every lump ,of which has the Goveriirnent stamp impressed on it.

I have tried lower grades of the Klingenburg, and some of our own clays (Amboy, &c.), but I have found none to combine the ex- cellent qualities of the best Klingenburg. I n its wet Rtate it is superlatively plastic, and free from every trace of grit, and in t h b state can be blended most intimately with the fine scales of black lead. It iR barely fusible by itself a t a white heat, and

6 THE MANUFAL'TLJRE O F BL.\CK LEAIJ ('KGCIBI,ES.

when mixed with an equal quantity of graphitic scales, as i n the crucible mass, it only softens at a white heat so far as to sur- round each scale, which it holds immovably in its place, while the equal quantity of scales prevents ariy further fus ion , e \ en when kept for 10 or mole hoiire at the highest wh i t e hwt. Viewed chcmically, Klingenburg clay is a hydrated silicxtci, containing i r i round num- bers about 8 alwliina, water, arid tlic halariw silica, w i th rninute quantities of oxide of ii.011, atit1 nlk:iline fluxing riiattcar. In its cwi- ployment for fire crucibles, t l i e orily considerntion is its contnit of if water when calculating the weights of the i~igreclic.iitx.

Sui~d.--Tlie third constitneiit of tht. graphite crucible is a mtlier coarse siliceous sand that will ctand a Iiiyh heat without flyiria irito fine powder. I ts action is mechanic:il, cansing a mor(' uniforrri air d r j ing, Ijrevious to burning, so as to avoid vixckiiig, : ind Iplayinp the limitcd part of a skeleton to maintain the shape. of tlic crucibl(>. A good infusible clay, hardened by buriii~ig, atid I)rokiaii and sift,cd :is a coarsc sand, was found t o ac*t :IS wcll ;is inritl , h i i t not I)erceptibly better.

Mizture jb i - C~ucibles.--'l'he only point of agrec~iiinit i n thc composition of the best crucibles seeiris t o he that when Iturried they should contain over 50 pr. ct. carbon, as determincd by analy- s is . T h e formula may vary within rather wide limits, !Jut our ex- I'erierice wi th good cruciblvs of the best makers and with our own, iiidicated that the burned crucible should show 55 pr. r t . carbon on analisis, In calculating the quantity 01 black lend used in :t

crucible from the determination of carbon, it is only safe t o add 6 pr. ct. for the siliceous sand and pyrites found in the black lead. Some of thc choicest black lead gt-sins now iri commerce h:tJTc. s:*arceIy 1 111'. ct. of foreign matter, so entirelj has the earthly con- stituent of plants or the small peicentage of ash ir7 anthracite dis- appeared from the mineral graphite. The proportions of black lead, air dried clay and Rand used by different makers, and by the same maker a t diti'erent times, vary considerably, but the following is given as illustrating approximately the composition for making the convenient amount of about 2,000 I h . of crucible mixture when burned, As a crucible maker, I prefer the weight of black lead to be 1,100 Ibs., so t.hnt, the burned clay and sand

THE MANUFACTURE OF BLACK LEAD CRUCIBLES. 7

may together make up about 1,000 Ibs., which will give the 55 pr. ct. carbon in the burned crucible:

Black Lead. Air Dry Clay. Sand. Total, when burned. 1,100 1,000 120 2,100 1,100 950 160 1,996 1,100 900 2 00 1,990

Every manufacturer prefers such composition as, in his judg- ment, works best in practice.

Micthg.-The air-dried clay of a given weight for a baich of crucibles, after bciiig roughly broken by hammer, is covered with water, and after being softeiied, by standinq, to a thin paste, re- ceives the due proportions of the finely groutid and sifted black lead and sand, and is then paltially incorporated by a shovel. Some makers, ambitious of 1 eputation for quality, judiciously pass their Iiands through the incorporntcjd mixture to detect and remove lumps O F gravel of pyrites or quartz. No amount of hand or shovel mixing can eqiial or supersede the operations of the Mixer or Dolly-tub, a wooden vat of 4 or 5 ft. diameter and height, stand- ing on end, to which the somewhat stiff pasty mass is tr:tnsferred. I ts simple machinery is a vertical shaft, revolviiig on the centie of the bottom, and provided with a series of horizontal knives, ar- rsiiyed a t a distatice from Pnch other El’irally, and extending nearly to the sides of the tub. The revolving knives, hwiiig their blades at a slight angle to the plaiie of revolution, cut the putty- like inass into separate strips which fall over the sloping blades, and again unite in neat layers, to be again cut, separated, re- united, in new positions. After thus working for some time a slide on the outside of the tub, near the bottom, is tlrawri and the blades dope in such a direction to their revolution that they pass the mass downwards and out of the sliding door. Thc protruding masses are cut off and throwii in above, and t1ii.i operation, often repeated, has the effect of blending the whole iiito a stiff paste of absolutely uniform composition, so that each flake of the graphite,

inch tliaiueter, is enveloped in plastic clay, and every particle of clay is in contaat with R dake. T h e wonderful s t rength of the black lead orucable i R due to this microscopic blending of gra- phite and clay.

H THE MANCFACTURE OF L;I.ACK LEAD CRUCIBLES.

'Yo niakc the crucible still more pei9'ec.t the finished mas8 of ibout a ton i n weight should be lai(1 by i n a damp cellar, covered with cloth*, and occasionally inoistctwd. h i spite ot tlie iestl, BY and reck1e.s d r i b iiig of our Ameriran n ~ ' ~ I i i i f : i ~ t ~ i r ~ , ~ , , they recognize that in all clay wart'\, the rewly-iiitxetl tiia*ses kept for .i long time make better ware9 than rliose freshly qiieezed out of the nol lp tub. The experience of tlie Chincw for ages in m ~ k i n g the finest clay wareb, l c d a potter to accumulate a quantity of mixed batches, ready for iiw, during ten, twenty-five arid more years, to he used by his son, grandson, ctc , as iri tlie case of sonie that had been similarly bequeathed to him.

Can this part of the manufacture of graphite crucibles, i. e. , making the dough, be improved? I offer the two following sug- gestions for consideration : 1. Scarcely any native clay is wholly free from occasional lumps of iron pyrites, which, happening to become located in the side of a crucible, might ruin the metal near it, or make a hole for the metal to ewape, and in either case injure the reputation of the maker. Careful makers sometimes feel for such in the soft clay mass, but why map not this mass be passed be- tween rollers of very small diameter, which would not pass the small gravel or lumps, but accumulate them on the feeding plate? Tf such arrangement will pay in brick or terra cotts ware, surely the costly crucible mass would bear it. 2 . The roughly mixed cru- cible mass, made very liquid with water, might be passed through rotating sieves, of smaller meshes than the sand, and the slip evap- orated to proper consistence on slidlow furnaces similar to those employed in drying white lead. These suggestionu con only be answered by the crucible maker or1 the grunnd of perfection of work, and economy.

Moulding.-All graphite crucibles, between Nos. 30 and 80, em- bracing those for steel, brass, silver, etc., are formed on plaster molds, centered on the potter7s table, or throwing lathe. The weighed mass for a crucible, being repeatedly cut and '' slapped," is pressed into the bottom of the mold, which &apes the outfide of the crucible, and while rapidly revolving, a steel or iron profile of the interior is gradually lowered into the mass,which is thurt pressed agamst the sides and raised to the top or the mold by revolu- tion, and gives the form of the interior of the crucible. This re-

THE MANUFACTURE O F BLACK LEAD CKUC1,BLES. 9

volving method, like the ancient potter’s throwing lathe, is far more important in this art, because it effectually disposes every scale of graphite, tangentially to the cylindrical or conical walls of the crucible, not merely on the inside and ontside, but throughout the whole mass. Here lies the great strength of the graphite crucible. I t is a mass of strong scales of carbon, that will not break at right angles to their Inininatioii, being rigidly held in their sheet-like disposal by burnt clay, that will not yield to any heat. It is a graphite crucible, infusible and unalterable, where the black lead is very much, and for a long time, prevented from burning away by its ciivelope of clay. It is a clay crucible, which will not soften i n the highest ten-hour, white heat employed in the arts, and will endure ten times the roughest usage oE any other material, except bar iron. For many years I employed excellent wrought iron cru- cibles for melting silver, but find that black lend crucibles are bet- ter adapted to the purpose.

The proposition to make a cheaper graphite crucible by merely pressing out the soft crucible mass in molds, without the IOSR of time in revolving, would utterly fail for lack of the strength of structure given by revolution. It like manner the suggested substitution of anlhracite, or any other form of carbon, for graphite, would signally fail to approximate to the strength and other qilalities of a black lead crucible.

Dryin9 is effected by keeping the formed crucibles in the plas- ter molds for a time, and then ranging them on shelves in warm, dry air, most economically in the.spaces around the upper half of the burning kiln. If dried too rapidly, or if frost be allowed to enter the drying-room, fine cracks, like crooked hair lines, barely visible, around the interior, indicate that the crucible should be remade from the foundation.

Bwniny.-Tlie crucibles must be thoroughly burned, and yet SO as to avoid burning out black lead, their chief source of strength and value. To attain this object they are burned in seggars, which more or leRs exclude air, cising two seggars for each uru- cible, one inverted over the other, and yet graphite is some- times partly burned out by the air entering between them. This has been partially obviated, by some makers, by siiiearing the joint on the outside with clay slip. Another method which I invented,

THE MhNUFAC'fURE Ob' BLACK LRAD CRUCIBLES. 1 1

say 4 inch, I should be disposed to throw off one-fourth, or more, of its value. If i t go to a half inch, I should reject wuch a crucible as wortlilcas, because a largc proportion of its life, its sti,ength, hao been burned out.

Use and L(fe o j UlacJc Leud Cr,icibles.--The most tAsr,eiisivc use of black Itad crncibler; is to melt hlistcred steel and cast i t into any deairet1 form, whence i t is termed cast-steel. Tens of thous- ands of crucibles are weekly employed for this purpose, the amouiit of steel :it each melt bcing 75 to 90 pounds, and a numbel- of such melts ccinstituting a day's work. Hence the great multiplication of furnaces, 01' of crucibles in a gas furnace, when 1,000 Ilounds (JI*

more arc cast a t a time. l'hc life of a crnci1)le for melting steel varies with tlie nature of the ntetjl to be cast. If i t I J C a highly car- bonized (fine) steel, n moderiite wliitc heat will soon melt it, and thc crucible may be repeatedly u.~ed. IC a low (common) steel be employed, approximating to bar-iroii, such as a loct1mo1,ive driving wheel, the crucible has to endure five ( 5 ) aiid more hours of the most intense wliitc h(Aat for a single castiii?, and yet it can endure several such nicltings. A crucible will bear repeated meltings of tool steel, aiid in order to extend its lifc, the outsideisoften coated with a good clay slip, with or witlinut an admixtiire of black lead, after each rnclt. The wonderful protective power of the clay, eni- bracing each particle of black lead, shows the advantnge of grind- ing the black lead to great fineness, making clay and graphite mu- tually protective. I n melting eteel, the melter has to consider the length of the time of melting, and, therefore, the qiiantity of addi- tional carbon the steel is assuming from tlie black lead pot, which excess he neutralizes by adding a certain quantitv of scraps of bar- iron to the melt

l'o show other possible applications of the crucible mase I may mention that syphons have been constructed of it, and succes8- fully employed for transferrino melted cast-iron from one vesssl to ano t t ier.

Black lead crucibles are also extensively employed in melting brass, bronze, German silver, gold and silver. I here add a few data 111 rehtion to the last two rnetals. The crucibles employed at the U. S . Mint, a t Philidelpliia, are so called No. 70 pots, of three gallons capacity-being 9 inches in diameter at the top and 13

ii!ches dec!p, Imth inside rncasuremcnt. ’I’hc wall.: ai’c 1 inch thick a t top, and 14-2 inches at Lottoill. In suc,li :L criwiblc 11-c usually me!t :it O I I C V , every If hoiiw, 5,400 o i inws nt‘ staiidard gold pure), or : 3 i O pounds, aroirdupois; S o i i i ~ melts, a moderate day’s work, equal, therefore, 1,180 pounds, o r 21,600 ounc‘c‘s. I’he value o f such R single iiielt is over $100,000. One sndi crucible is run for foiir (lays with f u l l confidence in its mfcty, : t r d feiiriiig no fi,aciure or loss of go!d; for although we have i ’ i i i i then1 f o r six (6) days it is found the economy does not I,alanc*c the possible (]anger of fixture and leaking. Taking tlie safe run of four days, w melt i n :i birigle c*i~uciblt~, with warcely aiiy loss, $51,600,000 worth of goltl a t the cixcible cost of about $ 2 . 5 0 .

W e usually melt 3,500 U I I I I C E ~ (-240 l)ouIicIs, avoirdupois,) of standaid hilver i n a c.iwci’ule (KO. S O ) a t one melt, and cast six such melts, without uiidiie haste, in a day, making 1,440 pounds, or ~ 1 , 0 0 0 ounces. Since it is s:ife to estimate its life a t five days, w e melt in one such crucible ltefore it is laid aside 7,200 pounds ( = 1 o j , O ~ O ounces) of standard silver, or about the same amount in dollar value. This, however, is not all of its life, but only its rnan- Iiood, for after doing duty for so long a time in perfect health, it i H piit aside to purify niid tougheii inferior silver and to gather into melt3 grains aiid residues, otherwise wande ihg off, for some time before i t is tlioroiighiy disabled and ground t o powder, to re- cover the 1)recious grains which it has concealed iri its body.

To one who knows the ease with which alkalies attack clay at a Iiigh heat, arid how readily fusing nitre will burn off carbnn, even black lead, it is quite a surprise to witness thc mortderful dura- bility of the black lead crucible, when in its nearly worn-out con- ditioii it is used for fluxing ~~esidues, and we can only attribute its strength to the minute and intimate blending of clay and graphite, mutually resisting destruction.

No doubt the life of these crucibles is proloiiged in ineltiiig bronze, brass, A(;., becauRe they are so tougli through the blendiiig of clay and paph i to that they rarely break sudilenly, but rather give notice of their intention to do so by gradually opening, and even then not uiitil they have been worn thin by long utie.

Some ye:m ago I preparcti tinrnc black leaf1 crucibles with more than usual care i i i order to tcst their life. \Vi> made from 40 melts

NOTU ON CAMPHOR MP,TlONS. 1 3

of silver, the lowefit limit, to 60 melts, thc higher limit, in a single crucible. I h w e no doubt that a careful study of the prmciples crf the manufacture of black lead crucibles here developed, somewhat fully, and even perchance their farther development, beyond my conception, can improve their quality RO as to double the life and strength ascribed to thun .

u. s. ~ I I S T , PHILADELPHIA, Dec. 31, 1864.

NOTE ON CAMPHOR MOTIONS. BY P. CASAMAJOP..

On the 4th of October, 18’17, I read a paper “ O n the Motions of Camphor on tlic Surface of Water,” before the American Chem- ical Society, in wliicli I described experiments, which had led me to the conclusim that these motions were due to electricity.

The extraordinnry motions which give an appearance of life to pieces of catnphor, swimming on the surface of water, are not to be seen at all times. Very often camphor will remain motionless, while a t other times the pieces gyrate with great animation. One of the earliest observers of these singular motions, Itomien (1748), came to the conclusion that they were due to electricity, while sub- sequent investigators, among whom may be counted the great Volta, have generally decided that there is no connection between electricity and the motion of camphor on water.

Iwas led to believe that camphor motions were due to electricity by the results of experiments, of which I will give a brief account.

When pieces of camphor are thrown on water, they may remain torpid or they may gyrate with every appearance of life. In the latter case, the motions may be instantly arrested by dipping a finger in the water on which the camphor moves. If we have pieces of camphor lying quietly on water, they may be made to move by dipping into the water a rod of either glass, sealing wax or rulcan- ite, electrified by friction. After every immersion. the glass is to be dried by wiping with a dry cloth or a piece of bibulous paper ; And, hefore every immersion, the rod is electrified by rubbing with a piece af silk or flannel. After one or more immersions of the electrified rod, the camphor motions invariably start, and by a fow ad- ditional immersions they increase in intensity. The fact that .these