DISCUSSION OF THIS PAPER IS-INVITED. It sllould ~>referpbly be presented in person at the Butte ~nceting Aug. IS to 21 1913 when nu al~strnct of the paper wlll be read. If this is impossible. then c~iecussii,d in writing nia; be skit to t.he Editor. Ali!crican Institute rlf hliuiug E~~gincers, 29 'Arest 39th S~rr:et. N e w Yi~rk. N. Y.. for prusent.ntion h?. t.he Sct:n:targ 01. nt,hrr rcprcscntntive of its ant.l~<,r.

. Unless sprcial nrrangeltteut is n ~ n i e , the iliscosnion of t.his paper will close Oct. 1. 1?113, when Vol. SL\'I. of the Tr<z ,~rnc l io~~s will go to press. Any discuasiori oflered t.hercnfter slluuld grefcrably he in the form of n new paper for publication in Vol. SLVII. (with suitable cross references iu both volumes).

Some Recent American Progress in the Assay of Copper-Bullion.

BY EDWARD IiELLER, PERTH ARIBOT, N. J.

(Butte Meeting, August, 1913.)

SO~XEONE some time ago relnarked that soine chemists still insist on telling 11s 1Gw to determine copper by the electrolytic nlet,hocl. The writer must confess that he believes that everyt,l~ing is not kllow11 defi- nitely as yet as to how the esact anioullt of coppeiis clet,ermined in such material as purest coilllnercial electrolytic copper. Some of us are not yet collvinced that the pure copper atonl is a t all times depositecl from an acicl' solution ancl that no osygen or hydrogea ?\rill, uulcler certain con- ditions, accoinp:t~ly it. Difficulties with inpurer m:iteri:~.l are frecluent, but erroneous results are not always apparent, since hllese do not speak so readily for themselves as those in the first case. By this is meant th:it if n, chelnist finds 100 per cent. of copper in electrolytic copper i t is pretty certain that he perceives the result to be wrong, while if he fiucls 0.1 per cent. of copper too much in a very impure nxiterial he is-far Inore likely to be uncollscious of his error. These, in a wide esperience, are frecluent happenings ancl the writer has always~looketl wit-11 interest to publicatioils on this subject. In turn, he-:feels justified in giving: to others a few of his o\vn observations.

Up to a few ye:trs ago there were two methods of electrolytic co1)I)er assay in technical use, ~vhich hacl in coininon, tbnt tlle :unouat of copper deposited on the catllode clid not exceed 2 g., and they differed i11 that, for the one a large sample1 (20 to 80 g.) was talien fro111 the general s,zluple by a splitting device, clissolvecl, and from the solution 4 sillall portion (to contaiu 1 or 2:g. of copper) illeasurecl out for the electrolj.tic depositmion; in the other inethocl the copper was deter~ninecl, ge~lerdly in 1-g. por- tions of the separated coarse and fine portioas of the sample, d l of which passed ,z 16 or 20-mesh screen, being scconlplished by a 40-nlesll screen,

1 W. C. Ferguson gave 3. thorougl~ descriptiou of the details :tnd prec:~utions necessary in this method. Journal Z~uluslric~l and Engineeri~ig Clien~istry, vol. 11, No. 5, p. 187 (May, 1910).

I i 2004 . ARlERICAN PR~GRESS' I N THE ASSAY OF COPPER-BULLION.

nncl the average assay was fiyrecl ncconling to the weight-ratio of the parts. .To use larger cluantities (5 g.) for electro-c1el)osit;ion on such copper as ,Lake -or conlnlercinl ele~t~rolytic 1l:tcl been recolnlllenclecl sollle years .agoll but trllis hael never been'attemptecl in a systematic way wit11 crr~cle coppers.

; , When in 1908, .John T. ~toddarc~"~ublished a paper in which lie pointeel out the fensil~ilit~y of rapid electro-clel)ositio11 of metals, with analytlical accuracy,. on stationary gauze cnthocles , ancl nritl~out, specinl stirriilg cle- vice for the ele~trolyt~e, i t occurrecl to the writer tha t this icle:i, in ~noclifiecl form, boulcl be taken up in the 1nl)oratories of. the copper smel- teries and refineries for the purpose of .more nccumte copper cleterminn- tions in the ~l;etnllic mnterids; however, not by reclucirig the time usun,lly required for cleposition, but hg nlultiplying the quantity of sample taken for the 3ssn.y. It' was ren,sonecl t,llat . . g'ai~ze c~at,hocles, for llluell work, woulclbe too flimsy &nil c&angenl:,le in weight through abrasion a11d t h i t i)erforn.ted plat~inmn sheet would nnsxvcr t,he . . purpose better. i;'For. certain work, ~cnthocles'mith larger l~erforatiolls hacl been rreolnlnended and used I.,efore by G. A. Heberlein3 of ~ + r ~ : t t . ~ n l l s , Mont. Itdeveloped after a few trinls t h i t with the new perfo~nted c:itliJdes4 5 g. of copper, fro111 crude- copper solution, coulcl be as clnickly. slid cohesively depositecl n s l g. or!. tlie sli~ooth cntliocle, wit11 equal.g~6ss~surfnie, ~vitllin tlie custonlary time

. . of 1s - to 20 hr.. Wit11 the perforateel c,?th&tle s current '.of 0.5 ampere \\?as applied; -~vllile ~vitli the snlooth c:ttliode 0.15 anlpere hntl been. found to be the upper lin~it for goocl work. - 3t was found impossil~le to ileposit, in good form, 5 g. of copper on n snlooth ~cathocl'e~ within 24 'hi. Most: importnnt \irith the 5-g. ~lletliocl is the fact, thiit the gener:il limit of n.gree- lllellt betnreen tluplicnte c~et~rliiillatiok ~vns nidved fro111 the seco~lcl ,lier- cent.;tg& decilnnl to the thircl, wlin,t,ev$r the absolute . . nccuri,cy might 'l.,e,' This in itself is sufficient proof of . the . fni~.ness of each of the 5-g. charges

' t i k & fronl the genrr:tl sanlple. . Besides, i t is tllk ~vrit&r's opinion t,hnt there .

is f:tr-more simplicity in this methot1 thnn i~ the ;,ne in nrhich n much larger siml;le'is dissolveel i!ncl, an aliquot liortio~l of tlie solution, 1vit11.a slliall clu:\n-

. . '

t i ty df 'copper (1 to 2 g.), niensured out. '. . . . . .

1 C;eorgc L. Hent.h, The Electrolytic Assay ns Applied to Refined Copper. Tra~js. . . . SSVII, 11. 3210 (1S9i).

R:ipitl Electro-Au:~lysis. with 'Stnt.ionary Electrodes. Jour,tal A,,IICI.~C(,I; C'hcr,aicnl So&'ety, vol. ,XXSI, 'p. 3S5 (1909). . . .

3 Fmnk Iilepetko, Discussion of .Heath's Paper on the Electrolytic Assay, etc. Trans. SSVII, 967 (1S9T). . .

4 NOTE: AS 110 priority controversy is tlcsiretl, the writer would st:lte that he pl:tcqd. llis ortler for perforated c:ztho,:les with B:iker t Co:, Inc., N e ~ : ~ r l i , N. .I., on Mircli 20,,1g09,~~n~cl that he eshihited then? before B meeting of. the'New York Sectidli of. the

. .. America11 Chemical society on hl'ljich 11, 19'10.

. . ' .

AMERICAN PROC4RESS I N THE ASSAY O F COPPER-BULLION. 30'35

The operation of this methocl for Anaconcl:~ copper, is now carried out in the following n1:tnner:

ASlock so1zstio~z.s:-Nitric acid (sp. gr. 1.42) one part to one part of water; sulphuric ncicl (sp. gr. 1.84) one p:trt to two nncl one-half pnrts of 1v:tterr; soclii~m chloride, 5.5 g. to the liter. The proper ratio of the h e portion

grams), is weighed and t l ~ e relllaini~lg part of the 5 g. made u p with the coarse portion. This is clroppecl into n 300-cc. lipless Jell:% beaker (t:rll form) which.seelns to be the smnllest size t,hnt call safely I I ~ 11secl for the solution of 5 g. of copper. Tests ~nncle ljy plncing a filter paper over cover glass :tad beaker and snugly folclecl clown over the edge of the lnttkr

. .FIG. 1.-Srs~~nr OF: COVERING ELECTROLYTIC BEAKER.. . . . ,

+ . . . .reveal&l ilo loss ,of .copper m~cl~ai~icnlly carried :%way.. Ten cubic centi- meters of stock sulphuric ncicl is first ndclecl to the copper, follo\vecl' by' 25 cc. of stock nitric acid; the purpose of the initial sulphuric aiici'is to retard the.action of the llitricacitl- but nfter~vnrcls to aid in the solr~tioil of the oxides present. The beaker, covered with n wiitch glass, is plncetl in 'a cool pnrt'of t he ho,ocl until thecopper'is dissolved ,2116 is then ljlacecl on i steam plate, carefully avoicling boiling, until coniplete c1is:~l)pe:tran~e of nitrous fumes; 2 cc. of tlie soclium chloride solutio~i is now added ant1 the \lot solutiori gently shake11 ulitil.the silver chloride is well co:zgulnt,e~l. Filtration is then performed through a 7-cm. filter into :x beaker of the same size and sh:tpe as the origilial. To nlnke up tlie full acidity of the electroljrte 30 cc. lllore of the stock sulphuric acid and 3 cc. of the nitric is necessary, All of .Rrhich is run through the filter to insure coniplete re- covery of the:copper. The whole'is ,diluted to. 225 cc. with clistillecl water.

2096 AMERTCA:-< PHOCRESS IN HE AS:AY OF COPPER-BULLION.

When uny difficulty in depositing the copper is experienced it may be attributed to insufficient dilu "ion of the electrolyte; addition of more watef' will overcome it.

The perforated platinum sheet constituting the closed cathode cylinder is 6 x 11 em. and has S(~ven perfora.tions of ab ut 0.5 mm. to the linear inch. The total height of the cylind r and stem is 23 cm.; they are some­what unnecc sarily heavy, weighin about 23 g. Those cylinders that have been in daily use for four years on Anaconda material lost on the average 1.7 milligrams per year. Others, which are used for copper high

Photo by C01JTteS1/ 0/ IVerner FeIZ.

FIG. 2.- • [.ECTROLYTIC OppgU DEPOS1TlON STAND.

in gold, gain very apm'e iably in wei ht after ev ry deposition; this beinp; due to the deposition, with the copp , of that portion of the p;old which is soluble in nitric acid. In course of time these cylinders become gold­plated. With the heavy current us d, i~1 is important that the henken; are well covered, so tlmt here c:.UJ he no Io. s of solution by spraying. Fig. 1 illustrates the scheme to accomplish this with the aid of sleveral setB of split watch glasses. Fig. 2 sh "", the comltruction of an electrolyti~ stand with series connections. The ammet(~r is not visible. It is here shown chiefly to call attention to the knif 'witches on the top of the bar which

AMERICAN PROGRESS IN THE ASSA~ ' OF COPP'ER-BULLION. 2097 . . . . . ( _ ...

enable the olwritor t>o renlovc the cnthocle anel simult,aneously to'close the circuit, which is not possi1:)le with tlie generally used plug. It 3s of the ut~nost importance to tl.~nifei.~"tlie cnthocLe..:wit,h it's copper deposit as quickly as possible fro111 the electrolyte into pure wnter, so as to lose a l~liniillurn of coI)per by re-solution.' It is dolie cis follows: Tlie covers are first relllovecl froin the bealrer, then the base block from under tlie latter with the right hand, holding the bealier with tlie left. Up to this molllent t,he current li:~sses ~&in te r ru~~ tec l l~ . Now tlie forefinger of tlie right hancl closes the switch :211d simultnneously the thumb presses the spri~lg re- lensink the csthocle; the left hnncl nt the snllie time dmnrs t,he beaker xnd cathode clown nncl :%way frolil the auode (the usual corkscrew spiral). By this timi3 the right linncl is frce to transfer the ,cathorle to several clean waters ailcl to djsolute alcohol, after which it is clriecl over a Bunsen

. . burner.

As dready st,:lted, the current .employeel for each aisay is 0 5 :%nipere; the time (over nigllt) for &omplete cleposition nbotit. IS hours. The latter point is nrrivecl :it wlle~i poln~.izntion (bubbles) a t the cathode has t ~ k e l i plnce for al),out one-hn.lf hour. Tlie beaker is then filled with clistillecl water; so that'tl~e~electrolyte touclies the cover-glasses and the current penriitted to continue' for n~nother half-hour. Each electrolyte is t&tecl for', tlie-

of copper by ~aturnt~ion nrith hyclrogen-sulphiclc gas. . . .

The cluestion of t h e accuracy of results should in all cases 'be'sub- jectecl to analysis. It lins alr&icly been hinted th:tt after n.11 the copper

, . ,h is 1)wn clepositecl on the cnthocle, there is n possibility of re-soliltion when renlovin$ it. froin the ncicl electrolyte. Tests mac.le on nlililerous individiinl ~let~erlninntious shonrecl . that ihc electrolytes colltainecl 0i0092 per dent. of the origi~lnl c'opper. Table I shows; on thc .otlier:li:lnd, that

. . . .

TABLE I.--In~p~~~-it . ics CO~L~(LZ.)LC~ ,61:)2 ~ ~ ~ ~ , c r - ~ ~ ~ l l i o n 'cmd Dipositid .wit/! Elcc1rolytic C o p p c ~ . (At~cc.lys.is oj 100 Gr(r.tt1.s.) , . .

I I

Tel lu r i~ r~ t l ,;,I. 1 ' i t 1 i n 1 s i c . ' I a~i>t

I'vr Cul~t. Pc :~ Ceut. Per Cent. I'cr Cent,. Sclct~t~l~ii . Per Ccnt.

1111pr1rit.itts ill co11vcrtt:r rap- . per. . . . . . . . . . . . . . . . .

Impurities ill eloct.rolyt,ic copper. . . . . . . . . . . . . .

Purtiori of impurities do posited a . . . . . . . . . . . .

a Golcl in t.his case wns not tlissolverl y d si1vc.r is coml~ l~ te ly climinntccl. a Bismr~tli is probably all tle1josited, the difference Iletween the two'figurcs of ttnaly?.sis

being n~ell \vithin the limits of experimental accuracy.

0.0lV3 .

t r : m

?

0.0040

0.0137

03.50 h l 0 J . 00 ?

0.01530

0.0031

4 . W

. .

0.0211

0.0009

4.20

0.0073

0.0016

23.22

the .copljer ~vh ic l~ . is deposited is not entirely pure, that in hhis case it corltnillec1 0.0093 per cent. of -ibs weight of impurit,ies rleljositecl frorn the electrolyte. T%esc two figures bnlnnce each btller very closely and in commerci:tl \irork usunlly no correctio~ls are m:tde.

I11 many. lnboratories i t has been customary to precipitate the silver clectrolyt~ically with the copl).er o n t'lie c:tt8hotle n11d then to. subtmct from the gi-oss perccnt:t.ge that of the silver :is c1eterminet:l 1)): sepnmte assay.. This lirorlis .\vcll up to a cert,aiil silver iontcnt; 0.3 per cent. or 100 oz. pcr ton prbljal~ly being the limit. When under this method the fitst difficulties with a, goor1 coppcr cle1)osit are esl>criencetl, i t is 1vcll .

to elillliiinte the silver fro111 the el~ct~rolyt~e. On a number of occ,nsions this mns the only prec:tution 11ecess:try to bring nbout :tn' excellent tle- posit of. cleqtrolyt,ic ccil~per.

When certain ilnpurities in crude coppcr, or coppcr-l:)ullion, csceed n cert,nin .cluailtit8y, it becomes ialpossil)le to elcctro-rlcposit from its solu- tion n copper of sufficient purity for con~mercinl nnnlyt,icnl requirement. We h:tve already seen that bismut~h is :~ll tlepositecl with thc copper, but this ~llctnl is rnrcly nlct in dist,urbing clu:~nt,it,y in co~lvcrter cupper. When mct in larger quantity in blnclr coppers it illtist Ile eli~lli~lntccl hefore the cl~ct~ro-cleposi t i of tlle cupper; :L lllethocl for ~vhich ~vill be descri1)ecl further on. - ' Sele~liulll is : L I ~ clcllle~lt whic11 is 111ore rcndily dcpoaitecl fro111 so1utic)n t11:tn copper ;mcl me niect it in appreciable cluant,ity in t,lle converter .coppers fro111 our South\vest. When the copper Ln the c:~tliocle is tlis- sqlved in dilutk nitric, ncicl the selenimn reinnins, n t lcnst in part, ps a retl ont ing, nncl some chcmists weigh t#l~is nncl use the weight ns ii mi!lys correction in their col3per assay. . This, 110 cloul)t, is but an nl~l)rc~~sil~l.:ttio?l. The follon~ing is n very simple method to remove cluantitntively t>llt; scleniuln from ally .clunntity of -copper, tile silver 1)cing re~l i~ i&l a t the ?s;tnle t i~ne.

. . _ - . _ Sele~liuill ancl copper cnlmot he completely sepnmtecl 1)y the alkaline

sulphicle methocl, ns there is always some insolul.~le sele~litlc fonned with the llenvy met:tl. Selelliunl is also precipitntecl \vith the copper when .

the latter is sepnratccl as sulphocynant,e fro111 a numher of ot,her elementas. In fact,, however, jny methotl that. ~voulcl nccessitnte t h e precipitatiyn of 5 g..of copper as n cherllical colllpou~lcl for the purpose of its purifica- tion would be unsntisfnctor-y. . The precipit,ntic)n of tl!e selenium from. t,he electrolyte.hy means of sulphur tliositle ~lat~urnlly suggestteci itself, by t ' i t was soon founcl thttt here also the two elements co~llbillecl to form copper selenide. - U p o n further investig:~tion it w:ts 1e:trnecl that i11. the presellce cf- copper

i11tl silver, in sulpl1:tte solution, the selenium, !\rllen lil~erntecl 1)y sulphur dioxide, had :t strong preferential afklity for silyer :~nd if the latter was

present,-.in sufficient .escess; the selenii~in ~vould be precipititecl cluanti- tatively ns silver selenide, Ag2Se, without n trace of copper. The excess of silver is then precipitated ns cllloricle nncl with the silver selenicle is filtered . nnd ;\vashecl . with dilute sulphuric n,cid anel water. I11 case too mucll of an excess of salt solut,ion has been nsecl, it is best now to evaporate to sulphuric ncl.icl fumes, ili orcler toclrive off the chlorl~yclric n.cicl and thus a.i~oic1 its deleterious effect on the chn.mcter of the copper clepdsit.

The 'presence of 'a11 apprecia1,le qunnt,it,y of tellurium will also iiiterfere with . . the acckrncy c,f . - the electrolytic copper deternlinntion alld it must, accorcliiigl$, be. eliillinnted before the electro-tlepositio of the copper. However, it is not oftell present in clist,urbing nlllolint. Tellurilirn is liot

'

very readily precipitntecl from the .copper sulphate solution by sulphur tliosicle,- but . what,ever portion of i t is reclucetl combines .wit,l~ .co],per t o form copper telhiride. It .is no riv:tl of seleniuln i11 the latter's nffinity for silver. A complete elimination nlethod will be described with that of the bismuth.

Ai?tiinolly and nrsenic a r e not very readily electro-deposited fro111 nitric-acid solution nncl only smnll ])ercentng&s of the original cluantities are fomlcl in the electrolj.tic copper; yet ,tliey become troublesome nt times, because they are generally the eleille~lts found in 1n.rgest quantit,y nssocintecl 1vit11 copper. It Iias bee11 claimer1 that certain compounds, I I aclcled to the electrolj.t,e will entirely prevent the clepp~it~ion of these elements. I11 tests m:~de in the Annconcln 1nborato:y with com- rnercinl electrolytic copper it was follntl 'with the ntltlitioil of such dopcs the results mere very noticenhly high.

To eliininate niitilllony ailtl n.rsenic when t,hey l~ecome distm'l~ing f:tctors, the writer ' prefcrs the tlouble-tlel>osition metliocl, which 11a~ provecl to I)e very snt.isf:~ctory nail in proof of which t,lle cln.tra of Tnblc I1 are illustmtive.. To execute this method the original deposit on the cnt,lioclc is treated with the usunl precautions nncl is then placecl, together with the anode, in a regular tlepositiiig l,e:~kcr, the complete electrolyte ncldetl ant1 the mhole'coverecl a s .per scheme of Fig. 1. Only gentle heat is 4,- plie'cl to insure the re-solut,ion of the tleposit anel the solut,ion is digested lsng ellougl~ to espel the recluction proclucts of the nitric acid.' When, in .

these cases, the copper deposit 112,s a slight ctinting of arsenic or antimony, there is 110 re-solution of the copper (luring the time of 'feinoval -of the c~tl~o(le:cylinder fro111 the electrolyte, since the former .ele~nents are first subject to attack.

Lencl i s one more element w1iich.i~ usually present in copper in small quantity, but whibh, mrhe11piesent even in 1:trger quantity,.m:~y be;reaclily elimil~:itecl ii1:the course of the regular routine of preparing the electro-

- ''George A. Guess. The Electrolybic'Ass:~~ o f Lencl nncl Copper. Tra.ns. 1XXSVI. 605 (1905). . ,

annlysis. In the first plice a inajor part of it inay be separatecl as sul- pllate from sulphate solution nncl the small relnaining part can be electro-c~epositec~ from nitric acid 'solution as j~eroxicle on the anode; it being only necessary tlmt the latter presents sufficient surface for the adhesion of the perosicle.

There is yet to be described n methoclby w11ich'l)ismuth ancl tellurium nlay be elilninntecl and nrliicll will, a t the same. time, inclucle the eleinents. for which incliviclual methods have been given. For this the writer be-

TABLE 1I.-A~sen@ in driyirza1 Copper-BtrlEiot~ and in Copp!'. of First. c1;)1d S C ~ C O . ~ ~ ~ Electrol.ytic Depositi0.n.

Arsenic in Origillitl Bulliorl, 2.609 per cent.

First ~lectrolytic ~ e p o s i t . ~ , Copper, Pr:r Ccnt. :

. . . . . . . . . 94.633; 94.678, 94. (32. 94.652, 94,690, 91.093.. . . . . . . . .

1 Avernge, 1 Per Cel~t .

First Electrolytic Deposit., Copper Dis- solvetl for Sccur11:l Deposit.ion, Pcr Cent.:

. . . . . . . . . 94. ,594, ,94. G2G, 94.576. . . . . . . . . 94.590, 94.652, 94.OGO..

. . . . . . . . . . . 94.652, 34.594, 94.724. 94.S24, 94.770, 94.770 . . . . . . . . . : I

Arsenic in First Deposit, Per Cent.

1 . .Second Electrolytic Deposit, Copper, ~ c r l Cent.. : I

94. .530, . '9-1.550? 94. .5'2li. . . . . . . . . . . . . . . . . . . 94.528, 94.553, 94.544. . . . . . . . . . . . 1)4.5!)6, !)4.572, 94.5114. . . . . . . . . . . . .94.(300, 94.526, .94.554. 1

Arsenic in Second Dcposit, Pel Ccnt.

0.0014(5; 0.056 of origiu:tl.

2.73 of first, deposit..

lieves the siinplest process to be t h e precipitation with ferric hycll~osicle in slightly ammoni:zcal solution with an aclclition of aniinoaim carbonate to precipitate the bismuth.' To carry out this methocl t h e copper ;is clissolvecl and the silver eliminatecl. as usual, 0.1 g. of ferrous sulphate haviag been aclcled to the'5-g. copper charge. The solution is nlncle slightly ~nlinoiiincal amcl a little ammoniunl carbonate aclclecl; it -should then be.kept near the boiling point for about 15 minutes. The ferric

. hydrosicle cnrries tlom with it all of the sele~iium, tellurium,. antinlony and arsenic, but ufortunately, and this is the. clrawbnck of the methocl, it also carries with i t an :tl,precid)le quantity of copper, so that after filtering ancl washing the precipit:tte with anllnoniacal water it must be re-clissolvecl, re-precipitated, filtered ancl washed, and the whole pro- cedure repeated four or five tinles to ikure the recov'ery of all .of the

AMERICAN PROGRESS, I N THE ASSAY O F COPPER-BULLION. 2101

copper. 111 each re-precipitation the same collclitiolls are to be ol~servecl as in the first one. All the filtrates are unitecl :tncl the regular cluantity of sulphuric acicl is added. Shoulcl the voluille of solutioil be too great it must be evaporated t80 the desired mark.

The nlarlied progress in mpiil elcctro-c1el)ositioi of lnetals in recent years, hy nlenns of high current density ancl the use of rot:tting electrocles or the rapid circulation of the electrolyte, is well lillo~nl. Thesc methocls, uncloubteclly, have their high merit for special purposes, where time is the chief factor. They clo not seen1 to have appealecl to the chenlists of copper works where largc llulnbers of accurate cleter~nillations are re- quired and in which the work of the electric current tluring the aight requires no attelltioil \vllntcver, ~vllile rotnting elcctrocles, motors, :tile1 violently stirred electrolytcs mould be sources of illuch concern.

From t,iine irnlneinorinl the met,l~ocls of assaying any lnaterials for silver ancl golcl were in reality llotlling but laborntory slnelting methocls. When in 1855, t,he writer arrived in Butte, Mont., he foullcl that these metals, contaulecl in copper bullion, were still eleterminecl by the :dl-fire assay, both in the same charge. There seenls to be no record as to when and where the so-calleel cornl~ination method (clissolving the copper in nitric acicl ancl precipitating thc silver 2 3 chloricle, etc.) was first intro- clucecl; but in the early nineties of the past century it became evident that for the salie of accuracy of the gold assay this metal must be deter- nlinecl by the all-fire method which, on the other hand, was quite un- satisfactory for silver. The coinbinatioil method l~ecaine the stanclnrcl llletllocl for silver ancl the all-fire the stailclnrel for gold. Froill that time on prol>ably nlost nssayers were longing for a, re1i:tble single method for both metals, since the simplicity of the combinntion method, with its accurate results for silver, colltrastecl strongly with the uuchemical, tedious ancl expensive all-fire method for golcl.

To many, the coi~lparative cost of the all-fire mcl sulphuric-acid assay- inethocls may be of interest. For the Anaconda laboratory, of Pert11 All- boy, it has been calculntecl with accuracy, that the materials per assay, exclusive of t,hose used in the parting for gold a i d for the correction-ass:~y (these being approsimntely the snille for both methods), amount to 5.5 ce~lt~s for the sulphuric-acid method anel 75.5 cents for the all-fire methotl; a saving of 67 cents per assay. The saving in lnl~or, too, is coasiclerable, although its value in our case has not been estnblishecl.

The first recorilecl atteinpt to inoclify the comhinatioa method in a way to obtain accurat,e golcl results was m:tilc 1)y L. D. Goclshall,' who

1 Assay of Copper Materi:tls for Silver and C;oll.l. Trc~t~s. XI-\;., 520 (1000).

1 2102 Irh!ERICAN PROGRESS I N TFIE ASSAY O F COPPEIL-BULLION. I '

\ .

suggestetl to reprcci1~it,:ite any golcl t,hat iiligl~t have gone into solution' \vit<li t1he col)ljer bj. co~lduct~ing Iiyclrogen-sulphicle. gas illto the solut,ion

. . 111 st~fiuient qilnntity to l>recipitnfc :dl the silver. \vit,h 110. copper. or oiily n nlininlu~n c l r~n~~t i ty thereof. 'A. R. Leelous nilel C:r.bell White11e:ttv .

])oint,ccl orit t,he defects ,of such :I, mct,ho;l. About tllc snlile time Iv; R. \'an Liew3 sho\ved tllnt :tccurnt,e golcl results coulc1'l)e ol~t,:iinetl 111,ocli- fying the coml~in:~tion iilet11~)cl ill t h e vr:ty thnt clilute nitric acid y:is aclilecl in sever:~l portions to the iiletnllic copper :~ncl tlie reaction con- cluctecl llilclcr ice-cooling. Thc tiilic requiretl ,for t,his 11lct11otl w:ts n factor very much ngninst its I>ecoming po11ill:tr. A.ne\ir it-lea .was introclucccl. by T1lom:ts B. S\vift,'' ~vlio first rnn:ilgam:tted thc surface of the co1q)c.r 11y lilenlls of mercuric nitrate before clissolviag tlie metnl with ~lit~ric ncicl. I11 this metliorl, the surfnce of ertch copper particle woulil relllnill co:ttccl with mercury cluri~ig the nrllole process of solution nncl the mercury would absorb tlie gc)lcl :~.ncl l)I.otect i t froin any solve~lt action. - The author g:tve lio il:ttn regartling silver.

During the period in which the afore-clescribecl efforts for 3 sinlplifiecl gol(1 nssny were mncle, attempts along the sanlc line ,Irere :tlso c:irrierl on in trlle, hlacontla laborntory. .The icle:~ was to fiiltl n reclucing meclium which ~voulcl quickly precipitate the golcl fro111 t,he nitric ncicl solutioil ~vit~liout precipit,nting copper i n any 'form. Goocl results were obtnincsl 1)). boiliilg the copper nitr:tte solutiol~ (.one nssajr t,on of copper), xidlicll contnined little nitric :tcicl in esc,ess nilel iio nit,rous products, with 25 cc. of form:tlclehyde, strength about 37 per cent. A few compar:ttiv~i results 11y m&thocls of tlmt t,ime :ire given in Til:,le 111. . A peculinr phenomenon uT:ts observecl in trying cane sugar for the &tile purpose; i11ste:lcl of reclucing :tnd precipitating the golcl which .hael been clissolveil 1jy the nitric ncicl, the greater port,ion of the t,otnl golcl woulcl be clissolvecl when the ~olut~ion was boilecl; Table I V gives the data.

I t w:ts a t first thought thnt chlorine was present in tile sugar nilcl that i t nrns responsible for the solutio~l of the, golcl, I ~ u t a t<est of the sugar solutioil as iirell as of t he bunlt residue revealed but :ti1 iildist,illct trace of thnt element, so that the fol.lowing fn.c.t,a may s:xtjiifactorily &splniil tlie phenoinenoii. When the copper nitratme solut,ic~n is boiled with the ncl- clitioi> of sugar the latter is cluantitntively coliverted illto os:tlic acicl ancl t,liis forms, ~v i t~h t,he col~per, nil inso1ril)le osalnte. The llitric ncicl

1 ~ d w n r d ~cellbr, TI^ Polr~bilit,y in Nit.ric Acid of Gold Cont:iine~:l in Coppcr Br~llion, Trcrtts. SLIII., 5S2 (1912).

2 Discussion of L. D. C;odsh:tll's pn.per, T ~ C L ~ L S . SSS., 1121 (1900). Losses in t,he Determinat,ion of C:oltl nntl Silver in Ccrpper Bullion, ctc. Et~gitleeriny

(~tzd 11lini)zg J o ~ o . ~ I c I ~ , vol. LSIS., No. 16, 11. 469 (April 21, 1900). 4 The Assay of Copper Bullion, Etlyi~eering and Ilfiuit~g Journal, ~ o l . LSSIV.,

No. 20, p. 650 (Nov. 15, 1902).

TABLE III.-C07??~~ar(i!ive co7d Assays by I7c1,~iozr.s iI1ebhod.s. Gold, ii~illi!lrrrii~s or oicnces per 1012.

AVERAGE.. . . . . 5 . ii7W 5.7:300 'I- F,. 5567 I 6 . G0'7'2

is reducetl t,o free nitrous acid nnd this ivill, the oshlic ncicl being inert, clissolve the gold.

Experiments on these lines were ~lis~ontinuecl mhea, early in 1908, it was learnetl that Frecleric F. Hunt, of New York, lincl clevisetl n new coml~iuntion method nrliicli yielded good results for silver niltl for goltl. This metllocl consist,erl in ntltling to 1 nssny to11 of copper 10 cc. of wst,6r nucl 100 cc . of sullihuric ncicl of 1.81 specific gravity; first heating on n hot-plate. n~ld finauy on 211 open flnnle until complete sulplintizing of the copper wns nccolnplishecl. There was no solritioll of the gold and itrhea the silver, -or n part of it, was dissolvecl i t was -precipit,nted ns chlvritle nncl the renlnining procedure was the snrne ns that well knonll in tlieoltl cornhination methocl. Some tlifficulty was espcricnced in sulphn.t,izing th'e copper to co~ilpleteness when the snmple was too coarse nncl wlien

the copper contained nppreciable' nnlourlts of sulphur. A little later in the same year Albert M. Smoot,' of Lecloux & Co., New York, iilforliled

TABLE IV.-Gold-S0176bi1.ity i ? ~ Cop?)er-N.il~crte Sol7rtion i?l, the Prese?ace of Catre Stiynr.

(Goltl prcscnt = 4.16 mg.)

the writer t,hnt copper first :~rnnlgnalntecl superficinlly nrlcl hentecl wit])

1 Private coulrnunic:ltion; siucc published with motlificntion, E~cgi,&eering nrtrl h f i l ~ i ? ~ g Jol~rilnl, vol. LSSSVII., No. 9, p. 465 (Feb. 27, 1909).

2 Private communication.

Grams, s t ~ ~ r r . . . . . . . . . . . . . . . . . . . . . . 1 2 3 .

0.30 0.31

--

Gold after boiling, m g . . . . . . . . . . . . . . .

4 .

0.39 . 0.89

5

0.33

2104 AMERICAN PROGRESS IN THE ASSAY OF COPPER-BULLION.

80 cc. of sulphuric acid (sp. gr. 1.84) Iler assay ton of copper was an im- provenlent over Hunt's method. Difficulties in the comblete sulpliatieing of the copper in certain b~illions continued and let1 to numerous tests in the haconcln laboratory which resulted in the final adoption of the follonring routine, by ~vhicli even coarse clrilli~lgs :~nd copper shot may be .cumplet,ely sulphatized m d of nrhich the resulting gold aiicl silver chloride may be scorified with a. total of 20 g. of lead in 2411. scorifiers and cupellecl in 1-in. cupels; the lead buttons weighing 5 g.

Stock sol~6t~imzs.-Mercuric nitrate, 25 g. of mercury per liter; sulphuric acid, sp. gr. 1.84; socliurn chloride, 19 g. per liter ( 1 0 cc. will precipitate 350 mg. of silver). The copper bullion clrilli~lg sample. has been ground

, to pass a 16-mesh screen ancl if by test it has been fouilcl that the coarse ancl fine parts,' separated by a 40-mesh screen, differ appreciably in pre- cious-metal content the parts are weighed separately in their pfoper

20'166 grams (C=weight of coarse; F=weigllt of fine 'ratio. The he;- C.

. . F portion of sample), is. weighed first ancl the remainder of tlie assay ton nlade up ~vitli.the coarse. This is now placed in an 800-cc. Jenn beiker, Griffin shape, 30 cc. of water a11d then- 10 cc. of tlie mercuric-nitrate solu- tion aclclecl (Hg =0.25 g.). The beaker is slinken until all the copper ap- pears am~t1g:tmated over its surface, then 100 cc. of sulphuric acid is ~ ?ddecl; the beaker is covered with a 5-in. watch g1:tss and placed 011 an electric hot-plate. The time necessary to conlplete the reactioil clepe~lils onrthe state of clivisioil of the sample; as also on the temperature of the plate. Table V. gives the time and temperature record of two samples.

For about one hour the liquid appears to boil, which, however, is only , a bubbling, clue to the evolution of sulphur-clioside gas, from the reduction

of the sulphuric ,Acid and the oxidation of the copper. This completed, the supernntnilt liquid assumes. a very dark green color, finally changing to a light gr:tyish hlue which, as experience has taught, is t.he i~ldicntion of the 6nisliing point; Boiling over an open flame has been abandoned,

. the escessive heat ilaving been found unnecessary aild the act of boiling being bound to entail some loss. The beaker is lest renlovecl from the p1:tte and placecl to cool on an asbestos sheet.. ~ o m p l e t e cooling is un- necessary as there is very little free sulphuric acid present. Four liundrecl and fifty cubic centimeters of water with the necessary amount of socliuln chloricle solution, tile latter, depending on both the ailloullt of the silver and the' amou~!t, of mercury present, a r e usecl. With 80 to 100 nlg. of silver and 0.25 g. of mercury for Anacoqla ~naterial 30 cc. of the stock solution or 0.57 g. of sodiu,nl. chloride is always a safe quantity. The beaker is. again placecl on the hot-plate and the ,solution brought .to a

TABLE V.-T.I:.))tc k i d Te,trpern.tt~re-Record: of Szlbplintizi~~~.g' A.nialganlnted ~ o ~ ~ e r - ~ ~ ~ l ~ i o , ~ Samples (0n.e- Assay To,&).

4 . 0 5

. , 4.15 4.25

Finish. . . . . . . . .4 .35

I Time, p. m.

2 . 5 5 3.0.5 3.15 3.25

Finish.. . . . . .3.57

boil, which clissolvea the copper sulphnte and coagulntes the silvir cllloricle. On removal of the bealier 150 cc. inore water is aclcled, the total nrnount now l~eing 600 cc., nihich is capable of keeping in solution all copper sul- phnte after: cooling. ' It is then a' matter of expediency to filter imme- diately or tile clay after.

Details as to the furnace operations of this' rnethocl are not deemed to be within the scope of this paper; they are much a ~nntter of inclividunl taste. For the clescription of nlechanical ant1 labor-saving devices the reader is referred elsewhere.' '

I t should be noted th,zt.with co~nparatively pure copper the amount of mercuric: nitrate may be reduced, while with copper high in sulphur content an increase in the amount of the mercuric nitrate will he recluirecl.

1t has bee11 notecl as 'a peculiarity :of this method that with certain low-gmde ljulliolls none of the silver is rendered sdlul~le ancl that upon addition of jsodiurn chloricle solution no silver chlori'de is fornlecl. Table VI. gives aivariety of clata on -this :subjec!. It is shorn that .a11 of the srsenic and, nearly d l of the'antimoay is dissolvecf. It was dso quali- tatively prdven th9t no selenium or tel/uriulnlrekairls in the:resi$ue.. The insoluble silver, therefore,. is not conlbined Tvith any of these elements.

It was found that with all of the linsoluble silver residues: there re- mained some mercury and with sample No: 4 always n little copper; the latter probably being in the forrn of sulphicle, as this sample contained

Edward Beller, L:~bor-Saving ~ d v i c e s in the works Laboratory, T~~ans., XXXVI., 3 (1906); SLI., 786 (1910).

. . oz. ,lor tun,. . . . . . . . : . . 570.33 131.10 i10.63 ' 84.33 129.53 214. 11; 53.; 35.93 8n.01 I ?5.3!1

A r c per cent.. . . . . . I . . . .I 2.50,:- 1 0.kll) 1 2.50l; 1 OU444 1 0.00 I 0.0444 I NOSI9 ( 0.00 ' 1 0.Wtj9 ( Dl*iS I 0.0 -1 3?%S '

Aut i~llvnx, per cent . . . . . . . . . . . O.OSb:, 0.00GO 0 4 U. 1000 - 0. 0054 0 1 5 0.0365 0 .lJ06O 0.0415 0.0344 0 .OOG2 0.04L~Ii ' . .

. . - . . . 1Iercuric Nitrate, 2U cc.; HzSOr. 100 CC.

. . . .

. . 1\1ercrlric Xitmte, 10 cc.: ~ z ~ d r 100 cc.; healed 1S hr.; 15 ~ n i n . over open flnnle

. . . . No 1\lcrcuric Nitrnte: Hz804 1110 cc.; lrenterl 18 hr.; 15 uiin. over open f ln~nc

. . . 1,lercuric Xitrate, 10 cc.; HlSl3r 201)cc.; heater1 IS hr.; 1 Iir. orer open flame . : . '-' . .

I - . , Silve:, ui . per ton . . . . . . . . . . . ' i03.~2 S;SI : il2:fiS I b?0<1.:10 1 6 . 3 6 / 21506 59.02 1 1 .i 1 LIO.lL4 ( b3i.60 1 0.4s ' 3SOi

I - ! , . I I . .

' . No hlercuric Nitr i t te; HSVr 21JO co.; heat6rl 18 hr.; l h r . over open BRNC

.. . . . . . . . . - , . . (. i 4 .

i u . r n . . . . . . . . . I ill 1 1 . , J.9S / 211.12 2li.10 1.9 1: 3 90.30 I O l S ( I ' S S , I ~ ~ . . '!I . I .

I , .

. . ,z Assayed. hy ,onr regulnr sulpburic acid method:'30 cc. w e e r . I O c c . mercuric nitrate solution. 100 cc. HISO, (sp. gr. 1S4). The volu~lle of water used in

all .of the above assays was constant. 30 cc. . , h.Nos. .?:nntl 4 samples. changed. . _ , ,. . . - . , . . . . .

, : , . , . , . . : . : .

TABLE V11.-~0k~.)~CL?td i .I(I~hl~l' ,ijl. C!oppw-B~~lL%ot~ by t / l C S l l d / ~ h . f l : ~ i ~ ~ ~ ~ ~ i d 11fetlt.od. I*l7.ith Vco.yi,t~.g dnlouds of 1l.lwc7cly jor the Anzcrlya?tint.~:on. of fAcCoppc7*. . . . . . . . . . . . . . . . .

! h i t <,ll.: 1. T.l7cight4 :.Afilliyrco,~s or Otct~ccs per. Ton.

~olr1111e of hicicu~:icii~it.ri~te solution :uit~ \v:itt:r co~~st : i~i t (35 cc.). . .

,. ..... ./I

3 Ar

' J ' I l j

.y ! j ,: . .O:, 6:)

, !a:!$

. . ,

Cofrected silver. . . . . 1 . . . . . . . . .

-- . . -

Silver. . . . . . . . . . . . . . . . . . . Silver correction.. . . . . . . . .

. . . . .

. . . . . . . . .

Avbrnge, ~il\;er-~oltl. :-. Less gold. . . . . . . . . . .:..

. . . . . .

. . . . . / l f . . . .:._

'

'.:.66l,.65 66.96 Q 7 , l t i

3t57.,!32 ??ti.: SS b6.50

c3ij(ji,~4 66. $10 66.72

i'd6:.50 66.70 66.9s

,167.14

. . . a One cubic centimeter of s:llt,.solut'ion-<contained 0.019 0. sodium chloride.. ' , . . "

. . . . . . . . ; , " . . ,. - . . .. . . .

-

66.450 0.906

I

. . . .

. . . . . . . . . . . . . . . :GOLD ASSAYS. . ,

- . 67.015 67.16 .67.22 67.02 f57.04 66.7s 615.94 (56 .09 67.06 67.00 67.33

,67.02 66.S.i

Uncomcterl . : . . . . . . . . . Correction. .....:. 1 . . : . . . .

. .

Corrected gol(1'. . . . . . . . . . .

-

G G . ~ ~ S 1.13s

- 67.20 67.20 66.02 66.06

.67.34 66.9s 67.26 67.13 66.96

- 67.16 67.3ti 67.1s 67.35

0.476b .0.0010

. . . -

0.4770

-

.66..672 . 0:999

. . .

-

0Oj.66 66.54 156.48 66.72 66 ;7ci 66.76 67.24 6ti .S3 66.72 66. 74 66.10 66.58 66.66

0.4kj.5 .iJ. 0015 -

0.4750

-- . . . . .

66.211 1.322

. . .

-

(i7.10 .

67.33 67.10 67. $2 (57.14 67.24 67.1s l j7.61

6 7 . 3 2 67.02 67.36 (i7.2'2 6 7 . 1 6

0.4iS.5' 0.1705

- 66.821

1.009

.0: 00.20. . . . . . . . . . . . -

0.4S05

-- ti7 .3" 67.1s 67.35 ti7 . O2 67. lW G7.0S 67.20 66 .DS 67.36 67.20 67.14 67.04 67.30

---

($.!)tj (j6.S2 6ti.!)2 l i l i . !)0 Mi. 92 6fj.!J2 ' 67.11) 67.11 67.12. 66. SO

- 66.65s

1.069

0.0015

--

,66:477 : 1.130

- - .-

.0.4SIO 0.4S4O 0.4765 0.4S-10 I . . : I:. . ,

2108 AMERICAN PROGRESS I N THE ASSAI;a,?F \~,o$PER-BULLION.

, 4 L , , 11'1

by far the most of that element. We may conclude" that, although the presence of mercury facilitates the solution of the silver as i t does that of the copper, all copper and all mercury m,yst,,ty, $issolvecl before all silver can go into solution. In the ordinary prodess of the assay, there is

' s l , l not enough sulphuric acid present and the heating is not continued suffi- ciently long to meet these conditions; therefore, with,little silver present none is dissolvecl, and with much silver presenteoqly a,portion is rendered

, . soluble. . . . . . . . , 1 . . . . . .

Table, VII. demonstrates that. a n ii~creased'~nmbunt.of mercury has no I . . . . . .

111arked.effect on the silver results if only the necessary increase in the amount of sodium chloride be provided! ,N+~I& bf the two substances can influence the golcl results. . ~ i , ; . 1

Table VIII. demonstrates that inlmediate filt-ition of the silver chloride k a y bechosen for ordinary purposes, while :$$& great accuracy is de-

I sirecl it is safer to 1e:tve i t fdr settling :mcl ~comj5lete cooling over night. , . .:. ,I:; !

Average. . . . . . . . . . . . . 1 86.0497 85.9040 . 0.1903 O..O46 . . . . . . . . o. 1457 Difference. . . . . . . . . . . .

. . . . . . . . 0.1457 -

: . . :I;) 1 hl.ill;'grams or o~c.iaccs! pcr L,o!L.

Table IX. gives compkrative results .for silver .ancl -gold; the-former . . . . . . . . . . by two a n d t h e latter by four methods. . , . ,. I .

In Tibld K a r e given pbbably somewh:it nlore convi;~cing, coihp&-a- tive figures for gold as determined by the once standard all-fire method

Diff<:rcuce I

~oruple l . N o .

i 1

19 ; 20 . 2 1 -

'

23 33 24 35 26 2 7 . 38 2 9 : 30 31 32 33 34 35

!

. . . . I

O\.er

. . . . . ' . . 0.03

. . . . . . 0.19 0.35

90 .07 ' : : ; . : :O .OG 0.33 0.29

0.'37 . . . . . . . 0.31

. . . . . . . 0.37 0.37 0.45 0.17

Differcure .

O v q Under

' . , ;;;; 1 Filtqreg

. ixt, ,Dr :*)

>I[)

.-:{ 1 S7:13 55.44

57..82 55.35. 90.01 87.39, 56.73 90.81, S5.6", 84.04 SS.14 89 .15 55 .56 S 6 . B 57.22 86.51

Uuder --

0.05 . . . . . . . 0.27 . . . . . . . . . . . .

. . . . . . .

. . . . . . .

........

. . . . ..: 0.47 . . . . . . . 0.34

. . . . . . .

. . . . . .

. . . . . .

. . . . . . ...

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 . 17 IS

Filtered At Oow?

57.1s. 85.41

S 4 . 3 9 . . ' 8 4 . 0 6 . 57.63

. 85.00 .

57.06 SG.43 9 0 . 5 9 , - . 0 : q 2 . ' 85.25 54.51 55.53. 89.39'

. 8.5.59 .

85.91 86.77 86.34

. 54.92 51.57 50.25 54.46 S3.91 S2.56 90.01

' 83 .97 52.%

:90.(52 , S 9 . 1 0 . . S7.61 .

87.43 S4.76 54.12 56.40 85.14 56.95.

84.59 51.79 79.97 54.13 52.73 52.60 90.06 53.78 82.10 00.72 SS.63 87.50 S7..56 84.50 . 84.30 55.53 S5.09 56.54

0.03 0 .0s 0.31 0.33 0.18 0.26

. . . . . . 0.19 0.06 . . . . :.. 0.47 O . , l l . . . . . . 0.26-

. . . . . . . 0.57 0.05 0.41

. . . . . .

. . . . . .

. . . . . :

. . . . . .

. : . . . .

. . . . . . 0.05

. . . . . . . . . . . . . 0.10, . . . . . . . . . . . . 0.14

....... 0.15 . . . . . .

. . . . . :. . . . . . .

,

A~IERICAN PROGRESS IN THE ASSAY OF COPPER-BULLION. 2109

TABLE I S . - C ' O ~ ) ~ ~ I ( L I - ~ S O I ~ of Seoernl dIetl~ods for Assnyiny Copper-Bztllion.

dIzll~grn?tzs or o~o~ces per 10th. I,, t o

SILVER : " C:I>LD

I C<>LIUINITION COII~INATIOX

o : ~ n i p ~ o n o . - iuet.nofl 0 . 1 Assny I Watci =( \Vntrr Mercury 1 R1ntcr I U e r c u g . Ton

Avernge weighing :dl gold buttons together. . . . . . . . . . . . . . . . . . ''I1

' , !

TABLE 1.-Gold As.say Test. I

'+ Teight, ?~zilligratt~s. '

, , , , . . * ; ! . I Uuoc~-s Per Tun Ounces Per Ton

:, , . . , & t I I Average tincorrectecl.. . . . . . . . . . . . . . . . . . . . . . . . Cot~ection (slag nnd cupel losses). . . . . . . . . . . . .

Avernge col~ected. . . . . . . . . . . . . . . . . . . . . . . . . . .

l,.l, 1 1 I t >.j k

I \ ; ~ :y,;.-: i.8

-2ii0 .AMERICAN PROGRESS IN THE ASSAT OF COPPER-BULLION.

. . I ! . ' 1 '

:ant1 the now ndoi~tecl sulphuric 'acid combinn.tion method. Clearly, the figures for 611e nll-fire nlethocl arealower than; those for the sulpliuric acid nletllocl wlieil the scorificatioil nncl cupellation losses are not taken into nccount; but when correctiolls nre lnncle for these -10,sses they m:ty justly 11e cleenlecl identical for all. practical and col~l~rnerhial p q o s e s .

This leads to the cm~siclerntioa of the borrjcted' yersrls tlie uncorrectecl. silver and gnlcl assays., Nearly 20 years ngdj ~ a i l . ' ~ t e t e f e l d t published n

I. I,:q)erl in ~vliicli he pbintecl out thnt,, in ass:xys-foi. silver. in silver nncl I/\ . I . '

silver-lent1 or& t h e losses ent,dlecl. in the ;comme1~cin.1 :~ssny methocls I1 ... . . . a@untecl t,o froni 5 to 80 per cent., /tlt;l,k~~cling I . . , , . . . . . on the grnde . nnrl composi- ti1111 of tlir ore, of whicli no nccomlt i~vns t:?ke!i. :;Tliere cnn be little cloubt

1 : , a ' > : that the silver losses in assaying c'opper ores :?re; equal, if not greater, tllan those in Stetefelclt's ores. Uilless sucl? loises Are carefully detkr-

. , . . , ! ! . . . ;.,;

. \IF. I J ~ (IE. of Silver per T G ~ I f ~ u l i d , h.lg. o r O E . ' O ~ S i l v~ r p e r ' . ~ o n a f t e r Hcurifir:tt.i~,n s n r l . f o ~ ~ u r l i n Slug a t l r l Cupels Kctai~icil i ~ r

Cupell:ltic,n (Correction) Slag n ~ r d Col~els

I ..'I

iniilecl :tntl tlie proper corrections macle on rill ldnterinls- from the ,nine to tlie refinery, the statistics of milling, snielting nncl refining-efficiency must he n c1eception;'tliey are unnble t'o tel1.u~ the trutll on conservntion. 1n' order to unclerstnnd this it must be rememherecl that percentage- losses in nssn$ing are by far the lo~vest in the higli-gmtle or fin:l.l protlucts of the"r~~etn1lurgic:tl estnl~lishments. For nn. esnni15le, let us take tlie loss

- for silver in tliese rilnterinls a t 8 per cent. n?cl thnt-in the ore as probnbly less than 10 per cellt,.; accordingly, the'mill receiving the ore would

he chnrgecl with olil~r 90 per cent. of the silver which it 11n.s :tct,un,IIy re- ceived. Supl$ose that in its:!~iglie*t: . . lifotlilct i t shoi\'s, by the same :tssny . - -

1 Tlie 1naccui.ncy or t~lie~Commeroial Ass:&~- for SiL\:er.:tntl.of. h1et.allurgical 8tmatist,ics ~.Sil.v.er. Mills,.et..c., Tiyns. S,?;IV, 530, (1S9-1.). . .. . . .

methods, a yield of 95 per cent., the appnrent loss through its 1v11ole process woulcl then be 5 per cent., while t,he true loss would be m:tcle up of the factors 10+5-2, or '13 per cent.

There are m:tny data given in chemical and nlet8allurgic:tl literature on the assay losses of silver and golcl, I,ut Table XI., giving data oa'silver only, taken from actu:tl practicc in our o\vn lnboratory :tncl dcrivecl froill ullifornl metliotls, gives :z wicler range than anything the writcr can now recall.

It clearly shows the slow increase in percentnge loss toward t,lle high- silver end, or tlie rapid increase of thcsc losses toxtrcl the low-silver elit1 of the table. Fig. 3 shows' the same cl:lt,a plotted and the general trencl illustratecl hy 3 curvc. There are no correspoilclillg c1nt:i for gold :tvailal,le, but it lnny be stat,ed tlmt the loss perce~ltnges for that metal, in tlic m:t- terials and by the llletllods under discussion, are far snlnllcr th~zn for silver. A similar relation holds true as regards value losses of tlie two mctnls, whicli is illustratecl in Table 111, the figures l~eing t,akcn fro111 a full mont,ll's run of Aiincoqdn copi~er-bullion. While thcsc values look sn1nll when considerccl for the single.ounce, they arc of commcrcinl importtlnce \vhen the great clunntities proclucecl per year are talrea.

I

Vnluc Ijcr ounce, silvcr = $0.60: rroltl = $20.67

Co~.rccLecl rcction Correctir~n; \!RIUP per I:Iz., Assay. Oa. per Oz. pcr 'ton Per Cent. Ceutv

Ton

- .-

Corrected nssnys shoultl not ollly be mndc for co~nlilercial reasons on high-gmde proclucts, but they sl~ould be univers:illy ndvocatetl for the sake of accuracy itself, for the est:tblishment of correct efficiency recards, ancl true conservation sbatistics.

In ~llalring these :tssny-loss correctiolls for such uniform material as the Anaconda copper or that of other large producers it is perfectly 'per.- lnissible to collect R S S : ~ ~ slags ancl cupels for a whole month's run and to apply the correction fouilcl to the indiviclual results of . the lllollth fol- lowing. The mode of operation is as follows: The slag and cupels 'are crushed in a slnnll jaw-crusher ancl thoroughly mixed. The whole or :tn aliquot part may be taken for the reduction-fusion in G crucibles, each of \vliicll is charged, in -gr:tms, with 200. slag and cupels, 70 borax, 70,

2112 .AMERICAN PROGRESS I N THE ASSAY O F COPPER-BULLION.

bicarbonate of sodiunl and 10 flour. The resulting lead buttons are scori- fied and cupeled; the resulting silver-gold buttons by weighing and parting yield the correctio~ls sought.

In order to obtain full recovery of the silver and gold from slags and cupels it is necessary to recluce practically all the lead from each crucible charge. For this 10 g. of flour with n stdt cover suffice; the salt cover

1 , serves no other purpose than the prevention of colllhustioil of the reducer. Inquiry into the absolute accuracy of the heretofore-described assay

nlethocls naturally suggests itself. We have already seen the slag and clipel losses for silver nncl gold and have note? that corrections are 1n:tcle for them. There are, ho\vever, other loshe.;, such as hy volatilizntion, I,y solution of the silver chloride, and in 1nech:~nicnl ways; their values :%re

4.0

3.5

3 3.0 . 0 .

2 2 . 5 y -

, iij 2.0

5 g 1.5 3

Z ,: 1.0

3.5

50 lor) 150 i?OO 5 0 WJ X5 BOD' 450 5iM: 559 W iOO3 700 750 bf.illigrnlns or OuuGs llcr Tou,Sil\'ar

ScoriEed anal Cupelled . . . . . . . . . . . . . . . . . . . . . . .

FIG. 3.-SILVER LOSSES IN ~CORIFICATION AND CUPELLATION. SILVER CHLORIDE PRECIPITATED FROM SOLUTION OF COPPER .BULLION; . . . . . . . . .

. - . .

of very difficult cletermination by direct ~i~ethocls. These losses are en- tirely or in part offset by the amount of iil~l)uiities which remain with the buttons and are weighed as precious metals. It is n sirnple rnatter to Analyze a sufficient number of silver buttons. Thirty grams of these, each weighing between SO and 100 mg., were,founcl to contain 0.16 per cent. lead nlld 0.15 per cent. bismuth, total 0.31 per cent., or the buttons. to be of a fineness of 996.9. Table XIII. shows n test in which fine silver was ~ubject~ed to exactly the same process ps-the silver in the assay of copper bullion, i. e., the fine silver mas clissolvecl'in a copper solutiop free from silye'r and precipitated as chloride, etc. It +ill be seen that the final- and corrected result sliows a slnall deficit, anlounting to 0.098 oz. per ton, or to 0.12 per cent. of ,the total silver. More estended tests were uilder-

I tnlien with more silver and in cbilpaiison with 'higher grade materials,

anode residues orslimes. Here, too, the fine silver was subjected- to the same t,reat,ment as the slimes, a sulphuric micl combination, assay, and through the furnace process slinles :tnd silver alternated in position, in scorifiers as ~vell as in cupels. One-tenth of an assay ton of slinles was taken; all of the sanle sample. The fineness of the buttons was deter- mined by titmtion by :Volhnrdls method, with potassium sulphocyanate. The results of such a test are given in T:tbles S IV. and YV.

In these t,nbles it will he ol,served th:tt the lnrge silver buttons are of slightly lower finelless t1in.n that ~\rhich was 'given for those of lighter weight. Of chief interest is the fact, that wllen to the finesilver of the assay huttons of the slimes is ndcled the slag and cupel correction and the volatilizntion and kis~ellnneous loss correction, :IS iletermined by the assay treatment pf fine silvy, the results corresponcl very closely to the usual results \vhen the slag :tnd cupel correction is adclecl to the assay .

button of t h e slimes. Repent,ecl tests confinned this m1c1 the collclusion follops, ' that impdrities in assny buttons $lid 'volatilizntion and miscel- laneous .losses bdaace each- other.. I t follows. that .the assay of anode residues for silver by this assay method is correct in every case to mithin about plus or niinus 0.1 per cent. of the.tota1 silver, a11 accui-kcy which could h:trdly be nttniaed by :iny other. chernicnl method. Of course, this degree of accumcy is only obtained with a sufficient number of determinn- tions, averaged to one result, .in our case 10, with 0.1 assay ton each of the nlaterial. . .

The.contract assny l~let~hocla for such materials are still of an prchaic kincl, of the all-fire nature, elnstic . . . beyond reason, in which results differing several per cent. :tre.often 01)tninecl. It is to be hoped th+t concise rhethocls will soon tnlre the place of the old.

For the'western (smeltery) 2nd the eastern (refinery) end of the Anacon- , c1:t Compnny, sampling hn,s been est:tblished on a scientific basis ancl the

lllost Accurate assay methods are employed to deterlnie the values of the copper-bullion shipped from one to the other. Any inaccuracy in snnlpling will offset the accura,cy of 'analysis, or vice versa; an eclual degree of accuracy is rkcluisite for both. The concordance of results obt~ined in monthly averhges a t the .two places is illustrated ill Table YVI.

The data given in this paper were, in the greater part, determined sac1 accun~ulated in the interest of the Anacoadn Copper Mining C.6, in its laboratory a t the Rnritan Copper Works, Perth Amb0yj.N; .J;. In this work the.laborat,ory staff nlust naturally have contributed its share ancl the writer herewith egpecially ncbonrledges the services of I<. W. M c C O ~ ~ S

. . . a ~ l d W. L. R:tup, Jr, . . - : . . - - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

,2414 AME5ICAN PROGRESS I N T H E ASSAY OF COPPER-BULLION.

TABLE.XIII.-EZ~IC/"~)Z.~C?L~ 10 8h0.t~ LOSSCS .il~,Silver AR.&J~,/L~ by the Co.))l- . . bi.untioi Mctl~od.

Silver Rccovercd. Cbrrcctctl Rlilligralus

-

S l . G I

- ' Fine Silver Weighccl Out . . RIilligrnllrs . .

. . . . .-

. . . , .

51.63

~ 3 . 5 1 93.57 83.51 SO. 73 85.0.5

Silver Recovcrcd hlilligw~ns

-

SO. 1-S

Averagc silver weighed out., lng. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .S4.870 Average silvcl. recuvc~~ccl, 11ig. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S:j. 4-13

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diffcrencc. 1.4'28

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Average silver weighed out., mg. S4. S70 Ayeragc silvcr recuvcrecl, corrcctctl, mg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S4.772

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DifFcrcllcc O O'JS . Correctioli for sl:ig nnd cupel losses' = 1.327 riig. = 1.33 mg.

: ,.. TABLE XIv.--F.i l~e S'z'll~e? T~ccllcd by Yztb,~~i~iwic A-icr! Assciy ilfethod. Si l tcr bilralio,c. hy ,S'~tlphocl/rr,rclf~.ct dfelllorl.

. . , ..

'- No. Finc Silver

\Vci yhed Out hlg.

Fine Silver Mg.

Difference Orig. Fiue

autl Butt#~n I'ine . h k . .

IiCNS 1 cc = 4.4907 Ay.

cc:

Assay But tons

My.

370.24 373 35 369 , fiS 370 . O(i 370.72 3(jt i .5fj 367 .7fj 370.5fi ., ." ob1 . 0'2, 3tiS .74

1111- purities

hIg.

1.55 1.30 0.99 1.37 1.58 1.47 '3. T3 1.87 1.93 2.30

. Average. ,373. l3(5 Slng nncl cnpcl cur-

: rection.. . . . . :. . .

. . . . Silver recovered by corrected assay.. . . . . . . . . . . . . . . 373.484 . I

Original fine silver.. . . . . . . . . . . . . . . . . . . < . . . . . . . . . . . 373.136 Differerlce. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O . 34s = 0.0933 per cent

1 .ti48

4.47 per M

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Original fine silver.. 373.136 . . . . . . . . . . . . . . . . . . . . . . . . . . Total silver recovered. 371. S36

. . . . . . . . . . . . . . . . . Volntilization and other losses.. 1.300 . . . . . . . . . . . . . . . . . . . . . . Fineness of assay buttons.. 995.53

'~oire'cted Assays 373.4%

3ti9. 472

1.012

5.315

. . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . .

ARlERICAN PROGRESS I N T H E ASSAY OF' COPPER-BULLION. 2115

TABLE SV.-Silver A s s a y o j Alaode R e s i d u e s b y Sulpl turic Ac id hfe lhod.

I Average. . . . :. . . . . . . . . . 371.112 . . . . 369.495 Corrcttiol~. . . . . . . . . . . . 3.860 . . . 1 3.SW Vol:~tilization, etc.. . . . . . . . . . . . . . . . . . . 1.300

Total. . . . . . . . . . . . 374.973 . . . . . 374. G55

1.G17 4.36 pcr hl.

Difference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.317 = 0.106 per cent. Fineness of assay buttons, 995.64.

TABLE S V I . - A S S ~ ; ~ - R ~ S ~ L ~ ~ S i?z Mon.thl:y Averages, East and W e s t , ~ b t a i n e ' d o n tile s a ~ r ~ e Copper-B.z~ZZ1:07z.

\

(Aljor~t 125 samples :issaycd per month).

~ I V N T R

-

1 2 3 4 5 6

- . . . . . Avcmgr. - - -- --

West,over . . : . Eastover . . . . .

WEST EAST --

--

--

. . . . . . . . . .

Silver, Oz. per Tod

S7.2453 88. 7S9S 91.1501

. 91.5903 S7.0271 S9.1750

S9.5006

0.0614 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Golrl. Oz. pcr 'ran

0.4692 0.1i057 0.4817 0.43s" 0.4S77 0.5143

-- 0.4966

. . . . . . . . . .