The Phosphate Situation

Size: px
Start display at page:

Download "The Phosphate Situation"

Transcription

1 .-l typiccrl pl~osphrrte operation ir~ Florirln slco~vir~g strippirag nf overbrrrrlerr nrarl hvdrcrrr1icl;ing of phos~~hrrtc? ntntris. T HE farmer pays tlie pl~osl~liatc. The Phosphate Situation By Paul M. Tyler and.)eerl serit.nilsly claliiaged, ancl ; large miner! Phosphorus is used ill Bertrand L. Johnson ndditio~lal acreage has s~rfferecl defifireworks; goes to ~attle in niili- nite loss of soil fertility. Nott.)nly art: Respectively Chief Erqineer and Associate lary smoke screens, incelldiary sl~ells. Mineral Economist, Nonmetal Economics ~~llosphorus and other \~alual,lr~ cleand tracer br~llets; and, ~ \~srmin- Division, U. S. Bureau of Mines: ment~ being mined out. of our soil by destroying pastes, does its part ill the Members, A..M.E. Earll~ crops but the stlil itself is hei~lg war against insects. A le~no~i phos- lost from our farms. phate can be had for n licke el at most iosphokus is n vital elenlent On Oct. 7, 1936, a joi~lt c:o~~~~uittrt:.. soda fountaills, ancl tens of thousands P ill atiiriial, ~lu~liati, a1ic1 l)la~it oi the A5sociatiotl of Land Grnr~~ Ctdof tons of pliospllate rock are mined ;11111ua1ly for use in tlie food industries, c:liiefly for making 1nonac:clciun1 phos- ~intrition. Phosl)l~orus. ~litrugetl. ant1 potassiuni are tile three rlenlet~ls that l~lants need ~nc~st, collsequer~tly they leges and Ulli\rersilies nllcl 01 tile Dc.- p;~rt~nent of Agric11lt111.e c1el)lored t11,: fact that re export 1,000,000 tolls ~iliate baking ~)o\vder. Sodiulil ~lios- llave to be replaced in ~ard-\\rorketl o!' phosphate rock annually (all tttlll~l~ate cleaning: \\lashing, atid scouring soils. Heavy cropping alreacl\r has dr- tages in this article are espreaeetl ill compounds collsullle snbsta~~tial qrron- pleted our s,,ils of yht~s~hc~rirs. U11les, tjr~g tons of s. ~rnlesa trther\visv tities; the irc)n and steel ilidustrirs we replace ii. the natitm is threatened ~lt-~tt-cl'~ ancl us^ art atlditicvtlal 1:1r~1%!iry a few thousant1 tons yearly to not only with decreasecl yielcls of crops ciucl~itit):, averagitlg al~out 100,OCO tollmake ferrophospl~or~ and to balance per acre and ~iglier prices fol. Euorls i~tl~iually, for ~lonfertilizer aucl 11,111- foundry-iron fi~rnace cl~nrges; and and fibers but also with tragic dam- Eilod pxposes. The Tennessee Valley even nonferrous ~netallurgists use a age to the. health oe animals i~litl even Authority annual report fur 1937 little.for phosphor bronze and otller clloys. Phospl~oric acicl, its salts, and of our 11u1nan pt:)pulatio~l. ~i~i~itecl a still nore nlarlrlil~g picture. nrged conservation even Lo the prohidiverse other derivatives of this yersa- batting soil erusion. r\ltllougli our :itiuli of exportsl and hla~>iecl our tile element have corl~~tless applica- ' lions: and industrial outlets are in- (:ceasing rapidly. especially in the United States. Nevertheless, in this country nearly 90 per cent and in tlic \\dlole worltl fully 95 per cent.of the phosphate rock consumed is nl.)sorhed ultimately it1 agriculture. country has rougldy 3 >illioti acres of far111 land, of wltich 600,000,000 acres are classed as tillable, onls about 350,000,OOCJ acres actually are under plow. The U. S. Depar~nient of Agriculture has estin~oted that 50,- 000,000 acres have 111:en co~u pletely ruined, another 50, acre?; lia\.a ~liglit on rlioclern civilization. 111 )ri~liitive or village life the soil's vital elements are. borro\yed 11y plants and ciriilt~als only to be returned again it1 the age-long cycle. as dust returns to dust in the Biblical formula. Now, SO rliarly people live in cities tliat yl~osphates in our foodstuffs a1.e "lost dowll SEPTEMBER,

2 ' ', sewers, tltrown (111 dutnps, or decently buried in cemeteries." n June 1938 a Congressional investigation of the phosphate resources and industry in the United States was '~egun by a joint cumn~ittee of the House ancl Senate, with Senator Pope, o daho, as chairman. Al~pointlnent of ihis committee followed a Presidential message affirming estimates of 7.2 billion tons of kno\vn domestic reserves of phosphate rock out of n world total of around 17.2 hillions hut calling attention to the fort that only 8.8 per cent of the clonlestic supplies were in Florida and Tennessee where over 95 per cent of the current output is mined. At prelimi- 11ar)~ hearings the Secretary of Agri- (:ulture, Henry A. Wallace, estim~lted lhat 2,(300,000 tons of elemental phos- ~~horus is lost annually in crops harvested and at least as much more througll soil erosion. Phosphorus, he said, promotes ioot growth, and as ~merican farmers become grass conscious nore and 111ore phosphates will he needed to develop pastures ancl conserve soil. Harcourt Morman, new? TVA chairman, predicted that much farm land in our Eastern States will le forced out of production \iiihin n few years unless inore phosphates sre added,, and insisted that the present rate of use affords no proper nleasure of how long our 1,hospllate reserves will last. ;;luu~inn conlent ordina'rily should be under 3 per cent. n Florida the depc~sits are unconsolidated ; the phosphate rock is intermingled with sand and clay and ranges in size from colloidal to large masses, although in the land-pebl~le field, which contributes 80 per cent of our national output, the particles are mostly smaller than in. The material is mined hydraulically, clay balls being further disintegrated in log \vashers and the phosphate recovered by screening and classifying,.snpplementecl at several plants by froth flotation or agglonlerate tabling of the finer' sizes. Wet rock fro111 ~vashers is railed to central drying l~lants, which are permanent, whereas the washing plants have to be moved every few years SO as always to be reasonably near their respective wining operations. n the Western States phospate rock occurs in highly disturbed bedded de- ~josits in "hard rock". ancl requires virtually no beneficiation. fertilizer works where it inay he combined \\.it11 nitrogen- and potash-bearing materials. Esperts agree oddly enough that the world's known reserves of 1,110s- ])hate rock aggregate at least 17.2 l~illion tons, including 7.2 billions in our own country, 5.9 billions in Eu- t~op0hiefly the U. S. S. R.), and 3.7 billions in North Africa. Various islands and Asia, although long suplying su)stantial outputs, are credited with a total of less than 200,000,- 000 tons, which is consideral~ly less than reserves in Mesico where virtually none has been mined. t is agreed: moreover, that these estimates are conservative - especially those for Asia, Australia, and South America: where little phosphate prosl)ecting has been dtsne. A breakdown of domestic reserves shows 550,000,000 tons in Florida, 103,000,000 tons in 'Tennes-- see, and 10,000,000 tons in South Carolina-a total of only about 665,- 000,000 tons in the Si~utheastern States where the bulk of our fertilizers is PRESENT AVERAGE) 1" Occurrence and Estimated Reserves HOSPHATE rock is an anlor- P o material consistiag of tric.:~lcium phosphate with various ;rmounts uc water, calcium carl~onate (usually less than 10 per cent'), flu- Forld protlrrcrior~ rrrcd co~~srrrrrptiorr of!~lrosphat rock by corr~inents, before nnd orine (usually 3 to 4 per cent). and nfter the Porld War. organic matter. t is di~tin~uishec] fl.oln apatite, Cal,,~,,(po4) ;, a crys- TO nlake phosphate available as cot~sumed. \lirtually all the r ~der tnlline mineral occurring in igneous plant food, raw rock is generally acid- is ill the West, chiefly in daho, which rocks. Sonle Phosll]late rcck tlel,orits ulated with measured quantities of is creditecl with almost 6,000,000,000 are or marine origin, fornling clistinct ""pll~tric acid, allout one ton of acid tons.,eds, often of high purity, l\ricle jeillg required to treat one ton of The United States, with 40 per cell[. areas. Others are sedinlentary del,oeits rodk. Triple superpllospllate, which of the wc,rld's reseryes and only 15 that are residual 01. are formed costs much more per,unit to make, is per cent of its total acreage under disintegration' and redistril~~lti~ll of nlallufactured l:ly acidulating with cultivatioll, is relatively well o-8. We ~~hoal~llate rock or phosphatic lime- iiquid pllosl~horic acid which may be could supply the present-day dematla st(~)ne fortnations. Phosphates result- ~reviously produced from phosphate throughout the world for 600 to 700 illg from pl~os~hatization of coral rock by several methocls-using sul- years without help from other coutllimestones by rail1 water leaching phuric acid, electric furnaces, or blast tries-at a high price. Colnparing ~hrough bird guano are mined esten- furnaces. Other procezses have been our reserves with dornestic consulnpsively on tropical islands. Colnmercial devised hut ordinary superphosphate tion, which seems to be stal~ilizing le- ~.d~osphate rock contains 60 to 80 per which contains roughly 16 per cent low 3,000,000 tons annually: we seeill cent (usually 68 to 77 per cent) P-0; is the hain outlet for phosphate to have enough phosphates to last 20 B.P.L., meaning bone phosphate of rock and it in turn may he the raw centuries, and if we draw upon Florlime, Ca:r(P04)2. ron oxide atla material for mising plants or general ida alone. the supply might last 200 3, MNNG AND METALLURGY

3 \:ears ul~less our cotisumptiu~l starts increasing again. Moreover, it is axiomatic in mineral econon~ics that new di~coveries tend to increase kno\vtl ~eserves a11a that hetter teclinology trnables us not only to use lower-gradr ore l~ut also to he less wastefrll crf our i.esonrces and thus get more nrct of 111e1n. Within a decacle tlie succ:essful ad01)tioti of frnth flotation, whicl~ rtouhled recoveries of )liost~liate a1 certain plants, has doubled the reserves in large areas were calculatiolls iad heen ~ased upcln wastef~tl practices forlnerly in vogue [lie successful operatioll of a pio~~eel. pla~lt' that produced ancl shipl,ecl elrluental ~hosphorus on a large coltl- ~ner~*ial scale forecast another extell-.;ion of our estimates to include its.c:serves tlie lower-gracle rock that this l~rocess can use as raw material. World Production and Consurnptio~ OMMERCAL production of phos- C phate rock hegan in England in soon after Lawes fot11id tl~at col~rolites could replace hones in superphosphate manufacture. Scat- [(:red supplies later began to coule rtorn other European cciuntries, the West ndies, andl in South Carolina. Not until sonle years after the tliscovery of the several Florida fields in 1G87 to 1890 did world output c~sceed 2,000,000 tons a year. hnt with ~\lgeriaii and Tunisia11 deposits like-!rise beginniug to l~rodic:e, \c~orld out- 1"tL had gro\\lll )y the turn of the cent, aid Austrcilia alnlost 10 per (:tblrtury to 3.000,000 tc.,ns, of ~vliicl~ cent; meaiiwliile the relative imporlhe United States sul)pliecl ap1)rosi- tance of Europea~i demand has clililillrltal.ely one-half. the reltlair~der corni~~g ished slightly atid that of our c-j\vt~ c*hie.fly from France. Nnrtll Africa. ~.:onntry sul~stantially. ;~tltl Eelginm in ul>out the order nal~ied. The ultiniate colisnml)tion OF 11110s- Shortly jefore the World War pro- C~V ion had inc.reased to about G.(!nO tolls: of this the United States '111,nished a trifle less 111an ialf, North 11Eric*;i slightly over one-third, and lrlrope and Oceania each n little over tr~le-twelfth. Tibclay. phosphate rock is lllitted in about GO countries scatterecl ~wcr the glolw. ant1 current supplies tave increased to more than 12,000,- 000 tons a year, the United States aricl Frehch colonies each producing about or~e-third. the U. S. 5. R. ahout one- 'ourth. and tlie British Enlpire inost 01 tlie remainder. chiefly Eroln mantluted islands in the Pacific:. Pr(nduction in Africa, including French Nortli Africa and Egypt. has far outstripped tllat in the Uuited States. and esports fro111 the United Sta'tes: although still ;~rou~~d a millioll tons a year, are no SEPTEMBER longer cis i~r~portant in world tlxde na [hey once were. Before the Worlcl War Europc cons~iinecl over 66 per cent of the total svai1al)le phospllate rock. A~ncrica 2: per cent. Asia less tia11-1. per cent. a~ld Australia less than 2 per c-etll. Alrica, furn~erly an insignificant co~isnmer, now ljuys ahout 2 per rent uf llie prewnt-day world sl~pl,ly, Asia (lnaitily Japan) inore that1 10 lber ~:oulitries of western Europe, but the aggregate European consuil~ption has 1.ontil111ed to increase because of much larger clemands from Scandinavian, ('itstern European, and tlie Mediterratlean countries. Less basic slag is ;~vailal)le in Europe for agricultural l,sr o\\~ing to tlie trend in- l~asic steel- ~nakiiig practice away Eroln the Besse- 111er and toward the open-hearth process. 111 effect. therefore, the distribu- ~ioll of apl~arent consumption of raw rock llas represeilted the actual or rtltin~ate ctonsumptiot~ of phosphates )y corltinents inore closely in recent years than it ever did before. )l~atrs. however. has not shilletl ( The Domestic Situation Analyzed cluile the same estrllt as has 1ha1 of consumption of phos- x\v phosphate rock. Marked clialiges W:Z?rock 11,s increased faster lavr occurred ill the mo~~e~tienl: of ~han consumption ill the Uniteel States srij>erl>l~o.~~l~atcx wliicli. being roughly [\\rice cis ~ulky as tlic mine prndnc>t. aiid shows evidence of continuing to grow. Domestic con=~~rnl)tion. the PC~.; t1.1 l>r 11ia;le loc,ally \\~llcre\~el. otlier iancl. after rising rapidly and c*o~~s~i~m~)tio~i l~rnmises to grow sulii- fairly steadily fro~n 100,000 tons in viently to justify huilcling the recluisiics 1 GZ0 to a maxi~nuni of over 3,000,000 ;1cidulnting l~lunt to cc~n\~ert 111e rnc.1, tons in 1920, lias fluctl~atecl violently into fornis more availal>le for l~lc~lr (luring tlie last two decades without food. n consequence some falling off has occurred ill overseas shipments of tluplicating tlie 1920 record. Histori- (.ally, it shows tlie typical S-shaped.;uper~lios~~hates from wester11 E~lropc,~ curve of a mature industry in with a correlative cli\rersion of shi1)- ments of raw rock to new consulnillg \\~l~icli consumptive demand still incieasrs but at a declining rate. Unplants. Consumption of superphos- less a new impulse comes from some bhate and basic slag. ~vliich competes \\lit11 the fonner for fertilizer use. lias source, early stabilization is indicated at a figure close to a calculated ceiling i.rniairled stationary or e1~e11 dimin- OE not quite 3,000,000 tons yearly. ished in rertai~l highly indnstl.ialized Apparently confirming this. domestic

4 . L ~~lattt food for his money than l l ever ~ ~ tlitl ~efore, 1)rlt he neecls n still xttrr ~argain. -- Note err Logi.\tic Ctrrr-es-Tl~r :Oittjr'3 plea vf ignarrance c~lncerning "logistic" curves!belowl ~rought the following explanatil~n from Mr. Jolins~~n: The c~gistic is one of several s41-calleil S-sliapecl prowtl~ c~irves. t ha tlrr grr~rrcll fi~rnit~la li Y =- 1 + en+h in \\,~: y the gruwing nuss s time r t~as? ot' natural ~,pal.ithms c = nplwr limit of the curve. t lras svveral i~riportant prupertiea: t l ) Finite ullger ancl lo\r7er limits. i*.~ \vhicti the curve is trsymgtotic. (2) -4 point of inflectiot~ mid\vay :~et\vee!l. tlie ullper an11 lower limits.. l)i.s~rihrrtiorr of jertilizer rorrsrtntptiorr irl tlre Urtited States irt 1937 nrrrl c1rcrrrye.s (3) Concave ul~\va~'d to left of ~~oi~it of : 928-'30. inflection a~rfl concave ilo\vtiv:nrd to right of it. (4) No.horizvntal slolx zscelbt :kt s = +- K, collslllnl,ti,~ltl las appruac]lrcl or evt.ll,.ellt ;lccording t, lllost arlt]lurities. (5) Curve is sstilmrtrical al~out the 1)oillt inflection. l~uslled tli~o~~gli this ceili~ig 011 three Such tonnage gain as may have oc- Thr cl~rvtl i + fitteil thri,t~glr llrrrr poi~lti.occasions otlly to drop sllarply durillg curred in recent years has ],eel1 due it1 rc[~~all!. tlistant-in tilne. l~err a1141,the following year. The 1937 prak large part to ])rogl-essi\'e red~lctiull ill ~, t p,,ints l ~ ~ 011 ~ tllr cur\.? \vrrta (ewas llot so lligj1 as the nlasimlllll, fertilizer prices co1npart.d with the trt'rl1irlrd fr~111 tlir f~,r11111la fi~r the curve. allcl rel,vrts forecast a ["'ices of other co~ii~iiodities the farmer Tlrr value- uf tile constants ill the ft~rtnola lluyor sells. Year Lifter year cullles were tleterminrd ~ ~ rather ct)~~rl)licateil mclitie of aruund 20 per cent for prol,lelll,,f di sll, ~)sitlg Of sllrpllls falr~rllllac givrll 1)y Raymontl Pearl. Jibhll.; naslnuch as the ratio of phosphate FTl~pliins. urrhii ha. written rather r~tvniivrl~,{(, otller fertilizer ingredierlls nlrrady "'"" products, we lialr al~ib~~t this type of curve. i, ]ligller in tlnited states tllau il these sllrpluses it is clifticult see llil\\' 111 tile tliagr:<m. t11~ b~ll,,uin: fill-11111la.; is abroacl: ~)hosphate deiiia~id is 1101 l'ar~iiers as a whole can make nore were 115rt: 3i71,likely sc,ull lo nutrull general fertilizel- ltlo"et 'Y 'lsing ''lore P~OS~,R~~ ruck: s : sales. Since ttle latter also llave 11~ougll illdividual far~uers may du su. + "4 l~~l-o.ll~o~x~ lagged ]le]lilld pc~lpulatii)ll grul+7111 ant(!:\'ic1e"tl~ the ""'Y sell more Ferti1izt.l.s: y, = TO40 ;ill 1932 tlley fell to the lowest 'crtilizer is tn rec1uc.e the 11ril.l- fur- l + +.l.:'#m?'.u,,",,,,, j since Altlio~~gli they cli~~il~ed to! a new record in 1937, this ~.ecorcl ol' 8 1 8,204,.000 tons (fertilizer to~lrlage here 1. 1: espressed in ). tolls') tupl,erl ; tht: l~revious record of 6,163,00() ttrlls 7,!; only t! slttall margin and no record 1 itt all ~roulcl havr been niacle last?;ear / Jtttd il ntnl reell for the distrihutiiir~ 6 1 OF sul~erj)l~ospliates ly tlie Tennessee rn \'alley Authority; com~nercial sales 2 5 nlont. were less ill 193'7 than in p 'rhe gro~vtli curve i~idicates early stah- _o ilizalion of fertilizer sales in tlie United.; Sl:~teh at. an average of slightly less rn c ~han 8,000,000 torts a year. 0 That fertilizers illcrease crop yields 3 H O 11ic)st lalids is known al~llost uni-. versall~-. ancl 3000 to 4000 corlnty :tgents of the Department of Agricul- 2 : 1tr1.e and double this nu~iil~er of vocat iolial agricultural teachers co~itil~ually, spread the gospel of nure and better plant nutritiori to every farmer ill tlie country. Few products are so well 0 :tdvertised. and yet sales volullle seetiis to be li~ilitecl to a fairly definite perc-erttage of farm income. about 2 per (:onslrrrtptiorl trends of phosphate rock ar~d fertilizers rrr the United Store (See note above.) 392 MNNG AND METALLURGY

5 THE Miner Gets ~ittle of Farmer's Dollar t,1 P-O;, f aciduatillg plant. At cut clu1v11 on tra~isport and ~ l ~ l,llosp~late colltellt of fertilizer brtilizer inixing works it costs 5k. n cllarges after the rock leave< the drier- 15 leck(,lled in terllls of so-called unit. n n 4-34 fertilizer the phos-,ltosl>l~orir acid or P-0;. The 1.- ldiate thus costs $4.32 at tlie fertilize^ A On rtlerals as elnployed in desrri1,- factory: all the active ingredients, ac- HARLES E. MUNROE. wliell chief iltg a typical lnised fertilizer, indicate c.orditig to a recent North Carolilia C cheniist of the euplo%ives division of that it contains the equivalent of 4 <urve), by D. S. Coltrane, cost onlj u. S. Bureau of Mines. gave exten* 1)t-r ('flit nitrogen. 8 per cent phos- -ive cc,nsideratinn to the bibliography of $25.17.,llt it costs $11.60 lllole ill tile literature of explosives. Hi* nlaliu- 1'11olir acid P20:,). and 4 ler cent l,,ising and distrihntillg chalges t,, script bil)liograpl~y. comprising 794 1)otasll ( KO. The sunl uf these fig- 1,,.ing it to near-by farmers. pagrs. cover. practically all the inipor- lles' l6 ]er cent this exallll)le~ is The i11,plication of these figures is tant journals priclr to when Chrv,ii- "ftel' 'he l'larlt co11- (.leare We do not.hi1> lor-grade cop- ru rlbstrons began. The titles a d lent. is ]lot strictly true hecause,er Uws or collcentrates froll 2ut1~rs are given chmnologically by the remaining 84 per cent is far froill westen, lnines; we melt tllelll fairly iounials. Dr. Munr~e retired from the lring inert; lin~e. sulphur. and a few active +ervice of the Bureau before 115 olher plant food elements are also close to the mines. Already a company c011ld ptovide the work with author and ~uesent and ob~~iously a carrier is ih ~naking ele~nental phosphnrus in +llbiect indices. T~, reiearcll work- ~teeded. No farmer could sprinkle Tennessee and shipping it long dis-..<. patent attorneys. and all 4)tit.r~ who 1)otassium or caustic lye on crops, nor tances in tank cars. Whether this i- nlay le interrstetl in the historical dcvel- (*~uld he use eletnental ~~hos1~horus or the technique for cheaper ~)hosphates c~pment of the science ant1 trchnolopy of,lie inert,,itlogen that already is ill for the farnier remains to be seen, but the evllj*ive.; illdllstr~. this bibliogra~ll~ obvjous~y our Westerll deposits canllot tilay be llelpfiil. To mahe copies availlhc air itself. Nevertheless, the fact ser\,e E~~~~~~~ lllall,ets ecollolllically ~hle to any interested. John W. Finch. c~~naitis that phospliorus in particdar with so-called trel,le sul,erl)hosdirector of the Bureau, has arranged with i+ ~nuch diluted by the tinle it gets to tlir Anlericati Documentation n~titute. llle farnler tllerefore, has to ldiate which, although it contains three care Science Service C~lnctitrttion 'teight and handling charges 011 a times as much P,Oi as the ordinary Avr,. N. W., Wasllingtoll. D. C.. pre- )luge quantity of extraneous tnaterial. kind. carries 21 pet,,are thebe on ~nicrofiltn. Copies can be ;\ en phosphate rock itself, t]loug]l cent of the esselltial constituetlt. l)llos- -,cured on order from the A.D.. if speci- ~~t,~~i~~ll! colltaining. say, 70 per cent 1)110r~~. Even Eastern nliners are not fied as Document NO nlentioning 13. p. L., carries olly 14 likely to pet a larger share of the the name of the artthnr and the subject c.ent elemental l,hosphorus. Made intc, fnr~iler'sddollar unless they contrive to nlattrr. ordinary superphosphate. it is diluted furthrr, 16 per cent P20n being equivalent to only 7 per cent of the vital ele~nent. and by the time it is nladr into mixed fertilizer the actual,l~os- ~~horus content of the product may he rlown to only 3 per cent. Phosphate rock technology has im- ]>roved greatly in recent years. Not- \vithstanding a 60 per cent increase in output from 1909 to 1929, census figures show 60 per cent fewer workers r~nployed. During this period the average value of the domestic output clrol~l~ed from $4.62 to per ton; it? 1937 it was reflecting further economies. n Tentlessee, the last stronghold of hand mining. mecliani~ xation is following the organization of larger productive units and causing a reduction in workers for a given tonnage. No longer can it be said that ~)hosphate mining in this country is inefficient. Any industry these days hat can strip. mine, wash. dry. and sell a concentrated product at $3 or less a ton is doing a good job. Further ilnprovements may reduce costs still more, but this cannot mean inuch to the farmer. The nliner sells P-O;, for 9c. a unit hut the average farnler pays 9Oc.. almost ten tiiiles as much. Ordi- lnry superphosphate costs around $3 : ton (2000 b.), roughly 50c. a unit SEPTEMBER, 1938 "LSTEN, RUNNNG WOLF, WHEN ~JANTUM SK~P YOU RNGUM BELL. NO MORE SMOKE SGNALS, SAVVY 7"