Mnr. 20, 1937 C f f EM IST I< Y AX D J XDUSTR Y 213

CASEIN MATERIALS AS APPLIED TO PLASTICS' By ROBERT DODD

(Paper read before the Plastics Group o f the Society on February 16, 1937)

Casein products 1i:ivc liccn knowi iitiil usc!d :IS n food by huiniinity since t,hc worltl bcgnnl nnil rcfcrciiccs to the subject n1)ountl i n Egyptian, Greck. i l l i d Roninti history. Tlic Pcrsinns cnllcd t,heir chccsc " Schcr Kist," which incniit. Itardcncd niilk, ant1 JXotlonis tells US tltiit cheese \vns ir staple food of the pcoplc iibout, 60 n.c. Tlic first reference I can find to the nse of casein iiiclitstriiilly :is distinct from its inilust,riiil use as n food, is ii i n ppytiis of iiticicnt Egypt in t.hc 18eh Dynasty \vIicn inention is ninrlc of its iisc :is :I nicclititn for fisirig pigiiicnts.

Cottditht of cciseiu itr nii~/c.-D'rotn :I liistoricitl stiuid- point tlircc gcnernl views hiivc .I)ceii proniiilgiit cd with regnrd to tlic condition of criscin i n inilk, tlint is in rclntion to inorgnnic constituents.

(1) Tltnt. c:iscin is coinlhccl with ciilciiini to form it salt, cnlciuni ciiscinatc.

(2) Tliiit ciiscin is chciniwlly conibiticd directly \vitli cnlciuin pliospltat c.

(3) That ciiscin is i i tloul)le siilt coiisist.ing of ciilciitni cnscinni.c coinhincd witJi cnlciurii phosphntc.

1i:irnmcrstcin sho\vcd t.liiit, ciiscin csists ii i tiiilk :IS n colloitlnl siispcnsion, not i n the free state hiit iii coin- biitritioii wit,li ciilciuin. 1.10 foiiiid that, this conipoiind, which 11c crtllccl cnlciiun ciiscinogcii:itc, eiivclol)cd tlic Init ter fi1.t globiilcs i i n d csliibitcd ccrt ii i i i pecitliiirit~ics which dist.in~uishcd it from other ciilci1ilii SiiltS of crisein. For iiistiincc, it, wis iiisoltilh in writer, existed iii a state of colloidnl suspension; iind togctlier with culciuiii pliospliirtc cniiilsificd the butter fiit, wlicrciis tlic other crilciuni siilts of cnsein \vc~'c soluble iti ~ i i t c r , foriiicd triic solut,ions, rind did not, llii\~c iiny c~niileifyiug

'I'ltttsc fitcts led liini to proposc tlic niii i ic ol' citlciuni ciiseitiogctiirtc for tlic casein coinplcs iis i t csists in milk iuid ciisciii for tlic ~)rccipitntctl . or coiigitlat,ed protluct. Cnsciii t h n itiriy he said to be ii liinc snlt in coinliinetion wit,Ii ailciuni pliospliiitc iind 1)rObitbly is 1wsL tlcscribed ns 11 pI1osp110 l~rotciii.

C'licttiistr,y of cnseirr.--Tlic cltciiiistry of ciisciii is w r y coitiplicrited. Its coiiiplcs titid colloitlnl tiiitiirc rcnrlcr its ppimtt,ion nnd piirificiitioii \'cry cliflicidt. Its solutions ctriitiot be ttiitlily filtcred, iiiid in itdrlition certrtiii g ro i tp urc rentlily splib oB from t Itc p:ircnt molcculc I)y the reitgents i i~et l in ])rceil)itrition nntl ptirificiit ion. In its olenicntnry coinposit ion it consists of t h c six elctticnts, citrlJon, hytlrogco, iiitrogcii, O S Y ~ C I I , sitlpliiir niid pliospltorus in the followi~~g I)roport-ioiis :

CtrdJOll . . . . . . . . .... 59.13 1lgtlrogc.n . . . . . . . . . . . . $ S O ( ; Sitrojpii . . . . . . . . . . 15.78

osygcll . . . . . . . . . . . . 22 *.II, Sutptiiir . . . . . . . . . . . . O - i i

o ~ e c ~ t s oll rrlt,.

~ ' ~ l O H ~ h O ~ l l t 3 . . . . . . . . . . . . 0*8 ( !

Its ItioIcctiIiir wiglit \vns stated to ribout 1135, but froin tlic inference t h t one :iton1 eiicli of sulphur niid

certain iiiniiio-iicids inust bc prcsciit, tlic miuimiini niolccit liir tvciglit, must. be roughly in the ncighbourhootl of 4300. 011 tlic other hand, Cohti, Rcndry, nnd Prciit.iss Iiiive suggested t,lint the iiiolccular wcight is n t lcnst 12,SOO, Init inorc probably 15 titncs this \ ~ I I I ~ ,

Still iiiore reccnt,ly C:qeiiter ltns slion.~i hy ult,ni- cciitrifiipl nicthods t,lint the N.l\'. is I)ctwecn 75,000 :itid 100,OOO.

1)liosl)lioriis iitid iit least olic niolcculnr equivalent, of

Il:lmcly 192,000. C 9490, R 13,425, X 2160, 0 2640, S ~ 1 5 ~ 2' 45.

His nniilysis lins slio\v~i : I'cr ccnt.

S . . . . . . . . . . . . . . . . 0.785 1' . . . . . . . . . . . . . . . . 0.8Bli Cystiiic . . . . . . . . . . . . . . . . 0.48s I 13 ptoplllulc . . . . . . . . . . . . I . e x

3.550 '1'yrosinc . . . . . . . . . . . . Iiistittinc . . . . . . . . . . . . . I TO

Consistent, with t,licse figurcs niid t,lic ;il)ove rmgc the 1I.W. \vollltl IIC 9s,ooo.

Cu.wi~t twlecde.-Tliis cuscin inolcculc niiiy be siiitl to be n coiiiples system of conjugiitctl iiiiiino-acids. 'l'licso i i 1 n i n o - i i d S :ire tlicinselvcs rclittivcly siniplc substniiccs i i n d ~ l i c st,ructurc of most. of t.licin is known. T\vo or inore of thcm ciin unite to form larger uggrcgittcs, wliich CIIII in turn unitc to forin still Iiirgcr OIICS. This building 111) continues until t lie ciisein molcculc is foruicd.

ciirbon rcsidiic, tire clinractcrieeil l ~ y tlicir iiniphoteric prol)crties, tlicy can iict, ns it I):ISC by virtitc of t,hcir iilniIto group, iiiitl ns t in acid Ly virtue of tlic C d J O X y l group. 'l'lic iiriiino group of oiie iicitl citn ittiite with tlic citrbosyl group of nnotlicr ttcid with tlic oliininiitioti of IL ~tiolcci~lc of tvtitcr to form 11 liirger coniples, t.lius

I T . .

I , I he iiniiiio-ids I\'I-E,*lE~COON, wlicrc It is t>ltc ltydro-

Nir2.ii.coo1-r + mr,.it.cooiI = N l i 2 ~ i ~ ~ C O ~ l \ l i 1 1 ~ C 0 O ~ I + H,O.

Tlic rcsiiltiiig siil)stitiicc ciin then enter into conibiu:i- t ion with iiiiot,licr ciinino-ncitl or witA ii Iiirgcr cotnplrs, atid so these iiniino-iicids iirc t.bc building stoues of ivliicli the ciiscin molecule is built. up.

They ciiti bo clnssifieil into the following groups : (1) Alipltii tic ~iiono nliiitio-ltlollociirbosylic acids. (2) Alipliiitic iiioiio ittiiiiio-tlicarbos;).lic rtcids. (3) Aliphtit,ic tliiiiiiiito-iiiotiocar~osylic iiciiis. (4) Sulp1111r cuntiiiiiiiig tiniiiio-ricitls, ,(6) Aromntic iunino-acids. (6) Ikt erocyclic tiniitio-ticitls, r i LIto first, titniiio-ncid tliscovcrutl w s 1circ.iiiu (Protist,

1818). Liubig isolnt cd II cryst~iillinc conipouitd ltfter liyclrolizing citscin with nlknli iititl this \V:IS lntcr sop;irntcd by llopp r i d I-lctiterberger its t#yrosiitc. Soritio glutnittic

iicid, nspnrtic :icid, ciiiiic next, niid tlicit coiiiplatctl t,hc list of amino acids wIiicIi Iii id becii isoliit cd froiii prot ciiis u p till 1892. The nict.hotls SO fitr follo\vctl Iiiitl h e l l iiloiig t lie coiivciit ioiiiil orgniiic iiictliods, oxidnt ion, rctlrictioii, dcstructive dist,illiitioiit Iiiilogcii:~tioii, iiiid SO

forth, h i t i t wiis not, ii i i t i l Eiiiil Pisclicr iipplictl tlic iiietliod of liydrolysis i i i the scpnrntioii of tlicse con- stituciit, ;iniiiio-:icitIs tlitit. t,lic rcnl iiatrire of the p o t eiii coiiiliositioii bcgiiii to bc reiiliccti.

Soiiie iiiiprovciiiciits on Fisclicr's iiictliotl Iiiivc siiicc beeii introduced liy Diikiii mid Foriiinii, :tiid much iiiforinnt ioii on tlic iiiiiouiit of t.Iic mrious iiiiiiiio-ncitls i i i cnsciii lins thus I m i i :ilt'ordctl. Tlic tot ii1 riiiiiiio-iicids iictiiiilly :iccoiiiitcd for iii thc nii:rlysis of cnsciii niiiouiits to 97':". :\ii iipprcciiiblc frnctioii tlicrcforc is still uiiiiccoiiiitctl for, siiicc thorcticnl rcco\.cry shoultl bc 1)ctireeii 110% iiiitl 120%. Thc :iiiiino-iicids arc

iiiiiius the water of' Iiytlrolysis ns they occiir i i i coiiiliiiiii- tioii.

He)i/re/ ctiuei)i.-So iiiiicli tlieii for the iinturc of criseiii. \Ye now coiiic to t lie iiiniiufiicturc! of reiiiict ciiseiii which- is the ciisciii usctl iii tlie productioii of our pliistic iiiiitcriiil. liciiiiiii, t IN: eiizyiiie of rciinct, iicts oii tlic ciilciuiii c:isciiiogcii:ittt of inilk C : I I I S ~ I I ~ tlic scpiirittioii of it jelly-like ciird, \vliicli is thc ~v~ll-kiiowii ch~cso curd or juiikrt, niitl ii clciir grcciiisli liqiiid or wliey. 'l'hc rciictioli is very rleliciite, siiicc rciiiict cuii clot 4 iiiillioii tiiiics its \vcigJit of cnsciii. Pciigcr sliows t l i n t rciiiict is cupiiblc of coiigiiliit iiig iiiorc tlinii 2 inillioii t iiiics its \veiglit of milk iii 10 iniiiutcs at, 40" C.

Tlic hest teiii~icr;itiirc rniige of rciiiict. rictioii is 3tio C. to 45OC. -11'C. is tlic licst tciiipcriiturc iiiicl gives tlic firiiicst curd. Oii encli side of tlie rniigc soft. curds riiid

iiicoiiiplctc coiigiiliit ioii occiir. Tlic iiiorc dilute t lie rciiliet , the loiiper is the t iiiic iiccessitry for tlic foriiiittioii of thc clot. 'J 'h prccipitittc foriiietl by tlie nctioii of rciiiiiii oii cnsciii solutions is ciillctl piirricnsciii. It possessc~s i i i i eleiiieiitiiry coiiiposit ioii itlciit icnl wit,li t hiit, of c'iisciii: iiiid its orpiiiic clicniistry iii gciicntl is also itleiiticiil, Iiut I\'icliolas cliiiiiis tliiit cnsciii i i i i t l Iiiiriiciisciii ciiii bc dill'twiit iatcd by seriiiii ~)rccipititt ioii iiictliotls.

1 hc nicc!iiiiiisiii of rciiiiiii coitgdatioii is soiiic\vhiit. iis follows. ' I ' h rciiiict acts oil tlic cnlciiiiii ciisciiiogciiiite. ( 1 ) I t splits tlic protciii ~ o i i i p l ~ ~ iiito two iiiolcciilcs of [JilI'ilC:lSCill. (2) 'I'he solul~lc liiiic salts IwcSeiit in the rciictioii misturc uiiit c with paracnsciii to foriii insoluble tdciiiiii piiriiciiseiii:it c or rciiiict crisciii of coiiiiiicrcc.

lliis cnlciuiii pnntcrisciiiittc is clioscii for t.hc iiiniiufitc- t ilre of IJlilSf icri bccnusc of its l~cciiliiirly toiigli IiropcrLics. On \\.iiriiiiiig iii ii moist coiidit ioii i t becoiiics glutiiioua iiiid call bc driiwii out into tlic fiiicst tlircittls, hence its s i i i t i i ld i t y i i i IJI'eft!lCiiCC to t hc ordiiiriry coiiiiiierciiil ncitl ciisciiis.

Llic iiiaiiufitcture is ciirricd oirt iis follows. Tlic clc:iii ~ i e i i t r i i ~ sepiriitctl iriilk is trcntcd with rciiiict iit, i t

tciiipcmturc riinging froin 37" C. to 41" C. 11s so011 iis t lic inilk is set to tlic gel coiitlitioii iiii ngitnt.ioii is stiirtctl itiid tlic tcni~ienttirre is rniscil to tiso C. Tlic protein is this t h r o w out in liirc piirticlcs nntl tlicii allo\~cd 1.0 scttlc t o tlic Ilottuiii r~l'tlic wit. Tlic coiitliiioii of tlic c p l is iiiiportiiiit iiiiil is CtJlltloll~?ti to SCJIIIU cstcilt 11y the syicctl of tlic iigitntor. I t is i inpormt . l)ccitust! of

c:llculnted as colnplctc IIloIcculcs, nnd not ns lllolccules

, >

, *

,*

I

tlic wnsliiiig tvIiicli trikes plncc to rciiiovo the \rliey. 'I'oo slow ngitntioii produces lnrgc clots iii ivliicli tlic wlwy gets lockcd i i p , wliilc too fust ngitntioii ciiiiscs too line ii

curd to IJC l)recipitntcd, t.hiis rcsultiiig i n loss t Iirough difficulty in sepnriit,ioii iiftcr ciich wnsliiiig.

Tlic ~vnshiiig sliould lie iis tlioroiigli iis possil)lc to reiiiovc tlic whey, othcr\visc oii dryiiig tlic curd iliscolorii- tioii tiikes plucc owiiig to t Iic prcsciicc of 1itct:ilbiiiiirii. The scpnriited curd iiow ~viisliccl iiiitl frcc froiii wlicy is tlrictl hy pissiiig t.lirougli 11 rotnry drier. Tlic curt1 slides clowii ii spcciiil cliiitc aiid hot nir rims counter to tlw flow of tlic ciisciii.

/[i.s/ory o j rtrseiri plnstics.---diitl iiow wc coiiic t o t l i e iiiiiiii siibjcct of tlic I X I ~ W , liiii>icly, tlic protluctioii of the plustic iiiiitcriiil. Aliout the p i r 1397, \V. I<risclic, ii

printer iii Hniiovcr, evolved the idcn of coiitiiig whit I:

ciird1)oard with a solution of cnscii:, tliiis producing i i

filiii which lie iiitciitlcd to Iiiirtleii iiiicl to reiitlcr water- proof by suliscquciit cheiniciil t rciitiiicnt. At t lie sniiii' t,iiiic Adolpli Spittcler, of I'rieii i i i Ihviiriii, \viis working upoii tlic problerii of \viiterproofiiig ciisciii. As thc rcsiilt of :I colliiborntioii tlirsc two workers discovered t lie foriiiiiItlcli~tlc-rnsciii reiict ioii, oii which the wliolc iiidiis- try is 1)iisctl.

Tliey fouiitl tliiit foriii:iltlcliydc foriiis iiiore or lcss stcililc coiiipoiiiids with ciisciii, iiltcriiip its propert ics iipl)rcciiibly. T h y iiotcd that soluliilit,y in w t c r i i i i i l

ciipncity for liydriitioii lind l m i i lost, and fiirt.Iicr, tliiit the coiiipoiiiid produccd wis iiisoluble iii ncid. In the further iiivestigiit ioii of tliis react ioii, Ucricdiceiitc sly- gcstcil t l i i t t tlie iicltlitioii of foriiinidchydc to n protciri occiirs iis :L tylic of i i l t l~hyt l~ iiiiiiiioiiiii rcrict ioii.

it .KH, i 1-1 a-i .o = 11 .si.r .cii,oii iii i t l the ciisc of rciiioviil of tlic 11 .c'l-I.O by stciiiii dis- t illiit,ioii suggests t.hiit. this rciictioii involving tlic iicitl i i i i i i t l v groups m:ty he the lxiiicipiil liiikngc for foriiiiildt*-

I31iiii1, oii t lie 'otlier Iiaiid, suggests i.liiit tlic rrrict,ioii involves the foriiiiit ioii of inetliylciie iiiiiiio-coiiiiioiiiit~~.

Iiytles iiiid potciiis.

A piitelit wiis tiikcii out i i i Octol,rr, l8!)7, i i i i t l t h y t.licii tlcvotctl tlieir ciicrgics to tlic csploitiit ioii of this rliscovcry. '1'lic.y worked iiiorc oii tlic itlcii of 1)roduciiig plnst ic i i i i i t cricils in thc form of' iii:isscs, nit I i t b r i,liiin:iis protcctivc coiit iiigs. Tlic process wns fiiiiilly tiikcii I I ~ J Iiy thc Giiliilitli Coinp:iny of Hiirlnirg, iiiitl tlcvclolirtl Iiy t,hciii us ii coiiiiiicrciiil ~irnpositioii.

l!lic history of t.hc dcvclopiiiciit of t l i t ! iiitliistry in this coiiiit ry is iilso iiitcrest,iiig. In 1909, i i Russiiiii student, Victor 8rliirtac, of liigii, pttciitctl ii process for tlir. iiiiiiiiifiiciurc! ol' solid pliist ic iiiiit.criii1 froiii i i i i l k curtlr. 'rhis process wis lioiiglit by nil 15iiglid coinpiny, i i i i i l ti

pliiiit, \viis crcctctl to \vorl< i t . 'l'hc 1)roccs.q iis ~iiitciitrcl 11y Scliut zc wis f'ouiitl t o I)c iiii~irr~cticiil~lc, lieiiig Iiiirc.il oii w h i t is kiio\vii ris tlic \Vet ~irocess, ' 1 ' 1 1 ~ 15iiglisli coiii- piiiiy l i i i t l thcret'orc to w i r k oiit qiiitc iiitlc~icii~lciit 1y :I iiiotliliciit ioii of this ~irt~c+css. This \viis tloiic siic*c-cssfiilly i i i i t l the process so workctl out is iiow kiio\vii :is tire Ihy ~ J W X S S i i i i i l is iiiiiwrsiilly iitloiitlvl iis t l i t l stiiiitliii~l Illctllod. ,

Il'et, ~~rocess.-l'crltii~~s it) \vould be ~vell to coiisidcr first thc Wet process. as this \VDS tlic o r i g i d method by ~vliicli pliist ics wcrc first produced. !l!lic Wct proccss is t i longer one thiui tltc Dry, but in sonic rcsl~ects it yields ti superior product. Thc ~n:itcriiil produceti by this process is softer iitid niorc easily worked, niid a quitlity iti the niottletl colours is obtoitictl which hiis never I~ccii mat cltctl by tlic Dry process. Tlic produc- t ion cost, liowcvcr, would iilwiys be Iiiglt, ccrtiiinly from &l. to .Id. pcr 11). : i b o \ ~ the cost. of thc Dry process, :ind for t,liis rcitson itloiie the ~)roccss has fallcli itito tlisusc. Aii acid cttscin ctin IN used, itlid tlic curd coiigiiltLtrd froni scl~nrtitcd inilk with iicctic, or better still, with syrupy pliosplioric ticid. Tlic cnscin so pro- duced is covered with wrttcr nnd nllo\ved to soak over- night. Furl Iicr witt cr is ndtlcd in tlic iiioriiiug to cover t lie ciiscin t i i i t l 100 C.C. of 80% ncct,ic ticid is ntldctl to a ti0 kilo soak. Wood pulp which lins becii ~~rc\~iously prcpnred by Imting to it gcl coutlitioii in water, is iidtlctl i i t t.his stiigc. 2.5% to 3 % is tlie t i i : i s i t t i i in i cellulose \vhicli t.lie curt1 will hold.

The tcinpcriiturc is iiow rttiscd to 70" C., tlic tiiixturc iigitntctl, iind grutlunlly :I huge coagulntc is tlirown out,

late is iio\v rcriiovcd to n dough mising niiichinc, wntcr at 80" C'. is iidtlctl and the whole iiinss is worked up into ii glutinous conditioii ; tlic :irnis of the iniscr pi111 t lie tlougli iiito long rubl)cr-likc cords. 'l!ltc wasliitig w t e r is now run OR, tlic intiss is cut; up into blocks t int1 rollcd out through st ctiiii ltciitcd rollers. Tlic rollers tire reversible tiiitl :ire iidjristiil)lc so tliiit. ciiiy thickness

course for sliriuktipc. The sliects iirc iiow placed in citiivus-liiicd tiioulds

itnd pressed out i n scrcw prcsscs for 2'4 houis. The prcssiirc Itiis to bc follo\vctl up, :itid this citii oiily be tlonc 11s t.lic1 colloid brcnlis clown ; no aniount of liydrnulic pressure will force tlic wtiter out. Tlic sheets arc thcii dried in riicks 011 glilzcd shccts ~iiirtlc of citrdboiird treated with 13akclitc. 'I'h tcinpcraturc lins to be low, tilwut 26" C. (80" P.) a i d i t plcutifitl supply of air is Ilcccssilry. be st,riiiglttt~tictl out. !I'his is dotic by dipping i i i hot water nntl prcssitig I)ctweeii inctnl plrites. The straiglitciictl shccts tlicii pass into t,lic IE.CIE.0 to formnlizc, I Itcy iire iigiiiii d r i d niitl fiiinlly pressed in tin-lincrl itioultls iitttler 1iytlr:tulic prcssiirc to tlic cstict t liiclincss rcquirctl. Rods cruinot bc tiindo stit isfitctorily 113: t.ltis process oii iiccount of tlic high iiioist,urc content, ol' t.lic curd. i\tiytliitig iiliove i i 15% wiitcr contciit, will colliipse oti seiisotiittg out.

Dry proccsa.-'I'lic proccss is siil~stitiiti:illp iis follows. Tlio ciiseiii is t rcittctl l)y iiiciiiis of hcitt, ittit1 pressure with the tiiiniiitutii quiitit,ity of wiitcr to dt'cct its flow during the procvss of iiiiitiufttct~~~re. Iiciiiicte ciisciii is usctl exclusively it i t he protluct ion of qtisciii pliistics by t.lw Dry ~iroc(!ss iind t.ltc dry rciiiict, ciisciti is ground to pass it 4o-in. nicsli. 'It, is important. to iiotc tltiit the tciiilicrirturc! of tlic ciiseitt is kcpt iis low ns possiblc during tltc process 01' grinding, ot Iicrwisc discoloriitioii of t,liu cirsoiti will rcsiilt. The t,ypc of tiiill usui~lly used for this griiidiitg is t lit! flour-inill t,ypc, in wliiclt t l i t 1 l l l i l t c~'iJlI 1)iisscs Ibct weeti finely corri~gtitctl steel

iiud it clr:iii.sc~~itrritioii of \vittcr tiikcs plncc. The coiigll-

of sheet ciiii be 0l)tiiiticd. i\lh\viitiec h:ts to I)(! tititdc of

l'hc sllcets of coltrsc curl up &lid have to

rollers ; GO kilos of tlic groiind casein is considered n stnndnrtl charge for nn operation. The charge is pliiccd i t i i i suititblc mixer, niid itny dry pignieiits which liavc to be adtletl nrc tnisctl at t.liis stage.

The colours :ire protlucecl mostly hy tlic ndditioii of iicitl dycst,uffs. The dyc is dissolved iti :I definite proportioti of wntcr niitl sprityctl o t i to t hc mixing ; tlic inisitig is then further cotitiriuetl uiitil u unifonu tlistribut ioti of tlic dye solution t:ikcs placc througliout the niuss. 'l'lic inisinp iniichiiics wliicli iire used for this process tire of tlic cloitgli-inisiitg type. Tlic dyed po\v(lor is itow fed to cstrutliitg iiiitchitics. Tlicse tiincliiiics :ire of thc sanic t , y p ns arc used in tlic nil)bcr intlustry. l'liey arc niodified in viirious ways to iiieet p:trticul:tr rcqiiirenieiits, nucl consist of ii jiicketed worin, iirrniigctl so that coinplete teinpraturc coiitrol caii be obtaiiictl eit,licr l ~ y stentii or \s-nter circulatioa. They arc fitted at one ctitl with n iiozzlc which Iiits viirious screens inserted to control thc flow of tlic niiitcrinl as i t piisses tliroirgli tlic nincliiiic.

1 . 1 1 ~ scrtw pliisticizc!s tlic dyed poivder as it, cotiies 'for\viirtl to the iiozzlc ; tlic scrcctts put up n rcsistnncet it ttd iissist i n thc product ion of i i thorouglily liotnogctieous product. Tlic inaterial its it. now Ictivcs the nozzle of tlic tiiiicliiuc is in n soft uiid rul)l)ery condition. Mottled colours arc produccd by niisitig the fccd po\vder wit.h nibs of tlic cotiiplcnieiitary colour or colours rcqitirctl. Thc iiil)s iirc iiiiitlc by extruding through aiiotltcr niitchiiic rods of iihout .L-iitni. diitnicter. !l!licsc thin rods nrc cut up by clioppitig innchilies into -1-iiiiii . Iciigbhs. Such sninll pieccs arc knowti techiiiciilly ;is nibs. The fitct, tliiit, t.liesc tiihs ltnvc pitsscd through tlic mnchinc ensures ;i prclititin:try plasticizing cnuscd by the tiction of tltc sere\\-. \Vlieti t h y arc now tnised witlt tlic Iiiisc powder itiitl itgitin fed in the tnisturc to t.hc miichinc, they nrc ol)riously hitrdcr and tougher that1 tlic I)iise powder, and thus stntitl out i i i relief to forin tlic required pattcrii and colour.

Tlic plastic material cstru(lotl hy tlic itincliinc is iiiiidc in t,lie forin of rods, rilhoiis, or tubes as tuity be required. I f shccts iirc being iiitiiiufacturcd, t.lic ribbons or rods lire cut to n dcfiiiit c lciigtlt, wcighcd ofT according to tlic tltickncss of tlic shcct required, and plttccd in n steel tiioultl. 'I'he tiioultls arc then pliiccd in n hydraulic p s s and tlic rniitcrini is subjected to h i i t uiid press~tre. l'lic fi t i i i l prcssurc iniiy r n n p froiii 150 t o 200 tons on t lie pliiten. I!lic iiinteriiil is cooled bcforc reiiioriiig froin tlic ~nould. At this stirgc it will bc found to bc still i i t ti soft nnd soiiic\vIiitt, rubbcry condition, but it is sufliciciitly rigid to s t u d upright in nicks. l'licsc r i d s coiitiiiiiiiig t,Iic cnscitt sltcct s t Iteii pnss into tlic forniiil- tlehydc tiinks ~vlicrc t i proloiiged trciit iiicnt in ti 4"/, to 5'); solitt iott of foriiiiiltlcliytlc is givctt. !I'lic thickiicss ol' t,Iic titiit cbriiiI of coiirsc tIctcrniincs the Icngtsli of tintc tliiit the sliet:ts ltiivc to lie iitiiiicrsctl, itnd this t r'etit tiiciit tnny w r y froin ten tlnys to tcn \vcc!ks.

room ittit1 itre dricd out, i i i ii plcntiful supply of iiir, the tctnpcritturc Iicing kept ribout, 27' to 32" C. 1)iiritig this drying tlic sliccts inuy wirp coiisiiIcriil)ly, i i i d tlicy hive to bc filially stmiglitciicd. This is dotic. i i i liydriiulic ~~rcsscs. The shccts iire first softcued by dry liciit, i t ~ t d tltcti pressed out. ,\ftcr titis I i i i i i l striiiglitwiitg, thup

, 7

I t 1 I I C sheets t h l piss from tlle tnults to tlic tlryiiig

reinnin rigid i i i i d ;ire rc:itly for the niiirkct. T h c size of tlic slicct which is ninnufiicturcd is iisiinlly 20 in. 1’s I(\ in.

To ret,urn to t . 1 ~ extruding nincliinc, t,hc iiint erinl which hns to bc made into rods is cut. off in 30-in. or 4O-in . lengths, cooled, nnd plncctl in tmys. If tuhcs :ire requirctl, the iioezlc of thc cstxiitling niiicliiiic is fitted with i i screen \rliicIi ciirrics cciitmlly a pin. ‘i’liis pin pnsscs t,lirough tlic nozzlc :ind ninp project, sliglit ly at tlic nioiitli of tlic iiozelc. ‘rlic niatcrinl flows roiiiid t,he pin iind so fornis tlic rcqiiircd tubc. Tho t,ul)es : I I I ~ rods iirc plnccd in trays iind then pnss into tlic foriiinl- dchydc tniiks wlicrc tdicy reinnin unt il complctc fornializ- iug tnkcs pliicc. The circulnt.ion of t,hc forniiilin in tlic tnnks is of tlie ut,niost. import:incc, as is also nn :iccurntc tcnipcniturc coi:t,rol. Both these fnctors hnvc i i dcfinitc bearing on t,he length of tirnc rcquircd in t,hc forninlizin~ process. \\‘lien t,hc . rods and tubcs arc comph!tcly forinnlizctl, t,hcy iirc dried i n rotating driinis throiigli which hot nir is pnsscd. !L’licy conic out, of 1 . 1 1 ~ drurns at the end of tlic drying ~iroccss pcrfcctly strnig!t. This finishes the nctuiil ni:inufricturiiig process. Sanding t.hc sheet to a sniooth surface, tmpping thc rods (\vIiicli is n process of cciitml grinding) t,o nccurntc dimensions, and fiually polishing, 110th shcrts nnd roils, arc niorc in t.lie nnturc of finishing opcriitions t;linn nct.unl mnniifncture.

Propertics of /Ire )~m/eric~l.-l’lic spccific gravity of tlic crisein plnstic nintcrial is 1 *33 to 1 e3.1 ; age nntl ntinos- phcric conditions inny C:IIISC n rnriiition of t.lic figure ranging o m - n 1inlf 1)cr ccnt. citlicr \ray.

Acbio)t u d c r hca/.--At 130”’ C., t,ho nintcrinl sti1rt.s to discolour, hit t,Iiis cliscolornt.ion is very sliglitf niiil only shows in the niorc dclicntc coloum. At 160” C. the discoloriit,ion slio\vs i n all colorirs, h i t tlic i n i i t t 4 i i l still rctniiis its pliistic nntl colicsivc nntiirc. At 2 0 ” C., d t e r sonic niiniitcs, rlisiiitcgcitioii tnkcs pliicc. Tlic nintcriiil is ~ioii-iiifl:iiiiiiiiil~lc ant1 will only h r n oii being held i n n fiiinic. It is sornc\rhnt hygroscopic : i i d can hc softciied in hot. wntcr, moulded, a i d 1)rcssiirc-polislicC. It is tin esccllcnt: insulntor niitl can I)c uscil for 1111 low- tcnsion ivork, but on nccoiint of its Iiygroscopic proper- t,ies it. is not suitnl~lc for liipli tension or ootdopr work of tiny tlcscript,ioii. In niost respects it, is workcd tikc horn :tiid ivory ; it. ciin bc turnctl, drilled, polislictl, s t ninpcd, iiiotiltlctl, n ntl eiigritvcd.

Altogctlicr i t I I ~ I S foulid its way int,o 30 or 110 t,rndcs, nnd i t is now looked iipon as n thoroughly rcliiiblc and provccl mntcri:il. It, is n l~caiitiful intitcrial to handle rind cnn bc usctl i n tlic proclact,ion of tlic niost tleliaite pnstcl shndcs :IS \rcll ns for rich nnd rlccoriitive colour schcnics. On this iiccount niid nlso on iiccount of its rclnt ivcly low prodiiction cost,, tlic rii:itrrinl is wry populiir hi t.hc world of dccor n t,’ IVC iirt.

In conclusion T slioultl like to nckno\rlctlgc. iny indcbtctliirss to Dr. I\‘. TJ. Dii\.ies for information iuitl rcfcrcnccs ol~tiiinrtl from his Iiook “ !l’lic Clieinistry of Milk ” rqyrdiiig Ctwiii, nntl to JIr. 15. Pctcrseii for inforni:it,ion rcpiirtlirig tlic! JIistor? of Cnsvin l’lnstics in Gcrninny.

THE EXCURSION OF THE INTERNATIONAL SOCIETY OF SOIL SCIENCE: GREAT BRITAIN

By MADAME JADWIGA MARSZEWSKA-ZIEMIkCKA’

‘ I Soil profiles forin tlic c.sscntinls of our rsciirsioii,’’ l)r. J. U . Lipmnn told IIIC. I\‘e hib\’C Iiec~l slio\\-ii 5 clews of liolcs.~ Tlic “ Profile dc lose ” Iiiitl cntriincc s t e p covcrctl with i t cnrpct. Tlic first cliiss profilc had two rntnuiccs but no carpet. Tlic second class profile hrttl only onc plnin entrance, rind tlic tliirtl cliiss hnd no cntrtiucc a t i i l l . AII cxtrit cliiss of ‘ I nliliit(!ur profile ” contiiinctl n bntli.3 We were offcrctl the hist in Scotlnntl, wlicre tlic ‘ I rdginic scc ” \rns being less markedly ohscrvcd t h n i n England.

Very nicnioral)lc nws tlie *‘ Approncli to the l’rolilc,” thus : ii soil profilc liolc gives tlic spccinl signs of its existcncr. Ahout 160 people d e m d from tlic ’buses, and begin to inovc in tlic direction indicatcd. lt is u. rncing party riitlicr tliirn n wnlk. ‘l’he party hiis sooii foriiiulritctl its rrilcs. Constitiitioniil vigour plus thc sncrcd Pctlologicnl Pirc did niirnclcs for tlic Rurvivirl of tho qliickcst. After ti fcw rcpctitions, :r liicrarcliy cstnblishcd it,s rights to thc soil prolilcs. 1’rof’8, l~o1ynov, Uiktnszcwski, Strcninic, Shriw, tlic liov. Urndc 13irlrs, nnd just n few othcrs iirrivctl tlic first n t tho soil profilc,

got into it, tiirnctl t.licir I)ricks to tlic o t h r s iintl stiiyctl tlicrc t,o outlitst t,lic rest. hliss Liy, Yiss I;cc, mid it

lot of poungcr soil-scientists ciinic iicst, iintl they Ibrnied n tlcnsc row on tlic edgcs of tlic liolc in hopc of getting :it lctist ~~rol)hyliict~ic trwtinciit. Tlic next ro\v ivns fornictl hy i r l l sorts of’ literill outsitlnrs. Xost of tlicni l)clongcd t,o tlic clnss of pliotogrnplicrs, wlio evcry dny took dozciis of snnpsliotj, mostly of 1iuiii:in conglonicrntcs. Sonic of tlie pliotogriqhxs spccirtlizcd in Intlics’ profilcs, sonic hiintcd for intcrcsting yonng couples, but surely tho bncks of the pcdologicnl irristc.1- crncy irerc tlic higgcst succcss. At lnst tlic ‘iitlso- rans ” rcnchctl t h niciintinic conclcnsctl crowd. Soirie of the lndics did not hido their contciiiptiiouu fcclings for thc sight of rill tliosc eitgcr middy pcdologiciil bricks. ’ It \\WY rciilly worth wliilo secing ho\r iLlfcctio1intc sonic pcoplc were for the soil profile. ‘l’lic!y collcctcd saniples of it, they ~crntclictl it, tlicy sniclt it, occi~sionrrlly cveii tnstcd it. Evitlcntly tlicrc niiut csist soiiio rcsciublrtncc bctwccii a soil prolilc niitl i i ciikc. ‘I’lic only troiiI)lc with tho Hail ~irofilcs \vrrs sonictimcfi their insi1flic:icnt