114s UIIEMISTRY AND INDUSl’RY Drc. ei,lo:li

WOOD PRESERVATIVES By N. A. RICHARDSON

Scientific Officer of the Forest Products Research Laboratory

(Pope; read before the Road and Building Materials Group on December 7 , 1937)

The iiuiiti ngciicics rcspoitsiiblc for t.he tletcriornt,ioti of titiibcr iii scrricc are fitiigi, itisect,s ntitl cert,ni!i ninriiic organistiis, and fire. As fnr (is t,Iiis coutttry is conccriictl, wood-dcstroying fungi arc by fnr tltc most ittiportniit, hut the conditions utttlcr wliicli tlicsc cnti develop nrc fiiirly well understood. Two csseiitinl rcquirctiteut~s for the growth of wood-destroying futigi iire iiir iiitd tnoisturc togcthcr, so thnt wood coiitiiiunlly ltcpt thoroughly wct or dry will iiot decny. It is iinportnnt to rctticttibcr t,liis fact, ns it is oftcii possible to clrcct tlic prcscr\’ilt,iott of tiiiibcr by proper nttcntioii to coiistructioiinl tiictliocls, c.Q., in buildiiig titiibcrs, niitl tvlierc such tnctliotls ciiii bc suitnbly ciirricd out t h y nre to be prefcrrcd to the practice of using chctnicd wood prcservntivcs. 1 \vould stress t l tn t wootl is iiot inhcrctitly n p i ~ b i i b l ~ tttateriiil- in fact, i t is ~ h ~ ~ ~ i ~ i i l l y stnblc ntid duriihlc-ant1 it is only wlieii it is uscd under cotidit,ioiis f i i ~ ~ ~ ~ i t i g tlic tlevclopinent of tlic various destructive itgcttcics t,lint t,he necd for prescrrntioii uriscs.. In i t iiuiiibcr of cnscs, lioivevcr, it is not possilh for

tlic tiin\)er to rciit;iiii continuously uiidcr cit,licr wet or dry conditions, niid it is utidcr tlicse int~crttiedicite conditions that decay of t,he timber is usunlly only a iiinttcr of time. At tlic ])rcsciit tiiiic the oiily incthod of nrrcst,ittg decay in such circuxustctnccs is by iiiiprcgttat,iiig tlie wood with yntiscptic liquids or solutions.

Jlil1iy clietiiicals l i i i \ ~ beeti suggcstcd froiii tlic ciirlicst timcs for tlic prescrvntioii of tinibcr, h i t tliosc which hnvc fouiiil gcitcral nppliciitioti iirc rctiinrkiilly few. \\‘ood prescrvutivcs cuii coiivciiiently bc eliissifictl undcr thrcc hcndings, i.e., oil, wiitcr-soluLlo, rind sol\~eiit types. l’ructically it11 coiiitiiercial itnprcgiiation trentiiiciits arc cnrriccl outwith the oil- or wntcr-solu\h types, ns the high cost of tlic solvcnt used with tlie third typc prc- cludes their use for trcntiiictits involviug high nbsorptions of liquid.

Before denliiig wit11 tlic vurious l)resgcrwtiws, 1 would like to rcfcr to tho import:ince of thc iiicthod of npplyitig the prcscrvativc to tho tiin1)er. For satisf:ictory results the trcatmciit or imprcgiiatioii of the tinilm is iis inipor- tnnt ns the nctual antiseptic uscd. Ilisnppoi~itincnts niid failures hnm frcqucntly bccii cxpericnccd, cvcn when the most cflicicnt of prcswvntivcs ltiivc 1)ccii uscd, niid iiivcstigiition of such ciiscs hits invariubly showii t l t u t failurc hiis bccii duo solcly to itiiidcquntc or otlicrwise unfirttisfnctory trcutiiiciit,. This qitcstion of suitirblc nnd cfficiciit iiiiprcgiintion of the titiibcr ciitinot tic over- ’111 ihasizcd.

“he clioicc of tlio most siitisfnctory prcscrvntive for n spccilio purpose is, l i o ~ ~ ~ c \ ~ c r , \*cry ittiportiitit, rind soillo- tiiitcs prcsottts soiitc difiiculty. All wood prcscrvnti\*cs

possess certiiiii tlisntlvntititges, r t t t d notic is itled, Init most of t81iciii hnvc properties or utlvmtngcs wliich uiakc them suitnl)lc for specid liurposcs.

Thc tiiost importiitit desidcr:itiL in i i wood prcscrviit~irc arc gciier:illy coiisidcrctl to bc t,hc following :

(1) It sliould be tosic to mood-tlcstroyittg fuitgi, itisccts, ctc. ;

(2) It should bc perntntictit ; (3) It slioiilcl ITC rcndily n\.riilnl)le i n lrrrge qiiiitititiw

(4) It B h O i i ~ d pciictrntc thc wood rc~nsottiil~ly well, i.e.,

(5) It should I J C Lion-poisonous to liuiiiirti Iiciitgs iiiitl

( G ) It sltoultl not be corrosivc to tttctiils ; (7) It sliould not render thc ~ ~ o o d tiiorc ittlltittii~tiil~lc.

The clioicc niid use of cltcniictils for thc ~~rcservi~tioti of vnrioiis clnsses of tinibcr is li~rgcly dctcrntiitctl by tllc extent to \rliicli tlic nborc rcqitirciticitts tire sritisficd, and this should I)c Iiortie i u mind ivlieti cottsidnritig the use of n prcscrviitivc for ii pnrticulur purpose. 1 will now rcfcr hricfly to tltc vnrious prcscrviitivc:s coiiiiiiotily itsccl.

OIL TYPE Birst therc is tlic oil typc, of whicli cod t ~ i r crcosote

is by far tlic most ittiportnut, hiivittg bccii in usc fur over n ccntury for tlic prcscrviition of st.ructuritl i t l i d othcr timlicrs uscd uitdcr the most ficverc conditions ol‘ csposurc. Creosote is the tioriiinl prcscrvntivc used for rnilwuy sleepers, triinsnrission poles, iitid iitiwiiic piling. Tlicrc is no iiecil for ntc to sity iiitytltitig rcgiirdiitg t l w production of this oil, cxccpt tltrtt tlic \vide rnitgc of oils produced uiidcr tltc dcscriptioti of cold tiir crcosotc oil hnvc all pro\wI vcry cll’cct.ivc prcserviit-ivcs.

111 id1 iiiiportnttt creosote-~~rutlitciii~ coutttricv tlir crcosotc iiitctitlctl for wood prcserviition is prcpiircd to ib specificiition wliich iii the niiijority of ortscs litis booii drnwti up by rcpresctitiitivcs of thc producers ntid itscrs. Owing to hick of dcfiiiitc sciciitific: iiiforttiirtion it; hiis not bccti possiblc to tlishgitisli IJct\\wtt thc cfiicicttcirs of various crcosotcs, so t . l i i t t i n the itiuiii such q)ccifit:ii- tioiis hnvc bccti drttwn up to iiicludc thosc gctieriilly aviiilablc iiftcr cxpcricttcc hits sltowti tltciii to IJC sat is- fiictory for purposes of prescrviition. ‘i’ltc qiecificiitiott in usc i n this country hns I)ccti publisltetl Iiy tltc Iiritislt Stniiilnrds lnstit,utioii its I3ritislt Stwitlard Sl~ccifioiitlioit No. 144, Tlic origiiiitl sl)ecificiitioit ivits ~ ~ r c ~ ) u r c d i r t 1021, but hits I)cctt rcvisctl titid cstctttletl i u 1!)3(i. In

nnd be low in cost ;

should iiot be too viscous ;

i~tiiiiiiils ;

DrC. 26,103i CHISBIISTRY AN11 INDUSTRY 1149

iiddition to thc specificrit,ions, standard mctliods of test itre also described. The British Spccificntion covers practically all tlic crcosotcs produced in this country, which are groupcil undcr tlircc henclings, no superiority of any one typc over the otliers bcing iniplicd.

As olready incntioned, crcosotc oil is uscd to a greater cxtcnt than any otlicr singlc I)reservnt,iw, atid it.s niniii ~~dvnn tagw arc :

(1) thut it, is liigltly toxic to wood-destroying ngcncics, such ns fungi, inscct, and niarinc Ijorcrs ;

(2) t l i t r t owing to its slight solubility i n wutcr and its high boiling point, it is rc1:ltivcly very pcrnianeiit ; irntl

(3) thiit it is itv:iil:~ble i n Inrgc rpintitics and is c:onip:rriLthly c1ic:ip.

FurtJier, it. is eiisy to tipply to tlic titiibcr iind docs not seriously corrode nictds, atid conscquctitly tm.xtiiig plants have a long life, :ind nietal fittings, screws, and niiils in coiitnct with treated t i i n l m arc likcwisc not iippci:ihly affcctcd. ' l h dept.11 to which t,hc oil p i c - trotcs tlic t.inilm is rcndily scen on ii frcslily cut cross- scctioit.

Cotitrury to tlic view tltiit ltiis bccn espresscd froin tiittc to time, crcosotc docs not \wtcrproof t in i lm to :iny great cstcnt, and its eflicncy as a wood 1Jrcscrvritiw ciLnnot I I C nt,tribut,ctl to any uction in this dirccbioti, nncl it is ulniost entircly due to its liigli tosicity to wood- tlcstroyiitg fungi etc., conibiiicd witli its high degrcc of ~)crniaiicitcc. Actually pctroleuni oil lias better tiioisturc-proofiiig prol)crties, but since it has littlc or no tosicity, it. is not snrprising that this oil when uscd ulone has bcen found to afl'ortl but lit,tle protection to tlic tinibcr. 111 both ciiscs tlic oil fills tlic ccll spiccs, atid i t is cxtrcmcly doubtl'ul wlictlier iiny qutintity pctictrutcs tlic ccll wid1 itself. i\Iorcovcr, tho ltygro- scopic wood siibstiincc is C I I ~ R I ) I C of ribsorhing nioisturc r e d l y if kcpt i n coittiict with wntcr or under Iinniid conditions, even wlieii the pores or cell spnccs ;ire fillctl with oil, so thatt a t thc best tlic oil inercly acts its n rnoisturc rct,nrcler nnd not ii proofcr.

Crcosotc oil hi iv sonic tlisiitlviiiitogcs which niiike its itsc undcsir;ii)lc i n ccrttiin cnscs. l t s cliiircictcrist,ic snicll is objcctcd to I)y sonic pcoplc, so that i t is not ntlvisublc to usc crcosoted wood for certain doincstii: purposes, irlthougli tlie smcll usuiilly disuppcnrs nftcr ii tinic. For tlic siLnic reason it should itot be used for tlic Iwcscrviition of rcfrigcrntor tiinbcrs or otlicrs wltcrc tlicrc is nny 1)ossil)ility of tihiling footlstull's. Agniu, it is not possiblc 1.0 p i n t creosotcd wood sutisfnctorily. Crcosotctl wood slioultl uot be itsctl in bnildittgs in closc prosiniity to plirutcr work if it is dcsircd to cliniinntc tlie risk of stuining or tliscolorut,iott, {is tlicrc is no s i ~ l ' ~ \wy of prcvcnting this.

Much has becn publishctl coticcrning thc cons~ituettts of creosote oil tlttit itrc tiiliinly rcsponsiblc for its cfl'cct,ivc pwscrvutive quiilitics, untl tho ncutrd hydrocnrlmns, tar ncid8, iintl tiir buses Iinvc nil a t one tiinc or iinotltcr bccn held rcsponsiblc. 11 citn bc fiiirly slifcly nssunictl thnt no single cotitpoutid or clussofcottipountl is priniiirily coticcrncd, nnd i t scenis c1uit.e liltcly tliiit if tlie tosicity is provitlctl by 0110 group of sitljstiiticcs, t h l)criiiiincncc

is brought about by tlic presence of higli boiling oils of relatively low toxicity.

A year or two ngo I hiid the opportunity of cxaniiniiig sonic sections tnkcn from tclcphonc polcs itnd railway slccpcrs, the life history of which was known. Ext,raction of the creosote rcninining in thc timber and its nnalysis provided certain intcresting information. It nppcaretl t h n t thcre was n high loss of low hoiliiig oils during the first ten ycars or so, although cren after a number of yenrs (25-50) tar acids and nnphthalene were not, ciitirely removed. The rcsidual crcosotcs were not ns toxic to wood-destroying fungi as ordinary crcosotc, and thesc could not bc rcgnrdcd as being solely rcsponsiblc for prescrring tlic wood throughout tlic \vIiolc period. RIorc than liltcly the ninin function of tlic rcsidiial high boiling oils was to rctnrd thc loss through leaching and ev:iporation of the niorc volatilc and niorc highly toxic lower boiling subst,nnces.

Otlicr prescrvntires of tlic oil typc inclutlc crudc coitl tar nnd wood tar and its distillntcs, but for various rcnsons t h s c nre only used to n lintitcd cstcnt. In conncsion with oils, I should nietition thitt petrolcuni oils Iinving but little tosicity townrds wood-destroying fungi nrc only uscd for dilut,ing crcosot.e, whicli rcninrks d s o npply, to wntcr gas txr distillatcs.

WATER-SOLUBLE TYPE PRESERVATIVES

Conipnrcd with tlic oil type, thc wutcr-soluble prcser- vntivcs hil\rc certnin advuiitiigcs as \veil as disndvaiitnges. Gcnernlly they iirc iiiucli clienper, nnd sincc thcy cn t i be linndlcd in tlic solid or concciitr;tted form, thcy arc easier to transport. Tlic . iiinjority involve very 1itt.k fire risk, niid thcy iirc gcncriilly otlourlcss. 7 % ~ trcnted wood, :iftcr drying, cun usu:illy be sntkfnctorily pnintcd with ortlintiry oil p i n t s or wrnishes. Such prcserva- tivcs, t.liercforc, nrc of spccinl valuc for thc trcntmcnt of t,inibcrs uscd unilcr conditions fuvourablc to decay \vIicrc these specinl propcrtics tire itlso of iniportnnce. 7'11~s tinilicrs such as thosc cniploycd in builtling con- struction or for oninil)its, conch, or cnr bodies nre frcqucntdy trcatctl wit,li prcscrwitiws of this typc. On the otlicr ltnnd, 1)cing wntcr-solublc t h y iirc usually uiorc readily Icnchctl ont of tlic wood if uscd .in contact with tlic ground, iintl are, thcrcforc, not so suitable as the oil typc for use untlcr thcsc conditions. Recciit dcvelopnicnts in this type of prcservntivc have aimed a t producing wntcr-insolitblc conipounds in tlic wood frotii mistxrcs that tire wfitcr-soluble n t the time ot' t,rcntnicnt.

'l11ic usc of \ratcr-solul)lc stilts niiturdly entails thc rc-drying of tho tinibcr Ilcforc it cnn bc put into servicc. T l i ~ tilost, \\.cll-lilio\\.11 of t,llcsc prcscr\~ilti\~cs nrc zinc oliloritlc, sodium Booriclc, coppcr sulpliute, iuercuric cliloritlc, tn:igncsiuni silicofiuoridc, nnd nrscnic, but tlic iititoittits of zinc chloritlc nntl soclium fluoride uscd fnr cscecd the totiil uinount of u11 otlicr wutcr-soluble salts.

'l'lic use of zitic cltloridc iis II wood prcscrvntive \viis first proposed by Sir \\'illiutii .Burnett. iibout 1838, and it Iins been in continuous usc ever sincc. !t'odap it is probiibly the niost cstcnsi\wly iipplictl wutcr-soluble Iircscrviitivc. It is piirticulnrly suitoblu for tlw protec- tion of tinil~crs out of coiitiict; witlt t,ltc groutid, butt

.. .>

1160 CHEfilISTRY LUD IXDUSTRY IWC. 26, 103i

which nrc nt. the sniiic t.iiiic cxposcd to contlit,ions fnrour- able to decay. Il'lnis the roofing tiiiibers of fnctories jii which iiiiiiiiifnct.iiriiig processes iirc ciirrieil out uiidcr conditions of high humidity, such ns in cotton niills, iirc typical of thc clnss of timbers tlint ran be iuid arc sntisfiictorily trcnted with zinc cliloridc. BIincs providc :inot,lier esnniplc of sitlintions i n which such it wood prcservittivc is cniincntly suitiible. Tlic best results nrc obtained by an impregnation tmiitiiirnt such ns n pres- sure process, or by mi iippropriatc open tiilk trcntnicnt. -1 corninon strciigtli for tlic solution is froiii 3% to 5y0, iilid iis high concciitrntions result i n t,Iic wood siibstancc being nttncked, it is iiot advisable to use solutions strongcr t,hnn 5%. When rcdried, tlic tiinbcr cnn be painted if so desired. This trcntnicnt lins tlic fiirthcr niivnnthgc of rendering t,lic wood sligl~t,ly niorc firc- resistant.

Zinc chloride soluthis hitvc it slight corrosive nctioii on iron and steel, but this is not, sufficicntly scrious to prccludc the usc of treiltjlig plant, such ns is cniploycd for crcosotiiig. Tlic dcprccintion would, liowcver, be grentcr t,linn in the cnse of crcosotc.

SwZizirn Jluoride.-Sodiuni fluoridc lins lieen ti po11ulnr water-soluble prcserviitirc i n Europe for n iiuriilxr of yeiirs, nnd is the biisis of scveral proprictnry prcscrvn- ti vcs of Contincnt:il origin, piirticuldy i n admisturc with diiiitropliciiol illid iilknli dicliroiiiiitcs. l'hc ordinary iron nnd steel trcrit.iiig pltints ciiii be used wit.li this prcscrviitivc, ns i t lins 110 serious corrosivc propcrtics. It. is somewhat niorc cspcnsivc t,linii ziiic chloritlc, and this is probnbly O ~ C of tlic main reiisolis why i t lins iiot been used so cxtensircly ns tlie Inttcr salt. Sodiuni fluoridc is not, very soluble in water, n .I% solution being substantially saturatcd i t t ordinnry t.cmpcrutiircs, but it is highly toxic to \rood-destroyiag fungi. Solut,ions of from 20/, to 40/, :ire commonly eniploycd, iind soft witter is prcfcrnblc for usc in tlicir prepamtion, iis insolublc fiuorides iirc precipitated in Iiiird water.

,SiZico-fluoritles,-Siil ts of hydrofluo lilicic iicitl arc toxic to wood-destroying fungi, but tlic niilgnesiuni or ziiic salts arc tlic oncs gcncrally iiscd, owiiig to thc lo\\- solubility of the otlicrs. Jlngncsiuni silico-fluoriclc is frcqucutly rccoiiiincndcd as a prcscrvntivc ngiiinst dry rot.. As this snlt cllcmicitlly iittncks iiict,nl niitl gliiss, it dioiild not be used in contiict with tlicin, :tiid t,hc treating solution, which is gcncrdly iipplicd hy briisli, sliould be nindc up in il wooclc~i coiitttincr.

Copper sul~)lrcire.--Coppcr sulplintc (blue-stone) I p s not been cstcnsivcly cinployed i n this couiit.ry, probitldy because of its clicn~icnl iictioli on iron, wliicli prcvuiits it from being u s d in ordiiiury trcitting plrints. It is applied to ir limited cstcnt in Fritncc to tlic trcut.nicnt of grccii poles by the 13ouclicric process. Alt~ l i~ug l i quitc toxic to wood-destroying fiii~gi, it 1 1 i t ~ t,lie dis- ndvnntngc of low pcniiiiiiciicy 011 nccoiiiit of its liigli soluhility.

1Merctrric clrloride.-JIcrcuric cl~loride (corrosive siiI)Ii- miite) is cstrcnicly tosic to woo(l-(lcstroyi~~g f1111gi, itnd solutiouR of this siilt form the treating solutioii of tlle Kyniiising IJrOCCSS first; patcntctl in 1832. 1 ts cxtrelilc tosicity to huniiia hcings iintl iiiiiiniils, iiiicl its corrosiyc

action, arc sufticiciit rcnsonr why it hiis iiot been used to niiy oxtciit in this country for purposes of prefiervation. It is still used, liowevcr. on the Continent. for the trcatmcnt of poles.

rl rseriic.--llrsenic in vnrions forins, such ns arsenious oxide, nrsenites, nntl itrscnntes, litis bccn ii coilinion iiigrcclicnt of prcservnt(ives wlicrc protcction of the tiniber against wliitc iiiit :it,tiick hns bccu clcsired. Howcvcr, on accoui!t of its poisonous nitturc srsciiic is iiot likely to bc used in ttliis coiintry, ns i t hits no spcciiil ndrnritagcs ovcr other coinnion 1)rcservntires thnt iire wry iiiucli less tosic to Iiuiiinn bciiigs.

Iteceiit tlecelol~rt~etits iri icnter-solrille suZts.--Nunicroiis :ittempts hnve been made to ovcrcoinc the lnck of perniiinence which clinrncterizes \\*iitcr-~oltiblc snlt.s, iind of these two nrc of spccinl iiitercst. The first scicntificp investigntion on the sulijcct wiis Inadc by L. 13. Curtin, who, nftcr tlicorcticnl consideri~tions nnd prnctkal tests, suggested the usc of zinc mctn-iirseiiitc (Z.3l.A.). Ilricfly t,he theory of tlic action of this prcscrvativc is as follows : zinc mcta-nrsciiitc, thoupli prncticnlly insolii- ble in wntcr, is solublc in dilutc acids, so thiit I)y using n soliibion obtninecl with the iiitl of it volntilc acid such as ncctic ncitl, tlic zinc-:trsenitc is slowly deposited in tlic wood nftcr trcntiiiciit8 and drying. Wood-destroying fungi linvc been found to secrtitc tlilutc ncids, itlid it is clniiiicil thnt tlicsc dissolve sonic of the salt cont.ninctl in the wood nnd arc thereby Rcl f-poisoned.

Tlic ot.licr nicthod of fisitt,ioii of sn1t.s in t,lic wood is by the iisc of ttlknli dichromiitc1.s. Potnssiuin or sodiuin iliclironintc Iinvc for n long t.iine bccn coninion ingre- dients of preserviitivc salt, niistiirrs, hing nddcd for thp purpose of rcducing t,lieir corrosive action on nictnls. Of rcccnt, ycnrs it lins I)ccn rccognizcd t h t t h w cliroinntcs itrc rcclucctl nl id iiro able to form insoli~ble snlts in thc wood, and scvcriil piitclits hive I~ccn taken out in rccciit years for woocl prescrviitivc salt inisti~rcs contniiiing alkali cliromntes. Stilts contiiiiiing copper and nrscnic in pnrticuliir hnve becn tlic subject; of scvcrnl patent spccificnt,ions, biit, thcsc prcscrvativcs linvc not becn in iisc for a sufikicntly long period to cnnble their cn'cctivcness t 0 . h proved in ])riict,icc.

SOLVENT-TYPE PRESERVATIVES Solvciit-type prcservntivcs conrjist of n tosic clicniiciil

dissolved in 11 voliitilc oil or spirit r;dvcnt, whicli, i i f h trcntnicnt, cvitporatcs and lcitrcs tlic clissolvcd tosic clieinicnl iii tlie wood. On tlic whole tliesc prcservativcs, cspccinlly t.liosc containing solvent, nitplitliii, pcnctrittc t,llc wood sliglit,ly better tl i i t i i chlicr types, iuid arc thus iiiore suititblc for surfitcc trcirt,~iient of tlic tiniber lty brush or spriiy. I n iiiiy ciise, tlic rcliitivuly high coat of tho solvent usiutlly liiiiita tlwir use to t,liis i'onii of t.rc:ttinciit.

Tlic toxic clicniiciils used iIrc niinicroi~s, Ll1t coillliioll oiics includc iiietallic soitps or siilts (cspcciiilly of copper niid zinc) of orgiinic iicids, ~ i i c l i iis iiitphtlic?iiic, ahictic, niid olcic ncids, phenols sucli 113 [~-nitplitliol, cliloriiiiitctl plicnols, itiitl clilorinutcd Iiytlrociirboiis siieli iis chlori- nrttcd iiiii~litliitlciic.~, ti l l of whidi proilucc (pito good preservirtivcs. Tlic rcliLtively high price of thcse, hoivcvcr, tends t o limit tdieir iiwl'ul irppliciit ioii.

Dec. 95,1937, CHEJl ISTRY AND .INDUSTRY 1151

PATENTED A N D PROPRIETARY PRESERVATIVES

Tlicrc are a consitlcrii Me iiiiiit ber of prcserviiti\rcs on t,hc niitrkct that arc for t,lic inost pnrt sold i n stniill containers for t,hc bendit of thc ortlinnry houscltoldcr or sninll biiiltlcr. Such prescrv;ttives iirc risctl for surfitcc iippltcntioti, ns t,hey nre gclieritlly too cxpcnsivc to i L 1 1 0 ~ of inipregnation of tlic tiinlicr, which fnct niust be trtkcn into account wlicii coiisitlcriiig tlicir viilac. Frequently, estrnvitgant clitiiiis :ire ittiirle for tlicsc prcscrviitivcs without due rcgitrd to the cotiipnrativcly sninll protcc- tion nflorordcd t,lic tiirilxr by tlir skin-tlccp trcittnicnt tlint, rcsulbs from I siirfiicc iipplicittion. No inattcr how toxic tlw prescrviitivc solut.ion ~iiity h, such pcnctrnt,ion gi vcs only liriii tecl protcctioii.

i l l1 tlic types previously tiicltt.ioitcd :ire rcprescntctl i n t.ltis clitss of prcscrvitbivc, h i t its fiir ns this count,ry is c~onccrnctl thc oil type ~ i ~ c ~ l o i ~ l i ~ ~ i ~ t c ~ . JIittty of the Iiittcr ilre derived froni coal or wooti t w o r itiistirrcs of t,licsc, i r n d are gcneriilly relined to protlucc clciincr i i n t l tiiorc pnctrtiting oils thin ortliniiry creosote.

TESTING OF WOOD PRESERVATIVES At the bcginititig of' t,liis tiilk I referred to the dcsiritlh

propcrtics of ii \voocl Iircscrviit,ivc, nntl purely froin it prcscrvativc point of view three of tlicsc ;ire of inorc iniportnncc tliiitt the rest. 21 gooti preservative niust ~'OSSCSS :

(1) tosicity towiircls wootl-tlcst.r.oyiiig iigciicics, (2) i~ higli tlcgrcc of pcriiiiiiicncc, (3) good pellct,riitiltg powers. In tlic testing of wood 1mscrvitt.ivcs t,lie viiluc of it11

tliesQ propcrtiw cnii only bc inciisurcd in one test if tliis tiikcs the forni of iin tictltitl scrvicc test,, ivhicli, unfortiinittcly, tiilics ii very long tiriic to complete. IZfforts h v c , t,lirrcf'orc, been niiirlc to ol)tiiin iiidications of tlicsc properties by mittis of itcccleriitctl Inbowtory tests, liut up to tltc prcseiit it his been wry' dillicult to corrclntc t,lie rcsiilt,s of sucli tests wit.11 thosc obtiiinetl froni csposurc or scrvicc tests.

Tlic niensurcnicnt of t.hc tosicity of it prcscrviitivc towitrds specific wood-destroying fungi is carried out, by two nicthocls : tlic iigm iriitl wood block rtiethotls. IN thc fortiter, t,lic iiiiiiitnutn quitnt.ity of prcscrviitivc ttcccssary to prcrcnt thc growt,li of n ccrtniti test fungus i r t ii 2% nidt iigiir tiicdiurii is dctcniiitictI, ~ t i t t l this so-called " tosic: point " ciili I x conipiircd witti tltc corrcsponding figurc *otit.iiinitig for other prcserviitivcs. 1 liis ~tictltod hiis bccii risetl t(J it Inrgc cstciit i n tlic U.S.A., but hiis IJccn frtyiiiwtly criticized by 1l:iiropciui niycologists oil tlic groiilttls t h t t,lic fungus is iillowecl to grow in I I I itrtificiiil ~ t ~ e ~ l i u t ~ ~ , and thcy prcfi:r the wood Mock test, i n wliioli t l t c ! fiingiis is ttct.iutlly itllowctl to itthick slwciinciis of wood iiiiliregnittctl with vitryiw 9 c.oiicentrutioiis of tlic prcscrvirti\.e. After fottr niontlts cspositru t,o fiingiil itttriick, tlic Iilocks itrc cx~iniiued i i i i d t I I C niiioutit of tlcciiy wliicli hiis titkcn plitce is tiiciistld lip tho loss ill wciglit of t,lw I)loc!ks cnusctl by the tiction ~f t,lic fungus. 111 the pist t,lirrc Itits bccii it Iitck of stiiticliirtliziitioti i i i t,lic proce(ltirc of tlicsc tcst.s, hit, it coitiniittcc of tltc 13,S.l. litis ltiitl tliis tiict,liorl iiiiclcr consitlcriitioii iiiid it is I iop~~l tlilit it will lw ittloptctl i t i this country its ii s t i i i i d d nicthotl of tcst,itig tosicit,y.

, 1

The agar inctliotl is rcgiirded ns bcing useful for lire- liminary tests ant1 for thc c ~ ~ t i p i ~ ~ i ~ ~ t i of purc cheniicnts of sitniliir nirtitrc. Howcvcr, cvcn whcn ciirrictl out uiitlcr stnndiirtl conditions, tlicsc tosicitty tncnsurcnicnts ciit1 only give such rcsuks i ts cniiblcs one to cotiipirc toxicities, i1tid do not tiikc into nccount the ot,licr iinportiint properties of R preservative, such :is pcrniit- ncnce. It inay bc thought that the pliysiciil propert,ics of iL prcscrvutivc which govcrii its perinnncncc could bc dctcrniiticd i n tlic liiboratory, liut the problem is by 110 tticuns 8s simplc ns i t nppcnrs. In t,lic first plncc, diKcrciit prcscrvativcs, e . ~ . , oils niitl \vat cr-soluble prc- serviitivcs, disnppcur from t,lic wood froiii cnt,ircly clill'crcnt causes. Witli \\7iit~r-SO~libh! sitlts, tlie main loss occurs through lcitchittg of the prescrviitivc, but i t is itliiiost impossible to reproduce in tlic Iiilioriitory tlic conditions tl int prcviiil in prnct,icc, iis tltc niovcniciit of :L I)rcscrv:itivc froni tlic interior to thc sitrfircc of iL piece of wood is n difl'usion phcnonienon wlticli t:iililiot ncccs- siirily tic 'itcccleriitcd. Apitrt froin the tiivcrsity of thought niid opinion t,ltiLt exists r c p d i n g t,lic vnluc of sricli tests, ant1 itlso tlic intcrprctitt,ioii of rcsult.s, thcrc is iilso frcqucnt criticism of t,lie nietliotl cniploycd for leiicltitig. A s it is not possiIJIc to cstiiblisli i i i i cspcri- ntcntal procedure tliiit will corrcsliontl to tltc coiiditions t l t i t t iirisc in nctriiil priictice, the itini of it siitkf:ictory test is to stniitliirtlize coiitlit.ions wliicli rcscntble priicticnl condit,iotis its fiir iis Iiossihlc. For tliis rciison tlic use of liot wiitcr for leidting hits Iiccti crit,iciectl, iititl niost workers prefer to use colt1 iviitcr.

A conitlion nietliotl of citrrying out t h cstriiction is to sltitkc tlic trcittctl tiiiittplc for it tlcliiiitc niinilicr of tiincs i n bottle or contiiincr witti it fisetl volunic of colt1 w t c r , iiftcr wliicli t,Iio wiiter is iiitidyst:d for tlic itnioiiiit of clicniicitl wiislictl out. The n i i h objectioit to this inctliotl is i~ tcritleitcy, cs1icciiilly iti tlic cnsc of prcscrviitivcs of low solubility, for tlic ivitter to bcconie siitiirittcd OP ticirrly SO with respect, to the siiltr, ittit1 t,ltc results sliow tlic ~~rcscrviitive i n it too fitvoririible light. it' t.lic wittcr is chiingcd scvcritl tiinus, thc itniouiit of

'

WISII iviitcr for iinnlysis bccoliics Iilrgc illit1 ciiIiiIicrsonic to tlcitl witti.

r i 1 lie itppirrittus iidoptcd itt, tlic .Forest 1'rotluct.s 'llcseiircli hborittory to overcoiiic tht:sc olijcctioiis coiisists of it niotlificd fortti of ii Soslilct e s t ~ ~ c t o r . Tlic ivittcr viipour is Icd to t,lic top of tlic cotitlcnscr, which is of' t,lie spiriil type : t i l t1 of ittlcr1iiitt.c clinicnsions, so tltiit tlic wiitcr fdling on to tlic wood cotitainctl in the cxt.r;tctor is ivcll cooled. LTsc of this iipprittus pcrtiiits of stitntliirdizcd wiisliing of t,lic sitniplcs, iising ii relti- t i d y sniiill iiniount of witsliittg wiitcr, wliilst tltc wood is being constiintly \vtislicd with frcsli wiitcr.

Ihforc concludiitg, 1 will briefly refer to tlic cliiss of prcscrvtit.ives usctl t.0 rcndcr wood lire-resisting. Wood hring ill1 orgitnic niiitcriitl, it is, of course, not possihlu tu rentlor it '' fireproof," IIS is so ofteii cltiinictl. By iniprcgiiittioii with ccrtitiii , cllcniic*iils it is puyiblc, Iiowcvcr, to reiitlcr \vootl tire-rcsistiitg in t h t t it .will iiot. fliiiiic or glow, rind will thus not iissist tlic sprcttd of Are. 'l'lic coninion clicniicitls used fur tliis pirposc tire viirioiis iininioiiiiiiii salts, such iis tlic iiiiiitiotiiiitii plios- pliittcs, *iininioniiitii sulpltiitc, eli!oritlc, i i i i t l IJromitlc,

Loriis, boric ncid, ntid vnrioits misturcs of tliese. It. will be noted tlint these are nll water-solublc snltu.

Recent rcscnrcli work n t i'riticcs liisboroitgli lins shown thnt when wood is cnrbonieed in tlic prcseticc of ccrtciiii salts, tlic chnrconl yield is gently iiicrcasctl, iti sotlie CRSCS being double thnt froin unt,rcntcd wood, mid nll the chciiiicnls which givc t,liis i ticrcnscd yield of chnrconl arc well recognized for the property of rendering wood fire-rcsisting. It \vould i i p p r , ~licrc- fore, thnt the iiiniii nctioii of n firc-rctiirding ngcnt is to pro(lucc, on ltenting the wootl, ii tlctise clinrconl wit11 ti

tiiitiimum quniitity of thc ot.ltrr t t i i i i t i product of ciir- boiiiestiou, the ititiniiiin:il~lc griscs. l-iciicc txeatcd wood docs not fiaiiie, but merely cltiirs. I~urthcniiorc, i t hiis hecti fo!iiid that tlic coinpoiitids Itiiviiig this propcrty arc thosc which tlissocintc on hcnting to prohce a free acid radicle, ntitl stnblc salts lire not. so cflcctive. Uoriis :it first :Ippcnrcd to be tlic otic exception, but it is possiblc t l in t hentctl in the prescticc of iuethyl alcohol, borax also tlissociiites, giving the frcc acid, nnd this csplannt,iot~ \vould ))ring this sulJstnnce into line with the otlicrs.

SOME LUTES AND CEMENTS USED IN THE HEAVY CHEMICAL INDUSTRY

By H. D. GREENWOODl M.Sc., A.M.I.Chem.E., and F. C. SNELLING (Paper reod ot o Conference of the Chemical Engineering Group, held at King's College, London,

on Thursday, November 18, 1937)

The choice of ii sititiilh ccriictit. for :I s~~ccifio purlmse is rcndcrcd dificiilt I)y tlic Inrgc nunibcr of formukc, recipcs nttd proprietnry ccniciits, many of \rlii~di clnitn to fulfil thc conditions reqitircd. Tlic sclcct,ioti of tlic most suitnblc mntcrinl i n t l i c iil~scticc of first,-lwicl knowlcilge is t.lius cit,licr it Iiiitt.tcr of cliiitice, or else iiivolvcs iiit iiircstjgntioti of tlic propertics of scvcriil liiiitcrinls whiali nppciir most likely to h:i\.c tlic rcqiiirctl clinriicterist,ios. Wit11 this dilficu1t.y in Itiitid, i t is proposed to discuss oiily ii liiiiitecl ~iiitiil)cr of cciiiciits i it id lutes, : id ns fiir ns possi1)lc otily cwitctits \rliicli the iiutliors have found to bc s:iti.sfnctory arc' rwoti i - mciidctl in rclnt,ioti to specific iises. Thc list of cements selcctcd for t,lic viirioits l)~irposes is not tlicrcforc ititctitlctl to be ii i iitiy way coriil)rclictisi\,e, i i t id it is iipprcciiitccl thtt t tlicrc ilrc doubt,less tii:itiy otlwr cetiiciits yiclrling equally sntisfiictory rcsults.

'those tmployeil for tlicir wid-resisting properties, dctiiiitids cotisitlmtblc ciirc iti tlicir I)rep:irntioti niid tiictliod of iipplicnt,ioti. l'liis npplics c\'cti to proprictiiry I)riinds, wliicli it, niiglit I N tissutiictl Iiiivc only to IE ii~odc up in occorilniicc wit,li spccificatioti. IYitIi titnity cctncnts satisfactory performiitice is Inrgcly ilctcrntincd by tlic timc wliioli is nllo\vccl for tliciii to bccomc thoroughly sct bcfore IISC, iitid tii:tiiy (!s~itiipIcs of fiiiliirc tliic to I)renint.urc iisc h w hccii csl)cricticrtl.

,I lltc suc.ccssful l lSC of lllrllly ccnlclrts, ~""t~iculilrl~

( I ) SODIUM SILICATE CEMENTS Owing to its pcodiiir physicxil i i t i d clictiiic.iil (!liiiriic-

t cristics, sodiuni silicntc! forlng the Imis I J f i t Iiirgc itiimbcr of ucicl-resisting cctneiits. JJiiiiy of tltcsc cciiictita dclwiid for their etl'ect.i\?ciicss oii the i i i it .wii1 iidIic~i\~c pro~)crt,y of sodiitt~i siltciitc solittiotts , i d t,lle consequelit biridiag cflcct iritli ccrtiiiii iiicrt, iiggrcyites. 1 he hrrrdciiing or scttiiig of su(:Ii tiiistiircs is rluc to loss 1 1

of \rater frotii the I I I I I ~ S , e i t h r :it uttiiospIil.rio OL' cIc\.ittctI fmipmturcs, iuid tlicy iiiny I ic getier:dly cltissified iis

slo\r-set,t,itig siliciitc cctiictit s." " Quick-sott,ing cetiictits " usunlly dcpciid, for their

riii)id-linrtlciiitig prolicrties, \ipoii soiiic chcinicirl rciictioii bctwccti t.lie silicntc titid oiic or more COiii]lOtlCtit8 of tlic :iggrcgiitc. Siibscquctit niotlificiit.ioii 'of t,lic sitrfncc of formed silicnte cciiiciit. tiinsscs or joiiits may he brouglit. ;ibout hy trenttiictit with ( ( 1 ) ccrtiiiti dknlis or ulkdiiic c.iirt.~i stilts, WJ., colciiiiii cliloritle, or (6) sulpltitric ticid, i i i wliii*Ii ciisc t lie siiiciitc is coti\.r~rtctl'to ii tough iti6olul)lc

For IISO i i i coiiipoiiticling cctiwtits, socliutii silic:itc slioultl bo of such roliiposit,ioii tlirit t . h riitio Nit,O : SiO, lics bct\rccn 1 : 3 .2 i i t id 1 : 3.5, iitid tlic soliit'ioii should bc of :L concciit..rntioii cqiii\wleiit to 11 daiisity of 1 *35 (70' Tw.). Tti (:oiiiiiioti with cctiictits gctieriilly, silicntc ceiiicnts must, Iw uscd spiiritigly, ntitl the thitincst pssiblc joiiits usctl wlieii I)ondiiig bric:kwork, t>ilcs or :id-proof tiiasoiiry.

A furt,licr iinportml. coiisitlcriitkm in coiitiusioti iritli the use of tlicsc ceitictits is tliiit suliieicnt. titno diould IJC ;illo\rctl for limlctiiiig of the tiiiiss ld'orc i t is iillo\\~cd to corti(! i n cotitiict with ivcnl; or a d t , solutioii.

Siliciite C C I I I ~ I I I s goiic!riilly iirr! t tot i i bsolittely rcsist,atilf to wiitcr or \vciil; i iclitcoti~ solutioiis, I)iirt~icitliirly t i t .

clc\.titetl teiiilicriit.iires, i i i i t l ciltlio~igli lipilroIy& iiiiiy, iiiiilcr tAcsc coiitlit.iotis, ttikc pliicr iit t I IC surfiicc of tlic ccnicnt with tlic forriiiit,ioti of it protcct,ivc g~,!l, ittioliiitigcd sodiutti siliciitc will piiss S I O W I ~ into soliil.iotr, with cotiscqucnt piirtiitl tlisititigriit,ioti ol' the cctitet~t~ tiiiiss. \Ylicrc wccik solutkm iirc to br! Itrit~tllctl, tho cuinciita sitrfncc shoitld I N trcotetl \ritli siilpliuric rtoid bcforc itse, hit, this slioitltl not, I I P tlotic ittitil t-lie cctnctit h i i s

gel.

C'Olll] ,lot 01 y hn 1'1 lollctl,