* . properties unequalled by any otlier resln iind liave good form stability. Little is kno\vn of tlic propcrties of tlic various heterocyclic nnd polycyclic annlogucs. ’J’hc various acrylic resins nrc better lilio\vn and i1rc niorc susceptiblc to clnssificntion siricc they form two homo- logous scries, thc polyacryliites and the polymctlia- crylntcs. As \vc risccnd each series the polyniers bccon~c softer and softer nnd finally censc to be solids. Thus the polylauryl esters of iicrylic iind mcthacrylic acid are syrupy liqnids. Polyniethiicrylic ncid esters arc invariably harder t hrin the corresponding polyiicrylic acid esters.

When we pass from the polyacrylic and met hncrylic esters of nionohydric nlcohols to those of polyhydric alcohols a marked chnngc in properties takes plncc. Solubility, clarity, and mouldnbility disnppenr, the products being infusible, opnqnc bodies nisolublc in organic solvents.

The general properties of the comnierciiilly ri\Tailablc polyacrylic and nicthacrylic acid esters iirc nlso well known. Polymet liyl acrylatc is distinguislied by its remarkable cliisticity iind toughness in film form. ‘l‘he softening point is, tiowever, low and there is no present likelihood of the polymer heing used ns n rohbcr sub- stitute or in the moulding industry. In cliirity iind light stability polymethyl ncrylntc is outstiindingly good. Polymcthyl nicthncrylnte is rcmtirkablc not only for its ext raordinnry opt icril properties, which we have alrendy mentioned its ii feiiturc coninion to the styrene and acrylic resins, but, d s o for its nicchnnical strength and its stn1)ility at ill1 tempcratures i ind hi~niiclities likely to be experienced nndcr the most ndversc climatic conditions. Thc polymer moulds \veil eit her by injection or compression. At its softening point it is much less fluid than polyst yrcnc iind, therefore, requires higher injection 1)re5snrcs.

APPLICATIONS Some of the appliciitions have been touched on in the

preceding discussion. Polystyrene finds niriny electrical uses because of its low power factor aud ease of injection. The softer acrylic resins iire used extensively in the textile industry and as Iiiniinntcd glciss intcrlayers. Thc harder oiies, in prticular, polymcthyl ~ncthcicrylritc, are finding inc rcahg I I S ~ S not only in thc forin of light- weight transparent sheets, but also, in thc form of lacquers and of inoulding powders, for tlic prcpiiriit ion of strong clear or colourcd iirticlcs of great, bciiuty. Tlic use of styrene and acrylic resins in cmulsion form is rapidly increasing. Although polyacrylic iicid ester emulsions are a t present most iniportiint polymetliacrylic acid ester emulsions iirc entering the field.

FUTURE DEVELOPMENTS The greatest disparity bctwecn the thcrniopl~istic

styrene and acrylic resins on t hc one lirind r ind the thcrniohnrdcning phenol rind urea-foriniildcliydcs on the other is iit present in cost of production. As we havc seen, 11o\vcvcr, they iirc a11 cripiiblc of bcing niiide from one of the chenpst rind most iibundunL of riiw materialr;, namely cod. The mmc cincrgeiicy which might accelcrntc tlic use of coiil iis fi basic riiw niiitcriiil and encourage the clevclopiiieiit of olternntivc Rynt hcsetl

for the niononicrs, would nndoubtetlly hasten tlic dcvelopnicnt of ncw npplici~tions .for thcsc resins, as, for instance, tlic IISC of tmnsparcnt plastics for acroplme windows nnd hoodings. Both factors-higher output, rind cheaper ultimatc mw niaterials--will rciict in the same \vny to lower costs of production, nnd although the complicated nature of the synthesis of styrcuc and iicrylic resins from coal will prevcnt costs cvcr bcconiing cst.ruinely low, thcy will undoubtedly reach n Ic \d at which in thc Ileilr fiiturc our clot,hcs, radio ant1 tclcvision sets, telephones and inany other of our Iionsc- hold requircnicnts will makc frec iisc of this class of t hernioplast in.

ELECTROSTATIC DUST SEPARATION TWO NOTABLE P O W E R STATION PLANTS

Further inforination has been madc availablc conceni- ing the two I‘ Lodge-Cottrell ” electrostatic plants now operating a t l h 1 s Hnll and Princes Street (Nechells) power stations (Uirniinghnm Corporiition) for thc removal of dust from the chimney gnses of pulvcriscd coal ficd boilers. This serious probleni has bccii successfully solved, and the remarkable guartrnteed dust contcnt of not niore than 0.10 grains per cubic foot in the gnscs, as dischnrged, hns been iniprovcrl upon in practice.

Hiinis I in l l now lins two I:irgc ncw brick chinincys 350 ft.. high by 20 ft. internal diumctcr a t tho top, ench \\~eighing 5200 tons, and one of these tnkcs all the combustion gases from fivc piil\wised fuel fired boilers after the dust has been scparat,ed in the precipitators.

!J!he clectrostntic plnnt, which is the lnrgest in Great Britiiin, supplied, as n t Ncchells, by Lodge Cottrell, Ltd., of Birmingham rind Lolidon (Bush Iioiise, W.C.2), comprises eight horizontal reinforced concrcte ‘. trcittcr ” chambers, operating in pnrallcl, each with its own inlct and outlet shut-off danipers, through which tho com- bustion gases pass” from tho boilers to the el!imney Eucli ‘ l treater ” hiis four baiiks of ciirthed electrodes of the firm’s pntent rod-curtain type, designed specially for free expansion cind cnsy rcniovnl of tho dust. Tho electrodes on which tlic dusl; is deposited cousist of long vertical rods closcly q m c d together, forming curtains hung in thc direction of tlic giis f!ow, allowing a clear unobstruct.cd passiigc. Between tliesc rows of

collecting ” electrodes nrc l1111ig ccntrully heavy t,wistcd squnrc section “ dischnrgc ” electrodes, niiiin- tnincd iit. ii high potcntinl, ribout, 50,000 volts.

!rhc (lust particles in tlic giis rcccivc i i iicgtitivc chiirgc and iirc rit oncc prccipitritcd on t.lic collecting rod curtains, froin wliich they tire continuously rcniovcd by nieiitis of ciutomiit.ically o~~erriting mecliitnicnl rapping gcnr, fornietl of spring-loiitlcd hiininiers opcrritccl by coinr;Iirifts, t,lic dust; fnlliiig into hoppers froni wliich it is rcinovcd by con~wyors. For supplying tlic liigli tciisioii currc~it~ six trnnsforincr-rectifier iiiiits are iiist iilled, Iiou~cd in it separiite control room, with t,lic nccessiiiy switch gew, riutoiiiiith devices, iind int,ru- mc11ts.

11 I W ~ large inild steel duct, up to 19 ft. dianietcr, conicys the combustion gases from the roof of the

boiler house to tlic clectrostntic precipitators, tlic volunic of gases when tlic boilers nrc on innsiniuni lond being 880,OOo cb. ft. per niinutc nt n temperature of nl~out 300' P. u p to 100 tons of dust nrc removed per 24. hours, nearly all belo\v 10 microns in size, the bulk being about 5 microns, witli a large proportion only 3 microns (one micron = 0.001 inin.).

A t Nechells four lnrgc boilers are operated by pul- verized con1 firing iind four iiidcpcndent clectrostcltic trentcr units, rated for a combined volu~nc of 396,000 cb. ft. per minute, iire nrrniiged in pairs, e:ich taking thc gases from two l)oilcrs, but having in tcrconnesioii flues. The clectrostntic plant is siiniliir to tliitt at HnmP Hall, nnd operates with equal SUCGC~S, the outlet gnses, after treatment, being tlischnrgcd to n large new h ick chimney 350 f t . high.

Collected dust from the lioppers is discharged by conveyors to tlic nsh sluicc system of the boilers, and included nrc three high tension , transformer-rectifier change-over high tension s~vitches to enable any traus- formcr set to supply any section of the precipitators, and automatic circuit brenkers, lanip signnls, mid nliimi horn.

REACTION MECHANISM OF SOME PROTEOLYTIC ENZYMES

By DR. JOSEPH WEISS 1 I'roteolytic enzymes, such ns pipiiii and cnt~licpsiii,

c:in split (hydrolyze) the peptide linkngc (-C'O.HX-) of proteins. In R similar w y iircnse trniisforiiis urca into iiinnioniuni carbunintc.

HS- groups have been cst.nblishcd in thcsc enzyiiics whose aqtivity largely dcpcnds oil the presence of thm

Thic-jpxt rciictivity of t ~ i c Iiyclrogcii i i i ccrtiiiii orgiinic SH-conipounds hiis been rccognizctl, cspccinlly since the fiiiitiiimcntol work of I?. G. I-lopkins. This fnct liiis

been tIcnioiistratcd iigiiin rccciitly by pliotochcmicnl csperinicnts, wlicn it wiis slio\ni tha t itt is possible to obtain molecular hydrogen mid the corrcspoiidiiig clisulphidc from various SI-E-compoiinds by irrndintion in tho near i~ltraviolct.~ This rcnctioii ciin also bc obtnincd in t,lie visible region of tlic spcct,runi by scnsiti- zntion witli a fluorescent

reiictivc H:-ittoln (frorii t,lic HS- group) in these oiizynies, wliicli priiiicirily iit,t,iicl<s the substrate -it is possil~lc to give ii wry siiiiplc niiil possible picture of this chss of ciizyiiiiit ic ~~roccsses.

1 . dlecli(ic,iis~/i o f j q m i i i c o i d cnllicpii i uctioii Tlic eiizyiiie denoted by Eiiz-SIX iittiicl;~ t.hc protein

rnolcoule (R, - CO*"1I - X 2 ) i i i iL rctluct.ion process ciccorcliiig to :

(14 . It,--CO*]Nkl-\C2 1i ,-CO

-- g KO 1, ps!i

By iissuniiirg

-> \ + Il,N-R,, El& SEnz

giving t'hc ciiiiiiio coui l~o~i~ id (M2 - It2)-

Tliis is follo~vctl by the Iiytlrolysis of the (labile) cnzynic-substrate compound \vit,li the forinntion of the ciirho..r~-I compouiid (R, - COCH) and tlic reforiiintion of the cllzyn'c :

(1 b) It , - -C= 0 -+ 1{l-coo14 -+ I~hz-SH

\ . . . .

tlO'1-i

\SEllL

. .

1ie;ictions iiniilogoi~s to rciictioli (111) Ii:ivc I)ecn studied pnrticiilnrly by 11'. ~ l i c l ~ l e r ~ i111tl it. hiis been cstn1)lishctI that siniple tliiocarbonic iicids arc hydrolyzed, yielding t,lie ncid mid tlic lnercaptiill (ns nssunied in rcnction 11)).

The cnqnics mentioned i11)ovc nrc :ilso able to catalyze the reverse reiictioii.4 It. is possiLlc wit,li csscntinlly the snnie nssii~nption of the mobile I.l-ntoni to esp1:iin this fnct, by iissi~niiiig t,he following types of reaction :

P4 ,o 1-1 ,SEnz

K.,--C=O -+ EIIZ-SH -> RI-C-OH 1

\OH /SEnz

+ 11,C=O + HzO (2b)

R,-C=O -> Ii~--CO.SH--R~ + Elyi-SH . . . . . . . . . .

\:sEnz

R,--N 11. M

2. NecJin~iisui of tireuse cldiou

The SIX group of the enzynic (Ur - SII) reacts with t,hc iircii nccording to : (311)

,XI& ,NHz co . --> CO +NH, \

urs.1-1

. . . . . . . . . . \SUr \:SH 2

. . . . . . . .

!l'h ciizyiiic conipoiinil is then Iiydrolyzcd by tliu i~iiinionii~ni hydroside formed i l l rciiction (311) ilccording to : (3b)

,N I 1 1 /NH p

\ ,..... \ONI.f, co -> co . + ur-SH

\.SUr

NHIO 11 ... ...

giving iiiriinoiiiiiiii c~irlinii~ntc niitl the ciizyine.