iiietliods of niinlysis I \vns vcry glad to scc tlic pnpcr 11) -3lr. T\vytiii~ii (CIIEAI. & IND., April 1 illid 8, 1027). It wns high tinic tliat such iL clear niid iiut1iorit:itivc stnteiiiciit 011 tlic wbolc snbjcct of '. spcctruin aiinlysis ?' A s n coiifirincil uscr for sc~critl ycars of of purity would bc more easily done by spectral nicniis tlinii by chciiiicnl. 111 iiiniiy cases tlic requircmcnt is tli:it soiiic impurity slinll not cscccd a specified pcrccntnge, mid in such C ~S C S spectroscopic or spcctrographic control is particularly suitable. T l ~c nccuracy which cnn IIC obtaiiied with only iL moclcratc amount of espcriciicc (and without any spccinl appnriitus for measuring tlic deiisity of the lincs) is rcliinrlinblc. Tlic Burcan of Stniidnrds Paper FXQ. 1 A'peclra of lecid-tin ctlloys. A'ok lillle clifscrc~tcc i t 1 sliectrcr. for widely dijfering major composition ns it stands to-thy shoiiltl \I(! avnil;i.b!c iii t,liis country, nlt lioiigli By :I. coiiiciclciicc tlicrc appcars in tlic Chciiiicnl Socicty's '. Aiiiiunl 'Itcp0rt.s " this ycnr n good survcy on similiir lines-thc first in 23 ycars.
illost; renders iuiist bc fntiiiliiir with the brontt o u t h c s of q d i t n t i v c spcctriitii analysis, although it is to bc fcnrcd tlint -cry few will linvc got evcii as fiir iis, for CSIIII~IIIC, observitig tlic " D " line :is a tlouhlct,. It is tlic Inst part of Jlr. T\vyiiinn's ~mper, clcnliiig with quniitit:itivc \-ark, tliiit will IIC iicw to iienrly JI, nntl No. 444, by ltcggcrs, liicss, niiil Stiinsoii (quotcd by Nr. Twytiiiin), gives spectrogrnphic rcsiilts mitliiii O*O23{, of the chciiiicnl, wliicli is tlic nvcrngc discrepnncy, biit this cnii bc rcdnccd to 0.010/, in inany cases if tlic rangc of compmison smiiplcs is wcll cliosen.
Iror tlic bcncfit of tliosc who iiiny be sccpticnl or uticertniii, I should lilrc t o cnipiiasise four points witli regard to qunntitntivc spectriim niinlysis \vIiich JIr. T\vyiiinti lins not, pcrliilps, fully brought out.
First, i t is usclcss to try to iiinkc n complcto analysis by slxxtriil nictlioils. Fig. I iiiclicutcs this olciirly ciioiigli ; tlic SIJCC~IX of tlic tlirec alloys of \ d e l y tliflcriig conipositioii arc iicnrly idciiticnl.
Sccondly, it is tlic spcciiil pro\hcc ot qiiantitntivc spcctrutii iinnlpis to cstimntc thc siiiall pc~~cc~itiigcs (i.s., 194 or Icss). A coilipnrisoii of Big. 2 witli Fig. 1 will Iiialtc this plain. 'l'ltc tliffcrciiccs bct\*ccn tlic Thirdly (iiiitl sottic iire very sccpticnl about this), tlic spcctrii or tllc tl1rce nlloys nrc very I11,lrkctl. i.16 CHENISTRY AND INDUSTBY AUg. 10, 1027
clicinicnl rcsiilts do sgrcc with tlic spectrographic. In Pig. 3 arc sho\.ii the spcctra of lcnd containing tin in unknown pcrccntngc (z), and, bclow, of lend containiiig 0*20%, 0-45y0 aid 0.6% of tin rcspcctivcly. Tlic '' stcps " lictwccn tlic coinpnrison snrnplcs bcing irregular and Inrgc, 110 grcnt accuracy was cspcctcd, but in tliis cnsc the spcctrogrnpldc cstimatioii (0.5% Sn) ngrccd with tlic clicmicnl (0.5%) wry wll. Onc took 45 min. t o carry out, tlic otlier a clay.
Fourtldy, thc iunjor composition 06 comparison snniplcs nud of tlic iiiil~no\~n niust bc npprosimatcly tlic same. Fig. 4 is mi cnlargcmcnt of part of a spectrogram of metals of thc composition shown, with coppcr for comparison. The lincs 2824 and 2618 of coppcr 1 2018 arc rcspcctivcly nbsciit nnd mncli faintcr in the 85/15 alloy tlinu in tlie tin, iiltliougli tlic pcrccntiigc of coppcr is tlic sanie in cnch cnsc. 31r. Twyinnu's Pig. 9 may niislcnd bcginucrs OII bliis point, which is of ii~iportaiicc, and lins bcen cinplinsiscd by Ccrliicli,
In conclusion onc mny csprcss thc liopc that much wider iisc will bc made in tliis country of thcsc modern methods of spectrum analysis. It may bc :is \ d l to point out that n sriialt qiinrta spectrograph, with a prism of h s c about 23 mm., is by uo incaw difficult to niakc, and is suflicicnt for inany purposes, giving, ns it docs, n spcctram about 4 in. long. Thc one on which all thc accoinpniiying spcctrogrnrns wcrc taken cost under f 15, including tlic splicro-cylindrical condensing lcns, and was nmlc n1~1 adjnstcd by Inyscclf.