AMSTUN ~i e
n!ethocl is oonsidcrcil in which plnto -cnlibmtion is curried ont using nictnllic 1'cncils of known romposition. nnd tho cnlibrntion cnrre ia n log plot of concentrntion ngninst tho opncitj' rntio of the ~tnnilerd to impurity lino. The gcncrnl orpintion for this enlibrntioii rurvc ia i l r r i r i ~ nnd from it tho following nm dcilucccl : (1) tho qnnntitntivc effcct of n diffcrcnm in wnrc-length hotwcen stqndnrd nnd im1nirity IineR; ( 2 ) tlie slope of tho cnlibrntion curvo;
(3) tho t~ignilicnnm of tlic nseful crposum rnngc, nncl (4) tho rcnsons for Iilnto cnlibrntion. Tho pliotogrnphic constnnts nrc clotcrmincd, using ns n ronstnnt sonrco n hot mercury nrc, nncl vnrying the oxposurcs. In tliiaronnexion tlic effcct of rrriprority fniiun? is cliscuseecl.
Somo pmrticnl iiniilysrs iim ronaiilcrcil in tho light of the ntrovo theoruticnl rcsults, wing tho dctcrniined photogrnpliic constnnts. Two proccws for diirnluniin nro compnntd, nnd us n fiirtlier ernniplo the estiruntion of colrpcr 1mc1 nntiniony in nn nlloy is consiclemd.
It is proposed in this pnj)er to consider tlie,effects of the photpgraphic process on the Itlost usual form of tho internal stniidnrd nietliotl of spect.rogrupliic analysis, when opacities, as riiensurcd hy n inicrophotohicter, lire iised in tlie ciilculution of results. Nntiirally, in order to olitriiii iiny qiuntitutivc results iu sucli. nil iinwtigation, i t is iiecrssiiry to know uceumtely tli? churacteristtics of the plirtcs used. Such duta, Iiowever, lire scurce and norninlly only apply to es1rerimcnts conductetl with white light, whereus in nenrly all nictnllurgiciil work the ultru-violet is Iry fiir tlic niost useful rcgion. Probably for this rcusoii ti Iiirge n u n i h of workers Ilnve not consitlcrctl tlic effects of the photogrnpliic process sufficiriitly, rind Iinve selected the conditions for the analysis of .u given alloy empiriciilly. A certnin degree of einpiricisin is iiiinroiduble iu s1'crctrognipliic aurilysis, since very coniplcs fiietors are-inrolred, such as the. conrlitioiis existing in nn electric dischurgc betwen clectrodcs of viiryiiig coinposition. The nutliors feel, however, tliuf this !ins overstresscd the enqiiricul nspect of the wliolc subjcct, TLis is to, be regrctted, since the best ' photogrnphic conditio!is can be predicted, thus rcuioyhg one of the vnriiibles in deterruining tlie best process for tlie uiiulysis of an ulloy. In udditiou, nu uiidcrstniiding of tlie pliotograpliic fnctors involved oftoii helps to esplaiii uud avoid many of tlie small, but irritating, vtrriations wlricli occur iu routine spectrographic analysis.
It lius been stated that errors arising from the photographic process arc small,' but in this connoxion it is