IN eat.imating hypolphoaphoiroas acid by mea'ns of merouric chloride aomrding to then met'hod given by Treadwdl (" Qua,nt,it,ative Ana(lysis," p. 2S9), i t was found tha.t the1 oxida.tion procmedeld rela.dily to pholsphorous acid, but, rellaLivdy slo,wly t o phosphomric acid. It was tjhelrefo,re de.cide,d t,ol investigate, the1 progress of the i-elact'ion, and c.ert.ain f a.c8ts werei netted in t,ha firstl s8tla.ge-the oLxidatbon t'ol phosphoro'us acid-which arel, b'rielfly : (1) The coiioetnt'r adiojn o.f mercuric c,hlo,ride, a,ppeiarecl trot ha,vel no inflimnoel 0 1 1 1 t'he reectdoln vellocity eixcept, whe'n velry dilutei. (2) The, reactiotn was a,cceleratsd b.y the1 addition of hydrolchlosic acid. (3) It was the'retforei autowat,alyt\io, owing t,o tlhel hydrochloric acid proiducetd. (4) The initia(1 vellolcity wa,s approxima,teily pro~portional t,oi the pro'ducti olf t$e concentra,tliom oC the1 hydrogeln ions and the1 hypophosphoroas a'cid. From them fact,s, it wa,s conoluded t,hat the oixidat'ioii t.0 phosphorolus aaid involved tlwol suceeIssive reia,ctions, : the! first,, of melasura8blel vellocity, in which t,hhe> mercuric chloride1 t-oak no1 patr.t, a,nd t'hel secolnd, o,f relat'ively p a t , ,ve,loclit,y, in which the1 melrcuric cihloiridei f unct'io'ned. No coinventiona,l hypot.helsis appeared adequa.telly t'o explain them facts. I n o'rder ta investiga,te certain points inolre fully, an ana.logous reaction was soughtl in which the analytica,l rneltho'd used would be of grelat'es a,pplicab,i!ity. The. relactio'n with iodine was found to be acc,ura,tely colrnpa,rable, a n d is here, delscrihd. That wit$ rnelrouric chlojridel will be communicateld la.ter, but itl may bet melntdoneld that compara8tivs e,:iperimelnts with iofdinel and meircuric chloride!, respeot.ively, showeld that the melasurable8 velocity was identical in the two ca.ses, t,hus lending a.dditiona1 support tot the! vielw that, only hypolphosphorous acid functions in the slolwer raction. Stredel (T., 1907, 9 1, 1641) ha8d already invc8stigateid the reaction svit,h iodinel, and o'btaineld the1 same1 gelneral res,ult.s a.s alsoive. For the1 relactio8n H,PO, + I, + II,Q = H,PQ, + 2131 he 0Eere.d t,hel follo3wing ex-planabion : the slo'w stage is represented by which procselds, libelrating free1 ionia chargee, if thejrel is also preselntl a