We wish to thank Professor A. C. FRAZER for his interest and for facilities to carry out this investigation. One of us wishes to acknowledge the award of an I.C.I. research fellowship (J-P.) SUM&I-\RY An accurate and rclmblc colorlmctrlc method of slhcon dctcrmmatlon m the prcscncc of phosphorus IS rcportecl The method rnvolvcs the sclectlvc cxtractron of phosphomolybdate with ethyl acetate and detcrmlnatlon of the aqueous phase after reduction to molybdenum blue lsoamyl acctatc extracts phosphomolybdate to a lcsscr degree than ethyl acetate Unc mbthodc colorlmbtrlquc cst proposdc pour Ic dosayc du slhclum cn pr&cncc dc phosphorc. Pnnclpc cutractlon du phosphomolybdatc par l'ac6tatc d'dthylc et dosage colorlmdtrlquc apr&r rdductlon dc la phase aqucusc cn blcu dc molpbd&nc ZUSAXIXIENI;ASSUNG Es wlrd clnc hIcthodc bcschrlcbcn zur color~metrlschcn Ucstlmmung \ on Slhzlum 111 Gcgcnwarl von Phosphor. I~hosphormolybdat wlrd mlt hcthylacctat sclcktlv cxtrahrcrt, das Sllrcomolybdnt zu Motybdanblau rcduzlert und colorlmctr~~h bcstlmmt Rl3FERENCES 1 hf C %XIWAHTZ, Ind E',,g C/rem , tl md Ed , 14 (lg.)z) 893. 2 Bf A 1)EsISSA AND L. 13 ROGEHS, A?lUI Chmr , rf.3 (1954) 1278. 3 0. I' CASE,