Par G. PIRLOT (Liege) et E.?V. ROUIR (Gembloux) S D M M~I .-The tlc4erniination of bitamin D2 in the presence of tliflrrcnt irradiation prndiicts of ergostcrol is rather difficult b y simple iiltrit-uiolct nbsorption spctroacopy, dur to the suprrposition of t h e ,ihqorption I)anrI* of Ihrse substances.It is thus necessary to resorl lo cheiriiral transforninlioiis i i i order In get producls wich absorb in different wavclcnght rangrh for the ~t~v r r a l substances in presencc. The proccdurr we have worked out; basrd on a reaction given by Sobel and ctworkcrs, i4 siiitrd to the determination of vitamin D, prepared from rrgo4rrol.

de la vitamine D:! en solution pure et en pr6sence cle sels calciqires par V. LASAREFF (Liege) et E. V. ROUlR (Gembloux) SLXMA~<> , --'I'ht, sc.iisitivit) ol ii direct specl rophi~t~nietrir tlciterrnination of vitartiin D,, (calciferoll, ]lased on its ultra-violet absorptiori. proved to be 1 microg~am/ml., or better. Compared with the currenl colorimetric trchiiiqtres, the ultra-violet method is capnble of a much higlicr ;Iccuriicg.--Thr ultra-violet absorption spcctrum o f calciferol rcmaiii1; tii~chiiiiged in the prcsencc of calcium phosphate or gluconntc?. The lattor conipouiids show only a slight rontinuous absorption in the ~m c spi~,l r;il range. Coiiscquently. fhc iiltra-violct determination of i:;~lcjf~~rfil t'nil Iw pt~forinc~tl without j)revinus climiiialiori of calciuin qalts.

The quantitative determination of metals in organic substances is performed usually by ashing the material, followed by the spectrographic analysis of the ash. Because of the long duration of the chemical process employed for preparing samples, we have endeavored to find an easier method for the direct analysis of plastic materials. The procedure consists in dissolving the solid matter in an appropriate solvent in the presence of a reference element. The spectrum of the mixture is then directly recorded by the method of the rotating graphite disk. In this study, we have compiled the results obtained with a Geon compound.