98 Volume of Distillate. THE ANALYST, Percentage by Volume. Refractive Index n E . NOTE ON SOME COMMERCIAL SAMPLES OF MONOBROMBENZENE. BY J. H. COSTE, F.1.C- MONOBROMBENZENE is a material which, from the fact that its boiling-point is so far from that of benzene on the one hand, and of either of the dibrom-derivatives on the other, should be easily obtained in a state of purity. Some time ago the author had occasion to calibrate some thermometers for temperatures near 150" C., and attempted to make use of a sample of monobrombenzene of German manufacture and supposed to be pure. I t was found to have a somewhat wide range of boiling- point, and to leave a crystalline residue when distilled to a temperature somewhat above the boiling-point of pure monobrombenzene (155' C.).A sample recently obtained from an English firm, but probably made in Germany, and also supposed to be pure, was found not to be of constant boiling- point. A portion measuring 300 C.C. was slowly distilled, using a 15-disc Young's rod and disc column. The following table gives the amounts and properties of the distillates obtained : Temperature. 1. Below 100' C. 2. 100-110" c. 3. 110-153" C. 4. 153-155" C. 5. 155-156" C. 6. 156-157" C. 7. 157-158" C. 8. 158-159" C. Total .._ ... 1 C.C. 9 C.C. 13 C.C. 99 C.C. 137 C.C. 19 C.C. 6 C.C. 3.5 C.C. 0-3 3.0 4.3 33.0 45.7 6.3 2.0 1-2 287.5 C.C. I 95.8 1.4975 1.5442 1 5502 1.5586 1.5590 1.5596 1.5596 1.5595 The residue in the flask was about 10 C.C. in volume, and on cooling solidified to a crystalline magma. The white crystals thus obtained weighed 10.0 grams, and melted at 83-84' C., and were This was broken up and pressed between filter-paper.THE ANALYST, 99 evidently crude dibrombenzene.The presence of unbrominated benzene was indicated by the odour of the first fraction, and the low refractive index of that and the two following fractions. Fractions 6, 7, and 8 were mixed and distilled from a small Ladenburg flask. A distillate of 25 C.C. was obtained between 1/54' and 156" C. This portion was mixed with fractions 4 and 5 , and yielded on distillation 239 C.C. of a liquid boiling between 153" and 154" C., at a pressure of 751.8 mm. of mercury, and having a refractive index at 20" n,=1*5589. Jahn and Moller found the refractive index at 13.2" C. to be i z D = 1.5635, and using the correction for 1" given in Landholt and Bornstein on the authority of Perkin-0.00054, this should equal 1.5598 at 20"-somewhat higher than the figure obtained by the author, who used an Abbe refractometer, and deter- mined the index at different temperatures below and above 20", and obtained a correction figure-0-00057-very close to Perkin's figure. Although monobrombenzene from the nature of things is a difficult material to prepare by direct bromination of benzene without obtaining some amount of the dibrom-compound, it should, in the opinion of the author, be carefully fractionated before sale, and certainly when sold as pure should contain no benzene, and much less than 3 per cent, of dibrombenzene.