1602 PERMEABILITY 03' GLASS TO IODINE AND BROMINE VAPOURS. CLXXIX.-The Permeability of Glass to Iodine .and Byornine Vapours. By JAMES BRIERLEY FIRTH. IN a previous conilnunication (P. 1913 29 112) the author described experiments which showed that ordinary glass is not permeable to1 the vapours of iodine and bromine a t 360° after fifty days and after two years at the ordinary temperature. In the present paper the results are recorded after the experi-ments have been continued for a further period of seven and a-half years making nine and a-half years in all. After two years the tubes of the second series were again heated for a further period of fifty days at' 360° and then the tubes of both series set aside and examined periodically. After a period of nine and a-half years the silver in the tubes of the first series namely those which had not been heated showed no indication of attack by the halogen but in the case of the tubes which had been heated to 360° (100 days in all) the silver in two of the tubes showed distinct attack in the case of iodine whilst in the case of bromine in this series also there was no indication of any action on the silver.The tubes were then broken up and the thickness of the walls of the bulb; was accurately measured by means of a micrometer gauge. The silver foil in every case was carefully examined and the presence of silver iodide confirmed in the two cases. The measurement of the thinnest part of the bulb is given in each case. I n the first series the thickness of the bulbs varied in the case of bromine from 0.206 to 0.332 mm.and in the ease of iodine from 0.204 to 0.338 mm. I n the second series the thickness varied from 0.207 to 0.364 mm. in the case of bromine and 0.208 to 0.385 mm. in the case of iodine. I n the tubes in which thel silver was attacked by iodine the thicknesses of the bulbs containing the halogen were 0.208 mm. and 0.211 mm. respectively and the conditions (a) vacuum inside and outside ( b ) vacuum outside and atmospheric pressure inside a t the ordinary temperature. It should be noted that in the case of the tubes which had been heated the iodine condensed on the walls of the bulb as a thin film whereas in the case1 of the tubes which had not been heated, the iodine was in small crystals VELOCITY OF DECOMPOSITION OF HIGH EXPLOSIVES ETC.1603 The experiments indicate that it is possible for iodine to pass through a thin glass partition under certain conditions but the rate of diffusion is exceedingly slow the iodine taking about nine years to1 diffuse through a thickness of 0-2 mm. of glass. There is no evidence whatever of the passage of bromine through a similar thickness of glass even after nine and a-half years. The experiments do not in any sense support the explanation of Zengelis for the loss observed in Landolt’s experiments since the time taken in the cases where a positive result has been obtained is considerably greater than the duration of Landolt’s experiments and further the thickness of the glass penetrated woald be much less than the thicknem of the glass used by Landolt. In conclusion therefore it may be stated that iodine and bromine do not diffuse through a glass partition under ordinary experimental conditions but only in extreme cases involving the use of very thin glass over a very long period does the possibility arise. THE CHEMICAL DEPARTMENT, UNIVERSITY COLLEGE, N OTTIN OH AM. [Receiued November 16& 1920.