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By a careful determination of the limiting density of hydrogen chloride, Gray and Burt (1909) found the molecular weight to be 36.187 (H = 1). Hence, the atomic weight of chlorine (H = 1) is 36.187 - 1 = 35.187 or 35.458 (O = 16). By decomposing the gas with heated aluminium they found that 2 vols, gave 1.0079 vols. of hydrogen at S.T.P.
The gravimetric composition of hydrogen chloride was directly determined by Dixon and Edgar (1905), who burnt pure hydrogen from a weighed bulb containing palladium, in pure chlorine from a bulb of liquid chlorine prepared by the electrolysis of silver chloride, and passed into a previously evacuated glass bulb,
 | Fig: Atomic weight of chlorine by direct union of chlorine and hydrogen |
the gases being ignited by a spark. The hydrogen chloride was absorbed in water in the bulb. Edgar (1908) omitted the water (which gave a little oxygen when chlorine was used in excess), used quartz apparatus, and condensed and weighed the dry hydrogen chloride in a nickel-plated steel bomb placed in liquid air. The hydrogen, chlorine, and hydrogen chloride were all weighed.
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