LXXII.—On the atomic weight of tellurium

W. L. Wills
1879 Journal of the Chemical Society Transactions  
Student in the Owens College Chemical Laboratories. TBE atomic weight of tellurium has been determined twice ; in the first place by Berzelius, and secondly by von Hauer. The former (Pogg. An%., 18*34, 32, 16) oxidised a known weight of tellurium with dilute nitric acid, and weighed the dioxide formed, obtaining the numbers 128.13, 127.96, and 127.95 (0 = 15.96). Berzelius calculated his number from the lattcr two experiments which give Te = 127.955. The method employed by him for purifying his
more » ... m for purifying his tellurium was that of distilling in hydrogen the tellurium obtained from potassium telluride. Subsequently von Hauer (J. pr. Chem., 1858, 72, 98) determined the atomic weight of tellurium by the analysis of a double bromide of tellurium and potassinm, the amount of bromine in the salt being ascertained by precipitation with silver nitrate. As a mean of five experiments varying between Te = 126.86, and = 128.49, voii Hauer obtained the number 127.74 as the atomic weight of tellurium (Br = 79.75, K = 39.04). Dumas (Ann. Chenz. Pharm., 1860, 113, 30) from experiments not published in detail, concludes that Te = 129. Deville and Troost (Compt. rend., 56, 871) determined the density of tellurium vapour as 9.00 at 1390", which gives Te = 130.5. The present investigation was undertaken with the view of ascertaining whether a careful repetition of Berzelius's experiments, made with pure tellurium, would yield a number agreeing with the hitherto adopted atomic weight, or whether it would harrnonise with Mendelejeff's classification ( A m . C h e w Pha~m., 1871, Supp. Bd., 8, 133). According to this classification, we should expect tellurium to have an atomic weight lying between that of iodine = 126.53, and that of antimony = 122, thus taking its place in the same series as sulphur and selenium, the atomic weight which Mendelejeff assigns to it being 125. The experimental results which 1 have obtained agree closely with those of Berzelius and von Hauer, according to which tellurium has a higher atomic weight than that of iodine, and must, therefore, be placed after this element in Mendelejeff's system, Prepuration of Pure TeZlzcrium.-lOO grams of crude tellurium was obtained from Trommsdorff, and a preliminary examination of this showed that it contained copper, bismuth, antimony, tin, &c., BY impurities. The following mode of purification was adopted :-The powdered substance was mixed with three times its weight of dry sodium car-
doi:10.1039/ct8793500704 fatcat:fuf437jpffczxavtemhi4dn6oy