| | -- |Pt_{n}H* |21·4 | 9·2 |1,775° | | | -- | -- |19·3 | 10 |1,045° | | HgE_{2} --| -- | -- |13·6 | 15 | -39° | | TlE_{3} -- --| -- | -- |11·8 | 17 | 294° | | PbE_{4} -- -- --| -- | -- |11·3 | 18 | 328° | | BiE_{3} -- --| -- | -- | 9·8 | 21 | 269° | | | | | | | | | | -- | -- |11·1 | 21 | ? | | | | | | | | | | -- | -- |18·7 | 13 |2,400°?| +-------------------------+------------+---------+-----+-------+-------+ [A] From analogy there is reason for thinking that the atomic weight of selenium is really slightly less than 79·0. Columns 1, 2, 3, and 4 give the molecular composition of the hydrogen and metallo-organic compounds, exhibiting the most characteristic forms assumed by the elements. The first column contains only those which correspond to the form RX_{4}, the second column those of the form RX_{3}, the third of the form RX_{2}, and the fourth of the form RX, so that the periodicity stands out clearly (see Column 16). Column 5 contains the symbols of all the more or less well-known elements, placed according to the order of the magnitude of their atomic weights. Column 6 contains the atomic weights of the elements according to the most trustworthy determinations. The names of the investigators are given in parenthesis. The atomic weight of oxygen, taken as 16, forms the basis upon which these atomic weights were calculated. Some of these have been recalculated by me on the basis of Stas's most trustworthy data (_see_ Chapter XXIV. and the numbers given by Stas in the table, where they are taken according to van der Plaats and Thomsen's calculations).